Co-reporter:William L. Hoffeditz, Michael J. Pellin, Omar K. Farha, and Joseph T. Hupp
Langmuir September 19, 2017 Volume 33(Issue 37) pp:9298-9298
Publication Date(Web):May 12, 2017
DOI:10.1021/acs.langmuir.7b00683
Often key to boosting photovoltages in photoelectrochemical and related solar-energy-conversion devices is the preferential slowing of rates of charge recombination—especially recombination at semiconductor/solution, semiconductor/polymer, or semiconductor/perovskite interfaces. In devices featuring TiO2 as the semiconducting component, a common approach to slowing recombination is to install an ultrathin metal oxide barrier layer or trap-passivating layer atop the semiconductor, with the needed layer often being formed via atomic layer deposition (ALD). A particularly promising barrier layer material is Nb2O5. Its conduction-band-edge potential ECB is low enough that charge injection from an adsorbed molecular, polymeric, or solid-state light absorber and into the semiconductor can still occur, but high enough that charge recombination is inhibited. While a few measurements of ECB have been reported for conventionally synthesized, bulk Nb2O5, none have been described for ALD-fabricated versions. Here, we specifically determine the conduction-band-edge energy of ALD-fabricated Nb2O5 relative to that of TiO2. We find that, while the value for ALD-Nb2O5 is indeed higher than that for TiO2, the difference is less than anticipated based on measurements of conventionally synthesized Nb2O5 and is dependent on the thermal history of the material. The implications of the findings for optimization of competing interfacial rate processes, and therefore photovoltages, are briefly discussed.
Co-reporter:Karen L. Mulfort and Joseph T. Hupp
Inorganic Chemistry September 15, 2008 Volume 47(Issue 18) pp:7936-7938
Publication Date(Web):June 13, 2008
DOI:10.1021/ic800700h
A 2-fold interwoven metal-organic framework has been chemically reduced and doped with Li+, Na+, and K+. At low pressures and temperatures, the reduced and doped materials exhibit enhanced H2 uptake—up to 65% higher than for the neutral framework. Notably, at similar doping levels, H2 binding is strongest with Li+ and decreases as Li+ > Na+ > K+. However, the uptake increases in the opposite order. We attribute the behavior to structural changes accompanying framework reduction.
Co-reporter:Zhanyong Li, Aaron W. Peters, Ana E. Platero-Prats, Jian Liu, Chung-Wei Kung, Hyunho Noh, Matthew R. DeStefano, Neil M. Schweitzer, Karena W. Chapman, Joseph T. Hupp, and Omar K. Farha
Journal of the American Chemical Society October 25, 2017 Volume 139(Issue 42) pp:15251-15251
Publication Date(Web):October 4, 2017
DOI:10.1021/jacs.7b09365
Few-atom cobalt-oxide clusters, when dispersed on a Zr-based metal–organic framework (MOF) NU-1000, have been shown to be active for the oxidative dehydrogenation (ODH) of propane at low temperatures (<230 °C), affording a selective and stable propene production catalyst. In our current work, a series of promoter ions with varying Lewis acidity, including Ni(II), Zn(II), Al(III), Ti(IV) and Mo(VI), are anchored as metal-oxide,hydroxide clusters to NU-1000 followed by Co(II) ion deposition, yielding a series of NU-1000-supported bimetallic-oxo,hydroxo,aqua clusters. Using difference envelope density (DED) analyses, the spatial locations of the promoter ions and catalytic cobalt ions are determined. For all samples, the promoter ions are sited between pairs of Zr6 nodes along the MOF c-axis, whereas the location of the cobalt ions varies with the promoter ions. These NU-1000-supported bimetallic-oxide clusters are active for propane ODH after thermal activation under O2 to open a cobalt coordination site and to oxidize Co(II) to Co(III), as evidenced by operando X-ray absorption spectroscopy at the Co K-edge. In accord with the decreasing Lewis acidity of the promoter ion, catalytic activity increases in the following order: Mo(VI) < Ti(IV) < Al(III) < Zn(II) < Ni(II). The finding is attributed to increasing ease of formation of Co(III)–O• species and stabilization of a cobalt(III)-oxyl/propane transition state as the Lewis acidity of the promoter ions decreases. The results point to an increasing ability to fine-tune the structure-dependent activity of MOF-supported heterogeneous catalysts. Coupled with mechanistic studies—computational or experimental—this ability may translate into informed prediction of improved catalysts for propane ODH and other chemical reactions.
Co-reporter:Tina C. Li;Márcio S. Góes;Paulo R. Bueno;Francisco Fabregat-Santiago;Tobin J. Marks;Juan Bisquert;Chaiya Prasittichai
The Journal of Physical Chemistry C October 22, 2009 Volume 113(Issue 42) pp:18385-18390
Publication Date(Web):Publication Date (Web): September 17, 2009
DOI:10.1021/jp906573w
We report here the utilization of atomic layer deposition to passivate surface trap states in mesoporous TiO2 nanoparticles for solid-state dye-sensitized solar cells based on 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD). By depositing ZrO2 films with angstrom-level precision, coating the mesoporous TiO2 produces over a two-fold enhancement in short-circuit current density, as compared to a control device. Impedance spectroscopy measurements provide evidence that the ZrO2 coating reduces recombination losses at the TiO2/spiro-OMeTAD interface and passivates localized surface states. Low-frequency negative capacitances, frequently observed in nanocomposite solar cells, have been associated with the surface-state mediated charge transfer from TiO2 to the spiro-OMeTAD.
Co-reporter:Martino Rimoldi, Ashlee J. Howarth, Matthew R. DeStefano, Lu Lin, Subhadip Goswami, Peng Li, Joseph T. Hupp, and Omar K. Farha
ACS Catalysis February 3, 2017 Volume 7(Issue 2) pp:997-997
Publication Date(Web):December 30, 2016
DOI:10.1021/acscatal.6b02923
Metal–organic frameworks (MOFs) are highly versatile materials that find applications in several fields. Highly stable zirconium/hafnium-based MOFs were recently introduced and nowadays represent a rapidly growing family. Their unique and intriguing properties make them privileged materials and outstanding candidates in heterogeneous catalysis, finding use either as catalysts or catalyst supports. Various techniques have been developed to incorporate active species into Zr-MOFs, giving rise to catalysts that often demonstrate higher performances or unusual activity when compared with their homogeneous analogues. Catalytic functions are commonly incorporated at the zirconium-oxide node, at the linker, or encapsulated in the pores. Representative examples are discussed, and advantages in adopting Zr- and Hf-MOFs in catalytic applications are highlighted.Keywords: catalysis; encapsulation; hafnium; linker; metal−organic framework; node; zirconium;
Co-reporter:William L. HoffeditzHo-Jin Son, Michael J. Pellin, Omar K. Farha, Joseph T. Hupp
ACS Applied Materials & Interfaces December 21, 2016 Volume 8(Issue 50) pp:
Publication Date(Web):November 30, 2016
DOI:10.1021/acsami.6b10844
Organic and porphyrin-based chromophores are prevalent in liquid-junction photovoltaic and photocatalytic solar-cell chemistry; however, their long-term air and light instability may limit their practicality in real world technologies. Here, we describe the protection of a zinc porphyrin dye, adsorbed on nanoparticulate TiO2, from air and light degradation by a protective coating of alumina grown with a previously developed post-treatment atomic layer deposition (ALD) technique. The protective Al2O3 ALD layer is deposited using dimethylaluminum isopropoxide as an Al source; in contrast to the ubiquitous ALD precursor trimethylaluminum, dimethylaluminum isopropoxide does not degrade the zinc porphyrin dye, as confirmed by UV–vis measurements. The growth of this protective ALD layer around the dye can be monitored by an in-reactor quartz crystal microbalance (QCM). Furthermore, greater than 80% of porphyrin light absorption is retained over ∼1 month of exposure to air and light when the protective coating is present, whereas almost complete loss of porphyrin absorption is observed in less than 2 days in the absence of the ALD protective layer. Applying the Al2O3 post-treatment technique to the TiO2-adsorbed dye allows the dye to remain in electronic contact with both the semiconductor surface and a surrounding electrolyte solution, the combination of which makes this technique promising for numerous other electrochemical photovoltaic and photocatalytic applications, especially those involving the dye-sensitized evolution of oxygen.Keywords: atomic layer deposition; dimethylaluminum isopropoxide; dye enshroudment; increased dye stability; porphyrin dye; protective coating;
Co-reporter:Joseph T. Hupp;Omar K. Farha;Thomas W. Hamann
The Journal of Physical Chemistry C December 11, 2008 Volume 112(Issue 49) pp:19756-19764
Publication Date(Web):2017-2-22
DOI:10.1021/jp807395g
Atomic layer deposition (ALD) has been used to create conformal TiO2 blocking layers on fluorine-doped tin-oxide substrates in dye-sensitized solar cells (DSSCs), effectively eliminating shunting. ALD has also been used to deposit, in controlled fashion, ultrathin coatings of alumina on nanoparticle-based TiO2 DSSC photoanodes. These modified electrodes enable ferrocenium/ferrocene, an outer-sphere redox couple, to be used as a shuttle. The photovoltaic performance and interfacial charge-transfer dynamics were investigated in DSSCs employing this shuttle. It was found that a single ALD cycle is able to passivate surface states, resulting in a dramatic improvement in photovoltaic performance. Subsequent alumina deposition resulted in exponentially increasing electron lifetimes as a function of alumina layer thickness, indicating that the layers behave as barriers to electron tunneling. The characterization of DSSC photovoltaic performance and interfacial charge-transfer dynamics was extended to cells employing derivatives of ferrocenium and ferrocene featuring more positive redox potentials; these cells yielded larger open-circuit photovoltages.
Co-reporter:Timur Islamoglu, Subhadip Goswami, Zhanyong Li, Ashlee J. Howarth, Omar K. Farha, and Joseph T. Hupp
Accounts of Chemical Research April 18, 2017 Volume 50(Issue 4) pp:805-805
Publication Date(Web):February 8, 2017
DOI:10.1021/acs.accounts.6b00577
ConspectusMetal–organic frameworks (MOFs) are periodic, hybrid, atomically well-defined porous materials that typically form by self-assembly and consist of inorganic nodes (metal ions or clusters) and multitopic organic linkers. MOFs as a whole offer many intriguing properties, including ultrahigh porosity, tunable chemical functionality, and low density. These properties point to numerous potential applications, including gas storage, chemical separations, catalysis, light harvesting, and chemical sensing, to name a few. Reticular chemistry, or the linking of molecular building blocks into predetermined network structures, has been employed to synthesize thousands of MOFs. Given the vast library of candidate nodes and linkers, the number of potentially synthetically accessible MOFs is enormous. Nevertheless, a powerful complementary approach to obtain specific structures with desired chemical functionality is to modify known MOFs after synthesis. This approach is particularly useful when incorporation of particular chemical functionalities via direct synthesis is challenging or impossible. The challenges may stem from limited stability or solubility of precursors, unwanted secondary reactivity of precursors, or incompatibility of functional groups with the conditions needed for direct synthesis. MOFs can be postsynthetically modified by replacing the metal nodes and/or organic linkers or via functionalization of the metal nodes and/or organic linkers.Here we describe some of our efforts toward the development and application of postsynthetic strategies for imparting desired chemical functionalities in MOFs of known topology. The techniques include methods for functionalizing MOF nodes, i.e., solvent-assisted ligand incorporation (SALI) and atomic layer deposition in MOFs (AIM) as well as a method to replace structural linkers, termed solvent-assisted linker exchange (SALE), also known as postsynthethic exchange (PSE). For each functionalization strategy, we first describe its chemical basis along with the requirements for its successful implementation. We then present a small number of examples, with an emphasis on those that (a) convey the underlying concepts and/or (b) lead to functional structures (e.g., catalysts) that would be difficult or impossible to access via direct routes. The examples, however, are only illustrative, and a significant body of work exists from both our lab and others, especially for the SALE/PSE strategy. We refer readers to the papers cited and to the references therein. More exciting, in our view, will be new examples and new applications of the functionalization strategies—especially applications made possible by creatively combining the strategies. Underexplored (again, in our view) are implementations that impart electrical conductivity, enable increasingly selective chemical sensing, or facilitate cascade catalysis. It will be interesting to see where these strategies and others take this compelling field over the next few years.
Co-reporter:Timothy C. Wang, Idan Hod, Cornelius O. Audu, Nicolaas A. Vermeulen, SonBinh T. Nguyen, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces April 12, 2017 Volume 9(Issue 14) pp:12584-12584
Publication Date(Web):March 20, 2017
DOI:10.1021/acsami.6b16834
We report the design and synthesis of a metal–organic framework (MOF)–polythiophene composite that has comparable electronic conductivity to reported conductive 3-D MOFs, but with display and retention of high porosity, including mesoporosity. A robust zirconium MOF, NU-1000, was rendered electronically conductive by first incorporating, via solvent-assisted ligand incorporation (SALI), a carefully designed pentathiophene derivative at a density of one pentamer per hexa-zirconium node. Using a cast film of the intermediate composite (termed pentaSALI) on conductive glass, the incorporated oligothiophene was electrochemically polymerized to yield the conductive composite, Epoly. Depending on the doping level of the polythiophene in the composite, it can be tuned from an insulating state to a semiconduting state with conductivity of 1.3 × 10–7 (S cm–1), which is comparable to values reported for 3-D conductive MOFs. The porosity of the thin-film MOF–polythiophene composite was assessed using decane vapor uptake as determined by quartz crystal microgravimetry (QCM). The results indicate a porosity (pore volume) for Epoly essentially identical to that of bulk pentaSALI, and ∼74% of that of unmodified NU-1000. PentaSALI, and by inference Epoly, displays both micro- and mesoporosity, and features a BET surface area of nearly 1,600 m2·g–1, i.e., substantially larger than yet reported for any other electronically conductive MOF.Keywords: electronic conductivity; electropolymerization; metal−organic framework; polythiophene; QCM porosity measurement; solvent-assisted ligand incorporation;
Co-reporter:J. R. Avila;A. W. Peters;Zhanyong Li;M. A. Ortuño;A. B. F. Martinson;C. J. Cramer;J. T. Hupp;O. K. Farha
Dalton Transactions 2017 vol. 46(Issue 18) pp:5790-5795
Publication Date(Web):2017/05/09
DOI:10.1039/C6DT02572B
To grow films of Cu2O, bis-(dimethylamino-2-propoxide)Cu(II), or Cu(dmap), is used as an atomic layer deposition precursor using only water vapor as a co-reactant. Between 110 and 175 °C, a growth rate of 0.12 ± 0.02 Å per cycle was measured using an in situ quartz crystal microbalance (QCM). X-ray photoelectron spectroscopy (XPS) confirms the growth of metal–oxide films featuring Cu(I).
Co-reporter:Sayed Ali Akbar Razavi, Mohammad Yaser Masoomi, Timur IslamogluAli Morsali, Yan XuJoseph T. Hupp, Omar K. Farha, Jun WangPeter C. Junk
Inorganic Chemistry 2017 Volume 56(Issue 5) pp:
Publication Date(Web):February 14, 2017
DOI:10.1021/acs.inorgchem.6b02758
The rational design of functionalized porous metal–organic frameworks (MOFs) for gas adsorption applications has been applied using three spacer ligands H2DPT (3,6-di(pyridin-4-yl)-1,4-dihydro-1,2,4,5-tetrazine), DPT (3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine), and BPDH (2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) to synthesize TMU-34, [Zn(OBA)(H2DPT)0.5]n·DMF, TMU-34(−2H), [Zn(OBA)(DPT)0.5]n·DMF, and TMU-5, [Zn(OBA)(BPDH)0.5]n·1.5DMF, respectively. By controlling the pore size and chemical functionality of these three MOFs, we can improve the interactions between CO2 and especially CH4 with the frameworks. Calculated Qst(CH4) for TMU-5, TMU-34, and TMU-34(−2H) are 27, 23, and 22 kJ mol–1, respectively. These Qst values are among the highest for CH4–framework interactions. For systematic comparison, two reported frameworks, TMU-4 and TMU-5, have been compared with TMU-34 and TMU-34(−2H) in CO2 adsorption.
Co-reporter:Martino RimoldiVarinia Bernales, Joshua Borycz, Aleksei Vjunov, Leighanne C. Gallington, Ana E. Platero-PratsI. S. Kim, John L. FultonA. B. F. Martinson, Johannes A. Lercher, Karena W. Chapman, Christopher J. Cramer, Laura GagliardiJoseph T. Hupp, Omar K. Farha
Chemistry of Materials 2017 Volume 29(Issue 3) pp:
Publication Date(Web):January 5, 2017
DOI:10.1021/acs.chemmater.6b03880
NU-1000, a zirconium-based metal–organic framework (MOF) featuring mesoporous channels, has been postsynthetically metalated via atomic layer deposition in a MOF (AIM) employing dimethylaluminum iso-propoxide ([AlMe2OiPr]2, DMAI), a milder precursor than widely used trimethylaluminum (AlMe3, TMA). The aluminum-modified NU-1000 (Al-NU-1000) has been characterized with a comprehensive suite of techniques that points to the formation of aluminum oxide clusters well dispersed through the framework and stabilized by confinement within small pores intrinsic to the NU-1000 structure. Experimental evidence allows for identification of spectroscopic similarities between Al-NU-1000 and γ-Al2O3. Density functional theory modeling provides structures and simulated spectra, the relevance of which can be assessed via comparison to experimental IR and EXAFS data. The catalytic performance of Al-NU-1000 has been benchmarked against γ-Al2O3, with promising results in terms of selectivity.
Co-reporter:Zhanyong LiAaron W. Peters, Varinia Bernales, Manuel A. Ortuño, Neil M. Schweitzer, Matthew R. DeStefano, Leighanne C. Gallington, Ana E. Platero-PratsKarena W. Chapman, Christopher J. Cramer, Laura Gagliardi, Joseph T. HuppOmar K. Farha
ACS Central Science 2017 Volume 3(Issue 1) pp:
Publication Date(Web):November 30, 2016
DOI:10.1021/acscentsci.6b00290
Zr-based metal–organic frameworks (MOFs) have been shown to be excellent catalyst supports in heterogeneous catalysis due to their exceptional stability. Additionally, their crystalline nature affords the opportunity for molecular level characterization of both the support and the catalytically active site, facilitating mechanistic investigations of the catalytic process. We describe herein the installation of Co(II) ions to the Zr6 nodes of the mesoporous MOF, NU-1000, via two distinct routes, namely, solvothermal deposition in a MOF (SIM) and atomic layer deposition in a MOF (AIM), denoted as Co-SIM+NU-1000 and Co-AIM+NU-1000, respectively. The location of the deposited Co species in the two materials is determined via difference envelope density (DED) analysis. Upon activation in a flow of O2 at 230 °C, both materials catalyze the oxidative dehydrogenation (ODH) of propane to propene under mild conditions. Catalytic activity as well as propene selectivity of these two catalysts, however, is different under the same experimental conditions due to differences in the Co species generated in these two materials upon activation as observed by in situ X-ray absorption spectroscopy. A potential reaction mechanism for the propane ODH process catalyzed by Co-SIM+NU-1000 is proposed, yielding a low activation energy barrier which is in accord with the observed catalytic activity at low temperature.
Co-reporter:Matthew R. DeStefanoTimur Islamoglu, Sergio J. GaribayJoseph T. Hupp, Omar K. Farha
Chemistry of Materials 2017 Volume 29(Issue 3) pp:
Publication Date(Web):January 6, 2017
DOI:10.1021/acs.chemmater.6b05115
UiO-66 is an archetypal zirconium-based metal–organic framework (MOF) that is constructed from hexanuclear zirconium oxide clusters as secondary building units (SBUs) and 1,4-benzenedicarboxylate (bdc) linkers. For the first time, a room-temperature solution-based synthesis is reported for UiO-66 and several of its derivatives, UiO-66-X (X = NH2, OH, or NO2), resulting in materials that are as porous and crystalline as those made at elevated temperatures. In addition, via modulation of the temperature at which UiO-66 is synthesized, the number of defect sites can be varied. It was found through N2 sorption isotherm analysis and potentiometric acid–base titrations that increasing the synthesis temperature from 25 to 130 °C results in a systematic decrease in the number of defect sites in UiO-66. The results suggest that, with respect to this synthetic procedure, a maximal number of defect sites is achieved [∼1.3 missing linkers per Zr6O4(OH)4(bdc)6] at a temperature of 45 °C.
Co-reporter:Carla F. Pereira;Ashlee J. Howarth;Nicolaas A. Vermeulen;Filipe A. Almeida Paz;João P. C. Tomé;Omar K. Farha
Materials Chemistry Frontiers 2017 vol. 1(Issue 6) pp:1194-1199
Publication Date(Web):2017/06/01
DOI:10.1039/C6QM00364H
Solvent-assisted linker exchange (SALE) is performed on the Zr-based metal–organic framework (MOF), UiO-66, to exchange benzene-1,4-dicarboxylate with benzene-1,4-dihydroxamate linkers. Characterization of the material before and after SALE is performed using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen adsorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and thermogravimetric analysis (TGA). The stability of the parent and daughter material is evaluated at pH 1 and 12 and the structural integrity evaluated by PXRD, mass balance and porosity measurements.
Co-reporter:Zhanyong Li;Aaron W. Peters;Jian Liu;Xuan Zhang;Neil M. Schweitzer;Omar K. Farha
Inorganic Chemistry Frontiers 2017 vol. 4(Issue 5) pp:820-824
Publication Date(Web):2017/05/16
DOI:10.1039/C7QI00056A
Ni(II) ions have been deposited on the Zr6 nodes of a metal–organic framework (MOF), UiO-66, via an ALD-like process (ALD = atomic layer deposition). By varying the number of ALD cycles, three Ni-decorated UiO-66 materials were synthesized. A suite of physical methods has been used to characterize these materials, indicating structural and high-surface-area features of the parent MOF are retained. Elemental analysis via X-ray photoelectron spectroscopy (XPS) indicates that the anchored Ni ions are mainly on surface and near-surface MOF defect sites. Upon activation, all three materials are catalytic for ethylene hydrogenation, but their catalytic activities significantly vary, with the largest clusters displaying the highest per-nickel-atom activity. The study highlights the ease and effectiveness of ALD in MOFs (AIM) for synthesizing, specifically, UiO-66-supported NiyOx catalysts.
Co-reporter:Hyunho Noh, Yuexing Cui, Aaron W. Peters, Dale R. Pahls, Manuel A. Ortuño, Nicolaas A. Vermeulen, Christopher J. Cramer, Laura Gagliardi, Joseph T. Hupp, and Omar K. Farha
Journal of the American Chemical Society 2016 Volume 138(Issue 44) pp:14720-14726
Publication Date(Web):October 25, 2016
DOI:10.1021/jacs.6b08898
Molybdenum(VI) oxide was deposited on the Zr6 node of the mesoporous metal–organic framework NU-1000 via condensed-phase deposition where the MOF is simply submerged in the precursor solution, a process named solvothermal deposition in MOFs (SIM). Exposure to oxygen leads to a monodisperse, porous heterogeneous catalyst, named Mo-SIM, and its structure on the node was elucidated both computationally and spectroscopically. The catalytic activity of Mo-SIM was tested for the epoxidation of cyclohexene. Near-quantitative yields of cyclohexene oxide and the ring-opened 1,2-cyclohexanediol were observed, indicating activity significantly higher than that of molybdenum(VI) oxide powder and comparable to that of a zirconia-supported analogue (Mo-ZrO2) prepared in a similar fashion. Despite the well-known leaching problem of supported molybdenum catalysts (i.e., loss of Mo species thus causes deactivation), Mo-SIM demonstrated no loss in the metal loading before and after catalysis, and no molybdenum was detected in the reaction mixture. In contrast, Mo-ZrO2 led to significant leaching and close to 80 wt % loss of the active species. The stability of Mo-SIM was further confirmed computationally, with density functional theory calculations indicating that the dissociation of the molybdenum(VI) species from the node of NU-1000 is endergonic, corroborating the experimental data for the Mo-SIM material.
Co-reporter:Qishui Chen, Junling Sun, Peng Li, Idan Hod, Peyman Z. Moghadam, Zachary S. Kean, Randall Q. Snurr, Joseph T. Hupp, Omar K. Farha, and J. Fraser Stoddart
Journal of the American Chemical Society 2016 Volume 138(Issue 43) pp:14242-14245
Publication Date(Web):October 24, 2016
DOI:10.1021/jacs.6b09880
We describe the incorporation of a bistable mechanically interlocked molecule (MIM) into a robust Zr-based metal–organic framework (MOF), NU-1000, by employing a post-synthetic functionalization protocol. On average, close to two bistable [2]catenanes can be incorporated per repeating unit of the hexagonal channels of NU-1000. The reversible redox-switching of the bistable [2]catenanes is retained inside the MOF, as evidenced by solid-state UV-vis-NIR reflectance spectroscopy and cyclic voltammetry. This research demonstrates that bistable MIMs are capable of exhibiting robust dynamics inside the nanopores of a MOF.
Co-reporter:Pravas Deria, Diego A. Gómez-Gualdrón, Idan Hod, Randall Q. Snurr, Joseph T. Hupp, and Omar K. Farha
Journal of the American Chemical Society 2016 Volume 138(Issue 43) pp:14449-14457
Publication Date(Web):October 21, 2016
DOI:10.1021/jacs.6b09113
Catalytic activity for acyl transfer from N-acetylimidazole (NAI) to different pyridylcarbinol (PC) regioisomers (2-PC, 3-PC, and 4-PC) is demonstrated for a set of topologically diverse, zirconium-based (porphinato)zinc metal–organic frameworks (MOFs). The MOFs studied are PCN-222, MOF-525, and NU-902, which are based on the csq, ftw, and scu topologies, respectively. The experimentally obtained reaction kinetics are discussed in light of molecular modeling results. The catalytic activity is shown to vary across the series of MOFs due to the different extent to which each topology facilitates reactant preconcentration and alignment of PC and NAI via coordination to framework porphyrin sites (orientation effects). Trends of experimental initial reaction rates with MOF topology and PC regioisomer are consistent with preconcentration effects, which depend on the number of porphyrin sites per volume of MOF, as well as with orientation effects, which depend on the number of porphyrin pairs per volume of MOF that bind PC and NAI in such a way that they are primed to form the required transition state. The present work shows how the proper alignment of catalytic linkers can enhance reaction rates in MOFs.
Co-reporter:Zhanyong Li; Neil M. Schweitzer; Aaron B. League; Varinia Bernales; Aaron W. Peters; Andrew “Bean” Getsoian; Timothy C. Wang; Jeffrey T. Miller; Aleksei Vjunov; John L. Fulton; Johannes A. Lercher; Christopher J. Cramer; Laura Gagliardi; Joseph T. Hupp;Omar K. Farha
Journal of the American Chemical Society 2016 Volume 138(Issue 6) pp:1977-1982
Publication Date(Web):February 2, 2016
DOI:10.1021/jacs.5b12515
Developing supported single-site catalysts is an important goal in heterogeneous catalysis since the well-defined active sites afford opportunities for detailed mechanistic studies, thereby facilitating the design of improved catalysts. We present herein a method for installing Ni ions uniformly and precisely on the node of a Zr-based metal–organic framework (MOF), NU-1000, in high density and large quantity (denoted as Ni-AIM) using atomic layer deposition (ALD) in a MOF (AIM). Ni-AIM is demonstrated to be an efficient gas-phase hydrogenation catalyst upon activation. The structure of the active sites in Ni-AIM is proposed, revealing its single-site nature. More importantly, due to the organic linker used to construct the MOF support, the Ni ions stay isolated throughout the hydrogenation catalysis, in accord with its long-term stability. A quantum chemical characterization of the catalyst and the catalytic process complements the experimental results. With validation of computational modeling protocols, we further targeted ethylene oligomerization catalysis by Ni-AIM guided by theoretical prediction. Given the generality of the AIM methodology, this emerging class of materials should prove ripe for the discovery of new catalysts for the transformation of volatile substrates.
Co-reporter:Rachel C. Klet, Timothy C. Wang, Laura E. Fernandez, Donald G. Truhlar, Joseph T. Hupp, and Omar K. Farha
Chemistry of Materials 2016 Volume 28(Issue 4) pp:1213
Publication Date(Web):February 10, 2016
DOI:10.1021/acs.chemmater.5b04887
The combination (AIM-ME) of atomic layer deposition in metal–organic frameworks (MOFs) and metal exchange (ME) is introduced as a technique to install dispersed metal atoms into the mesoporous MOF, NU-1000. Zn-AIM, which contains four Zn atoms per Zr6 node, has been synthesized through AIM and further characterized through density functional calculations to provide insight into the possible structure. Zn-AIM was then subjected to modification via transmetalation to yield uniform porous materials that present nonstructural Cu, Co, or Ni atoms.
Co-reporter:Rachel C. Klet, Yangyang Liu, Timothy C. Wang, Joseph T. Hupp and Omar K. Farha
Journal of Materials Chemistry A 2016 vol. 4(Issue 4) pp:1479-1485
Publication Date(Web):12 Jan 2016
DOI:10.1039/C5TA07687K
Potentiometric acid–base titration is introduced as a method to evaluate pKa values (Brønsted acidity) of protons present in the nodes of water stable Zr6- and Hf6-based metal–organic frameworks (MOFs), including UiO-type MOFs, NU-1000, and MOF-808. pKa values were determined for the three typical types of protons present in these MOFs: μ3-OH, M–OH2, and M–OH (M = Zr, Hf). Additionally, the data was used to quantify defect sites resulting from either a surfeit or shortage of linkers in the MOFs and to provide information about the true proton topology of each material.
Co-reporter:Subhadip Goswami, Lin Ma, Alex B. F. Martinson, Michael R. Wasielewski, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 45) pp:30863
Publication Date(Web):October 21, 2016
DOI:10.1021/acsami.6b08552
Owing to their ability to act as light-harvesting scaffolds, porphyrin-containing metal–organic frameworks (MOFs) are in the forefront of research on the application of highly ordered molecular materials to problems in solar-energy conversion. In this work, solvent-assisted linker exchange (SALE) is performed on a pillared paddlewheel porphyrin containing MOF thin film to collapse a 3D framework to a 2D framework. The change in dimensionality of the framework is confirmed by a decrease in the film thickness, the magnitude of which is in agreement with crystallographic parameters for related bulk materials. Furthermore, NMR spectroscopy performed on the digested sample suggests a similar change in geometry is achieved in bulk MOF samples. The decreased distance between the porphyrin chromophores in the 2D MOF film compared to the 3D film results in enhanced energy transfer through the film. The extent of energy transport was probed by assembling MOF thin film where the outermost layers are palladium porphyrin (P2) units, which act as energy traps and fluorescence quenchers. Steady-state emission spectroscopy together with time-resolved emission spectroscopy indicates that excitons can travel through about 9–11 layers (porphyrin layers) in 2D films, whereas in 3D films energy transfer occurs through no more than about 6–8 layers. The results are difficult to understand if only changes in MOF interlayer spacing are considered but become much more understandable if dipole–dipole coupling distances are considered.Keywords: energy transfer; fluorescence quencher; layer-by-layer; metal−organic framework; postsynthetic modification
Co-reporter:Unal Sen, Mustafa Erkartal, Chung-Wei Kung, Vijay Ramani, Joseph T. Hupp, and Omar K. Farha
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 35) pp:23015
Publication Date(Web):August 19, 2016
DOI:10.1021/acsami.6b05901
Herein, a room temperature chemical process to synthesize functional, hollow nanostructures from zeolitic imidazolate framework-8 (ZIF-8) and poly(vinylphosphonic acid) (PVPA) is reported. Syntheses are initiated by physically blending the components—a process that is accompanied first by encapsulation of ZIF-8 crystallites by PVPA and then by fragmentation of the crystallites. The fragmentation process is driven by partial displacement of the methyl-imidazolate ligands of Zn(II) in ZIF-8 by phosphonate groups on PVPA. Differences in rates of diffusion for the components of the reactive mixture yield a Kirkendall-like effect that is expressed as a hollow-particle morphology. The obtained hollow nanostructures feature hybrid shells containing PVPA, ZIF-8, and their cross-reacted products. The hybrid structures display substantial proton conductivities that increase with increasing temperature, even under the anhydrous conditions prevailing at temperatures above the boiling point of water. For example, at T = 413 K the proton conductivity of ZIF-8@PVPA reaches 3.2 (±0.12) × 10–3 S cm–1, a value comparatively higher than that for PVPA (or ZIF-8) in isolation. The high value may reflect the availability in the hybrid structures of free (and partially free), amphoteric imidazole species, and their hydrogen-bonding interactions with phosphonate and/or phosphonic acid units. The persistence of ample conductivity at high temperature reflects the elimination of phosphonic acid group dehydration and dimerization—an effect that strikingly degrades the conductivity of pure PVPA under anhydrous conditions.Keywords: fuel cell; hollow nanostructures; proton conductivity; PVPA; ZIF-8
Co-reporter:Aaron W. Peters, Zhanyong Li, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 32) pp:20675
Publication Date(Web):August 3, 2016
DOI:10.1021/acsami.6b04729
Few-atom clusters composed of nickel and sulfur have been successfully installed into the Zr(IV)-based metal–organic framework (MOF) NU-1000 via ALD-like chemistry (ALD = atomic layer deposition). X-ray photoelectron spectroscopy and Raman spectroscopy are used to determine that primarily Ni2+ and S2– sites are deposited within the MOF. In a pH 7 buffered aqueous solution, the porous catalyst is able to produce H2 gas at a rate of 3.1 mmol g–1 h–1 upon UV irradiation, whereas no H2 is generated by irradiating bare NU-1000. Upon visible light irradiation, little H2 generation was observed; however, with the addition of an organic dye, rose bengal, NiS-AIM can catalyze the production of H2 at an enhanced rate of 4.8 mmol g–1 h–1. These results indicate that ALD in MOFs (AIM) can engender reactivity within high surface area supports for applications in the solar fuels field.Keywords: atomic layer deposition; hydrogen evolution; metal−organic framework; nickel sulfide; photocatalysis
Co-reporter:Jason R. Avila, Jonathan D. Emery, Michael J. Pellin, Alex B. F. Martinson, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 31) pp:19853
Publication Date(Web):July 25, 2016
DOI:10.1021/acsami.6b05427
Examinations of enzymatic catalysts suggest one key to efficient catalytic activity is discrete size metallo clusters. Mimicking enzymatic cluster systems is synthetically challenging because conventional solution methods are prone to aggregation or require capping of the cluster, thereby limiting its catalytic activity. We introduce site-selective atomic layer deposition (ALD) on porphyrins as an alternative approach to grow isolated metal oxide islands that are spatially separated. Surface-bound tetra-acid free base porphyrins (H2TCPP) may be metalated with Mn using conventional ALD precursor exposure to induce homogeneous hydroxide synthetic handles which acts as a nucleation point for subsequent ALD MnO island growth. Analytical fitting of in situ QCM mass uptake reveals island growth to be hemispherical with a convergence radius of 1.74 nm. This growth mode is confirmed with synchrotron grazing-incidence small-angle X-ray scattering (GISAXS) measurements. Finally, we extend this approach to other ALD chemistries to demonstrate the generality of this route to discrete metallo island materials.Keywords: atomic layer deposition; grazing incident small angle scattering; island nucleation; manganese oxide; porphyrin; quartz crystal microbalance; vapor metalation
Co-reporter:Idan Hod, Omar K. Farha and Joseph T. Hupp
Chemical Communications 2016 vol. 52(Issue 8) pp:1705-1708
Publication Date(Web):15 Dec 2015
DOI:10.1039/C5CC09695B
Herein we demonstrate the use of host–guest chemistry to modulate rates of charge transport in metal–organic framework (MOF) films. The kinetics of site-to-site of charge hopping and, in turn, the overall redox conductivity, of a ferrocene-modified MOF can be altered by up to 30-fold by coupling electron exchange to the oxidation-state-dependent formation of inclusion complexes between cyclodextrin and channel-tethered metallocenes.
Co-reporter:Sol Ahn, Nicholas E. Thornburg, Zhanyong Li, Timothy C. Wang, Leighanne C. Gallington, Karena W. Chapman, Justin M. Notestein, Joseph T. Hupp, and Omar K. Farha
Inorganic Chemistry 2016 Volume 55(Issue 22) pp:11954
Publication Date(Web):October 31, 2016
DOI:10.1021/acs.inorgchem.6b02103
Developing structurally well-defined, supported oxide catalysts remains a significant challenge. Here, we report the grafting of Nb(V) oxide sites onto the nodes of the Zr-based metal organic framework (MOF) NU-1000 as a stable, well-defined catalyst support. Nb(V) oxide was deposited with loadings up to 1.6 mmol/g via two postsynthetic methods: atomic layer deposition in a MOF, and solution-phase grafting in a MOF. Difference envelope density measurements indicated that the two synthetic methods resulted in different local structures of the Nb(V) ions within NU-1000. Despite their high Nb(V) loadings, which were equivalent to >60% surface coverage, nearly all Nb(V) sites of the MOF-supported catalysts were active sites for alkene epoxidation, as confirmed by phenylphosphonic acid titration. The MOF-supported catalysts were more selective than the control Nb-ZrO2 catalyst for cyclohexene epoxidation with aqueous H2O2 and were far more active on a gravimetric basis.
Co-reporter:Casey J. Stephenson, Joseph T. Hupp, and Omar K. Farha
Inorganic Chemistry 2016 Volume 55(Issue 4) pp:1361-1363
Publication Date(Web):January 29, 2016
DOI:10.1021/acs.inorgchem.5b02880
2-Methylimidazolate linkers of Pt@ZIF-8 are exchanged with imidazolate using solvent-assisted linker exchange (SALE) to expand the apertures of the parent material and create Pt@SALEM-2. Characterization of the material before and after SALE was performed. Both materials are active as catalysts for the hydrogenation of 1-octene, whereas the hydrogenation of cis-cyclohexene occurred only with Pt@SALEM-2, consistent with larger apertures for the daughter material. The largest substrate, β-pinene, proved to be unreactive with H2 when either material was employed as a candidate catalyst, supporting the contention that substrate molecules, for both composites, must traverse the metal–organic framework component in order to reach the catalytic nanoparticles.
Co-reporter:Ashlee J. Howarth, Timothy C. Wang, Salih S. Al-Juaid, Saadullah G. Aziz, Joseph T. Hupp and Omar K. Farha
Dalton Transactions 2016 vol. 45(Issue 1) pp:93-97
Publication Date(Web):18 Nov 2015
DOI:10.1039/C5DT04163E
A Zr-based MOF, NU-1000, comprised of Zr6 nodes and tetratopic pyrene-containing linkers is studied for adsorption and extraction of SO42− from water. The adsorption capacity and uptake time of SO42− in NU-1000 is determined at varying concentrations to give an overall maximum adsorption capacity of 56 mg SO42− per g of MOF. Selective adsorption of SO42− by NU-1000 in the presence of other anions as well as regeneration of the sorbent is also explored.
Co-reporter:Yan Xu, Ashlee J. Howarth, Timur Islamoglu, Cleiser T. da Silva, Joseph T. Hupp, Omar K. Farha
Inorganic Chemistry Communications 2016 Volume 67() pp:60-63
Publication Date(Web):May 2016
DOI:10.1016/j.inoche.2016.03.002
•A non-catenated nickel (II) pillared paddlewheel metal-organic framework is prepared;•The combination of solvent-assisted linker exchange and transmetallation is applied;•The Ni(II)-based metal-organic framework appears to be unattainable de novo;•Ni(II)-MOF has enhanced N2 uptake compared to its isostructural Zn(II) analogue.A non-catenated nickel (II) pillared paddlewheel metal-organic framework is synthesized through a combination of solvent-assisted linker exchange and transmetallation. Compared to its isostructural Zn(II) analogue, the nickel (II) pillared paddlewheel metal-organic framework features an enhanced N2 sorption performance. It is notable that the nickel (II)-based metal-organic framework could not (in our hands) be synthesized de novo. The experimental results validate that multiple building-block-replacement (BBR) methods can be utilized to access materials that are challenging to synthesize directly.A new non-catenated nickel (II) pillar-layer metal-organic framework is achieved through the combination of solvent-assisted linker exchange (SALE) and transmetallation.
Co-reporter:Dr. Peng Li;Dr. Nicolaas A. Vermeulen;Xirui Gong;Dr. Christos D. Malliakas; J. Fraser Stoddart; Joseph T. Hupp; Omar K. Farha
Angewandte Chemie International Edition 2016 Volume 55( Issue 35) pp:10358-10362
Publication Date(Web):
DOI:10.1002/anie.201605547
Abstract
Ionic metal–organic frameworks (MOFs) are a subclass of porous materials that have the ability to incorporate different charged species in confined nanospace by ion-exchange. To date, however, very few examples combining mesoporosity and water stability have been realized in ionic MOF chemistry. Herein, we report the rational design and synthesis of a water-stable anionic mesoporous MOF based on uranium and featuring tbo-type topology. The resulting tbo MOF exhibits exceptionally large open cavities (3.9 nm) exceeding those of all known anionic MOFs. By supercritical CO2 activation, a record-high Brunauer-Emmett-Teller (BET) surface area (2100 m2 g−1) for actinide-based MOFs has been obtained. Most importantly, however, this new uranium-based MOF is water-stable and able to absorb positively charged ions selectively over negatively charged ones, enabling the efficient separation of organic dyes and biomolecules.
Co-reporter:Dr. Peng Li;Dr. Nicolaas A. Vermeulen;Xirui Gong;Dr. Christos D. Malliakas; J. Fraser Stoddart; Joseph T. Hupp; Omar K. Farha
Angewandte Chemie 2016 Volume 128( Issue 35) pp:10514-10518
Publication Date(Web):
DOI:10.1002/ange.201605547
Abstract
Ionic metal–organic frameworks (MOFs) are a subclass of porous materials that have the ability to incorporate different charged species in confined nanospace by ion-exchange. To date, however, very few examples combining mesoporosity and water stability have been realized in ionic MOF chemistry. Herein, we report the rational design and synthesis of a water-stable anionic mesoporous MOF based on uranium and featuring tbo-type topology. The resulting tbo MOF exhibits exceptionally large open cavities (3.9 nm) exceeding those of all known anionic MOFs. By supercritical CO2 activation, a record-high Brunauer-Emmett-Teller (BET) surface area (2100 m2 g−1) for actinide-based MOFs has been obtained. Most importantly, however, this new uranium-based MOF is water-stable and able to absorb positively charged ions selectively over negatively charged ones, enabling the efficient separation of organic dyes and biomolecules.
Co-reporter:William L. Hoffeditz
The Journal of Physical Chemistry C 2016 Volume 120(Issue 7) pp:3731-3740
Publication Date(Web):February 10, 2016
DOI:10.1021/acs.jpcc.6b01020
Dye-sensitized solar cells (DSCs) are an established alternative photovoltaic technology that offers numerous potential advantages in solar energy applications. However, this technology has been limited by the availability of molecular redox couples that are both noncorrosive/nontoxic and do not diminish the performance of the device. In an effort to overcome these shortcomings, a copper-containing redox shuttle derived from 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (PDTO) ligand and the common DSC additive 4-tert-butylpyridine (TBP) was investigated. Electrochemical measurements, single-crystal X-ray diffraction, and absorption and electron paramagnetic resonance spectroscopies reveal that, upon removal of one metal-centered electron, PDTO-enshrouded copper ions completely shed the tetradentate PDTO ligand and replace it with four or more TBP ligands. Thus, the Cu(I) and Cu(II) forms of the electron shuttle have completely different coordination spheres and are characterized by widely differing Cu(II/I) formal potentials and reactivities for forward versus reverse electron transfer. Notably, the coordination-sphere replacement process is fully reversed upon converting Cu(II) back to Cu(I). In cells featuring an adsorbed organic dye and a nano- and mesoparticulate, TiO2-based, photoelectrode, the dual species redox shuttle system engenders performance superior to that obtained with shuttles based on the (II/I) forms of either of the coordination complexes in isolation.
Co-reporter:Jason R. Avila, Michael J. Katz, Omar K. Farha, and Joseph T. Hupp
The Journal of Physical Chemistry C 2016 Volume 120(Issue 37) pp:20922-20928
Publication Date(Web):July 11, 2016
DOI:10.1021/acs.jpcc.6b02651
Electron transfer (ET) phenomena at and near semiconductor/molecule interfaces are of fundamental significance for applications involving liquid-junction photovoltaics, organic photovoltaics, and electrochemical heterogeneous catalysis. To probe mechanisms of electron delivery through barrier layers at such interfaces, we make use of atomic layer deposition to deposit ultrathin films of TiO2 conformally onto SnO2 electrodes. In the presence of TiO2 films (i.e., barrier layers) up to 10 Å thick, electrons are delivered from the electrode to molecules in solution by tunneling through the layers, as evidenced, in part, by an exponential decrease in ET rate with layer thickness. For films thicker than 10 Å, there is little change in ET rate as a function of TiO2 thickness. To our surprise, thermally annealing a 55 Å layer of TiO2 on SnO2 yielded a 10-fold decrease in ET rate compared to that imposed by the as-deposited layer. At applied potentials near the conduction-band edge of SnO2, and significantly below the band edge of TiO2, electrochemical impedance spectroscopy with nominally flat, as-deposited TiO2 indicates the presence of nearly twice the density of electronic states as found with air-annealed samples. These and related observations point to a barrier-layer-thickness-dependent change in the mechanism of electron delivery, from the underlying electrode to solution species, from one based on tunneling to one entailing trap-facilitated hopping. The findings have design implications for the application of interfacial barrier layers to electrochemical and photoelectrochemical problems.
Co-reporter:Yasemin Çimen, Aaron W. Peters, Jason R. Avila, William L. Hoffeditz, Subhadip Goswami, Omar K. Farha, and Joseph T. Hupp
Langmuir 2016 Volume 32(Issue 46) pp:12005-12012
Publication Date(Web):November 7, 2016
DOI:10.1021/acs.langmuir.6b02699
Transition metal sulfides show great promise for applications ranging from catalysis to electrocatalysis to photovoltaics due to their high stability and conductivity. Nickel sulfide, particularly known for its ability to electrochemically reduce protons to hydrogen gas nearly as efficiently as expensive noble metals, can be challenging to produce with certain surface site compositions or morphologies, e.g., conformal thin films. To this end, we employed atomic layer deposition (ALD), a preeminent method to fabricate uniform and conformal films, to construct thin films of nickel sulfide (NiSx) using bis(N,N′-di-tert-butylacetamidinato)nickel(II) (Ni(amd)2) vapor and hydrogen sulfide gas. Effects of experimental conditions such as pulse and purge times and temperature on the growth of NiSx were investigated. These revealed a wide temperature range, 125–225 °C, over which self-limiting NiSx growth can be observed. In situ quartz crystal microbalance (QCM) studies revealed conventional linear growth behavior for NiSx films, with a growth rate of 9.3 ng/cm2 per cycle being obtained. The ALD-synthesized films were characterized using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) methods. To assess the electrocatalyitic activity of NiSx for evolution of molecular hydrogen, films were grown on conductive-glass supports. Overpotentials at a current density of 10 mA/cm2 were recorded in both acidic and pH 7 phosphate buffer aqueous reaction media and found to be 440 and 576 mV, respectively, with very low NiSx loading. These results hint at the promise of ALD-grown NiSx materials as water-compatible electrocatalysts.
Co-reporter:Casey J. Stephenson;Cassra L. Whitford; Peter C. Stair; Omar K. Farha; Joseph T. Hupp
ChemCatChem 2016 Volume 8( Issue 4) pp:855-860
Publication Date(Web):
DOI:10.1002/cctc.201501171
Abstract
Au nanoparticles of size 2.2 nm were encapsulated in a zeolitic imidazolate framework ZIF-8 framework (Au@ZIF-8). The composite was used as a catalyst for the selective hydrogenation of crotonaldehyde to crotyl alcohol with 90–95 % selectivity. Hydrogenation of 1-hexene yielded n-hexane in approximately the same conversion as crotonaldehyde, whereas cis-cyclohexene did not detectably react. To account for the confined environment of the ZIF, we supported Au nanoparticles on the outside of ZIF-8 (Au/ZIF-8). Using Au/ZIF-8 as a catalyst, 1-hexene and cis-cyclohexene were hydrogenated in low conversion whereas crotonaldehyde would only react at higher pressures in 70 % selectivity towards crotyl alcohol. Post-experiment TEM analysis of Au/ZIF-8 showed significant sintering whereas the median particle size of Au@ZIF-8 remained almost unchanged. Au@ZIF-8 was recycled as a catalyst for the hydrogenation of crotonaldehyde three times without significant loss of activity or selectivity.
Co-reporter:Pravas Deria; Diego A. Gómez-Gualdrón; Wojciech Bury; Herbert T. Schaef; Timothy C. Wang; Praveen K. Thallapally; Amy A. Sarjeant; Randall Q. Snurr; Joseph T. Hupp;Omar K. Farha
Journal of the American Chemical Society 2015 Volume 137(Issue 40) pp:13183-13190
Publication Date(Web):September 20, 2015
DOI:10.1021/jacs.5b08860
“Breathing” metal–organic frameworks (MOFs) are an emerging class of soft porous crystals (SPCs) with potential for high working capacity for gas storage applications. However, most breathing MOFs have low stability and/or low surface area. Here we report a water-stable, high surface area, breathing MOF of ftw topology, NU-1105. While Zr6-oxo clusters as nodes introduce water stability in NU-1105, its high surface area and breathing character stem from its pyrene-based tetracarboxylate (Py-FP) linkers, in which the fluorene units (F) in the FP “arms” play a key role in promoting breathing behavior. During gas sorption studies, the “closed pore” (cp) ↔ “open pore” (op) transition of NU-1105 occurs at a propane pressure of ∼3 bar. At 1 bar, NU-1105 is in its cp form and adsorbs less propane than it would in its op form, highlighting improved working capacity. In situ powder X-ray diffraction during propane sorption was used to track the cp ↔ op transition, and molecular modeling was used to elucidate the structure of the op and cp forms of NU-1105. According to TD-DFT calculations, the proposed conformations of the Py-FP linkers in the op and cp forms are consistent with the measured excitation and emission spectra of the op and cp forms of NU-1105. Similar structural transitions are also observed in the porphyrinic MOF NU-1104 depending on the identity of the porphyrin core; we observed breathing behavior if the constituent Por-PTP linker is nonmetalated.
Co-reporter:M. Hassan Beyzavi; Nicolaas A. Vermeulen; Ashlee J. Howarth; Samat Tussupbayev; Aaron B. League; Neil M. Schweitzer; James R. Gallagher; Ana E. Platero-Prats; Nema Hafezi; Amy A. Sarjeant; Jeffrey T. Miller; Karena W. Chapman; J. Fraser Stoddart; Christopher J. Cramer; Joseph T. Hupp;Omar K. Farha
Journal of the American Chemical Society 2015 Volume 137(Issue 42) pp:13624-13631
Publication Date(Web):October 4, 2015
DOI:10.1021/jacs.5b08440
Tandem catalytic systems, often inspired by biological systems, offer many advantages in the formation of highly functionalized small molecules. Herein, a new metal–organic framework (MOF) with porphyrinic struts and Hf6 nodes is reported. This MOF demonstrates catalytic efficacy in the tandem oxidation and functionalization of styrene utilizing molecular oxygen as a terminal oxidant. The product, a protected 1,2-aminoalcohol, is formed selectively and with high efficiency using this recyclable heterogeneous catalyst. Significantly, the unusual regioselective transformation occurs only when an Fe-decorated Hf6 node and the Fe–porphyrin strut work in concert. This report is an example of concurrent orthogonal tandem catalysis.
Co-reporter:Rachel C. Klet; Samat Tussupbayev; Joshua Borycz; James R. Gallagher; Madelyn M. Stalzer; Jeffrey T. Miller; Laura Gagliardi; Joseph T. Hupp; Tobin J. Marks; Christopher J. Cramer; Massimiliano Delferro;Omar K. Farha
Journal of the American Chemical Society 2015 Volume 137(Issue 50) pp:15680-15683
Publication Date(Web):December 14, 2015
DOI:10.1021/jacs.5b11350
A structurally well-defined mesoporous Hf-based metal–organic framework (Hf-NU-1000) is employed as a well-defined scaffold for a highly electrophilic single-site d0 Zr–benzyl catalytic center. This new material Hf-NU-1000-ZrBn is fully characterized by a variety of spectroscopic techniques and DFT computation. Hf-NU-1000-ZrBn is found to be a promising single-component catalyst (i.e., not requiring a catalyst/activator) for ethylene and stereoregular 1-hexene polymerization.
Co-reporter:Michael J. Katz, Su-Young Moon, Joseph E. Mondloch, M. Hassan Beyzavi, Casey J. Stephenson, Joseph T. Hupp and Omar K. Farha
Chemical Science 2015 vol. 6(Issue 4) pp:2286-2291
Publication Date(Web):24 Feb 2015
DOI:10.1039/C4SC03613A
The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO2 and UiO-66-(OH)2 showed little to no change in hydrolysis rate. However, UiO-66-NH2 showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe2 and UiO-67-NH2. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH2 is a faster catalyst than UiO-67 and UiO-67-NMe2. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.
Co-reporter:Pravas Deria, Yongchul G. Chung, Randall Q. Snurr, Joseph T. Hupp and Omar K. Farha
Chemical Science 2015 vol. 6(Issue 9) pp:5172-5176
Publication Date(Web):01 Jul 2015
DOI:10.1039/C5SC01784J
Water stability in metal–organic frameworks (MOFs) is critical for several practical applications. While water instability is mainly thought to stem from linker hydrolysis, MOFs with strong, hydrolysis-resistant metal-linker bonds can be susceptible to damage by capillary forces, which cause cavities and channels to collapse during activation from water. This study utilizes metal node functionalization as a strategy to create vapor-stable and recyclable MOFs.
Co-reporter:Sherzod T. Madrahimov, James R. Gallagher, Guanghui Zhang, Zachary Meinhart, Sergio J. Garibay, Massimiliano Delferro, Jeffrey T. Miller, Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen
ACS Catalysis 2015 Volume 5(Issue 11) pp:6713
Publication Date(Web):September 23, 2015
DOI:10.1021/acscatal.5b01604
NU-1000-(bpy)NiII, a highly porous MOF material possessing well-defined (bpy)NiII moieties, was prepared through solvent-assisted ligand incorporation (SALI). Treatment with Et2AlCl affords a single-site catalyst with excellent catalytic activity for ethylene dimerization (intrinsic activity for butenes that is up to an order of magnitude higher than the corresponding (bpy)NiCl2 homogeneous analogue) and stability (can be reused at least three times). The high porosity of this catalyst results in outstanding levels of activity at ambient temperature in gas-phase ethylene dimerization reactions, both under batch and continuous flow conditions.Keywords: (bipyridyl)nickel complexes; catalysis; ethylene dimerization; gas-phase reaction; metal−organic framework
Co-reporter:Kainan Zhang, Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen
ACS Catalysis 2015 Volume 5(Issue 8) pp:4859
Publication Date(Web):July 10, 2015
DOI:10.1021/acscatal.5b01388
A series of porphyrin-based porous organic polymers (PPOPs) were synthesized in excellent yields via the Yamamoto–Ullmann couplings of tetrabromo spirobifluorene with several brominated porphyrin monomers. After isolation and demetalation, the metal-free PPOP can be postsynthetically metalated to form a MnIII–PPOP that is catalytically active toward the selective double-epoxidation of divinylbenzene to divinylbenzene dioxide.Keywords: divinylbenzene; divinylbenzene dioxide; epoxidation; Mn(porphyrin); porous organic polymer
Co-reporter:Idan Hod, Matthew D. Sampson, Pravas Deria, Clifford P. Kubiak, Omar K. Farha, and Joseph T. Hupp
ACS Catalysis 2015 Volume 5(Issue 11) pp:6302
Publication Date(Web):September 18, 2015
DOI:10.1021/acscatal.5b01767
Realization of heterogeneous electrochemical CO2-to-fuel conversion via molecular catalysis under high-flux conditions requires the assembly of large quantities of reactant-accessible catalysts on conductive surfaces. As a proof of principle, we demonstrate that electrophoretic deposition of thin films of an appropriately chosen metal–organic framework (MOF) material is an effective method for immobilizing the needed quantity of catalyst. For electrocatalytic CO2 reduction, we used a material that contains functionalized Fe-porphyrins as catalytically competent, redox-conductive linkers. The approach yields a high effective surface coverage of electrochemically addressable catalytic sites (∼1015 sites/cm2). The chemical products of the reduction, obtained with ∼100% Faradaic efficiency, are mixtures of CO and H2. These results validate the strategy of using MOF chemistry to obtain porous, electrode-immobilized, networks of molecular catalysts having competency for energy-relevant electrochemical reactions.Keywords: CO2 reduction; electrocatalysis; Fe-porphyrin; metal organic frameworks; redox conductivity; solar fuel
Co-reporter:Ho-Jin Son, Chul Hoon Kim, Dong Wook Kim, Nak Cheon Jeong, Chaiya Prasittichai, Langli Luo, Jinsong Wu, Omar K. Farha, Michael R. Wasielewski, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 9) pp:5150
Publication Date(Web):February 19, 2015
DOI:10.1021/am507405b
Dye aggregation and concomitant reduction of dye excited-state lifetimes and electron-injection yields constitute a significant mechanism for diminution of light-to-electrical energy conversion efficiencies in many dye-sensitized solar cells (DSCs). For TiO2-based DSCs prepared with an archetypal donor–acceptor organic dye, (E)-2-cyano-3-(5′-(5′′-(p-(diphenylamino)phenyl)-thiophen-2′′-yl)thiophen-2′-yl)acrylic acid (OrgD), we find, in part via ultrafast spectroscopy measurements, that postdye-adsorption atomic layer deposition (ALD) of ultrathin layers of either TiO2 or Al2O3 effectively reverses residual aggregation. Notably, the ALD treatment is significantly more effective than the widely used aggregation-inhibiting coadsorbent, chenodeoxycholic acid. Primarily because of reversal of OrgD aggregation, and resulting improved injection yields, ALD post-treatment engenders a 30+% increase in overall energy conversion efficiency. A secondary contributor to increased currents and efficiencies is an ALD-induced attenuation of the rate of interception of injected electrons, resulting in slightly more efficient charge collection.Keywords: atomic layer deposition (ALD); dye aggregation; dye-sensitized solar cells (DSCs); interfacial electron injection; post-treatment
Co-reporter:Chung-Wei Kung, Joseph E. Mondloch, Timothy C. Wang, Wojciech Bury, William Hoffeditz, Benjamin M. Klahr, Rachel C. Klet, Michael J. Pellin, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 51) pp:28223
Publication Date(Web):December 4, 2015
DOI:10.1021/acsami.5b06901
Thin films of the metal–organic framework (MOF) NU-1000 were grown on conducting glass substrates. The films uniformly cover the conducting glass substrates and are composed of free-standing sub-micrometer rods. Subsequently, atomic layer deposition (ALD) was utilized to deposit Co2+ ions throughout the entire MOF film via self-limiting surface-mediated reaction chemistry. The Co ions bind at aqua and hydroxo sites lining the channels of NU-1000, resulting in three-dimensional arrays of separated Co ions in the MOF thin film. The Co-modified MOF thin films demonstrate promising electrocatalytic activity for water oxidation.Keywords: atomic layer deposition; cobalt oxide; electrocatalyst; metal−organic frameworks; pyrene; water oxidation
Co-reporter:Monica C. So, Gary P. Wiederrecht, Joseph E. Mondloch, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 vol. 51(Issue 17) pp:3501-3510
Publication Date(Web):12 Jan 2015
DOI:10.1039/C4CC09596K
A critical review of the emerging field of MOFs for photon collection and subsequent energy transfer is presented. Discussed are examples involving MOFs for (a) light harvesting, using (i) MOF-quantum dots and molecular chromophores, (ii) chromophoric MOFs, and (iii) MOFs with light-harvesting properties, and (b) energy transfer, specifically via the (i) Förster energy transfer and (ii) Dexter exchange mechanism.
Co-reporter:Monica C. So, M. Hassan Beyzavi, Rohan Sawhney, Osama Shekhah, Mohamed Eddaoudi, Salih S. Al-Juaid, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 vol. 51(Issue 1) pp:85-88
Publication Date(Web):17 Oct 2014
DOI:10.1039/C4CC05727A
Herein, we demonstrate the robustness of layer-by-layer (LbL)-assembled, pillared-paddlewheel-type MOF films toward conversion to new or modified MOFs via solvent-assisted linker exchange (SALE) and post-assembly linker metalation. Further, we show that LbL synthesis can afford MOFs that have proven inaccessible through other de novo strategies.
Co-reporter:Pravas Deria, Song Li, Hongda Zhang, Randall Q. Snurr, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 vol. 51(Issue 62) pp:12478-12481
Publication Date(Web):06 Jul 2015
DOI:10.1039/C5CC04808G
CO2 capture is essential for reducing the carbon footprint of coal-fired power plants. Here we show, both experimentally and computationally, a new design strategy for capturing CO2 in nanoporous adsorbents. The approach involves ‘complementary organic motifs’ (COMs), which have a precise alignment of charge densities that is complementary to the CO2 quadrupole. Two promising COMs were post-synthetically incorporated into a robust metal–organic framework (MOF) material using solvent-assisted ligand incorporation (SALI). We demonstrate that these COM-functionalized MOFs exhibit high capacity and selectivity for CO2 relative to other reported motifs.
Co-reporter:Peng Li, Rachel C. Klet, Su-Young Moon, Timothy C. Wang, Pravas Deria, Aaron W. Peters, Benjamin M. Klahr, Hea-Jung Park, Salih S. Al-Juaid, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 vol. 51(Issue 54) pp:10925-10928
Publication Date(Web):11 Jun 2015
DOI:10.1039/C5CC03398E
The synthesis of nano-sized particles of NU-1000 (length from 75 nm to 1200 nm) and PCN-222/MOF-545 (length from 350 nm to 900 nm) is reported. The catalytic hydrolysis of methyl paraoxon was investigated as a function of NU-1000 crystallite size and a significant enhancement in the rate was observed for the nano-sized crystals compared to microcrystals.
Co-reporter:Jason R. Avila, Dong Wook Kim, Martino Rimoldi, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 30) pp:16138
Publication Date(Web):July 20, 2015
DOI:10.1021/acsami.5b04043
Atomic layer deposition (ALD) has been shown to be an excellent method for depositing thin films of iron oxide. With limited iron precursors available, the methods widely used require harsh conditions such as high temperatures and/or the use of oxidants such as ozone or peroxide. This letter aims to show that bis(N,N′-di-t-butylacetamidinato) iron(II) (iron bisamidinate or FeAMD) is an ideal ALD precursor because of its reactivity with water and relative volatility. Using in situ QCM analysis, we show outstanding conformal self-limiting growth of FeOx using FeAMD and water at temperatures lower than 200 °C. By annealing thin films of FeOx at 500 °C, we observe the formation of α-Fe2O3, confirming that we can use FeAMD to fabricate thin films of catalytically promising iron oxide materials using moderate growth conditions.Keywords: atomic layer deposition; hematite; in situ; iron bisamidinate; iron oxide; quartz crystal microbalance
Co-reporter:Marianne B. Lalonde; Joseph E. Mondloch; Pravas Deria; Amy A. Sarjeant; Salih S. Al-Juaid; Osman I. Osman; Omar K. Farha
Inorganic Chemistry 2015 Volume 54(Issue 15) pp:7142-7144
Publication Date(Web):July 20, 2015
DOI:10.1021/acs.inorgchem.5b01231
Solvent-assisted linker exchange (SALE) has recently emerged as an attractive strategy for the synthesis of metal–organic frameworks (MOFs) that are unobtainable via traditional synthetic pathways. Herein we present the first example of selective SALE in which only the benzimiadazolate-containing linkers in a series of mixed-linker zeolitic imidazolate frameworks (ZIF-69, -78, and -76) are replaced. The resultant materials (SALEM-10, SALEM-10b, and SALEM-11, respectively) are isostructural to the parent framework and in each case contain trifluoromethyl moieties. We therefore evaluated each of these materials for their hydrophobicity in condensed and gas phases. We expect that selective SALE will significantly facilitate the design of improved, and potentially complex, MOF materials with new and unusual properties.
Co-reporter:Pravas Deria, Wojciech Bury, Idan Hod, Chung-Wei Kung, Olga Karagiaridi, Joseph T. Hupp, and Omar K. Farha
Inorganic Chemistry 2015 Volume 54(Issue 5) pp:2185-2192
Publication Date(Web):February 9, 2015
DOI:10.1021/ic502639v
Solvent-assisted ligand incorporation (SALI) is useful for functionalizing the channels of metal–organic framework (MOF) materials such as NU-1000 that offer substitutionally labile zirconium(IV) coordination sites for nonbridging ligands. Each of the 30 or so previous examples relied upon coordination of a carboxylate ligand to achieve incorporation. Here we show that, with appropriate attention to ligand/node stoichiometry, SALI can also be achieved with phosphonate-terminated ligands. Consistent with stronger M(IV) coordination of phosphonates versus carboxylates, this change extends the pH range for retention of incorporated ligands. The difference in coordination strength can be exploited to achieve stepwise incorporation of pairs of ligands—specifically, phosphonates species followed by carboxylate species—without danger of displacement of the first ligand type by the second. Diffuse reflectance infrared Fourier-transform spectroscopy suggests that the phosphonate ligands are connected to the MOF node as RPO2(OH)¯ species in a moiety that leaves a base-accessible −OH moiety on each bound phosphonate.
Co-reporter:Olga Karagiaridi, Nicolaas A. Vermeulen, Rachel C. Klet, Timothy C. Wang, Peyman Z. Moghadam, Salih S. Al-Juaid, J. Fraser. Stoddart, Joseph T. Hupp, and Omar K. Farha
Inorganic Chemistry 2015 Volume 54(Issue 4) pp:1785-1790
Publication Date(Web):January 29, 2015
DOI:10.1021/ic502697y
Intentional incorporation of defect sites functionalized with free carboxylic acid groups was achieved in a paddlewheel-based metal–organic framework (MOF) of rht topology, NU-125. Solvent-assisted linker exchange (SALE) performed on a mixed-linker derivative of NU-125 containing isophthalate (IPA) linkers (NU-125-IPA) led to the selective replacement of the IPA linkers in the framework with a conjugate base of trimesic acid (H3BTC). Only two of the three carboxylic acid moieties offered by H3BTC coordinate to the Cu2 centers in the MOF, yielding a rare example of a MOF decorated with free −COOH groups. The presence of the −COOH groups was confirmed by diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS); moreover, these groups were found to be available for postsynthesis elaboration (selective monoester formation). This work constitutes an example of the use of SALE to obtain otherwise challenging-to-synthesize MOFs. The resulting MOF, in turn, can serve as a platform for accomplishing selective organic transformations, in this case, exclusive monoesterification of trimesic acid.
Co-reporter:Jared B. DeCoste, Tyler J. Demasky, Michael J. Katz, Omar K. Farha and Joseph T. Hupp
New Journal of Chemistry 2015 vol. 39(Issue 4) pp:2396-2399
Publication Date(Web):07 Jan 2015
DOI:10.1039/C4NJ02093F
Zirconium-based metal–organic frameworks (MOFs) are of great importance as sorbents due to their increased chemical and thermal stability when compared to other MOF families. Here we report a novel analogue of UiO-66 modified with oxalic acid via solvent-assisted ligand incorporation. This analogue has the ability to remove ammonia, cyanogen chloride, sulphur dioxide, nitrogen dioxide and octane at levels greater than or equal to the base UiO-66. We report here the highest known capacities exhibited by a MOF for SO2 and NO2, at pressures less than 0.10 bar and at room temperature, by UiO-66-ox. Furthermore, we show here the importance of the secondary building unit of the MOF in the removal of ammonia and cyanogen chloride.
Co-reporter:Dr. Yangyang Liu;Dr. Ashlee J. Howarth; Joseph T. Hupp; Omar K. Farha
Angewandte Chemie 2015 Volume 127( Issue 31) pp:9129-9133
Publication Date(Web):
DOI:10.1002/ange.201503741
Abstract
The photooxidation of a mustard-gas simulant, 2-chloroethyl ethyl sulfide (CEES), is studied using a porphyrin-based metal–organic framework (MOF) catalyst. At room temperature and neutral pH value, singlet oxygen is generated by PCN-222/MOF-545 using an inexpensive and commercially available light-emitting diode. The singlet oxygen produced by PCN-222/MOF-545 selectively oxidizes CEES to the comparatively nontoxic product 2-chloroethyl ethyl sulfoxide (CEESO) without formation of the highly toxic sulfone product. In comparison to current methods, which utilize hydrogen peroxide as an oxidizing agent, this is a more realistic, convenient, and effective method for mustard-gas detoxification.
Co-reporter:Dr. Su-Young Moon;Dr. Yangyang Liu; Joseph T. Hupp; Omar K. Farha
Angewandte Chemie 2015 Volume 127( Issue 23) pp:6899-6903
Publication Date(Web):
DOI:10.1002/ange.201502155
Abstract
A nerve-agent simulant based on a phosphate ester is hydrolyzed using a MOF-based catalyst. Suspensions of MOF-808 (6-connected), a material featuring 6-connected zirconium nodes, display the highest hydrolysis rates among all MOFs that have been reported to date. A plug-flow reactor was also prepared with MOF-808 (6-connected) as the active layer. Deployed in a simple filtration scheme, the reactor displayed high hydrolysis efficiency and reusability.
Co-reporter:Idan Hod; Wojciech Bury; Daniel M. Gardner; Pravas Deria; Vladimir Roznyatovskiy; Michael R. Wasielewski; Omar K. Farha
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 4) pp:586-591
Publication Date(Web):January 26, 2015
DOI:10.1021/acs.jpclett.5b00019
The installation of ferrocene molecules within the wide-channel metal–organic framework (MOF) compound, NU-1000, and subsequent configuration of the modified MOF as thin-film coatings on electrodes renders the MOF electroactive in the vicinity of the ferrocenium/ferrocene (Fc+/Fc) redox potential due to redox hopping between anchored Fc+/0 species. The observation of effective site-to-site redox hopping points to the potential usefulness of the installed species as a redox shuttle in photoelectrochemical or electrocatalytic systems. At low supporting electrolyte concentration, we observe bias-tunable ionic permselectivity; films are blocking toward solution cations when the MOF is in the ferrocenium form but permeable when in the ferrocene form. Additionally, with ferrocene-functionalized films, we observe that the MOF’s pyrene-based linkers, which are otherwise reversibly electroactive, are now redox-silent. Linker electroactivity is fully recovered, however, when the electrolyte concentration is increased 10-fold, that is, to a concentration similar to or exceeding that of an anchored shuttle molecule. The findings have clear implications for the design and use of MOF-based sensors, electrocatalysts, and photoelectrochemical devices.
Co-reporter:Dr. Su-Young Moon;Dr. Yangyang Liu; Joseph T. Hupp; Omar K. Farha
Angewandte Chemie International Edition 2015 Volume 54( Issue 23) pp:6795-6799
Publication Date(Web):
DOI:10.1002/anie.201502155
Abstract
A nerve-agent simulant based on a phosphate ester is hydrolyzed using a MOF-based catalyst. Suspensions of MOF-808 (6-connected), a material featuring 6-connected zirconium nodes, display the highest hydrolysis rates among all MOFs that have been reported to date. A plug-flow reactor was also prepared with MOF-808 (6-connected) as the active layer. Deployed in a simple filtration scheme, the reactor displayed high hydrolysis efficiency and reusability.
Co-reporter:Dr. Yangyang Liu;Dr. Ashlee J. Howarth; Joseph T. Hupp; Omar K. Farha
Angewandte Chemie International Edition 2015 Volume 54( Issue 31) pp:9001-9005
Publication Date(Web):
DOI:10.1002/anie.201503741
Abstract
The photooxidation of a mustard-gas simulant, 2-chloroethyl ethyl sulfide (CEES), is studied using a porphyrin-based metal–organic framework (MOF) catalyst. At room temperature and neutral pH value, singlet oxygen is generated by PCN-222/MOF-545 using an inexpensive and commercially available light-emitting diode. The singlet oxygen produced by PCN-222/MOF-545 selectively oxidizes CEES to the comparatively nontoxic product 2-chloroethyl ethyl sulfoxide (CEESO) without formation of the highly toxic sulfone product. In comparison to current methods, which utilize hydrogen peroxide as an oxidizing agent, this is a more realistic, convenient, and effective method for mustard-gas detoxification.
Co-reporter:Yangyang Liu, Su-Young Moon, Joseph T. Hupp, and Omar K. Farha
ACS Nano 2015 Volume 9(Issue 12) pp:12358
Publication Date(Web):October 20, 2015
DOI:10.1021/acsnano.5b05660
The nanocrystals of a porphyrin-based zirconium(IV) metal–organic framework (MOF) are used as a dual-function catalyst for the simultaneous detoxification of two chemical warfare agent simulants at room temperature. Simulants of nerve agent (such as GD, VX) and mustard gas, dimethyl 4-nitrophenyl phosphate and 2-chloroethyl ethyl sulfide, have been hydrolyzed and oxidized, respectively, to nontoxic products via a pair of pathways catalyzed by the same MOF. Phosphotriesterase-like activity of the Zr6-containing node combined with photoactivity of the porphyrin linker gives rise to a versatile MOF catalyst. In addition, bringing the MOF crystals down to the nanoregime leads to acceleration of the catalysis.Keywords: CEES; chemical warfare agents; DMNP; dual function; GD; heterogeneous catalysis; metal−organic frameworks; Simulant; Soman; VX;
Co-reporter:Aaron W. Peters, Zhanyong Li, Omar K. Farha, and Joseph T. Hupp
ACS Nano 2015 Volume 9(Issue 8) pp:8484
Publication Date(Web):August 4, 2015
DOI:10.1021/acsnano.5b03429
Atomic layer deposition (ALD) has been employed as a new synthetic route to thin films of cobalt sulfide on silicon and fluorine-doped tin oxide platforms. The self-limiting nature of the stepwise synthesis is established through growth rate studies at different pulse times and temperatures. Additionally, characterization of the materials by X-ray diffraction and X-ray photoelectron spectroscopy indicates that the crystalline phase of these films has the composition Co9S8. The nodes of the metal–organic framework (MOF) NU-1000 were then selectively functionalized with cobalt sulfide via ALD in MOFs (AIM). Spectroscopic techniques confirm uniform deposition of cobalt sulfide throughout the crystallites, with no loss in crystallinity or porosity. The resulting material, CoS-AIM, is catalytically active for selective hydrogenation of m-nitrophenol to m-aminophenol, and outperforms the analogous oxide AIM material (CoO-AIM) as well as an amorphous CoSx reference material. These results reveal AIM to be an effective method of incorporating high surface area and catalytically active cobalt sulfide in metal–organic frameworks.Keywords: atomic layer deposition; metal−organic framework; nanoscale Co9S8 films;
Co-reporter:Michael J. Katz, Michael J. DeVries Vermeer, Omar K. Farha, Michael J. Pellin, and Joseph T. Hupp
The Journal of Physical Chemistry B 2015 Volume 119(Issue 24) pp:7162-7169
Publication Date(Web):August 15, 2014
DOI:10.1021/jp506083a
A series of dye-sensitized solar cells (DSCs) was constructed with TiO2 nanoparticles and N719 dye. The standard I3–/I– redox shuttle and the Co(1,10-phenanthroline)33+/2+ shuttle were employed. DSCs were modified with atomic-layered-deposited (ALD) coatings of Al2O3 and/or with the surface-adsorbing additive 4-tert-butyl-pyridine. Current–voltage data were collected to ascertain the influence of each modification upon the back electron transfer (ET) dynamics of the DSCs. The primary effect of the additives alone or in tandem is to increase the open-circuit voltage. A second is to alter the short-circuit current density, JSC. With dependence on the specifics of the system examined, any of a myriad of dynamics-related effects were observed to come into play, in both favorable (efficiency boosting) and unfavorable (efficiency damaging) ways. These effects include modulation of (a) charge-injection yields, (b) rates of interception of injected electrons by redox shuttles, and (c) rates of recombination of injected electrons with holes on surface-bound dyes. In turn, these influence charge-collection lengths, charge-collection yields, and onset potentials for undesired dark current. The microscopic origins of the effects appear to be related mainly to changes in driving force and/or electronic coupling for underlying component redox reactions. Perhaps surprisingly, only a minor role for modifier-induced shifts in conduction-band-edge energy was found. The combination of DSC-efficiency-relevant effects engendered by the modifiers was found to vary substantially as a function of the chemical identity of the redox shuttle employed. While types of modifiers are effective, a challenge going forward will be to construct systems in ways in which the benefits of organic and inorganic modifiers can be exploited in fully additive, or even synergistic, fashion.
Co-reporter:Pravas Deria, Joseph E. Mondloch, Olga Karagiaridi, Wojciech Bury, Joseph T. Hupp and Omar K. Farha
Chemical Society Reviews 2014 vol. 43(Issue 16) pp:5896-5912
Publication Date(Web):11 Apr 2014
DOI:10.1039/C4CS00067F
Metal–organic frameworks (MOFs) are hybrid porous materials with many potential applications, which intimately depend on the presence of chemical functionality either at the organic linkers and/or at the metal nodes. Functionality that cannot be introduced into MOFs directly via de novo syntheses can be accessed through post-synthesis modification (PSM) on the reactive moieties of the linkers and/or nodes without disrupting the metal–linker bonds. Even more intriguing methods that go beyond PSM are herein termed building block replacement (BBR) which encompasses (i) solvent-assisted linker exchange (SALE), (ii) non-bridging ligand replacement, and (iii) transmetalation. These one-step or tandem BBR processes involve exchanging key structural components of the MOF, which in turn should allow for the evolution of protoMOF structures (i.e., the utilization of a parent MOF as a template) to design MOFs composed of completely new components, presumably via single crystal to single crystal transformations. The influence of building block replacement on the stability and properties of MOFs will be discussed, and some insights into their mechanistic aspects are provided. Future perspectives providing a glimpse into how these techniques can lead to various unexplored areas of MOF chemistry are also presented.
Co-reporter:Idan Hod;Wojciech Bury;David M. Karlin;Pravas Deria;Chung-Wei Kung;Michael J. Katz;Monica So;Benjamin Klahr;Danni Jin;Yip-Wah Chung;Teri W. Odom;Omar K. Farha
Advanced Materials 2014 Volume 26( Issue 36) pp:6295-6300
Publication Date(Web):
DOI:10.1002/adma.201401940
Co-reporter:M. Hassan Beyzavi ; Rachel C. Klet ; Samat Tussupbayev ; Joshua Borycz ; Nicolaas A. Vermeulen ; Christopher J. Cramer ; J. Fraser Stoddart ; Joseph T. Hupp ;Omar K. Farha
Journal of the American Chemical Society 2014 Volume 136(Issue 45) pp:15861-15864
Publication Date(Web):October 30, 2014
DOI:10.1021/ja508626n
Porous heterogeneous catalysts play a pivotal role in the chemical industry. Herein a new Hf-based metal–organic framework (Hf-NU-1000) incorporating Hf6 clusters is reported. It demonstrates high catalytic efficiency for the activation of epoxides, facilitating the quantitative chemical fixation of CO2 into five-membered cyclic carbonates under ambient conditions, rendering this material an excellent catalyst. As a multifunctional catalyst, Hf-NU-1000 is also efficient for other epoxide activations, leading to the regioselective and enantioretentive formation of 1,2-bifuctionalized systems via solvolytic nucleophilic ring opening.
Co-reporter:Ryan K. Totten, Laura L. Olenick, Ye-Seong Kim, Sanjiban Chakraborty, Mitchell H. Weston, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Science 2014 vol. 5(Issue 2) pp:782-787
Publication Date(Web):09 Oct 2013
DOI:10.1039/C3SC52010B
Porous organic polymers (POPs) with tunable pore volumes and surface areas can be made from a series of SnIV(porphyrins) functionalized with labile, bulky trans-diaxial ligands. Varying the ligand size allows for the tuning of the micropore volume while supercritical CO2 processing resulted in excellent enhancements of the total pore volumes.
Co-reporter:Huong Giang T. Nguyen, Neil M. Schweitzer, Chih-Yi Chang, Tasha L. Drake, Monica C. So, Peter C. Stair, Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen
ACS Catalysis 2014 Volume 4(Issue 8) pp:2496
Publication Date(Web):June 2, 2014
DOI:10.1021/cs5001448
The OH groups on the Zr-based nodes of ultrastable UiO-66 can be metallated with VV ions in a facile fashion to give the derivative VUiO-66. This metallated MOF exhibits high stability over a broad temperature range and displays high selectivity for benzene under low-conversion conditions in the vapor-phase oxidative dehydrogenation of cyclohexene (activation energy ∼110 kJ/mol). The integrity of the MOF is maintained after catalysis as determined by PXRD, ICP-AES, and SEM.Keywords: cyclohexene oxidation; gas-phase catalysis; metal−organic framework; UiO-66; vanadium
Co-reporter:Diego A. Gomez-Gualdron, Oleksii V. Gutov, Vaiva Krungleviciute, Bhaskarjyoti Borah, Joseph E. Mondloch, Joseph T. Hupp, Taner Yildirim, Omar K. Farha, and Randall Q. Snurr
Chemistry of Materials 2014 Volume 26(Issue 19) pp:5632
Publication Date(Web):September 16, 2014
DOI:10.1021/cm502304e
A metal–organic framework (MOF) with high volumetric deliverable capacity for methane was synthesized after being identified by computational screening of 204 hypothetical MOF structures featuring (Zr6O4)(OH)4(CO2)n inorganic building blocks. The predicted MOF (NU-800) has an fcu topology in which zirconium nodes are connected via ditopic 1,4-benzenedipropynoic acid linkers. Based on our computer simulations, alkyne groups adjacent to the inorganic zirconium nodes provide more efficient methane packing around the nodes at high pressures. The high predicted gas uptake properties of this new MOF were confirmed by high-pressure isotherm measurements over a large temperature and pressure range. The measured methane deliverable capacity of NU-800 between 65 and 5.8 bar is 167 cc(STP)/cc (0.215 g/g), the highest among zirconium-based MOFs. High-pressure uptake values of H2 and CO2 are also among the highest reported. These high gas uptake characteristics, along with the expected highly stable structure of NU-800, make it a promising material for gas storage applications.
Co-reporter:Mitchell H. Weston, Yamil J. Colón, Youn-Sang Bae, Sergio J. Garibay, Randall Q. Snurr, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Journal of Materials Chemistry A 2014 vol. 2(Issue 2) pp:299-302
Publication Date(Web):04 Oct 2013
DOI:10.1039/C3TA12999C
A porous organic polymer decorated with high densities of copper(catecholate) groups was prepared and characterized. Single-component propylene and propane isotherms measured at ambient temperatures and ideal adsorption solution theory (IAST) calculations revealed increasing propylene/propane selectivities with increasing pressures.
Co-reporter:Pravas Deria, Wojciech Bury, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2014 vol. 50(Issue 16) pp:1965-1968
Publication Date(Web):09 Jan 2014
DOI:10.1039/C3CC48562E
Solvent-assisted ligand incorporation (SALI) was utilized to efficiently insert various carboxylate-derived functionalities into the Zr-based metal–organic framework NU-1000 as charge compensating moieties strongly bound to the Zr6 nodes. SALI-derived functionalities are accessible for further chemical reactions such as click chemistry, imine condensation and pyridine quaternization.
Co-reporter:Joseph E. Mondloch, Michael J. Katz, Nora Planas, David Semrouni, Laura Gagliardi, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2014 vol. 50(Issue 64) pp:8944-8946
Publication Date(Web):30 Jun 2014
DOI:10.1039/C4CC02401J
Metal–organic frameworks (MOFs) built up from Zr6-based nodes and multi-topic carboxylate linkers have attracted attention due to their favourable thermal and chemical stability. However, the hydrolytic stability of some of these Zr6-based MOFs has recently been questioned. Herein we demonstrate that two Zr6-based frameworks, namely UiO-67 and NU-1000, are stable towards linker hydrolysis in H2O, but collapse during activation from H2O. Importantly, this framework collapse can be overcome by utilizing solvent-exchange to solvents exhibiting lower capillary forces such as acetone.
Co-reporter:Vennesa O. Williams, Erica J. DeMarco, Michael J. Katz, Joseph A. Libera, Shannon C. Riha, Dong Wook Kim, Jason R. Avila, Alex B. F. Martinson, Jeffrey W. Elam, Michael J. Pellin, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 15) pp:12290
Publication Date(Web):July 17, 2014
DOI:10.1021/am501910n
Highly ordered, and conductive inverse opal arrays were made with silica and subsequently coated with tin-doped indium oxide (ITO) via atomic layer deposition (ALD). We demonstrate the utility of the resulting mesostructured electrodes by further coating them with nickel oxide via ALD. The NiO-coated arrays are capable of efficiently electrochemically evolving oxygen from water. These modular, crack-free, transparent, high surface area, and conducting structures show promise for many applications including electrocatalysis, photocatalysis, and dye-sensitized solar cells.Keywords: atomic-layer deposition; catalysis; electrochemistry; inverse opals; nickel oxide; water oxidation
Co-reporter:William L. Hoffeditz, Michael J. Katz, Pravas Deria, Alex B.F. Martinson, Michael J. Pellin, Omar K. Farha, and Joseph T. Hupp
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 11) pp:8646
Publication Date(Web):May 14, 2014
DOI:10.1021/am501455b
Dye-sensitized solar cell (DSC) redox shuttles other than triiodide/iodide have exhibited significantly higher charge transfer resistances at the dark electrode. This often results in poor fill factor, a severe detriment to device performance. Rather than moving to dark electrodes of untested materials that may have higher catalytic activity for specific shuttles, the surface area of platinum dark electrodes could be increased, improving the catalytic activity by simply presenting more catalyst to the shuttle solution. A new copper-based redox shuttle that experiences extremely high charge-transfer resistance at conventional Pt dark electrodes yields cells having fill-factors of less than 0.3. By replacing the standard Pt dark electrode with an inverse opal Pt electrode fabricated via atomic layer deposition, the dark electrode surface area is boosted by ca. 50-fold. The resulting increase in interfacial electron transfer rate (decrease in charge-transfer resistance) nearly doubles the fill factor and therefore the overall energy conversion efficiency, illustrating the utility of this high-area electrode for DSCsKeywords: dark electrode; dye cell; fill factor; inverse opal;
Co-reporter:Gokhan Barin, Vaiva Krungleviciute, Oleksii Gutov, Joseph T. Hupp, Taner Yildirim, and Omar K. Farha
Inorganic Chemistry 2014 Volume 53(Issue 13) pp:6914-6919
Publication Date(Web):June 6, 2014
DOI:10.1021/ic500722n
We successfully demonstrate an approach based on linker fragmentation to create defects and tune the pore volumes and surface areas of two metal–organic frameworks, NU-125 and HKUST-1, both of which feature copper paddlewheel nodes. Depending on the linker fragment composition, the defect can be either a vacant site or a functional group that the original linker does not have. In the first case, we show that both surface area and pore volume increase, while in the second case they decrease. The effect of defects on the high-pressure gas uptake is also studied over a large temperature and pressure range for different gases. We found that despite an increase in pore volume and surface area in structures with vacant sites, the absolute adsorption for methane decreases for HKUST-1 and slightly increases for NU-125. However, the working capacity (deliverable amount between 65 and 5 bar) in both cases remains similar to parent frameworks due to lower uptakes at low pressures. In the case of NU-125, the effect of defects became more pronounced at lower temperatures, reflecting the greater surface areas and pore volumes of the altered forms.
Co-reporter:Olga Karagiaridi, Wojciech Bury, David Fairen-Jimenez, Christopher E. Wilmer, Amy A. Sarjeant, Joseph T. Hupp, and Omar K. Farha
Inorganic Chemistry 2014 Volume 53(Issue 19) pp:10432-10436
Publication Date(Web):September 8, 2014
DOI:10.1021/ic501467w
The synthesis of a permanently porous pillared-paddlewheel metal–organic framework (MOF) was achieved through transmetalation of Zn(II) with Ni(II). The MOF can be treated with liquid water, leading to the reversible displacement of 50% of its pillars by water molecules and resulting in a most unusual crystalline and permanently porous structure.
Co-reporter:Sherzod T. Madrahimov, Tulay A. Atesin, Olga Karagiaridi, Amy A. Sarjeant, Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen
Crystal Growth & Design 2014 Volume 14(Issue 12) pp:6320-6324
Publication Date(Web):September 29, 2014
DOI:10.1021/cg501066s
A series of metal–organic framework (MOF) materials containing AuI-carbon covalent bonds was prepared by solvent-assisted linker exchange (SALE) between (alkynyl)gold(phosphine)-functionalized bipyridine linkers and the bipyridyl naphthalene tetracarboxydiimide struts in Zn pillared-paddlewheel MOFs. These new materials could not be obtained by the authors through de novo synthesis or post-synthesis modification, both of which lead to the decomposition of the organometallic complex. In contrast, the SALE process occurs readily under mild conditions that preserve the integrity of both the pillared-paddlewheel structure and the organometallic complex. For bipyridine linkers with similar basicities, the rate of the SALE exhibits a strong inverse dependence on the size of the phosphine ligand in the incoming (alkynyl)gold(phosphine)-functionalized linker, with smaller ligands reacting faster.
Co-reporter:Lauren E. Kreno, Nathan G. Greeneltch, Omar K. Farha, Joseph T. Hupp and Richard P. Van Duyne
Analyst 2014 vol. 139(Issue 16) pp:4073-4080
Publication Date(Web):05 Jun 2014
DOI:10.1039/C4AN00413B
The potential for discriminating between analytes by their unique vibrational signature makes surface-enhanced Raman scattering (SERS) extremely interesting for chemical detection. However, for molecules that weakly adsorb to non-functionalized plasmonic materials, detection by SERS remains a key challenge. Here we present an approach to SERS-based detection where a polycrystalline metal–organic framework (MOF) film is used to recruit a range of structurally similar volatile organic compounds for detection by SERS. MOF films were grown on the surface of Ag “films-over-nanospheres” (FONs), which have previously been shown to enhance Raman signals of surface adsorbates by a factor of 107. Upon exposing the MOF-coated FON to benzene, toluene, nitrobenzene, or 2,6-di-tert-butylpyridine, the MOF film traps the vapors at the FON surface, allowing the unique Raman spectrum of each vapor to be recorded. By contrast, these analytes do not adsorb to a bare FON surface and thus cannot be detected by conventional SERS substrates. Pyridine was also tested as a Ag-adsorbing control analyte. Concentration dependence and time resolved measurements provide evidence for the hypothesis that the vapors are reversibly adsorbed on the surfaces of MOF nanocrystals exposed at grain boundaries. This represents a generalized approach for confining aromatic molecules through interactions with the MOF surface, which can be applied for future SERS-based sensors.
Co-reporter:Nora Planas, Joseph E. Mondloch, Samat Tussupbayev, Joshua Borycz, Laura Gagliardi, Joseph T. Hupp, Omar K. Farha, and Christopher J. Cramer
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 21) pp:3716-3723
Publication Date(Web):October 10, 2014
DOI:10.1021/jz501899j
Metal–organic frameworks (MOFs) constructed from Zr6-based nodes have recently received considerable attention given their exceptional thermal, chemical, and mechanical stability. Because of this, the structural diversity of Zr6-based MOFs has expanded considerably and in turn given rise to difficulty in their precise characterization. In particular it has been difficult to assign where protons (needed for charge balance) reside on some Zr6-based nodes. Elucidating the precise proton topologies in Zr6-based MOFs will have wide ranging implications in defining their chemical reactivity, acid/base characteristics, conductivity, and chemical catalysis. Here we have used a combined quantum mechanical and experimental approach to elucidate the precise proton topology of the Zr6-based framework NU-1000. Our data indicate that a mixed node topology, [Zr6(μ3–O)4(μ3–OH)4(OH)4 (OH2)4]8+, is preferred and simultaneously rule out five alternative node topologies.Keywords: density functional theory; IR spectroscopy; node topology; tautomerism;
Co-reporter:Dong Wook Kim, Shannon C. Riha, Erica J. DeMarco, Alex B. F. Martinson, Omar K. Farha, and Joseph T. Hupp
ACS Nano 2014 Volume 8(Issue 12) pp:12199
Publication Date(Web):November 21, 2014
DOI:10.1021/nn503869n
Hematite (α-Fe2O3) is one of just a few candidate electrode materials that possess all of the following photocatalyst-essential properties for scalable application to water oxidation: excellent stability, earth-abundance, suitability positive valence-band-edge energy, and significant visible light absorptivity. Despite these merits, hematite’s modest oxygen evolution reaction kinetics and its poor efficiency in delivering photogenerated holes, especially holes generated by green photons, to the electrode/solution interface, render it ineffective as a practical water-splitting catalyst. Here we show that hole delivery and catalytic utilization can be substantially improved through Ti alloying, provided that the alloyed material is present in ultrathin-thin-film form. Notably, the effects are most pronounced for charges photogenerated by photons with energy comparable to the band gap for excitation of Fe(3d) → Fe(3d) transitions (i.e., green photons). Additionally, at the optimum Ti substitution level the lifetimes of surface-localized holes, competent for water oxidation, are extended. Together these changes explain an overall improvement in photoelectrochemical performance, especially enhanced internal quantum efficiencies, observed upon Ti(IV) incorporation.Keywords: absorbed photon-to-current conversion efficiency (APCE); green light; iron oxide; titanium incorporation; transient photocurrent; ultrathin film;
Co-reporter:Olga Karagiaridi;Dr. Wojciech Bury;Dr. Joseph E. Mondloch;Dr. Joseph T. Hupp;Dr. Omar K. Farha
Angewandte Chemie International Edition 2014 Volume 53( Issue 18) pp:4530-4540
Publication Date(Web):
DOI:10.1002/anie.201306923
Abstract
Metal-organic frameworks (MOFs) have gained considerable attention as hybrid materials—in part because of a multitude of potential useful applications, ranging from gas separation to catalysis and light harvesting. Unfortunately, de novo synthesis of MOFs with desirable function–property combinations is not always reliable and may suffer from vagaries such as formation of undesirable topologies, low solubility of precursors, and loss of functionality of the sensitive network components. The recently discovered synthetic approach coined solvent-assisted linker exchange (SALE) constitutes a simple to implement strategy for circumventing these setbacks; its use has already led to the generation of a variety of MOF materials previously unobtainable by direct synthesis methods. This Review provides a perspective of the achievements in MOF research that have been made possible with SALE and examines the studies that have facilitated the understanding and broadened the scope of use of this invaluable synthetic tool.
Co-reporter:Dr. Oleksii V. Gutov;Dr. Wojciech Bury;Dr. Diego A. Gomez-Gualdron;Dr. Vaiva Krungleviciute;Dr. David Fairen-Jimenez;Dr. Joseph E. Mondloch;Dr. Amy A. Sarjeant;Salih S. Al-Juaid;Dr. Rall Q. Snurr;Dr. Joseph T. Hupp;Dr. Taner Yildirim;Dr. Omar K. Farha
Chemistry - A European Journal 2014 Volume 20( Issue 39) pp:12389-12393
Publication Date(Web):
DOI:10.1002/chem.201402895
Abstract
We designed, synthesized, and characterized a new Zr-based metal–organic framework material, NU-1100, with a pore volume of 1.53 ccg−1 and Brunauer–Emmett–Teller (BET) surface area of 4020 m2g−1; to our knowledge, currently the highest published for Zr-based MOFs. CH4/CO2/H2 adsorption isotherms were obtained over a broad range of pressures and temperatures and are in excellent agreement with the computational predictions. The total hydrogen adsorption at 65 bar and 77 K is 0.092 g g−1, which corresponds to 43 g L−1. The volumetric and gravimetric methane-storage capacities at 65 bar and 298 K are approximately 180 vSTP/v and 0.27 g g−1, respectively.
Co-reporter:Dr. Michael J. Katz;Dr. Joseph E. Mondloch;Dr. Ryan K. Totten;Dr. Jin K. Park; SonBinh T. Nguyen; Omar K. Farha; Joseph T. Hupp
Angewandte Chemie International Edition 2014 Volume 53( Issue 2) pp:497-501
Publication Date(Web):
DOI:10.1002/anie.201307520
Abstract
Inspired by biology, in which a bimetallic hydroxide-bridged zinc(II)-containing enzyme is utilized to catalytically hydrolyze phosphate ester bonds, the utility of a zirconium(IV)-cluster-containing metal–organic framework as a catalyst for the methanolysis and hydrolysis of phosphate-based nerve agent simulants was examined. The combination of the strong Lewis-acidic ZrIV and bridging hydroxide anions led to ultrafast half-lives for these solvolysis reactions. This is especially remarkable considering that the actual catalyst loading was a mere 0.045 % as a result of the surface-only catalysis observed.
Co-reporter:Olga Karagiaridi;Dr. Wojciech Bury;Dr. Joseph E. Mondloch;Dr. Joseph T. Hupp;Dr. Omar K. Farha
Angewandte Chemie 2014 Volume 126( Issue 18) pp:4618-4628
Publication Date(Web):
DOI:10.1002/ange.201306923
Abstract
Metall-organische Gerüste (MOFs) sind Hybridmaterialien, die anhaltendes Interesse auf sich ziehen – nicht zuletzt wegen vielfältiger möglicher Anwendungen, von der Gastrennung über die Katalyse bis hin zum Sammeln von Licht. Allerdings ist die De-novo-Synthese von MOFs mit gewünschten Eigenschaften nicht immer einfach: unerwünschte Topologien können entstehen, die Löslichkeit von Vorstufen kann zu gering sein, und die Funktionalität wichtiger Netzwerkkomponenten kann verlorengehen. Mit einem neuen Ansatz – dem lösungsmittelunterstützten Linker-Austausch (“solvent-assisted linker exchange”, SALE) – lassen sich diese Probleme umgehen, und tatsächlich wurden mit SALE bereits verschiedene MOF-Materialien erzeugt, die durch direkte Syntheseverfahren nicht erhältlich waren. Unsere Übersicht beschreibt Forschungsergebnisse über MOFs, die erst durch SALE möglich gemacht wurden, und diskutiert Studien, die das Verständnis dieses Verfahrens verbessert und sein Anwendungsgebiet erweitert haben.
Co-reporter:Christopher E. Wilmer, Omar K. Farha, Taner Yildirim, Ibrahim Eryazici, Vaiva Krungleviciute, Amy A. Sarjeant, Randall Q. Snurr and Joseph T. Hupp
Energy & Environmental Science 2013 vol. 6(Issue 4) pp:1158-1163
Publication Date(Web):07 Mar 2013
DOI:10.1039/C3EE24506C
We have synthesized and characterized a new metal–organic framework (MOF) material, NU-125, that, in the single-crystal limit, achieves a methane storage density at 58 bar (840 psi) and 298 K corresponding to 86% of that obtained with compressed natural gas tanks (CNG) used in vehicles today, when the latter are pressurized to 248 bar (3600 psi). More importantly, the deliverable capacity (58 bar to 5.8 bar) for NU-125 is 67% of the deliverable capacity of a CNG tank that starts at 248 bar. (For crystalline granules or powders, particle packing inefficiencies will yield densities and deliverable capacities lower than 86% and 67% of high-pressure CNG.) This material was synthesized in high yield on a gram-scale in a single-batch synthesis. Methane adsorption isotherms were measured over a wide pressure range (0.1–58 bar) and repeated over twelve cycles on the same sample, which showed no detectable degradation. Adsorption of CO2 and H2 over a broad range of pressures and temperatures are also reported and agree with our computational findings.
Co-reporter:Pravas Deria, Joseph E. Mondloch, Emmanuel Tylianakis, Pritha Ghosh, Wojciech Bury, Randall Q. Snurr, Joseph T. Hupp, and Omar K. Farha
Journal of the American Chemical Society 2013 Volume 135(Issue 45) pp:16801-16804
Publication Date(Web):October 31, 2013
DOI:10.1021/ja408959g
A new functionalization technique, solvent-assisted ligand incorporation (SALI), was developed to efficiently incorporate carboxylate-based functionalities in the Zr-based metal–organic framework, NU-1000. Unlike previous metal node functionalization strategies, which utilize dative bonding to coordinatively unsaturated metal sites, SALI introduces functional groups as charge compensating and strongly bound moieties to the Zr6 node. Utilizing SALI, we have efficiently attached perfluoroalkane carboxylates of various chain lengths (C1–C9) on the Zr6 nodes of NU-1000. These fluoroalkane-functionalized mesoporous MOFs, termed herein SALI-n, were studied experimentally and theoretically as potential CO2 capture materials.
Co-reporter:Ryan K. Totten ; Ye-Seong Kim ; Mitchell H. Weston ; Omar K. Farha ; Joseph T. Hupp ;SonBinh T. Nguyen
Journal of the American Chemical Society 2013 Volume 135(Issue 32) pp:11720-11723
Publication Date(Web):July 22, 2013
DOI:10.1021/ja405495u
An Al(porphyrin) functionalized with a large axial ligand was incorporated into a porous organic polymer (POP) using a cobalt-catalyzed acetylene trimerization strategy. Removal of the axial ligand afforded a microporous POP that is catalytically active in the methanolysis of a nerve agent simulant. Supercritical CO2 processing of the POP dramatically increased the pore size and volume, allowing for significantly higher catalytic activities.
Co-reporter:Monica C. So ; Shengye Jin ; Ho-Jin Son ; Gary P. Wiederrecht ; Omar K. Farha
Journal of the American Chemical Society 2013 Volume 135(Issue 42) pp:15698-15701
Publication Date(Web):October 15, 2013
DOI:10.1021/ja4078705
We report the synthesis and characterization of two thin films (DA-MOF and L2-MOF) of porphyrin-based MOFs on functionalized surfaces using a layer-by-layer (LbL) approach. Profilometry measurements confirm that the film thickness increases systematically with number of growth cycles. Polarization excitation and fluorescence measurements indicate that the porphyrin units are preferentially oriented, while X-ray reflectivity scans point to periodic ordering. Ellipsometry measurements show that the films are highly porous. Since there are currently few methods capable of yielding microporous MOFs containing accessible free-base porphyrins, it is noteworthy that the LbL growth permits direct MOF incorporation of unmetalated porphyrins. Long-range energy transfer is demonstrated for both MOF films. The findings offer useful insights for subsequent fabrication of MOF-based solar energy conversion devices.
Co-reporter:Chaiya Prasittichai ; Jason R. Avila ; Omar K. Farha
Journal of the American Chemical Society 2013 Volume 135(Issue 44) pp:16328-16331
Publication Date(Web):October 22, 2013
DOI:10.1021/ja4089555
Ultrathin films of TiO2, ZrO2, and Al2O3 were conformally created on SnO2 and TiO2 photoelectrodes via atomic layer deposition (ALD) to examine their influence upon electron transfer (ET) from the electrodes to a representative molecular receptor, I3–. Films thicker than 2 Å engender an exponential decrease in ET time with increasing film thickness, consistent with tunneling theory. Increasing the height of the barrier, as measured by the energy difference between the transferring electron and the bottom of the conduction band of the barrier material, results in steeper exponential drops in tunneling rate or probability. The variations are quantitatively consistent with a simple model of quantum tunneling of electrons through square barriers (i.e., barriers of individually uniform energy height) that are characterized by individually uniform physical thickness. The findings demonstrate that ALD is a remarkably uniform and precise method for modifying electrode surfaces and imply that standard tunneling theory can be used as a quantitative guide to intentionally and predictively modulating rates of ET between molecules and electrodes.
Co-reporter:Ho-Jin Son ; Chaiya Prasittichai ; Joseph E. Mondloch ; Langli Luo ; Jinsong Wu ; Dong Wook Kim ; Omar K. Farha
Journal of the American Chemical Society 2013 Volume 135(Issue 31) pp:11529-11532
Publication Date(Web):July 22, 2013
DOI:10.1021/ja406538a
Detachment (desorption) of molecular dyes from photoelectrodes is one of the major limitations for the long-term operation of dye-sensitized solar cells. Here we demonstrate a method to greatly inhibit this loss by growing a transparent metal oxide (TiO2) on the dye-coated photoelectrode via atomic layer deposition (ALD). TiO2-enshrouded sensitizers largely resist detachment, even in pH 10.7 ethanol, a standard solution for intentional removal of molecular dyes from photoelectrodes. Additionally, the ALD post-treatment renders the otherwise hydrophobic dye-coated surface hydrophilic, thereby enhancing photoelectrode pore-filling with aqueous solution.
Co-reporter:Joseph E. Mondloch ; Wojciech Bury ; David Fairen-Jimenez ; Stephanie Kwon ; Erica J. DeMarco ; Mitchell H. Weston ; Amy A. Sarjeant ; SonBinh T. Nguyen ; Peter C. Stair ; Randall Q. Snurr ; Omar K. Farha
Journal of the American Chemical Society 2013 Volume 135(Issue 28) pp:10294-10297
Publication Date(Web):July 5, 2013
DOI:10.1021/ja4050828
Metal–organic frameworks (MOFs) have received attention for a myriad of potential applications including catalysis, gas storage, and gas separation. Coordinatively unsaturated metal ions often enable key functional behavior of these materials. Most commonly, MOFs have been metalated from the condensed phase (i.e., from solution). Here we introduce a new synthetic strategy capable of metallating MOFs from the gas phase: atomic layer deposition (ALD). Key to enabling metalation by ALD In MOFs (AIM) was the synthesis of NU-1000, a new, thermally stable, Zr-based MOF with spatially oriented −OH groups and large 1D mesopores and apertures.
Co-reporter:Shengye Jin ; Ho-Jin Son ; Omar K. Farha ; Gary P. Wiederrecht
Journal of the American Chemical Society 2013 Volume 135(Issue 3) pp:955-958
Publication Date(Web):January 7, 2013
DOI:10.1021/ja3097114
Because of their efficient energy-transport properties, porphyrin-based metal–organic frameworks (MOFs) are attractive compounds for solar photochemistry applications. However, their absorption bands provide limited coverage in the visible spectral range for light-harvesting applications. We report here the functionalization of porphyrin-based MOFs with CdSe/ZnS core/shell quantum dots (QDs) for the enhancement of light harvesting via energy transfer from the QDs to the MOFs. The broad absorption band of the QDs in the visible region offers greater coverage of the solar spectrum by QD–MOF hybrid structures. We show through time-resolved emission studies that photoexcitation of the QDs is followed by energy transfer to the MOFs with efficiencies of more than 80%. This sensitization approach can result in a >50% increase in the number of photons harvested by a single monolayer MOF structure with a monolayer of QDs on the surface of the MOF.
Co-reporter:Wojciech Bury, David Fairen-Jimenez, Marianne B. Lalonde, Randall Q. Snurr, Omar K. Farha, and Joseph T. Hupp
Chemistry of Materials 2013 Volume 25(Issue 5) pp:739
Publication Date(Web):February 9, 2013
DOI:10.1021/cm303749m
Control over catenation in a pillared paddlewheel metal–organic framework was achieved via solvent-assisted linker exchange. The linker exchange was demonstrated on the noncatenated structure of DO-MOF, by using 4,4′-bipyridine (L4) and 4,4′-azobis(pyridine) (L5) as linkers, leading to noncatenated materials SALEM-3 and SALEM-4. The de novo synthesized analogues of SALEM-3 and SALEM-4 can only be obtained as 2-fold interpenetrated frameworks. The reaction progress of the linker exchange was monitored by NMR spectroscopy, and structure and framework catenation were characterized by powder X-ray diffraction and thermogravimetric methods.Keywords: catenation; linker exchange; metal−organic frameworks; SALE;
Co-reporter:Olga Karagiaridi, Wojciech Bury, Emmanuel Tylianakis, Amy A. Sarjeant, Joseph T. Hupp, and Omar K. Farha
Chemistry of Materials 2013 Volume 25(Issue 17) pp:3499
Publication Date(Web):August 22, 2013
DOI:10.1021/cm401724v
Solvent-assisted linker exchange (SALE) was performed on a pillared-paddlewheel metal–organic framework (MOF), SALEM-5, to achieve incorporation of longer linkers into the material. The 9-Å meso-1,2-di(4-pyridyl)-1,2-ethanediol pillar of SALEM-5 was successfully replaced by 11-Å, 14-Å, and 17-Å pillars to generate daughter MOFs SALEM-6, SALEM-7, and SALEM-8. The daughter frameworks possess more open cages, as was demonstrated by structural modeling from the powder X-ray diffraction patterns, and larger solvent accessible space, as was demonstrated by thermogravimetric analysis. Finally, a study was performed to examine the effect of pKa of monoprotonated dipyridyl pillars (as an indicator of the Zn–L bond strength) on the outcome of SALE.Keywords: metal−organic frameworks; pKa; solvent-assisted linker exchange;
Co-reporter:Shinya Takaishi, Erica J. DeMarco, Michael J. Pellin, Omar K. Farha and Joseph T. Hupp
Chemical Science 2013 vol. 4(Issue 4) pp:1509-1513
Publication Date(Web):07 Dec 2012
DOI:10.1039/C2SC21516K
Using recently reported robust porphyrinic metal–organic framework (RPM) materials, we have examined the systematic exchange of pillaring linkers/struts as a means of accessing new versions of these materials. Dipyridyl-porphyrin Zn(II) (Zn-dipy) struts were successfully replaced by M2-dipy (M2 = 2H(+), Al(III), Sn(IV)), forming crystalline solid solutions of Zn(Zn1−xMx)-RPM in variable ratios. In addition, post-synthetic metallation was demonstrated using Zn2H-RPM, again with retention of crystallinity. We examined catalytic activity for an epoxide ring-opening reaction with a series of ZnM2-RPMs. The catalytic activity depends strongly on the identity of the metal ion present in the dipyridyl-porphyrin unit.
Co-reporter:Chung-Wei Kung, Timothy Chiaan Wang, Joseph E. Mondloch, David Fairen-Jimenez, Daniel M. Gardner, Wojciech Bury, Jordan Matthew Klingsporn, Jonathan C. Barnes, Richard Van Duyne, J. Fraser Stoddart, Michael R. Wasielewski, Omar K. Farha, and Joseph T. Hupp
Chemistry of Materials 2013 Volume 25(Issue 24) pp:5012
Publication Date(Web):December 13, 2013
DOI:10.1021/cm403726v
A uniform and crack-free metal–organic framework (MOF) thin film composed of free-standing acicular nanorods was grown on a transparent conducting glass substrate. The MOF thin film exhibits electrochromic switching between yellow and deep blue by means of a one-electron redox reaction at its pyrene-based linkers. The rigid MOF stabilizes the radical cations of the pyrene linkers at positive applied potential, resulting in the reversible color change of the MOF film. The regular and uniform channels of the MOF allow ions to migrate through the entire film. The MOF thin film thus exhibits a remarkable color change and rapid switching rate.Keywords: electrochromism; metal−organic frameworks; one-dimensional nanorods; pyrene;
Co-reporter:Brad G. Hauser, Omar K. Farha, Jason Exley, and Joseph T. Hupp
Chemistry of Materials 2013 Volume 25(Issue 1) pp:12
Publication Date(Web):December 4, 2012
DOI:10.1021/cm3022566
Thermal treatment of highly stable porous organic polymers based upon the Yamamoto polymerization of 2,2′,7,7′-tetrabromo-9,9′-spirobifluorene was done. The polymers are shown to be thermally and chemically stable. Upon thermal treatment the polymers are shown to have BET surface areas of ca. 2,000 m2/g and 2,500 m2/g respectively.Keywords: gas storage; polymer processing; porous polymers;
Co-reporter:Ryan K. Totten, Mitchell H. Weston, Jin Kuen Park, Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen
ACS Catalysis 2013 Volume 3(Issue 7) pp:1454
Publication Date(Web):April 15, 2013
DOI:10.1021/cs4001738
Two robust catechol-functionalized porous organic polymers (catPOPs) with different Td-directing nodes were synthesized using a cobalt-catalyzed acetylene trimerization (CCAT) strategy. Postsynthesis metallation was readily carried out with La(acac)3 to afford catalytically active La-functionalized catPOPs for the solvolytic and hydrolytic degradation of the toxic organophosphate compound methyl paraoxon, a simulant for nerve agents.Keywords: catalysis; catechol; lanthanum; organophosphates; porous organic polymers
Co-reporter:Shannon C. Riha, Michael J. DeVries Vermeer, Michael J. Pellin, Joseph T. Hupp, and Alex B. F. Martinson
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 2) pp:360
Publication Date(Web):January 3, 2013
DOI:10.1021/am302356k
High specific surface area transparent and conducting frameworks, fabricated by atomic layer deposition (ALD), were used as scaffolds for fabrication of equally high area, ALD-formed hematite structures for photo-oxidation of water to dioxygen. The frameworks offer high transparency to visible light and robust conductivity under harsh annealing and oxidizing conditions. Furthermore, they also make possible the spatially distributed collection of photocurrent from ultrathin coatings of hematite layers, enabling the formation of photoanodes featuring both large optical extinction and a hematite layer thickness nearly commensurate with the hole-collection distance. The distributed-current-collection approach increases the efficiency of water oxidation with hematite (by about a factor of 3 compared with an optimized flat electrode), is highly adaptable to future advances in thin film technology, and is further applicable to a multitude of nanostructures and optoelectronic applications that require ultrathin films without sacrificing optical thickness.Keywords: atomic layer deposition; distributed current collector; Fe2O3; inverse opal; iron oxide; water splitting;
Co-reporter:Paul W. Siu, Zachary J. Brown, Omar K. Farha, Joseph T. Hupp and Karl A. Scheidt
Chemical Communications 2013 vol. 49(Issue 93) pp:10920-10922
Publication Date(Web):10 Oct 2013
DOI:10.1039/C3CC47177B
A hydrogen-bond donating MOF catalyst based on the UiO-67 framework, containing both urea-functionalized dicarboxylate and biphenyl-4,4′-dicarboxylate struts, was synthesized by a de novo route. The mixed strut framework has larger pore sizes and improved catalytic activity for Henry reactions than the pure strut analogue, which contains only the urea-functionalized dicarboxylate linker.
Co-reporter:Mitchell H. Weston, Gregory W. Peterson, Matthew A. Browe, Paulette Jones, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2013 vol. 49(Issue 29) pp:2995-2997
Publication Date(Web):12 Feb 2013
DOI:10.1039/C3CC40475G
Porous organic polymers bearing metal–catecholate groups were evaluated for their ability to remove airborne ammonia, cyanogen chloride, sulphur dioxide, and octane by micro-breakthrough analysis. For ammonia, the metal–catecholate materials showed remarkable uptake under humid conditions.
Co-reporter:Michael J. Katz, Zachary J. Brown, Yamil J. Colón, Paul W. Siu, Karl A. Scheidt, Randall Q. Snurr, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2013 vol. 49(Issue 82) pp:9449-9451
Publication Date(Web):06 Sep 2013
DOI:10.1039/C3CC46105J
A scalable, reproducible method of synthesizing UiO-66- and UiO-67-type MOFs, entailing the addition of HCl to the reaction mixture, has been investigated. The new protocol requires a fraction of the time of previously reported procedures, yields exceptional porosities, and works with a range of linkers.
Co-reporter:Sergio J. Garibay, Mitchell H. Weston, Joseph E. Mondloch, Yamil J. Colón, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
CrystEngComm 2013 vol. 15(Issue 8) pp:1515-1519
Publication Date(Web):22 Oct 2012
DOI:10.1039/C2CE26595H
Methyl-, hydroxymethyl-, and phthalimidomethyl-functionalized versions of the porous organic polymer PAF-1 have been obtained through de novo synthesis. The CO2 adsorption capacity of PAF-1–CH2NH2, obtained through the post-synthesis deprotection of PAF-1–CH2–phthalimide, has been shown to exceed that of PAF-1.
Co-reporter:Huong Giang T. Nguyen, Mitchell H. Weston, Amy A. Sarjeant, Daniel M. Gardner, Zhi An, Raanan Carmieli, Michael R. Wasielewski, Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen
Crystal Growth & Design 2013 Volume 13(Issue 8) pp:3528-3534
Publication Date(Web):June 25, 2013
DOI:10.1021/cg400500t
Through a combination of protecting groups, postsynthesis deprotection, and postsynthesis metallation, a homogeneously inaccessible, single-site vanadyl(monocatecholate) moiety can be incorporated into the dipyridyl struts of a Zn-based, pillared paddlewheel MOF. The resulting MOF, which has large pores, exhibits catalytic activity in the benzylic oxidation of tetralin in the presence of tert-butylhydroperoxide.
Co-reporter:Mitchell H. Weston, Amelia A. Delaquil, Amy A. Sarjeant, Omar K. Farha, Joseph T. Hupp, and SonBinh T. Nguyen
Crystal Growth & Design 2013 Volume 13(Issue 7) pp:2938-2942
Publication Date(Web):May 3, 2013
DOI:10.1021/cg400342m
A series of isostructural noncatenated, water-stable zinc-based dipyridyl pillared-paddlewheel metal–organic frameworks (MOFs) was synthesized with tunable pore hydrophobicity. Pore hydrophobicity was engendered through dipyridyl ligands decorated with alkyl chains of varying length (methyl to hexyl). The most hydrophobic MOFs exhibited selective sorption of ethanol over water.
Co-reporter:Marianne B. Lalonde, Rachel B. Getman, Jeong Yong Lee, John M. Roberts, Amy A. Sarjeant, Karl A. Scheidt, Peter A. Georgiev, Jan P. Embs, Juergen Eckert, Omar K. Farha, Randall Q. Snurr and Joseph T. Hupp
CrystEngComm 2013 vol. 15(Issue 45) pp:9408-9414
Publication Date(Web):06 Mar 2013
DOI:10.1039/C3CE40198G
Metal–organic frameworks (MOFs) are permanently porous, crystalline materials and promising hydrogen sorbents. However, the H2 heats of adsorption are generally too small to promote significant adsorption under desired storage conditions. Increasing the H2–framework interaction energy is a prominent goal of current MOF design. Hydrogen binds to MOFs through a variety of interactions, such as dispersion, charge–induced-dipole, charge–quadrupole, and even chemical bonding. To date, these interactions have been enhanced by incorporating strongly charged groups into the MOF structures, but the effects tend to be short-range and only effective at low loadings. In this work we report the structures and H2 storage properties of two zwitterionic MOFs. These structures feature zwitterionic characteristics arising from N-heterocyclic azolium groups in the linkers and negatively charged Zn2(CO2)5 nodes. These groups exhibit net charges of +0.5 and −1.0, respectively, and interact strongly with the H2 quadrupole. Isosteric heats of adsorption of up to 7.0 kJ mol−1 are observed in these zwitterionic MOFs.
Co-reporter:Joseph E. Mondloch, Olga Karagiaridi, Omar K. Farha and Joseph T. Hupp
CrystEngComm 2013 vol. 15(Issue 45) pp:9258-9264
Publication Date(Web):11 Oct 2013
DOI:10.1039/C3CE41232F
Crystalline metal–organic frameworks (MOFs) have emerged as a highly desirable class of solid-state materials. Some of their most attractive features include exceptionally high porosities as well as surface areas. A key aspect to the realization of high porosity is the removal of guest molecules from the framework while still maintaining its structural integrity (i.e., “activation”). This contribution highlights the strategies utilized to date for activating MOFs, including: (i) conventional heating and vacuum; (ii) solvent-exchange; (iii) supercritical CO2 (scCO2) exchange; (iv) freeze-drying; and (v) chemical treatment.
Co-reporter:Michael J. Katz, Michael J. D. Vermeer, Omar K. Farha, Michael J. Pellin, and Joseph T. Hupp
Langmuir 2013 Volume 29(Issue 2) pp:806-814
Publication Date(Web):December 17, 2012
DOI:10.1021/la303962y
Both the adsorption of t-butylpyridine and the atomic-layer deposition of ultrathin conformal coatings of insulators (such as alumina) are known to boost open-circuit photovoltages substantially for dye-sensitized solar cells. One attractive interpretation is that these modifiers significantly shift the conduction-edge energy of the electrode, thereby shifting the onset potential for dark current arising from the interception of injected electrons by solution-phase redox shuttle components such as Co(phenanthroline)33+ and triiodide. For standard, high-area, nanoporous photoelectrodes, band-edge energies are difficult to measure directly. In contrast, for flat electrodes they are readily accessible from Mott–Schottky analyses of impedance data. Using such electrodes (specifically TiO2), we find that neither organic nor inorganic electrode-surface modifiers shift the conduction-band-edge energy sufficiently to account fully for the beneficial effects on electrode behavior (i.e., the suppression of dark current). Additional experiments reveal that the efficacy of ultrathin coatings of Al2O3 arises chiefly from the passivation of redox-catalytic surface states. In contrast, adsorbed t-butylpyridine appears to suppress dark currents mainly by physically blocking access of shuttle molecules to the electrode surface. Studies with other derivatives of pyridine, including sterically and/or electronically diverse derivatives, show that heterocycle adsorption and the concomitant suppression of dark current does not require the coordination of surface Ti(IV) or Al(III) atoms. Notably, the favorable (i.e., negative) shifts in onset potential for the flow of dark current engendered by organic and inorganic surface modifiers are additive. Furthermore, they appear to be largely insensitive to the identity of shuttle molecules.
Co-reporter:Lauren E. Kreno, Kirsty Leong, Omar K. Farha, Mark Allendorf, Richard P. Van Duyne, and Joseph T. Hupp
Chemical Reviews 2012 Volume 112(Issue 2) pp:1105-1125
Publication Date(Web):November 9, 2011
DOI:10.1021/cr200324t
Co-reporter:Guang Lu;Omar K. Farha;Weina Zhang;Fengwei Huo
Advanced Materials 2012 Volume 24( Issue 29) pp:3970-3974
Publication Date(Web):
DOI:10.1002/adma.201202116
Co-reporter:Michael J. Katz, Shannon C. Riha, Nak Cheon Jeong, Alex B.F. Martinson, Omar K. Farha, Joseph T. Hupp
Coordination Chemistry Reviews 2012 Volume 256(21–22) pp:2521-2529
Publication Date(Web):November 2012
DOI:10.1016/j.ccr.2012.06.017
Iron(III)oxide in the form of hematite is, in many respects, an attractive material for the photocatalytic production of molecular oxygen from water. Especially over the past six years, several developments have advanced the performance of water oxidation cells based on this material. Nevertheless, the best versions of these photoelectrodes produce only about a fifth of the maximum photocurrent (and dioxygen) theoretically obtainable, while operating at photovoltages also well short of the theoretical maximum. Here we describe the factors limiting the performance of hematite as a photo-catalyst and outline approaches that have been, or might be, tried to overcome them. These factors include low hole mobility, bulk charge recombination, surface charge recombination, slow water oxidation kinetics, and poor light absorption. Whether hematite will soon become a practical photo-catalyst for water oxidation is uncertain. But, the schemes developed and the lessons learned will likely prove transferrable to other candidate photocatalyst materials.Highlights► Fe2O3 in the form of hematite is attractive for the photocatalytic production of O2 from water. ► Current Fe2O3 electrodes produce 1/5 of the photocurrent theoretically obtainable. ► Current Fe2O3 electrodes operate at photovoltages well short of the theoretical maximum. ► Limitations are low h+ mobility, charge recombination, slow kinetics, and poor light absorption. ► Cation doping, and surface modification can lead to improved hematite performance.
Co-reporter:Omar K. Farha ; Christopher E. Wilmer ; Ibrahim Eryazici ; Brad G. Hauser ; Philip A. Parilla ; Kevin O’Neill ; Amy A. Sarjeant ; SonBinh T. Nguyen ; Randall Q. Snurr
Journal of the American Chemical Society 2012 Volume 134(Issue 24) pp:9860-9863
Publication Date(Web):June 7, 2012
DOI:10.1021/ja302623w
We have synthesized, characterized, and computationally validated the high Brunauer–Emmett–Teller surface area and hydrogen uptake of a new, noncatenating metal–organic framework (MOF) material, NU-111. Our results imply that replacing the phenyl spacers of organic linkers with triple-bond spacers is an effective strategy for boosting molecule-accessible gravimetric surface areas of MOFs and related high-porosity materials.
Co-reporter:Nak Cheon Jeong ; Ho-Jin Son ; Chaiya Prasittichai ; Chang Yeon Lee ; Rebecca A. Jensen ; Omar K. Farha
Journal of the American Chemical Society 2012 Volume 134(Issue 48) pp:19820-19827
Publication Date(Web):November 7, 2012
DOI:10.1021/ja308725r
Dye-sensitized solar cells, especially those comprising molecular chromophores and inorganic titania, have shown promise as an alternative to silicon for photovoltaic light-to-electrical energy conversion. Co-sensitization (the use of two or more chromophores having complementary absorption spectra) has attracted attention as a method for harvesting photons over a broad spectral range. If implemented successfully, then cosensitization can substantially enhance photocurrent densities and light-to-electrical energy conversion efficiencies. In only a few cases, however, have significant overall improvements been obtained. In most other cases, inefficiencies arise due to unconstructive energy or charge transfer between chromophores or, as we show here, because of modulation of charge-recombination behavior. Spatial isolation of differing chromophores offers a solution. We report a new and versatile method for fabricating two-color photoanodes featuring spatially isolated chromophore types that are selectively positioned in desired zones. Exploiting this methodology, we find that photocurrent densities depend on both the relative and absolute positions of chromophores and on “local” effective electron collection lengths. One version of the two-color photoanode, based on an organic push–pull dye together with a porphyrin dye, yielded high photocurrent densities (JSC = 14.6 mA cm–2) and double the efficiency of randomly mixed dyes, once the dyes were optimally positioned with respect to each other. We believe that the organizational rules and fabrication strategy will prove transferrable, thereby advancing understanding of panchromatic sensitization as well as yielding higher efficiency devices.
Co-reporter:Olga Karagiaridi, Marianne B. Lalonde, Wojciech Bury, Amy A. Sarjeant, Omar K. Farha, and Joseph T. Hupp
Journal of the American Chemical Society 2012 Volume 134(Issue 45) pp:18790-18796
Publication Date(Web):October 22, 2012
DOI:10.1021/ja308786r
A zeolitic imidazolate framework material of SOD topology possessing primarily unsubstituted imidazolate (im) linkers has been synthesized via solvent-assisted linker exchange (SALE) of ZIF-8. The structure of the new material, SALEM-2, has been confirmed through 1H NMR and powder and single-crystal X-ray diffraction. SALEM-2 is the first example of a porous Zn(im)2 ZIF possessing a truly zeolitic topology that can be obtained in bulk quantities. Upon treatment with n-butyllithium, the open analogue exhibits Brønsted base catalysis that cannot be accomplished by the parent material ZIF-8. Additionally, it displays a different size cutoff for uptake and release of molecular guests than does ZIF-8.
Co-reporter:Omar K. Farha ; Ibrahim Eryazici ; Nak Cheon Jeong ; Brad G. Hauser ; Christopher E. Wilmer ; Amy A. Sarjeant ; Randall Q. Snurr ; SonBinh T. Nguyen ; A. Özgür Yazaydın
Journal of the American Chemical Society 2012 Volume 134(Issue 36) pp:15016-15021
Publication Date(Web):August 20, 2012
DOI:10.1021/ja3055639
We have synthesized, characterized, and computationally simulated/validated the behavior of two new metal–organic framework (MOF) materials displaying the highest experimental Brunauer–Emmett–Teller (BET) surface areas of any porous materials reported to date (∼7000 m2/g). Key to evacuating the initially solvent-filled materials without pore collapse, and thereby accessing the ultrahigh areas, is the use of a supercritical CO2 activation technique. Additionally, we demonstrate computationally that by shifting from phenyl groups to “space efficient” acetylene moieties as linker expansion units, the hypothetical maximum surface area for a MOF material is substantially greater than previously envisioned (∼14600 m2/g (or greater) versus ∼10500 m2/g).
Co-reporter:Ho-Jin Son ; Xinwei Wang ; Chaiya Prasittichai ; Nak Cheon Jeong ; Titta Aaltonen ; Roy G. Gordon
Journal of the American Chemical Society 2012 Volume 134(Issue 23) pp:9537-9540
Publication Date(Web):June 1, 2012
DOI:10.1021/ja300015n
A major loss mechanism in dye-sensitized solar cells (DSCs) is recombination at the TiO2/electrolyte interface. Here we report a method to reduce greatly this loss mechanism. We deposit insulating and transparent silica (SiO2) onto the open areas of a nanoparticulate TiO2 surface while avoiding any deposition of SiO2 over or under the organic dye molecules. The SiO2 coating covers the highly convoluted surface of the TiO2 conformally and with a uniform thickness throughout the thousands of layers of nanoparticles. DSCs incorporating these selective and self-aligned SiO2 layers achieved a 36% increase in relative efficiency versus control uncoated cells.
Co-reporter:John M. Roberts ; Branden M. Fini ; Amy A. Sarjeant ; Omar K. Farha ; Joseph T. Hupp ;Karl A. Scheidt
Journal of the American Chemical Society 2012 Volume 134(Issue 7) pp:3334-3337
Publication Date(Web):January 31, 2012
DOI:10.1021/ja2108118
A new urea-containing metal–organic framework (MOF) was synthesized to act as a heterogeneous catalyst. Ureas are well-known for self-recognition and aggregation behavior, resulting in loss of catalytic competency. The catalyst spatial isolation achievable in a porous MOF environment suggests a potentially general solution. The combination of a symmetrical urea tetracarboxylate strut, 4,4′-bipyridine, and Zn(NO3)2·6H2O under solvothermal conditions afforded a new microporous MOF (NU-601). This material is indeed an effective hydrogen-bond-donor catalyst for Friedel–Crafts reactions between pyrroles and nitroalkenes, whereas a homogeneous urea is much less competent. The higher rates of reaction of small substrates relative to larger ones with NU-601 strongly suggest that catalysis primarily occurs within the pores of this new material rather than on its exterior. To the best of our knowledge, this approach is the first example of specific engineering of successful hydrogen-bonding catalysis into a MOF material.
Co-reporter:Ho-Jin Son ; Shengye Jin ; Sameer Patwardhan ; Sander J. Wezenberg ; Nak Cheon Jeong ; Monica So ; Christopher E. Wilmer ; Amy A. Sarjeant ; George C. Schatz ; Randall Q. Snurr ; Omar K. Farha ; Gary P. Wiederrecht
Journal of the American Chemical Society 2012 Volume 135(Issue 2) pp:862-869
Publication Date(Web):December 18, 2012
DOI:10.1021/ja310596a
Given that energy (exciton) migration in natural photosynthesis primarily occurs in highly ordered porphyrin-like pigments (chlorophylls), equally highly ordered porphyrin-based metal–organic frameworks (MOFs) might be expected to exhibit similar behavior, thereby facilitating antenna-like light-harvesting and positioning such materials for use in solar energy conversion schemes. Herein, we report the first example of directional, long-distance energy migration within a MOF. Two MOFs, namely F-MOF and DA-MOF that are composed of two Zn(II) porphyrin struts [5,15-dipyridyl-10,20-bis(pentafluorophenyl)porphinato]zinc(II) and [5,15-bis[4-(pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II), respectively, were investigated. From fluorescence quenching experiments and theoretical calculations, we find that the photogenerated exciton migrates over a net distance of up to ∼45 porphyrin struts within its lifetime in DA-MOF (but only ∼3 in F-MOF), with a high anisotropy along a specific direction. The remarkably efficient exciton migration in DA-MOF is attributed to enhanced π-conjugation through the addition of two acetylene moieties in the porphyrin molecule, which leads to greater Q-band absorption intensity and much faster exciton-hopping (energy transfer between adjacent porphyrin struts). The long distance and directional energy migration in DA-MOF suggests promising applications of this compound or related compounds in solar energy conversion schemes as an efficient light-harvesting and energy-transport component.
Co-reporter:Byungman Kang, Josh W. Kurutz, Kyoung-Tae Youm, Ryan K. Totten, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Science 2012 vol. 3(Issue 6) pp:1938-1944
Publication Date(Web):26 Jan 2012
DOI:10.1039/C2SC00950A
Box-like tetrakis(metalloporphyrin) supramolecular assemblies possessing Zn and Al metal sites can catalyze the methanolysis of phosphate triesters with a high rate enhancement, up to 430 times faster than the uncatalyzed reaction. Mechanistic studies suggest that the observed rate enhancement can be attributed to a high local concentration of methoxide ion that operates in concert with a solvophobically driven encapsulation of substrates by the porphyrinic assembly.
Co-reporter:Mitchell H. Weston, Omar K. Farha, Brad G. Hauser, Joseph T. Hupp, and SonBinh T. Nguyen
Chemistry of Materials 2012 Volume 24(Issue 7) pp:1292
Publication Date(Web):January 31, 2012
DOI:10.1021/cm2034646
Robust catechol-functionalized porous organic polymers (POPs) with tunable porosities (560–1050 m2/g) and degrees of functionalization were synthesized using a cobalt-catalyzed acetylene trimerization (CCAT) strategy. Post-synthesis metalation can be readily carried out with a wide range of metal precursors (CuII, MgII, and MnII salts and complexes), resulting in metalated POPs with enhanced heat of hydrogen adsorptions compared to the starting nonmetalated materials.Keywords: hydrogen storage; metal catecholates; porous organic polymers;
Co-reporter:Marianne B. Lalonde, Omar K. Farha, Karl A. Scheidt, and Joseph T. Hupp
ACS Catalysis 2012 Volume 2(Issue 8) pp:1550
Publication Date(Web):July 3, 2012
DOI:10.1021/cs300260f
Metal imidazolates, an important class of constructs in metal–organic framework chemistry, are shown here to be precursors to N-heterocyclic carbene-like catalysts. By using n-butyl lithium to deprotonate tripodal imidazolate framework-1 (TIF-1), N-heterocyclic carbene (NHC) sites can be exposed. These sites are found to be remarkably competent as Brønsted-base-type NHC catalysts. An α,β-unsaturated ketone was converted to the corresponding benzyl ether with benzyl alcohol at a faster rate and in higher yield than with a traditional homogeneous NHC catalyst (1,3-bis-(2,4,6-trimethylphenyl)imidazole)), despite lower overall loading. Varying the size of the alcohol in the conjugate addition reaction yielded no change in reaction rate, even when the size of the alcohol exceeded the diameter of the MOF pores, suggesting that catalysis occurs exclusively on the surface of the MOF crystals, as opposed to within the framework pores.Keywords: conjugate addition; ethers; metal organic frameworks; N-heterocyclic carbenes;
Co-reporter:Ryan K. Totten, Patrick Ryan, Byungman Kang, Suk Joong Lee, Linda J. Broadbelt, Randall Q. Snurr, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2012 vol. 48(Issue 35) pp:4178-4180
Publication Date(Web):31 Jan 2012
DOI:10.1039/C2CC17568A
A series of metalloporphyrin dimers were modularly prepared and shown to catalyze the methanolysis of a phosphate triester, yielding rates that are large compared to the rate of the uncatalyzed reaction. Up to 1300-fold rate acceleration can be achieved via a combination of cavity-localized Lewis-acid activation and methoxide-induced methanolysis.
Co-reporter:Huong Giang T. Nguyen, Mitchell H. Weston, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
CrystEngComm 2012 vol. 14(Issue 12) pp:4115-4118
Publication Date(Web):01 Mar 2012
DOI:10.1039/C2CE06666A
A vanadyl(monocatecholate)-decorated metal-organic framework was synthesized using two sequential post-synthesis modifications. This material is catalytically active for the oxidation of organo-sulfide. In contrast to the homogeneous control catalyst, it can be tuned to be selective for the sulfoxide product using tert-butyl hydroperoxide as oxidant.
Co-reporter:Ibrahim Eryazici, Omar K. Farha, Brad G. Hauser, A. Özgür Yazaydın, Amy A. Sarjeant, SonBinh T. Nguyen, and Joseph T. Hupp
Crystal Growth & Design 2012 Volume 12(Issue 3) pp:1075-1080
Publication Date(Web):January 27, 2012
DOI:10.1021/cg201520z
Two noninterpenetrated MOFs with strikingly different structures, NU-108-Cu and NU-108-Zn, were prepared from a single hexa-carboxylated ligand. NU-108-Cu contains paddlewheel-coordinated copper ions as nodes and is based on a 3,24 network associated with an inherently noncatenating rht-topology. Modifications introduced in the hexa-carboxylated struts (uniquely placed phenyl spacers) lead to substantial changes in pore sizes, relative to those found in other MOFs based on 3,24 networks and paddlewheel-coordinated copper ions. NU-108-Zn features a new net based on (3,3,6)-connecter and octadehral Zn4O nodes in which all struts lie in a–b planes.
Co-reporter: Youn-Sang Bae;Dr. Chang Yeon Lee;Dr. Ki Chul Kim; Omar K. Farha;Dr. Peter Nickias; Joseph T. Hupp; SonBinh T. Nguyen; Rall Q. Snurr
Angewandte Chemie International Edition 2012 Volume 51( Issue 8) pp:1857-1860
Publication Date(Web):
DOI:10.1002/anie.201107534
Co-reporter: Youn-Sang Bae;Dr. Chang Yeon Lee;Dr. Ki Chul Kim; Omar K. Farha;Dr. Peter Nickias; Joseph T. Hupp; SonBinh T. Nguyen; Rall Q. Snurr
Angewandte Chemie 2012 Volume 124( Issue 8) pp:1893-1896
Publication Date(Web):
DOI:10.1002/ange.201107534
Co-reporter:Vennesa O. Williams, Nak Cheon Jeong, Chaiya Prasittichai, Omar K. Farha, Michael J. Pellin, and Joseph T. Hupp
ACS Nano 2012 Volume 6(Issue 7) pp:6185
Publication Date(Web):June 21, 2012
DOI:10.1021/nn3015695
A doubly coaxial photoanode architecture based on templated SiO2 aerogels was fabricated on transparent conducting oxides for use in dye-sensitized solar cells (DSSCs). These templates were coated with ZnO via atomic layer deposition (ALD) to yield an electronically interconnected, low-density, high-surface-area, semiconductor framework. Addition of a thin conformal layer of a second metal oxide (alumina, zirconia, or titania) via ALD was found to suppress the dissolution of ZnO that otherwise occurs when it is soaked in alcohol solutions containing acidic dyes used for sensitization or in acetonitrile solutions containing a pyridine derivative and the iodide/tri-iodide (I–/I–3) redox shuttle. Electron transport in SiO2–ZnO–TiO2 photoelectrodes was found to be nearly 2 orders of magnitude faster than in SiO2–TiO2 structures, implying that the interior ZnO sheath serves as the primary electron conduit. In contrast, rates of electron interception by the oxidized form of the redox shuttle were observed to decrease when a TiO2 shell was added to SiO2–ZnO, with the decreases becoming more significant as the thickness of the titania shell increases. These effects lead to improvements in efficiency for DSSCs that utilize I–/I–3, but much larger improvements for DSSCs utilizing ferrocene/ferrocenium, a notoriously fast redox shuttle. For the former, overall energy conversion efficiencies maximize at 4.0%. From a variety of experiments, the primary factor limiting aerogel-based DSSC performance is light loss due to scattering. Nevertheless, variants of the doubly coaxial structure may prove useful in devising DSSCs that can achieve excellent energy conversion efficiencies even with fast redox shuttles.Keywords: aerogel; atomic layer deposition; dye-sensitized solar cell; ferrocene redox shuttle; zinc oxide
Co-reporter:Guang Lu;Omar K. Farha;Lauren E. Kreno;Paul M. Schoenecker;Krista S. Walton;Richard P. Van Duyne
Advanced Materials 2011 Volume 23( Issue 38) pp:4449-4452
Publication Date(Web):
DOI:10.1002/adma.201102116
Co-reporter:Chang Yeon Lee, Omar K. Farha, Bong Jin Hong, Amy A. Sarjeant, SonBinh T. Nguyen, and Joseph T. Hupp
Journal of the American Chemical Society 2011 Volume 133(Issue 40) pp:15858-15861
Publication Date(Web):September 14, 2011
DOI:10.1021/ja206029a
A pillared-paddlewheel type metal–organic framework material featuring bodipy- and porphyrin-based struts, and capable of harvesting light across the entire visible spectrum, has been synthesized. Efficient—essentially quantitative—strut-to-strut energy transfer (antenna behavior) was observed for the well-organized donor–acceptor assembly consituting the ordered MOF structure.
Co-reporter:Omar K. Farha ; Abraham M. Shultz ; Amy A. Sarjeant ; SonBinh T. Nguyen
Journal of the American Chemical Society 2011 Volume 133(Issue 15) pp:5652-5655
Publication Date(Web):March 29, 2011
DOI:10.1021/ja111042f
On account of their structural similarity to cofactors found in many metallo-enzymes, metalloporphyrins are obvious potential building blocks for catalytically active, metal−organic framework (MOF) materials. While numerous porphyrin-based MOFs have already been described, versions featuring highly accessible active sites and permanent microporosity are remarkably scarce. Indeed, of the more than 70 previously reported porphyrinic MOFs, only one has been shown to be both permanently microporous and contain internally accessible active sites for chemical catalysis. Attempts to generalize the design approach used in this single successful case have failed. Reported here, however, is the synthesis of an extended family of MOFs that directly incorporate a variety of metalloporphyrins (specifically Al3+, Zn2+, Pd2+, Mn3+, and Fe3+ complexes). These robust porphyrinic materials (RPMs) feature large channels and readily accessible active sites. As an illustrative example, one of the manganese-containing RPMs is shown to be catalytically competent for the oxidation of alkenes and alkanes.
Co-reporter:Nak Cheon Jeong ; Bappaditya Samanta ; Chang Yeon Lee ; Omar K. Farha
Journal of the American Chemical Society 2011 Volume 134(Issue 1) pp:51-54
Publication Date(Web):December 12, 2011
DOI:10.1021/ja2110152
HKUST-1, a metal–organic framework (MOF) material containing CuII-paddlewheel-type nodes and 1,3,5-benzenetricarboxylate struts, features accessible CuII sites to which solvent or other desired molecules can be intentionally coordinated. As part of a broader investigation of ionic conductivity in MOFs, we unexpectedly observed substantial proton conductivity with the “as synthesized” version of this material following sorption of methanol. Although HKUST-1 is neutral, coordinated water molecules are rendered sufficiently acidic by CuII to contribute protons to pore-filling methanol molecules and thereby enhance the alternating-current conductivity. At ambient temperature, the chemical identities of the node-coordinated and pore-filling molecules can be independently varied, thus enabling the proton conductivity to be reversibly modulated. The proton conductivity of HKUST-1 was observed to increase by ∼75-fold, for example, when node-coordinated acetonitrile molecules were replaced by water molecules. In contrast, the conductivity became almost immeasurably small when methanol was replaced by hexane as the pore-filling solvent.
Co-reporter:Abraham M. Shultz, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Science 2011 vol. 2(Issue 4) pp:686-689
Publication Date(Web):04 Jan 2011
DOI:10.1039/C0SC00339E
The synthesis of a porous organic polymer (POP) containing free-base porphyrin subunits has been accomplished by the condensation of a bis(phthalic acid)porphyrin with tetra(4-aminophenyl)methane. Metallation by post-synthesis modification affords microporous materials incorporating either Fe or Mn(porphyrins) that have been shown to be active catalysts for both olefin epoxidation and alkane hydroxylation.
Co-reporter:Parminder Kaur, Joseph T. Hupp, and SonBinh T. Nguyen
ACS Catalysis 2011 Volume 1(Issue 7) pp:819
Publication Date(Web):May 25, 2011
DOI:10.1021/cs200131g
Porous organic polymers (POPs), a class of highly cross-linked, amorphous polymers possessing micropores, have recently emerged as a versatile platform for the deployment of catalysts. These materials can be divided into three major classes: POPs that incorporate rigid well-defined homogeneous catalysts as building blocks, POPs that can be modified post-synthesis, and POPs that encapsulate metal particles. This perspective article summarizes the recent developments in POP-based catalysis and outlines the potential of POPs as platforms of heterogeneous catalysts along with some of the challenges.Keywords: conjugated porous polymers; heterogeneous catalysis; hyper-cross-linked polymers; porous organic polymers
Co-reporter:Abraham M. Shultz ; Omar K. Farha ; Debashis Adhikari ; Amy A. Sarjeant ; Joseph T. Hupp ;SonBinh T. Nguyen
Inorganic Chemistry 2011 Volume 50(Issue 8) pp:3174-3176
Publication Date(Web):March 7, 2011
DOI:10.1021/ic101952y
From a combination of chiral Mn(salen) struts and the tetratopic ligand tetrakis(4-carboxyphenyl)benzene, a large-pore, noncatenated metal-organic framework (MOF) material, MnSO-MOF, has been synthesized. Following solvent exchange with hydrophobic CHCl3, treatment of MnSO-MOF with aqueous H2O2 allowed for the selective demetalation of Mn(salen) struts at and near the surface of the crystals. The resulting crystals displayed greatly enhanced size-selective catalysis compared to the as-synthesized material. Handling of the mechanically fragile MnSO-MOF crystals was greatly facilitated by activation with supercritical CO2.
Co-reporter:Youn-Sang Bae, Brad G. Hauser, Omar K. Farha, Joseph T. Hupp, Randall Q. Snurr
Microporous and Mesoporous Materials 2011 Volume 141(1–3) pp:231-235
Publication Date(Web):May 2011
DOI:10.1016/j.micromeso.2010.10.048
Incorporation of Li cations into MOFs by either of two methods, chemical reduction or cation exchange, significantly improves the CO2/CH4 selectivity. While the selectivity enhancement by the chemical reduction seems to come from favorable displacement of catenated frameworks, the selectivity improvement by the Li cation exchange comes from enhanced solid–gas interactions.Graphical abstractResearch highlights► Li cations were incorporated into MOFs by chemical reduction or cation exchange. ► Both methods significantly improve the CO2/CH4 selectivity. ► The first experimental report for CO2/CH4 separation by cation-doped MOFs.
Co-reporter:Jaesung Yang;Ji-Eun Lee;Dr. Chang Yeon Lee;Dr. Naoki Aratani;Dr. Atsuhiro Osuka;Dr. Joseph T. Hupp;Dr. Dongho Kim
Chemistry - A European Journal 2011 Volume 17( Issue 33) pp:9219-9225
Publication Date(Web):
DOI:10.1002/chem.201100236
Abstract
Single-molecule photophysical properties of two families of linear porphyrin arrays have been investigated by single-molecule fluorescence detection techniques. Butadiyne-linked arrays (ZNB) with extensive π-conjugation perform as photostable one-quantum systems. This demonstration has been suggested by the long-lasting initial emissive state and subsequent discrete one-step photobleaching in the fluorescence intensity trajectories (FITs). As in the behavior of a one-quantum system, ZNB shows anti-bunching data in the coincidence measurements. On the other hand, in directly-linked arrays (ZN) with strong dipole coupling, each porphyrin moiety keeps individual character in photobleaching dynamics. The stepwise photobleachings in the FITs account for this explanation. Most of the FITs of ZN do not carry momentary cessation of fluorescence emission, which has been explained by the strongly bound electron-hole pair of Frenkel exciton that suppresses charge transfer between the molecule and surrounding polymers. These results give insight into the influences of interchromophorinc interactions between porphyrin moieties in the multiporphyrin arrays on their fluorescence dynamics at the single-molecule level.
Co-reporter:Tina C. Li ; Francisco Fabregat-Santiago ; Omar K. Farha ; Alexander M. Spokoyny ; Sonia R. Raga ; Juan Bisquert ; Chad A. Mirkin ; Tobin J. Marks
The Journal of Physical Chemistry C 2011 Volume 115(Issue 22) pp:11257-11264
Publication Date(Web):May 18, 2011
DOI:10.1021/jp112139h
High-area photoanodes consisting of silica aerogels, overcoated by atomic-layer-deposited TiO2, were fabricated on transparent conducting oxide platforms for their use in dye-sensitized solar cells (DSCs) in a similar fashion as previously described. These films were characterized by scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, gas adsorption, and light and dark electrochemical impedance measurements. The use of aerogel-templated photoanodes in DSCs with a Ni(III/IV) bis(dicarbollide) redox shuttle results in a greater than 2-fold enhancement in photocurrent densities, in comparison to similar cells containing photoanodes constructed from TiO2 nanoparticles. This improvement in photocurrent is attributed to a combination of improved electron transport, increased recombination resistance across the TiO2/electrolyte interface, and increased light scattering within the aerogel films. As a result, DSC charge collection efficiencies with this comparatively fast exchanging outer-sphere redox couple are improved in the TiO2 aerogel templated photoanode.
Co-reporter:Nak Cheon Jeong, Omar K. Farha, and Joseph T. Hupp
Langmuir 2011 Volume 27(Issue 5) pp:1996-1999
Publication Date(Web):January 20, 2011
DOI:10.1021/la104297s
Ethanol-soluble amphiphilic TiO2 nanoparticles (NPs) of average diameter ∼9 nm were synthesized, and an α-terpineol-based TiO2 paste was readily prepared from them in comparatively few steps. When used for fabrication of photoelectrodes for dye-sensitized solar cells (DSSCs), the paste yielded highly transparent films and possessing greater-than-typical, thickness-normalized surface areas. These film properties enabled the corresponding DSSCs to produce high photocurrent densities (17.7 mA cm−2) and a comparatively high overall light-to-electrical energy conversion efficiency (9.6%) when deployed with the well-known ruthenium-based molecular dye, N719. These efficiencies are about ∼1.4 times greater than those obtained from DSSCs containing photoelectrodes derived from a standard commercial source of TiO2 paste.
Co-reporter:Nak Cheon Jeong, Chaiya Prasittichai, and Joseph T. Hupp
Langmuir 2011 Volume 27(Issue 23) pp:14609-14614
Publication Date(Web):October 12, 2011
DOI:10.1021/la203557f
Localized surface plasmon resonance (LSPR) by silver nanoparticles that are photochemically incorporated into an electrode-supported TiO2 nanoparticulate framework enhances the extinction of a subsequently adsorbed dye (the ruthenium-containing molecule, N719). The enhancement arises from both an increase in the dye’s effective absorption cross section and a modest increase in the framework surface area. Deployment of the silver-modified assembly as a photoanode in dye-sensitized solar cells leads to light-to-electrical energy conversion with an overall efficiency of 8.9%. This represents a 25% improvement over the performance of otherwise identical solar cells lacking corrosion-protected silver nanoparticles. As one would expect based on increased dye loading and electromagnetic field enhanced (LSPR-enhanced) absorption, the improvement is manifested chiefly as an increase in photocurrent density ascribable to improved light harvesting.
Co-reporter:Omar K. Farha and Joseph T. Hupp
Accounts of Chemical Research 2010 Volume 43(Issue 8) pp:1166
Publication Date(Web):July 7, 2010
DOI:10.1021/ar1000617
The emergence of metal−organic frameworks (MOFs) as functional ultrahigh surface area materials is one of the most exciting recent developments in solid-state chemistry. Now constituting thousands of distinct examples, MOFs are an intriguing class of hybrid materials that exist as infinite crystalline lattices with inorganic vertices and molecular-scale organic connectors. Useful properties such as large internal surface areas, ultralow densities, and the availability of uniformly structured cavities and portals of molecular dimensions characterize functional MOFs. Researchers have effectively exploited these unusual properties in applications such as hydrogen and methane storage, chemical separations, and selective chemical catalysis. In principle, one of the most attractive features of MOFs is the simplicity of their synthesis. Typically they are obtained via one-pot solvothermal preparations. However, with the simplicity come challenges. In particular, MOF materials, especially more complex ones, can be difficult to obtain in pure form and with the optimal degree of catenation, the interpenetration or interweaving of identical independent networks. Once these two issues are satisfied, the removal of the guest molecules (solvent from synthesis) without damaging the structural integrity of the material is often an additional challenge. In this Account, we review recent advances in the synthetic design, purification, and activation of metal−organic framework materials. We describe the rational design of a series of organic struts to limit framework catenation and thereby produce large pores. In addition, we demonstrate the rapid separation of desired MOFs from crystalline and amorphous contaminants cogenerated during synthesis based on their different densities. Finally, we discuss the mild and efficient activation of initially solvent-filled pores with supercritical carbon dioxide, yielding usable channels and high internal surface areas. We expect that the advances in the synthesis, separation, and activation of metal−organic frameworks could lead to MOFs with new structures and functions, better and faster separation and purification of these materials, and processing methods that avoid pore blockage and pore collapse.
Co-reporter:Guang Lu
Journal of the American Chemical Society 2010 Volume 132(Issue 23) pp:7832-7833
Publication Date(Web):May 20, 2010
DOI:10.1021/ja101415b
A ZIF-8 thin film-based Fabry−Pérot device has been fabricated as a selective sensor for chemical vapors and gases. The preparation of the ZIF-8 thin film and a series of ZIF-8 thin films of various thicknesses grown on silicon substrates are presented.
Co-reporter:Tina C. Li ; Alexander M. Spokoyny ; Chunxing She ; Omar K. Farha ; Chad A. Mirkin ; Tobin J. Marks
Journal of the American Chemical Society 2010 Volume 132(Issue 13) pp:4580-4582
Publication Date(Web):March 15, 2010
DOI:10.1021/ja100396n
Nickel bis(dicarbollide) is used as a fast, one-electron outer sphere redox couple in dye-sensitized solar cells. Device performances with this anionic shuttle are investigated with different electrolyte concentrations and additives, using only 0.030 M of the Ni(III) bis(dicarbollide) to efficiently regenerate the ruthenium dye. Atomic layer deposition of Al2O3 on the nanoparticulate TiO2 photoanodes is further used to improve device performances, increasing current densities almost 2-fold and attaining power conversion efficiencies ∼10× greater than its metallocene analogue, ferrocene/ferrocenium. Open-circuit voltage decay is used to probe the kinetics of the Ni(III)/(IV) bis(dicarbollide) redox couple, and electron interception is found to be ∼103× slower than ferrocene/ferrocenium, explaining the large discrepancy in open-circuit voltage potentials between these two redox shuttles.
Co-reporter:Chang Yeon Lee, Chunxing She, Nak Cheon Jeong and Joseph T. Hupp
Chemical Communications 2010 vol. 46(Issue 33) pp:6090-6092
Publication Date(Web):23 Jul 2010
DOI:10.1039/C0CC00257G
A π-extended porphyrin possessing two anchoring groups has been synthesized and successfully applied to dye-sensitized solar cells with a power conversion efficiency of 5.5%, rendering it comparable to the performance of N719-sensitized solar cells under the conditions employed here.
Co-reporter:Youn-Sang Bae, Alexander M. Spokoyny, Omar K. Farha, Randall Q. Snurr, Joseph T. Hupp and Chad A. Mirkin
Chemical Communications 2010 vol. 46(Issue 20) pp:3478-3480
Publication Date(Web):19 Apr 2010
DOI:10.1039/B927499E
Separations of CO2/CH4, CO2/N2, and O2/N2 mixtures were studied in three porous coordination polymers made of the same carborane ligand and Co(II) nodes. High selectivities for CO2 over CH4 (∼47) and CO2 over N2 (∼95) were obtained, especially in the material with coordinated pyridine. Unusual selectivity for O2 over N2 (as high as 6.5) was demonstrated in the materials with open Co(II) sites.
Co-reporter:Omar K. Farha, Youn-Sang Bae, Brad G. Hauser, Alexander M. Spokoyny, Randall Q. Snurr, Chad A. Mirkin and Joseph T. Hupp
Chemical Communications 2010 vol. 46(Issue 7) pp:1056-1058
Publication Date(Web):15 Jan 2010
DOI:10.1039/B922554D
A diimide based porous organic polymer (POP) post-synthetically reduced with lithium metal demonstrates a drastic increase in selectivity for carbon dioxide over methane.
Co-reporter:Chunxing She, Suk Joong Lee, James E. McGarrah, Josh Vura-Weis, Michael R. Wasielewski, Hanning Chen, George C. Schatz, Mark A. Ratner and Joseph T. Hupp
Chemical Communications 2010 vol. 46(Issue 4) pp:547-549
Publication Date(Web):08 Dec 2009
DOI:10.1039/B916392A
Photoinduced electron transfer in a self-assembled supramolecular ladder structure comprising oligomeric porphyrin rails and ligated dipyridyltetrazine rungs was characterized by transient absorption spectroscopy and transient direct current photoconductivity to be mainly from an oligomer (rail) to the center of a terminal tetrazine (rung), with the remaining hole being delocalized on the oligomer and subsequent charge recombination in 0.19 ns.
Co-reporter:Lauren E. Kreno, Joseph T. Hupp, and Richard P. Van Duyne
Analytical Chemistry 2010 Volume 82(Issue 19) pp:8042
Publication Date(Web):September 14, 2010
DOI:10.1021/ac102127p
Despite its high refractive index sensitivity, localized surface plasmon resonance (LSPR) spectroscopy has been generally restricted to large biological analytes. Sensing of smaller molecules is a compelling target for this technique; in particular, LSPR spectroscopy could be utilized to detect hazardous or toxic gases and manage industrial processes involving gaseous chemicals. Here, we report sensing of pure gases over Ag nanoparticles using LSPR spectroscopy, where the detected changes in bulk refractive index are <5 × 10−4 refractive index units (RIU). We further demonstrate a novel strategy for amplifying the sensing signal by coating the plasmonic substrate with a metal−organic framework (MOF) material. Cu3(BTC)2(H2O)3, BTC = benzenetricarboxylate, was grown on Ag nanoparticles using a layer-by-layer method in order to control the MOF thickness, which we show greatly affects the sensor response. Preferential concentration of CO2 within the MOF pores produces a 14-fold signal enhancement for CO2 sensing. In principle, MOFs can be tailored for sorbing different analytes, making them ideal materials for this amplification strategy. Because the sensing signal originates in the nanoparticle extinction spectrum and not in the MOF itself, this comprises a generalizable sensing scheme applicable to any porous MOF and any analyte.
Co-reporter:Alexander M. Spokoyny, Omar K. Farha, Karen L. Mulfort, Joseph T. Hupp, Chad A. Mirkin
Inorganica Chimica Acta 2010 Volume 364(Issue 1) pp:266-271
Publication Date(Web):15 December 2010
DOI:10.1016/j.ica.2010.08.007
Two new metal–organic framework (MOF) materials based on boron-rich cluster struts (p-carborane) are reported herein. Cu(I) catalyzed coupling chemistry was used to synthesize carboxylate-based ligands, which are substantially longer than the previously studied dicarboxylated p-carborane, leading to structures with greater porosity. Solvothermal syntheses involving these ligands and Zn salts were used to prepare two new Zn(II)-based MOFs with 2D and 3D open framework structures. Upon thermal activation, these MOFs retain the chemical identity of their frameworks, leading to highly porous materials.Two new MOF materials using extended boron-rich ligands comprised of p-carborane building blocks were synthesized and can be activated thermally, resulting in highly porous structures.
Co-reporter:KarenL. Mulfort;OmarK. Farha Dr.;ChristosD. Malliakas Dr.;MercouriG. Kanatzidis ;JosephT. Hupp
Chemistry - A European Journal 2010 Volume 16( Issue 1) pp:276-281
Publication Date(Web):
DOI:10.1002/chem.200902104
Abstract
A new, twofold interpenetrated metal–organic framework (MOF) material has been synthesized that demonstrates dramatic steps in the adsorption and hysteresis in the desorption of CO2. Measurement of the structure by powder X-ray diffraction (PXRD) and pair distribution function (PDF) analysis indicates that structural changes upon CO2 sorption most likely involve the interpenetrated frameworks moving with respect to each other.
Co-reporter:Chunxing She, Shanmugam Easwaramoorthi, Pyosang Kim, Satoru Hiroto, Ichiro Hisaki, Hiroshi Shinokubo, Atsuhiro Osuka, Dongho Kim and Joseph T. Hupp
The Journal of Physical Chemistry A 2010 Volume 114(Issue 10) pp:3384-3390
Publication Date(Web):February 23, 2010
DOI:10.1021/jp908767x
We report direct measurements of the excess polarizability volumes of butadiyne-bridged zinc porphyrin dimers at singly β-to-β (1Zn) and doubly β-to-β (2Zn) positions using the transient dc photoconductivity (TDCP) technique. The excess polarizability volumes of the singlet exciton for 1Zn and 2Zn are 110 and 270 Å3, respectively, while those of the triplet exciton are ∼100 Å3 for both dimers. Our measurements suggest that the singlet exciton is mainly localized on one porphyrin subunit for 1Zn, similar to the case for the porphyrin monomer. While the exciton is fully delocalized on two porphyrin subunits in the case of meso-to-meso linked dimer (3Zn), the extent of exciton localization/delocalization for doubly β-to-β linked dimer lies between those of singly β-to-β and meso-to-meso linked dimers. Electronic structure calculations show that the dramatically different extents of exciton localization/delocalization are the results of frontier orbital coefficients being small at β positions but large at meso positions. Two butadiyne linkages between the porphyrins at β positions (2Zn) clearly facilitate electronic communication between the two porphyrin subunits by virtue of stabilization of cumulenic charge resonance structures through enforced planarity.
Co-reporter:Chaiya Prasittichai and Joseph T. Hupp
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 10) pp:1611-1615
Publication Date(Web):May 4, 2010
DOI:10.1021/jz100361f
We report here the exploitation of ultrathin layers of Al2O3 deposited via atomic layer deposition (ALD) on SnO2 photoanodes used in dye-sensitized solar cells featuring the I3−/I− couple as the redox electrolyte. We find that a single ALD cycle of Al2O3 increases the lifetimes of injected electrons by more than 2 orders of magnitude. The modified SnO2 photoanode yields nearly a 2-fold improvement fill factor and a greater than 2-fold increase in open-circuit photovoltage, with a slight increase in short-circuit photocurrent. The overall energy conversion efficiency increases by roughly 5-fold. The effects appear to arise primarily from passivation of reactive, low-energy tin-oxide surface states, with band-edge shifts and tunneling based blocking behavior playing only secondary roles.Keywords (keywords): ALD; DSSCs; SnO2;
Co-reporter:Rebecca A. Jensen, Hal Van Ryswyk, Chunxing She, Jodi M. Szarko, Lin X. Chen and Joseph T. Hupp
Langmuir 2010 Volume 26(Issue 3) pp:1401-1404
Publication Date(Web):November 13, 2009
DOI:10.1021/la902991z
Two porphyrin-based dyes with carboxylic acid tethers of differing acidity in both protonated and deprotonated forms were examined on ZnO nanotube electrodes. All of the dyes have similar surface coverage, but only the more acidic dye in the acid form injects electrons well; this dye is the only one that corrodes the ZnO. In control experiments on TiO2 nanoparticle electrodes, both dyes load and inject in protonated and deprotonated forms. These results are consistent with a requirement that the dye must partially corrode the ZnO surface in order for efficient injection to occur. Alternatively, it may possibly point to a coupling of electron injection to proton uptake.
Co-reporter:Chang Yeon Lee and Joseph T. Hupp
Langmuir 2010 Volume 26(Issue 5) pp:3760-3765
Publication Date(Web):November 3, 2009
DOI:10.1021/la9031927
A zinc porphyrin derivative (2) and zinc porphyrin−bodipy dyad (3) have been prepared and applied to dye-sensitized solar cells (DSSCs). On the basis of absorption and fluorescence excitation spectra, dyad 3 efficiently transfers energy from the bodipy to zinc porphyrin constituent. The 3-sensitized solar cell demonstrates higher solar spectral coverage, based on incident photon to current efficiency (IPCE) spectra, and an improved power conversion efficiency (η = 1.55%) compared to that of the 2-sensitized cell (η = 0.84%). The better performance of the 3-sensitized cell is attributed largely to the gain in spectral absorbance provided by the bodipy constituent of 3. Also evident, however, are secondary effects reflecting (a) fill-factor improvement and (b) a slight gain in porphyrin red-edge absorbance due to bodipy-conjugate formation.
Co-reporter:AlexerM. Spokoyny;TinaC. Li;OmarK. Farha ;CharlesW. Machan;Chunxing She Dr.;CharlotteL. Stern;TobinJ. Marks ;JosephT. Hupp ;ChadA. Mirkin
Angewandte Chemie International Edition 2010 Volume 49( Issue 31) pp:5339-5343
Publication Date(Web):
DOI:10.1002/anie.201002181
Co-reporter:JeongYong Lee, Omar K. Farha, John Roberts, Karl A. Scheidt, SonBinh T. Nguyen and Joseph T. Hupp
Chemical Society Reviews 2009 vol. 38(Issue 5) pp:1450-1459
Publication Date(Web):17 Mar 2009
DOI:10.1039/B807080F
A critical review of the emerging field of MOF-based catalysis is presented. Discussed are examples of: (a) opportunistic catalysis with metal nodes, (b) designed catalysis with framework nodes, (c) catalysis by homogeneous catalysts incorporated as framework struts, (d) catalysis by MOF-encapsulated molecular species, (e) catalysis by metal-free organic struts or cavity modifiers, and (f) catalysis by MOF-encapsulated clusters (66 references).
Co-reporter:Tendai Gadzikwa ; Omar K. Farha ; Christos D. Malliakas ; Mercouri G. Kanatzidis ; Joseph T. Hupp ;SonBinh T. Nguyen
Journal of the American Chemical Society 2009 Volume 131(Issue 38) pp:13613-13615
Publication Date(Web):September 9, 2009
DOI:10.1021/ja904189d
A noncatenated, Zn-based metal−organic framework (MOF) material bearing silyl-protected acetylenes was constructed and postsynthetically modified using “click” chemistry. Using a solvent-based, selective deprotection strategy, two different organic azides were “clicked” onto the MOF crystals, resulting in a porous material whose internal and external surfaces are differently functionalized.
Co-reporter:Stacey D. Standridge ; George C. Schatz
Journal of the American Chemical Society 2009 Volume 131(Issue 24) pp:8407-8409
Publication Date(Web):May 27, 2009
DOI:10.1021/ja9022072
We have fabricated titanium dioxide based dye-sensitized solar cells that incorporate corrosion-protected silver nanoparticles as plasmonic optical elements of the photoelectrode. The thickness of the TiO2 layer separating the dye from the nanoparticles has been systematically varied using atomic layer deposition. Over the range of TiO2 coating thicknesses examined (2 to 8 nm) there is clear enhancement of the dye extinction when plasmonic particles are present, with the enhancement increasing as the TiO2 thickness decreases. The optical enhancements translate into photocurrent enhancements, with the best cells (thinnest TiO2 coatings) showing 9-fold current enhancements under optimal monochromatic illumination. Preliminary experiments indicate that substantially larger optical enhancements are achievable with even thinner dye/particle separation layers, suggesting that even greater photocurrent enhancements may be achievable.
Co-reporter:Omar K. Farha ; Christos D. Malliakas ; Mercouri G. Kanatzidis
Journal of the American Chemical Society 2009 Volume 132(Issue 3) pp:950-952
Publication Date(Web):December 29, 2009
DOI:10.1021/ja909519e
Metal−organic frameworks (MOFs), a hybrid class of materials comprising inorganic nodes and organic struts, have potential application in many areas due to their high surface areas and uniform pores and channels. One of the key challenges to be overcome in MOF synthesis is the strong propensity for catenation (growth of multiple independent networks within a given crystal), as catenation reduces cavity sizes and diminishes porosity. Here we demonstrate that rational design of organic building blocks, which act as strut-impervious scaffolds, can be exploited to generate highly desired noncatenated materials in a controlled fashion.
Co-reporter:Omar K. Farha, Alexander M. Spokoyny, Brad G. Hauser, Youn-Sang Bae, Samantha E. Brown, Randall Q. Snurr, Chad A. Mirkin and Joseph T. Hupp
Chemistry of Materials 2009 Volume 21(Issue 14) pp:3033
Publication Date(Web):July 1, 2009
DOI:10.1021/cm901280w
Co-reporter:Youn-Sang Bae, Omar K. Farha, Joseph T. Hupp and Randall Q. Snurr
Journal of Materials Chemistry A 2009 vol. 19(Issue 15) pp:2131-2134
Publication Date(Web):12 Mar 2009
DOI:10.1039/B900390H
Post-synthesis modification of a MOF by replacing coordinated solvent molecules with highly polar ligands leads to considerable enhancement of CO2/N2 selectivity.
Co-reporter:Tendai Gadzikwa, Omar K. Farha, Karen L. Mulfort, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2009 (Issue 25) pp:3720-3722
Publication Date(Web):26 May 2009
DOI:10.1039/B823392F
A Zn-based, mixed-ligand (pillared paddlewheel), metal–organic framework (MOF) has been covalently and quantitatively decorated with free carboxylic acids to demonstrate the utility of covalent post-synthesis modification in the construction of otherwise inaccessible carboxy-functionalized MOFs.
Co-reporter:Jeong Yong Lee, John M. Roberts, Omar K. Farha, Amy A. Sarjeant, Karl A. Scheidt and Joseph T. Hupp
Inorganic Chemistry 2009 Volume 48(Issue 21) pp:9971-9973
Publication Date(Web):October 8, 2009
DOI:10.1021/ic901174p
A new strut containing an imidazolium tetracarboxylic acid core has been successfully incorporated into a microporous material using paddlewheel-coordinated copper(II) ions as nodes. Sorption studies conducted on this permanently microporous material imply that it can separate carbon dioxide from methane with high selectivity.
Co-reporter:Chunxing She, Aaron A. Rachford, Xianghuai Wang, Sébastien Goeb, Ala'a O. El-Ballouli, Felix N. Castellano and Joseph T. Hupp
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 38) pp:8586-8591
Publication Date(Web):13 Jul 2009
DOI:10.1039/B908977B
Solvent-induced excited-state configuration mixing in a Pt(II) diimine chromophore with phenylene ethynylene containing acetylide ligands, [Pt(tBu2bpy)(PE3)2] (1), was characterized by nanosecond transient absorption spectroscopy and transient dc photoconductivity (TDCP). The mixing is a result of closely spaced triplet charge transfer (3CT) and intraligand-localized (3IL) triplet energy levels that are finely tuned with solvent polarity as ascertained by their parent model chromophores [Pt(tBu2bpy)(PE1)2] (2) and [Pt(P2)(PE3)2] (3), respectively. The absorption difference spectrum of the mixed triplet state is dramatically different from those of the 3CT and 3IL state model chromophores. The 3CT, 3IL and configuration-mixed triplet states led to distinct TDCP signals. The TDCP response is of negative polarity for 3CT excited states but of positive polarity for 3IL excited states. TDCP transients for 1 in mixed solvents are a combination of signals from the 3IL and 3CT states, with the signal magnitude depending on the polarity of solvent composition. The fraction of 3CT state character in the configurationally mixed excited state was quantified by TDCP to be ∼0.24 in pure benzene, while it decreased to ∼0.05 in 20 : 80 (v : v) benzene–CH2Cl2. The charge transfer fraction appears to increase slightly to ∼0.11 in the lower polarity 20 : 80 n-hexane–CH2Cl2 medium. TDCP is shown to be a useful tool for the identification of the lowest excited state in electrically neutral metal–organic chromophores.
Co-reporter:Alex B. F. Martinson, Márcio S. Góes, Francisco Fabregat-Santiago, Juan Bisquert, Michael J. Pellin and Joseph T. Hupp
The Journal of Physical Chemistry A 2009 Volume 113(Issue 16) pp:4015-4021
Publication Date(Web):February 10, 2009
DOI:10.1021/jp810406q
Dye-sensitized solar cells based on ordered arrays of polycrystalline ZnO nanotubes, 64 μm in length, are shown to exhibit efficient electron collection over the entire photoanode array length. Electrochemical impedance spectroscopy, open-circuit photovoltage decay analysis, and incident-photon-to-current efficiency spectra are used to quantify charge transport and lifetimes. Despite the relatively thick photoanode, the charge extraction time is found to be faster than observed in traditional TiO2 nanoparticle photoanodes. If the extraction dynamics are interpreted as diffusive, effective electron diffusion coefficients of up to 0.4 cm2 s−1 are obtained, making these pseudo-1D photoanodes the fastest reported for an operating DSC to date. Rapid electron collection is of practical significance because it should enable alternative redox shuttles, which display relatively fast electron-interception dynamics, to be employed without significant loss of photocurrent.
Co-reporter:Stacey D. Standridge, George C. Schatz and Joseph T. Hupp
Langmuir 2009 Volume 25(Issue 5) pp:2596-2600
Publication Date(Web):February 5, 2009
DOI:10.1021/la900113e
Plasmonic silver nanoparticles have unique properties that lend themselves to unusual optical applications, potentially including use as absorption amplifiers in dye-sensitized solar cells (DSSCs). However, these particles are easily damaged under oxidizing conditions. Atomic layer deposition of TiO2 onto transparent-conductive-oxide-supported silver particles was examined as a means of protecting particles while simultaneously incorporating them into DSSC-functional photoelectrodes. The resulting assemblies were exposed to corrosive I−/I3− solutions, and the degree of silver etching was determined via scanning electron microscopy and ultraviolet−visible spectroscopy. To form a pinhole-free (i.e., fully protective) crystalline TiO2 layer, 7.7 nm (300 cycles) must be deposited. If, however, a 0.2 nm (2 cycles) Al2O3 adhesion layer is included, only 5.8 nm (211 cycles) of TiO2 are necessary for the formation of a pinhole-free coating.
Co-reporter:Karen L. Mulfort, Thea M. Wilson, Michael R. Wasielewski and Joseph T. Hupp
Langmuir 2009 Volume 25(Issue 1) pp:503-508
Publication Date(Web):December 10, 2008
DOI:10.1021/la803014k
A permanently microporous metal−organic framework compound with the formula Zn2(NDC)2(diPyTz) (NDC = 2,6-naphthalenedicarboxylate, diPyTz = di-3,6-(4-pyridyl)-1,2,4,5-tetrazine) has been synthesized. The compound, which features a triply catenating, pillared-paddlewheel structure, was designed to be easily chemically reduced (diPyTz sites) by appropriate channel permeants. Reduction was achieved by using the naphthalenide anion, with the accompanying metal cation (Li+, Na+ or K+) serving to dope the compound in extraframework fashion. H2 uptake at 1 atm and 77 K increases from 1.12 wt % for the neutral material to 1.45, 1.60, and 1.51 wt % for the Li+-, Na+-, and K+-doped materials, respectively. The isosteric heats of adsorption are similar for all four versions of the material despite the large uptake enhancements for the reduced versions. Nitrogen isotherms were also measured in order to provide insight into the mechanisms of uptake enhancement. The primary mechanism is believed to be dopant-facilitated displacement of catenated frameworks by sorbed H2. More extensive cation doping decreases the H2 loading.
Co-reporter:Chunxing She, James E. McGarrah, Suk Joong Lee, Joshua L. Goodman, SonBinh T. Nguyen, J. A. G. Williams and Joseph T. Hupp
The Journal of Physical Chemistry A 2009 Volume 113(Issue 29) pp:8182-8186
Publication Date(Web):July 1, 2009
DOI:10.1021/jp903125t
Solution-phase transient dc photoconductivity (TDCP) measurements are used to address the question of exciton localization/delocalization in strongly coupled oligomeric porphyrins and in well-defined, higher-order assemblies of oligomers (ladder and prism assemblies). The approach used is determination of the excited-state excess polarizability volume, ΔαV—a quantity known to report on exciton delocalization. The measurements reveal for the oligomers that singlet excitons are substantially delocalized but that triplet excitons are much more localized. For each of the two higher-order assemblies, the measurements reveal that excitons are transiently confined to individual oligomeric subunits rather than being delocalized over the entire assembly.
Co-reporter:Thomas W. Hamann, Rebecca A. Jensen, Alex B. F. Martinson, Hal Van Ryswyk and Joseph T. Hupp
Energy & Environmental Science 2008 vol. 1(Issue 1) pp:66-78
Publication Date(Web):08 Jul 2008
DOI:10.1039/B809672D
The most efficient dye-sensitized solar cells (DSSCs) have had essentially the same configuration (nanoparticle TiO2 sensitized with [Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2] in contact with I3−/I−) for the last 17 years. In this article we outline the strategies for improving each of the three major photo-relevant components of a DSSC, review literature reports consistent with these strategies and suggest future directions. Finally we explore the potential of future generation DSSCs for advancing energy-conversion performance.
Co-reporter:Thomas W. Hamann;Alex B. F. Martinson;Jeffrey W. Elam;Michael J. Pellin
Advanced Materials 2008 Volume 20( Issue 8) pp:1560-1564
Publication Date(Web):
DOI:10.1002/adma.200702781
Co-reporter:Suk Joong Lee;Christos D. Malliakas;Mercouri G. Kanatzidis;SonBinh T. Nguyen
Advanced Materials 2008 Volume 20( Issue 18) pp:3543-3549
Publication Date(Web):
DOI:10.1002/adma.200800003
Co-reporter:Alex B. F. Martinson, Jeffrey W. Elam, Jun Liu, Michael J. Pellin, Tobin J. Marks and Joseph T. Hupp
Nano Letters 2008 Volume 8(Issue 9) pp:2862-2866
Publication Date(Web):August 14, 2008
DOI:10.1021/nl8015285
We introduce a new photoelectrode architecture consisting of concentric conducting and semiconducting nanotubes for use in dye-sensitized solar cells (DSSCs). Atomic layer deposition is employed to grow indium tin oxide (ITO) within a porous template and subsequently coat the high area photoelectrode with amorphous TiO2. Compared with control devices lacking a current collector within the pores, the new photoelectrode geometry exhibits dramatically higher current densities, an effect attributed to the radial collection of electrons.
Co-reporter:Suk Joong Lee, Rebecca A. Jensen, Christos D. Malliakas, Mercouri G. Kanatzidis, Joseph T. Hupp and SonBinh T. Nguyen
Journal of Materials Chemistry A 2008 vol. 18(Issue 31) pp:3640-3642
Publication Date(Web):08 Jul 2008
DOI:10.1039/B804629H
A highly efficient porphyrin synthesis facilitates a systematic investigation of the effects that secondary substituents have on the physical properties, crystal structures, and nanoparticle morphologies of amphiphilic (porphyrin)Sn(OH)2.
Co-reporter:Kyoung-Tae Youm, SonBinh T. Nguyen and Joseph T. Hupp
Chemical Communications 2008 (Issue 29) pp:3375-3377
Publication Date(Web):27 Jun 2008
DOI:10.1039/B800063H
Hollow, hexa-porphyrin prisms of two sizes were template-assembled and covalently locked, via cross-olefin metathesis, into permanent, torsionally rigid structures whose active sites (metal sites) can be both accessed and altered in a facile manner.
Co-reporter:Tendai Gadzikwa, Bi-Shun Zeng, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2008 (Issue 31) pp:3672-3674
Publication Date(Web):30 Jun 2008
DOI:10.1039/B714160B
A series of 4,4′-ethynylenedibenzoic acids were synthesized and used in the construction of Zn-based, mixed-ligand metal–organic frameworks; through variation of functionality in the 3- and 3′-positions of these linkers, a collection of MOFs with differing connectivities and varying levels of interpenetration was obtained.
Co-reporter:Tendai Gadzikwa, Guang Lu, Charlotte L. Stern, Scott R. Wilson, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2008 (Issue 43) pp:5493-5495
Publication Date(Web):08 Oct 2008
DOI:10.1039/B805101A
A Zn-cornered, mixed-ligand, metal–organic framework (MOF) bearing TMS-protected acetylenes has been constructed and its surface decorated with organic molecules via‘click chemistry’, in a demonstration of selective post-synthesis functionalization.
Co-reporter:Omar K. Farha ; Karen L. Mulfort
Inorganic Chemistry 2008 Volume 47(Issue 22) pp:10223-10225
Publication Date(Web):October 17, 2008
DOI:10.1021/ic8018452
A robust, noncatenated, and permanently microporous metal−organic framework (MOF) material has been synthesized by combining a new nonplanar ligand, 4,4′,4′′,4′′′-benzene-1,2,4,5-tetrayltetrabenzoic acid, with a zinc(II) source under solvothermal conditions. The new material features cavities that are readily modified via activation and functionalization of framework nodes (as opposed to struts). A preliminary investigation of the “empty cavity” version of the material and six cavity-modified versions reveals that modification can substantially modulate the MOF’s internal surface area, pore volume, and ability to sorb molecular hydrogen.
Co-reporter:Thomas W. Hamann ; Alex B. F. Martinson ; Jeffrey W. Elam ; Michael J. Pellin
The Journal of Physical Chemistry C 2008 Volume 112(Issue 27) pp:10303-10307
Publication Date(Web):June 18, 2008
DOI:10.1021/jp802216p
High surface area mesoporous aerogel films were prepared on conductive glass substrates. Atomic layer deposition was employed to coat the aerogel template conformally with various thicknesses of TiO2 with subnanometer precision. The TiO2-coated aerogel membranes were incorporated as photoanodes in dye-sensitized solar cells. The charge diffusion length was found to increase with increasing thickness of TiO2 leading to increasing current and efficiency. Initial devices exhibited power conversion efficiencies of up to 4.3% under 100 W m−2 light intensity. The novel fabrication technique provides a facile, oxide materials general method to prepare high surface area pseudo-one-dimensional DSSC photoanodes with promising performance.
Co-reporter:Youn-Sang Bae, Karen L. Mulfort, Houston Frost, Patrick Ryan, Sudeep Punnathanam, Linda J. Broadbelt, Joseph T. Hupp and Randall Q. Snurr
Langmuir 2008 Volume 24(Issue 16) pp:8592-8598
Publication Date(Web):July 11, 2008
DOI:10.1021/la800555x
The adsorption of CO2 and CH4 in a mixed-ligand metal−organic framework (MOF) Zn2(NDC)2(DPNI) [NDC = 2,6-naphthalenedicarboxylate, DPNI = N,N′-di-(4-pyridyl)-1,4,5,8-naphthalene tetracarboxydiimide] was investigated using volumetric adsorption measurements and grand canonical Monte Carlo (GCMC) simulations. The MOF was synthesized by two routes: first at 80 °C for two days with conventional heating, and second at 120 °C for 1 h using microwave heating. The two as-synthesized samples exhibit very similar powder X-ray diffraction patterns, but the evacuated samples show differences in nitrogen uptake. From the single-component CO2 and CH4 isotherms, mixture adsorption was predicted using the ideal adsorbed solution theory (IAST). The microwave sample shows a selectivity of ∼30 for CO2 over CH4, which is among the highest selectivities reported for this separation. The applicability of IAST to this system was demonstrated by performing GCMC simulations for both single-component and mixture adsorption.
Co-reporter:AlexB.F. Martinson;ThomasW. Hamann Dr.;MichaelJ. Pellin Dr.;JosephT. Hupp
Chemistry - A European Journal 2008 Volume 14( Issue 15) pp:4458-4467
Publication Date(Web):
DOI:10.1002/chem.200701667
Abstract
Modern dye-sensitized solar cell (DSSC) technology was built upon nanoparticle wide bandgap semiconductor photoanodes. While versatile and robust, the sintered nanoparticle architecture exhibits exceedingly slow electron transport that ultimately restricts the diversity of feasible redox mediators. The small collection of suitable mediators limits both our understanding of an intriguing heterogeneous system and the performance of these promising devices. Recently, a number of pseudo-1D photoanodes that exhibit accelerated charge transport and greater materials flexibility were fabricated. The potential of these alternative photoanode architectures for advancing, both directly and indirectly, the performance of DSSCs is explored.
Co-reporter:So-Hye Cho;Tendai Gadzikwa;Mitra Afshari;SonBinh T. Nguyen
European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 31) pp:
Publication Date(Web):26 SEP 2007
DOI:10.1002/ejic.200700302
The formation of coordination polymers by the reaction of [bis(catechol)salen]MnIII with several di- and trivalent metal ions is reported. These polymers are insoluble in a wide range of organic solvents and water but can be dissolved upon addition of excess pyrocatechol. They function as enantioselective heterogeneous epoxidation catalysts and exhibit catalytic activity comparable to that of the homogeneous[bis(catechol)salen]MnIII building block alone when used for the enantioselective epoxidation of 2,2-dimethyl-2H-chromene. After catalysis, catalyst isolation from the reaction mixture can be readily achieved by centrifugation and decantation. Under practical oxidant concentrations, the catalyst can be recycled up to ten times with little loss of activity and no loss of enantioselectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Co-reporter:So-Hye Cho, Baoqing Ma, SonBinh T. Nguyen, Joseph T. Hupp and Thomas E. Albrecht-Schmitt
Chemical Communications 2006 (Issue 24) pp:2563-2565
Publication Date(Web):23 May 2006
DOI:10.1039/B600408C
A new microporous metal–organic framework compound featuring chiral (salen)Mn struts is highly effective as an asymmetric catalyst for olefin epoxidation, yielding enantiomeric excesses that rival those of the free molecular analogue. Framework confinement of the manganese salen entity enhances catalyst stability, imparts substrate size selectivity, and permits catalyst separation and reuse.
Co-reporter:Suk Joong Lee, Karen L. Mulfort, Jodi L. O'Donnell, Xiaobing Zuo, Andrew J. Goshe, Paul J. Wesson, SonBinh T. Nguyen, Joseph T. Hupp and David M. Tiede
Chemical Communications 2006 (Issue 44) pp:4581-4583
Publication Date(Web):18 Oct 2006
DOI:10.1039/B610025B
Supramolecular porphyrin prisms have been obtained via coordinative self-assembly and characterized by 1H NMR, PFG NMR, electronic absorption spectroscopy and synchrotron-based measurements of solution phase X-ray scattering and diffraction.
Co-reporter:Alex B. F. Martinson, James E. McGarrah, Mohammed O. K. Parpia and Joseph T. Hupp
Physical Chemistry Chemical Physics 2006 vol. 8(Issue 40) pp:4655-4659
Publication Date(Web):13 Sep 2006
DOI:10.1039/B610566A
Intensity modulated photovoltage and photocurrent spectroscopies reveal that photoanodes based on nanorod arrays exhibit dramatically faster electron transport while retaining similar electron lifetimes (recombination times) compared to standard photoanodes assembled from colloidal nanoparticles.
Co-reporter:So-Hye Cho, Nolan D. Walther, SonBinh T. Nguyen and Joseph T. Hupp
Chemical Communications 2005 (Issue 42) pp:5331-5333
Publication Date(Web):26 Sep 2005
DOI:10.1039/B507541F
Catechol-functionalized (salen)Mn complexes can be supported on mesoporous anodized aluminium oxide disks to yield catalytic membranes that are highly active in the enantioselective epoxidation of olefins when being deployed in a forced-through-flow reactor.
Co-reporter:Chang Yeon Lee ; Youn-Sang Bae ; Nak Cheon Jeong ; Omar K. Farha ; Amy A. Sarjeant ; Charlotte L. Stern ; Peter Nickias ; Randall Q. Snurr ; Joseph T. Hupp ;SonBinh T. Nguyen
Journal of the American Chemical Society () pp:
Publication Date(Web):March 18, 2011
DOI:10.1021/ja200553m
A series of isostructural, noncatenated, zinc-pillared-paddlewheel metal−organic framework materials has been synthesized from 1,2,4,5-tetrakis(carboxyphenyl)benzene and trans-1,2-dipyridylethene struts. Substantial kinetic selectivity in the adsorption of propene over propane can be observed, depending on the pore apertures and the rectangular-plate morphology of the crystals.
Co-reporter:Abraham M. Shultz ; Amy A. Sarjeant ; Omar K. Farha ; Joseph T. Hupp ;SonBinh T. Nguyen
Journal of the American Chemical Society () pp:
Publication Date(Web):July 19, 2011
DOI:10.1021/ja204820d
A series of metallosalen-based metal–organic frameworks (MOFs) have been prepared by the post-synthesis modification of MnIIISO-MOF, a Mn3+(salen)-based MOF. Treatment of MnIIISO-MOF with H2O2 effects the removal of the Mn3+ ions from the salen struts, which can then be remetalated with a variety of metal precursors to form isostructural MSO-MOF materials. The presence of the new metallosalen struts in MSO-MOF was fully confirmed by ICP-OES, MALDI–TOF MS, PXRD, and TGA. Furthermore, the remetalated MnIISO-MOF material displays similar catalytic activity and porosity to the parent MOF.
Co-reporter:Karen L. Mulfort
Inorganic Chemistry () pp:
Publication Date(Web):June 13, 2008
DOI:10.1021/ic800700h
A 2-fold interwoven metal-organic framework has been chemically reduced and doped with Li+, Na+, and K+. At low pressures and temperatures, the reduced and doped materials exhibit enhanced H2 uptake—up to 65% higher than for the neutral framework. Notably, at similar doping levels, H2 binding is strongest with Li+ and decreases as Li+ > Na+ > K+. However, the uptake increases in the opposite order. We attribute the behavior to structural changes accompanying framework reduction.
Co-reporter:Monica C. So, M. Hassan Beyzavi, Rohan Sawhney, Osama Shekhah, Mohamed Eddaoudi, Salih S. Al-Juaid, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 - vol. 51(Issue 1) pp:NaN88-88
Publication Date(Web):2014/10/17
DOI:10.1039/C4CC05727A
Herein, we demonstrate the robustness of layer-by-layer (LbL)-assembled, pillared-paddlewheel-type MOF films toward conversion to new or modified MOFs via solvent-assisted linker exchange (SALE) and post-assembly linker metalation. Further, we show that LbL synthesis can afford MOFs that have proven inaccessible through other de novo strategies.
Co-reporter:Peng Li, Rachel C. Klet, Su-Young Moon, Timothy C. Wang, Pravas Deria, Aaron W. Peters, Benjamin M. Klahr, Hea-Jung Park, Salih S. Al-Juaid, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 - vol. 51(Issue 54) pp:NaN10928-10928
Publication Date(Web):2015/06/11
DOI:10.1039/C5CC03398E
The synthesis of nano-sized particles of NU-1000 (length from 75 nm to 1200 nm) and PCN-222/MOF-545 (length from 350 nm to 900 nm) is reported. The catalytic hydrolysis of methyl paraoxon was investigated as a function of NU-1000 crystallite size and a significant enhancement in the rate was observed for the nano-sized crystals compared to microcrystals.
Co-reporter:Pravas Deria, Song Li, Hongda Zhang, Randall Q. Snurr, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 - vol. 51(Issue 62) pp:NaN12481-12481
Publication Date(Web):2015/07/06
DOI:10.1039/C5CC04808G
CO2 capture is essential for reducing the carbon footprint of coal-fired power plants. Here we show, both experimentally and computationally, a new design strategy for capturing CO2 in nanoporous adsorbents. The approach involves ‘complementary organic motifs’ (COMs), which have a precise alignment of charge densities that is complementary to the CO2 quadrupole. Two promising COMs were post-synthetically incorporated into a robust metal–organic framework (MOF) material using solvent-assisted ligand incorporation (SALI). We demonstrate that these COM-functionalized MOFs exhibit high capacity and selectivity for CO2 relative to other reported motifs.
Co-reporter:Idan Hod, Omar K. Farha and Joseph T. Hupp
Chemical Communications 2016 - vol. 52(Issue 8) pp:NaN1708-1708
Publication Date(Web):2015/12/15
DOI:10.1039/C5CC09695B
Herein we demonstrate the use of host–guest chemistry to modulate rates of charge transport in metal–organic framework (MOF) films. The kinetics of site-to-site of charge hopping and, in turn, the overall redox conductivity, of a ferrocene-modified MOF can be altered by up to 30-fold by coupling electron exchange to the oxidation-state-dependent formation of inclusion complexes between cyclodextrin and channel-tethered metallocenes.
Co-reporter:Monica C. So, Gary P. Wiederrecht, Joseph E. Mondloch, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2015 - vol. 51(Issue 17) pp:NaN3510-3510
Publication Date(Web):2015/01/12
DOI:10.1039/C4CC09596K
A critical review of the emerging field of MOFs for photon collection and subsequent energy transfer is presented. Discussed are examples involving MOFs for (a) light harvesting, using (i) MOF-quantum dots and molecular chromophores, (ii) chromophoric MOFs, and (iii) MOFs with light-harvesting properties, and (b) energy transfer, specifically via the (i) Förster energy transfer and (ii) Dexter exchange mechanism.
Co-reporter:Mitchell H. Weston, Gregory W. Peterson, Matthew A. Browe, Paulette Jones, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2013 - vol. 49(Issue 29) pp:NaN2997-2997
Publication Date(Web):2013/02/12
DOI:10.1039/C3CC40475G
Porous organic polymers bearing metal–catecholate groups were evaluated for their ability to remove airborne ammonia, cyanogen chloride, sulphur dioxide, and octane by micro-breakthrough analysis. For ammonia, the metal–catecholate materials showed remarkable uptake under humid conditions.
Co-reporter:Pravas Deria, Wojciech Bury, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2014 - vol. 50(Issue 16) pp:NaN1968-1968
Publication Date(Web):2014/01/09
DOI:10.1039/C3CC48562E
Solvent-assisted ligand incorporation (SALI) was utilized to efficiently insert various carboxylate-derived functionalities into the Zr-based metal–organic framework NU-1000 as charge compensating moieties strongly bound to the Zr6 nodes. SALI-derived functionalities are accessible for further chemical reactions such as click chemistry, imine condensation and pyridine quaternization.
Co-reporter:Joseph E. Mondloch, Michael J. Katz, Nora Planas, David Semrouni, Laura Gagliardi, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2014 - vol. 50(Issue 64) pp:NaN8946-8946
Publication Date(Web):2014/06/30
DOI:10.1039/C4CC02401J
Metal–organic frameworks (MOFs) built up from Zr6-based nodes and multi-topic carboxylate linkers have attracted attention due to their favourable thermal and chemical stability. However, the hydrolytic stability of some of these Zr6-based MOFs has recently been questioned. Herein we demonstrate that two Zr6-based frameworks, namely UiO-67 and NU-1000, are stable towards linker hydrolysis in H2O, but collapse during activation from H2O. Importantly, this framework collapse can be overcome by utilizing solvent-exchange to solvents exhibiting lower capillary forces such as acetone.
Co-reporter:Michael J. Katz, Zachary J. Brown, Yamil J. Colón, Paul W. Siu, Karl A. Scheidt, Randall Q. Snurr, Joseph T. Hupp and Omar K. Farha
Chemical Communications 2013 - vol. 49(Issue 82) pp:NaN9451-9451
Publication Date(Web):2013/09/06
DOI:10.1039/C3CC46105J
A scalable, reproducible method of synthesizing UiO-66- and UiO-67-type MOFs, entailing the addition of HCl to the reaction mixture, has been investigated. The new protocol requires a fraction of the time of previously reported procedures, yields exceptional porosities, and works with a range of linkers.
Co-reporter:Chunxing She, Suk Joong Lee, James E. McGarrah, Josh Vura-Weis, Michael R. Wasielewski, Hanning Chen, George C. Schatz, Mark A. Ratner and Joseph T. Hupp
Chemical Communications 2010 - vol. 46(Issue 4) pp:NaN549-549
Publication Date(Web):2009/12/08
DOI:10.1039/B916392A
Photoinduced electron transfer in a self-assembled supramolecular ladder structure comprising oligomeric porphyrin rails and ligated dipyridyltetrazine rungs was characterized by transient absorption spectroscopy and transient direct current photoconductivity to be mainly from an oligomer (rail) to the center of a terminal tetrazine (rung), with the remaining hole being delocalized on the oligomer and subsequent charge recombination in 0.19 ns.
Co-reporter:Paul W. Siu, Zachary J. Brown, Omar K. Farha, Joseph T. Hupp and Karl A. Scheidt
Chemical Communications 2013 - vol. 49(Issue 93) pp:NaN10922-10922
Publication Date(Web):2013/10/10
DOI:10.1039/C3CC47177B
A hydrogen-bond donating MOF catalyst based on the UiO-67 framework, containing both urea-functionalized dicarboxylate and biphenyl-4,4′-dicarboxylate struts, was synthesized by a de novo route. The mixed strut framework has larger pore sizes and improved catalytic activity for Henry reactions than the pure strut analogue, which contains only the urea-functionalized dicarboxylate linker.
Co-reporter:Ryan K. Totten, Patrick Ryan, Byungman Kang, Suk Joong Lee, Linda J. Broadbelt, Randall Q. Snurr, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2012 - vol. 48(Issue 35) pp:NaN4180-4180
Publication Date(Web):2012/01/31
DOI:10.1039/C2CC17568A
A series of metalloporphyrin dimers were modularly prepared and shown to catalyze the methanolysis of a phosphate triester, yielding rates that are large compared to the rate of the uncatalyzed reaction. Up to 1300-fold rate acceleration can be achieved via a combination of cavity-localized Lewis-acid activation and methoxide-induced methanolysis.
Co-reporter:Tendai Gadzikwa, Bi-Shun Zeng, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2008(Issue 31) pp:NaN3674-3674
Publication Date(Web):2008/06/30
DOI:10.1039/B714160B
A series of 4,4′-ethynylenedibenzoic acids were synthesized and used in the construction of Zn-based, mixed-ligand metal–organic frameworks; through variation of functionality in the 3- and 3′-positions of these linkers, a collection of MOFs with differing connectivities and varying levels of interpenetration was obtained.
Co-reporter:Omar K. Farha, Youn-Sang Bae, Brad G. Hauser, Alexander M. Spokoyny, Randall Q. Snurr, Chad A. Mirkin and Joseph T. Hupp
Chemical Communications 2010 - vol. 46(Issue 7) pp:NaN1058-1058
Publication Date(Web):2010/01/15
DOI:10.1039/B922554D
A diimide based porous organic polymer (POP) post-synthetically reduced with lithium metal demonstrates a drastic increase in selectivity for carbon dioxide over methane.
Co-reporter:Tendai Gadzikwa, Omar K. Farha, Karen L. Mulfort, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2009(Issue 25) pp:
Publication Date(Web):
DOI:10.1039/B823392F
Co-reporter:Michael J. Katz, Su-Young Moon, Joseph E. Mondloch, M. Hassan Beyzavi, Casey J. Stephenson, Joseph T. Hupp and Omar K. Farha
Chemical Science (2010-Present) 2015 - vol. 6(Issue 4) pp:NaN2291-2291
Publication Date(Web):2015/02/24
DOI:10.1039/C4SC03613A
The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO2 and UiO-66-(OH)2 showed little to no change in hydrolysis rate. However, UiO-66-NH2 showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe2 and UiO-67-NH2. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH2 is a faster catalyst than UiO-67 and UiO-67-NMe2. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.
Co-reporter:Kyoung-Tae Youm, SonBinh T. Nguyen and Joseph T. Hupp
Chemical Communications 2008(Issue 29) pp:NaN3377-3377
Publication Date(Web):2008/06/27
DOI:10.1039/B800063H
Hollow, hexa-porphyrin prisms of two sizes were template-assembled and covalently locked, via cross-olefin metathesis, into permanent, torsionally rigid structures whose active sites (metal sites) can be both accessed and altered in a facile manner.
Co-reporter:Tendai Gadzikwa, Guang Lu, Charlotte L. Stern, Scott R. Wilson, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Communications 2008(Issue 43) pp:NaN5495-5495
Publication Date(Web):2008/10/08
DOI:10.1039/B805101A
A Zn-cornered, mixed-ligand, metal–organic framework (MOF) bearing TMS-protected acetylenes has been constructed and its surface decorated with organic molecules via‘click chemistry’, in a demonstration of selective post-synthesis functionalization.
Co-reporter:Ryan K. Totten, Laura L. Olenick, Ye-Seong Kim, Sanjiban Chakraborty, Mitchell H. Weston, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Science (2010-Present) 2014 - vol. 5(Issue 2) pp:NaN787-787
Publication Date(Web):2013/10/09
DOI:10.1039/C3SC52010B
Porous organic polymers (POPs) with tunable pore volumes and surface areas can be made from a series of SnIV(porphyrins) functionalized with labile, bulky trans-diaxial ligands. Varying the ligand size allows for the tuning of the micropore volume while supercritical CO2 processing resulted in excellent enhancements of the total pore volumes.
Co-reporter:Shinya Takaishi, Erica J. DeMarco, Michael J. Pellin, Omar K. Farha and Joseph T. Hupp
Chemical Science (2010-Present) 2013 - vol. 4(Issue 4) pp:NaN1513-1513
Publication Date(Web):2012/12/07
DOI:10.1039/C2SC21516K
Using recently reported robust porphyrinic metal–organic framework (RPM) materials, we have examined the systematic exchange of pillaring linkers/struts as a means of accessing new versions of these materials. Dipyridyl-porphyrin Zn(II) (Zn-dipy) struts were successfully replaced by M2-dipy (M2 = 2H(+), Al(III), Sn(IV)), forming crystalline solid solutions of Zn(Zn1−xMx)-RPM in variable ratios. In addition, post-synthetic metallation was demonstrated using Zn2H-RPM, again with retention of crystallinity. We examined catalytic activity for an epoxide ring-opening reaction with a series of ZnM2-RPMs. The catalytic activity depends strongly on the identity of the metal ion present in the dipyridyl-porphyrin unit.
Co-reporter:Pravas Deria, Yongchul G. Chung, Randall Q. Snurr, Joseph T. Hupp and Omar K. Farha
Chemical Science (2010-Present) 2015 - vol. 6(Issue 9) pp:NaN5176-5176
Publication Date(Web):2015/07/01
DOI:10.1039/C5SC01784J
Water stability in metal–organic frameworks (MOFs) is critical for several practical applications. While water instability is mainly thought to stem from linker hydrolysis, MOFs with strong, hydrolysis-resistant metal-linker bonds can be susceptible to damage by capillary forces, which cause cavities and channels to collapse during activation from water. This study utilizes metal node functionalization as a strategy to create vapor-stable and recyclable MOFs.
Co-reporter:Byungman Kang, Josh W. Kurutz, Kyoung-Tae Youm, Ryan K. Totten, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Science (2010-Present) 2012 - vol. 3(Issue 6) pp:NaN1944-1944
Publication Date(Web):2012/01/26
DOI:10.1039/C2SC00950A
Box-like tetrakis(metalloporphyrin) supramolecular assemblies possessing Zn and Al metal sites can catalyze the methanolysis of phosphate triesters with a high rate enhancement, up to 430 times faster than the uncatalyzed reaction. Mechanistic studies suggest that the observed rate enhancement can be attributed to a high local concentration of methoxide ion that operates in concert with a solvophobically driven encapsulation of substrates by the porphyrinic assembly.
Co-reporter:Abraham M. Shultz, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Chemical Science (2010-Present) 2011 - vol. 2(Issue 4) pp:NaN689-689
Publication Date(Web):2011/01/04
DOI:10.1039/C0SC00339E
The synthesis of a porous organic polymer (POP) containing free-base porphyrin subunits has been accomplished by the condensation of a bis(phthalic acid)porphyrin with tetra(4-aminophenyl)methane. Metallation by post-synthesis modification affords microporous materials incorporating either Fe or Mn(porphyrins) that have been shown to be active catalysts for both olefin epoxidation and alkane hydroxylation.
Co-reporter:JeongYong Lee, Omar K. Farha, John Roberts, Karl A. Scheidt, SonBinh T. Nguyen and Joseph T. Hupp
Chemical Society Reviews 2009 - vol. 38(Issue 5) pp:NaN1459-1459
Publication Date(Web):2009/03/17
DOI:10.1039/B807080F
A critical review of the emerging field of MOF-based catalysis is presented. Discussed are examples of: (a) opportunistic catalysis with metal nodes, (b) designed catalysis with framework nodes, (c) catalysis by homogeneous catalysts incorporated as framework struts, (d) catalysis by MOF-encapsulated molecular species, (e) catalysis by metal-free organic struts or cavity modifiers, and (f) catalysis by MOF-encapsulated clusters (66 references).
Co-reporter:Rachel C. Klet, Yangyang Liu, Timothy C. Wang, Joseph T. Hupp and Omar K. Farha
Journal of Materials Chemistry A 2016 - vol. 4(Issue 4) pp:NaN1485-1485
Publication Date(Web):2016/01/12
DOI:10.1039/C5TA07687K
Potentiometric acid–base titration is introduced as a method to evaluate pKa values (Brønsted acidity) of protons present in the nodes of water stable Zr6- and Hf6-based metal–organic frameworks (MOFs), including UiO-type MOFs, NU-1000, and MOF-808. pKa values were determined for the three typical types of protons present in these MOFs: μ3-OH, M–OH2, and M–OH (M = Zr, Hf). Additionally, the data was used to quantify defect sites resulting from either a surfeit or shortage of linkers in the MOFs and to provide information about the true proton topology of each material.
Co-reporter:Mitchell H. Weston, Yamil J. Colón, Youn-Sang Bae, Sergio J. Garibay, Randall Q. Snurr, Omar K. Farha, Joseph T. Hupp and SonBinh T. Nguyen
Journal of Materials Chemistry A 2014 - vol. 2(Issue 2) pp:NaN302-302
Publication Date(Web):2013/10/04
DOI:10.1039/C3TA12999C
A porous organic polymer decorated with high densities of copper(catecholate) groups was prepared and characterized. Single-component propylene and propane isotherms measured at ambient temperatures and ideal adsorption solution theory (IAST) calculations revealed increasing propylene/propane selectivities with increasing pressures.
Co-reporter:Youn-Sang Bae, Omar K. Farha, Joseph T. Hupp and Randall Q. Snurr
Journal of Materials Chemistry A 2009 - vol. 19(Issue 15) pp:NaN2134-2134
Publication Date(Web):2009/03/12
DOI:10.1039/B900390H
Post-synthesis modification of a MOF by replacing coordinated solvent molecules with highly polar ligands leads to considerable enhancement of CO2/N2 selectivity.
Co-reporter:Suk Joong Lee, Rebecca A. Jensen, Christos D. Malliakas, Mercouri G. Kanatzidis, Joseph T. Hupp and SonBinh T. Nguyen
Journal of Materials Chemistry A 2008 - vol. 18(Issue 31) pp:NaN3642-3642
Publication Date(Web):2008/07/08
DOI:10.1039/B804629H
A highly efficient porphyrin synthesis facilitates a systematic investigation of the effects that secondary substituents have on the physical properties, crystal structures, and nanoparticle morphologies of amphiphilic (porphyrin)Sn(OH)2.
Co-reporter:Chunxing She, Aaron A. Rachford, Xianghuai Wang, Sébastien Goeb, Ala'a O. El-Ballouli, Felix N. Castellano and Joseph T. Hupp
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 38) pp:NaN8591-8591
Publication Date(Web):2009/07/13
DOI:10.1039/B908977B
Solvent-induced excited-state configuration mixing in a Pt(II) diimine chromophore with phenylene ethynylene containing acetylide ligands, [Pt(tBu2bpy)(PE3)2] (1), was characterized by nanosecond transient absorption spectroscopy and transient dc photoconductivity (TDCP). The mixing is a result of closely spaced triplet charge transfer (3CT) and intraligand-localized (3IL) triplet energy levels that are finely tuned with solvent polarity as ascertained by their parent model chromophores [Pt(tBu2bpy)(PE1)2] (2) and [Pt(P2)(PE3)2] (3), respectively. The absorption difference spectrum of the mixed triplet state is dramatically different from those of the 3CT and 3IL state model chromophores. The 3CT, 3IL and configuration-mixed triplet states led to distinct TDCP signals. The TDCP response is of negative polarity for 3CT excited states but of positive polarity for 3IL excited states. TDCP transients for 1 in mixed solvents are a combination of signals from the 3IL and 3CT states, with the signal magnitude depending on the polarity of solvent composition. The fraction of 3CT state character in the configurationally mixed excited state was quantified by TDCP to be ∼0.24 in pure benzene, while it decreased to ∼0.05 in 20 : 80 (v : v) benzene–CH2Cl2. The charge transfer fraction appears to increase slightly to ∼0.11 in the lower polarity 20 : 80 n-hexane–CH2Cl2 medium. TDCP is shown to be a useful tool for the identification of the lowest excited state in electrically neutral metal–organic chromophores.
Co-reporter:Ashlee J. Howarth, Timothy C. Wang, Salih S. Al-Juaid, Saadullah G. Aziz, Joseph T. Hupp and Omar K. Farha
Dalton Transactions 2016 - vol. 45(Issue 1) pp:NaN97-97
Publication Date(Web):2015/11/18
DOI:10.1039/C5DT04163E
A Zr-based MOF, NU-1000, comprised of Zr6 nodes and tetratopic pyrene-containing linkers is studied for adsorption and extraction of SO42− from water. The adsorption capacity and uptake time of SO42− in NU-1000 is determined at varying concentrations to give an overall maximum adsorption capacity of 56 mg SO42− per g of MOF. Selective adsorption of SO42− by NU-1000 in the presence of other anions as well as regeneration of the sorbent is also explored.
Co-reporter:Pravas Deria, Joseph E. Mondloch, Olga Karagiaridi, Wojciech Bury, Joseph T. Hupp and Omar K. Farha
Chemical Society Reviews 2014 - vol. 43(Issue 16) pp:NaN5912-5912
Publication Date(Web):2014/04/11
DOI:10.1039/C4CS00067F
Metal–organic frameworks (MOFs) are hybrid porous materials with many potential applications, which intimately depend on the presence of chemical functionality either at the organic linkers and/or at the metal nodes. Functionality that cannot be introduced into MOFs directly via de novo syntheses can be accessed through post-synthesis modification (PSM) on the reactive moieties of the linkers and/or nodes without disrupting the metal–linker bonds. Even more intriguing methods that go beyond PSM are herein termed building block replacement (BBR) which encompasses (i) solvent-assisted linker exchange (SALE), (ii) non-bridging ligand replacement, and (iii) transmetalation. These one-step or tandem BBR processes involve exchanging key structural components of the MOF, which in turn should allow for the evolution of protoMOF structures (i.e., the utilization of a parent MOF as a template) to design MOFs composed of completely new components, presumably via single crystal to single crystal transformations. The influence of building block replacement on the stability and properties of MOFs will be discussed, and some insights into their mechanistic aspects are provided. Future perspectives providing a glimpse into how these techniques can lead to various unexplored areas of MOF chemistry are also presented.
Co-reporter:Chang Yeon Lee, Chunxing She, Nak Cheon Jeong and Joseph T. Hupp
Chemical Communications 2010 - vol. 46(Issue 33) pp:NaN6092-6092
Publication Date(Web):2010/07/23
DOI:10.1039/C0CC00257G
A π-extended porphyrin possessing two anchoring groups has been synthesized and successfully applied to dye-sensitized solar cells with a power conversion efficiency of 5.5%, rendering it comparable to the performance of N719-sensitized solar cells under the conditions employed here.
Co-reporter:Youn-Sang Bae, Alexander M. Spokoyny, Omar K. Farha, Randall Q. Snurr, Joseph T. Hupp and Chad A. Mirkin
Chemical Communications 2010 - vol. 46(Issue 20) pp:NaN3480-3480
Publication Date(Web):2010/04/19
DOI:10.1039/B927499E
Separations of CO2/CH4, CO2/N2, and O2/N2 mixtures were studied in three porous coordination polymers made of the same carborane ligand and Co(II) nodes. High selectivities for CO2 over CH4 (∼47) and CO2 over N2 (∼95) were obtained, especially in the material with coordinated pyridine. Unusual selectivity for O2 over N2 (as high as 6.5) was demonstrated in the materials with open Co(II) sites.
Co-reporter:J. R. Avila, A. W. Peters, Zhanyong Li, M. A. Ortuño, A. B. F. Martinson, C. J. Cramer, J. T. Hupp and O. K. Farha
Dalton Transactions 2017 - vol. 46(Issue 18) pp:NaN5795-5795
Publication Date(Web):2017/04/03
DOI:10.1039/C6DT02572B
To grow films of Cu2O, bis-(dimethylamino-2-propoxide)Cu(II), or Cu(dmap), is used as an atomic layer deposition precursor using only water vapor as a co-reactant. Between 110 and 175 °C, a growth rate of 0.12 ± 0.02 Å per cycle was measured using an in situ quartz crystal microbalance (QCM). X-ray photoelectron spectroscopy (XPS) confirms the growth of metal–oxide films featuring Cu(I).
Co-reporter:Carla F. Pereira, Ashlee J. Howarth, Nicolaas A. Vermeulen, Filipe A. Almeida Paz, João P. C. Tomé, Joseph T. Hupp and Omar K. Farha
Inorganic Chemistry Frontiers 2017 - vol. 1(Issue 6) pp:NaN1199-1199
Publication Date(Web):2017/01/30
DOI:10.1039/C6QM00364H
Solvent-assisted linker exchange (SALE) is performed on the Zr-based metal–organic framework (MOF), UiO-66, to exchange benzene-1,4-dicarboxylate with benzene-1,4-dihydroxamate linkers. Characterization of the material before and after SALE is performed using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen adsorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and thermogravimetric analysis (TGA). The stability of the parent and daughter material is evaluated at pH 1 and 12 and the structural integrity evaluated by PXRD, mass balance and porosity measurements.
Co-reporter:Zhanyong Li, Aaron W. Peters, Jian Liu, Xuan Zhang, Neil M. Schweitzer, Joseph T. Hupp and Omar K. Farha
Inorganic Chemistry Frontiers 2017 - vol. 4(Issue 5) pp:NaN824-824
Publication Date(Web):2017/03/09
DOI:10.1039/C7QI00056A
Ni(II) ions have been deposited on the Zr6 nodes of a metal–organic framework (MOF), UiO-66, via an ALD-like process (ALD = atomic layer deposition). By varying the number of ALD cycles, three Ni-decorated UiO-66 materials were synthesized. A suite of physical methods has been used to characterize these materials, indicating structural and high-surface-area features of the parent MOF are retained. Elemental analysis via X-ray photoelectron spectroscopy (XPS) indicates that the anchored Ni ions are mainly on surface and near-surface MOF defect sites. Upon activation, all three materials are catalytic for ethylene hydrogenation, but their catalytic activities significantly vary, with the largest clusters displaying the highest per-nickel-atom activity. The study highlights the ease and effectiveness of ALD in MOFs (AIM) for synthesizing, specifically, UiO-66-supported NiyOx catalysts.
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