Co-reporter:Yuxiang Chen; Chong Liu; Qing Tang; Chenjie Zeng; Tatsuya Higaki; Anindita Das; De-en Jiang; Nathaniel L. Rosi;Rongchao Jin
Journal of the American Chemical Society 2016 Volume 138(Issue 5) pp:1482-1485
Publication Date(Web):January 21, 2016
DOI:10.1021/jacs.5b12094
Understanding the isomerism phenomenon at the nanoscale is a challenging task because of the prerequisites of precise composition and structural information on nanoparticles. Herein, we report the ligand-induced, thermally reversible isomerization between two thiolate-protected 28-gold-atom nanoclusters, i.e. Au28(S-c-C6H11)20 (where -c-C6H11 = cyclohexyl) and Au28(SPh-tBu)20 (where -Ph-tBu = 4-tert-butylphenyl). The intriguing ligand effect in dictating the stability of the two Au28(SR)20 structures is further investigated via dispersion-corrected density functional theory calculations.
Co-reporter:Qing Tang and De-en Jiang
ACS Catalysis 2016 Volume 6(Issue 8) pp:4953
Publication Date(Web):June 20, 2016
DOI:10.1021/acscatal.6b01211
The 1T phase of transition-metal dichalcogenides (TMDs) has been demonstrated in recent experiments to display excellent catalytic activity for hydrogen evolution reaction (HER), but the catalytic mechanism has not been elucidated so far. Herein, using 1T MoS2 as the prototypical TMD material, we studied the HER activity on its basal plane from periodic density functional theory (DFT) calculations. Compared to the nonreactive basal plane of 2H phase MoS2, the catalytic activity of the basal plane of 1T phase MoS2 mainly arises from its affinity for binding H at the surface S sites. Using the binding free energy (ΔGH) of H as the descriptor, we found that the optimum evolution of H2 will proceed at surface H coverage of 12.5% ∼ 25%. Within this coverage, we examined the reaction energy and barrier for the three elementary steps of the HER process. The Volmer step was found to be facile, whereas the subsequent Heyrovsky reaction is kinetically more favorable than the Tafel reaction. Our results suggest that at low overpotential, HER can take place readily on the basal plane of 1T MoS2 via the Volmer–Heyrovsky mechanism. We further screened the dopants for the HER activity and found that substitutional doping of the Mo atom by metals such as Mn, Cr, Cu, Ni, and Fe can make 1T MoS2 a better HER catalyst.Keywords: 1T MoS2; basal plane; catalytic activity; hydrogen evolution reaction; substitutional doping; Volmer−Heyrovsky mechanism
Co-reporter:Qing Tang and De-en Jiang
Chemistry of Materials 2016 Volume 28(Issue 17) pp:5976
Publication Date(Web):August 16, 2016
DOI:10.1021/acs.chemmater.6b01740
From chemical functionalization of an inorganic substrate to protection/passivation of a nanocluster/nanoparticle surface, the organic–inorganic interface is key to chemistry of many materials. Herein computational insights into the structure, bonding, and energetics of several representative covalent organic–inorganic interfaces are reviewed mainly from the authors’ work and based on density functional theory. We start with the zero-curvature substrates including graphene, metal surfaces, and MoS2 and discuss their covalent functionalization by the attachment of the aryl group via the diazonium chemistry. We then move on to large-curvature, ligand-protected gold nanoclusters where we focus on the ligand–gold interface. The theoretical studies have produced both general trends that help understand the experimental results and specific predictions that have been confirmed or are yet to be verified. Opportunities abound in coupling theory and experiment to understand the roles of the covalent organic–inorganic interfaces in synthesis and application of nanomaterials.
Co-reporter:Cheng Zhan, Yu Zhang, Peter T. Cummings and De-en Jiang
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 6) pp:4668-4674
Publication Date(Web):08 Jan 2016
DOI:10.1039/C5CP06952A
Recent experiments have shown that nitrogen doping enhances capacitance in carbon electrode supercapacitors. However, a detailed study of the effect of N-doping on capacitance is still lacking. In this paper, we study the doping concentration and the configuration effect on the electric double-layer (EDL) capacitance, quantum capacitance, and total capacitance. It is found that pyridinic and graphitic nitrogens can increase the total capacitance by increasing quantum capacitance, but pyrrolic configuration limits the total capacitance due to its much lower quantum capacitance than the other two configurations. We also find that, unlike the graphitic and pyridinic nitrogens, the pyrrolic configuration's quantum capacitance does not depend on the nitrogen concentration, which may explain why some capacitance versus voltage measurements of N-doped graphene exhibit a V-shaped curve similar to that of undoped graphene. Our investigation provides a deeper understanding of the capacitance enhancement of the N-doping effect in carbon electrodes and suggests a potentially effective way to optimize the capacitance by controlling the type of N-doping.
Co-reporter:Chad Priest, Ziqi Tian and De-en Jiang
Dalton Transactions 2016 vol. 45(Issue 24) pp:9812-9819
Publication Date(Web):22 Jan 2016
DOI:10.1039/C5DT04576B
Recent experiments have shown that the neutral Ca2UO2(CO3)3 complex is the dominant species of uranium in many uranyl-containing streams. However, the structure and solvation of such a species in water has not been investigated from first principles. Herein we present a first principles molecular dynamics perspective of the Ca2UO2(CO3)3 complex in water based on density functional theory and Born–Oppenheimer approximation. We find that the Ca2UO2(CO3)3 complex is very stable in our simulation timeframe for three different concentrations considered and that the key distances from our simulation are in good agreement with the experimental data from extended X-ray absorption fine structure (EXAFS) spectroscopy. More important, we find that the two Ca ions bind differently in the complex, as a result of the hydrogen-bonding network around the whole complex. This finding invites confirmation from time-resolved EXAFS and has implications in understanding the dissociative equilibrium of the Ca2UO2(CO3)3 complex in water.
Co-reporter:Yanfeng Yue, Chenxi Zhang, Qing Tang, Richard T. Mayes, Wei-Po Liao, Chen Liao, Costas Tsouris, Joseph J. Stankovich, Jihua Chen, Dale K. Hensley, Carter W. Abney, De-en Jiang, Suree Brown, and Sheng Dai
Industrial & Engineering Chemistry Research 2016 Volume 55(Issue 15) pp:4125
Publication Date(Web):October 30, 2015
DOI:10.1021/acs.iecr.5b03372
In order to ensure a sustainable reserve of fuel for nuclear power generation, tremendous research efforts have been devoted to developing advanced sorbent materials for extracting uranium from seawater. In this work, a porous aromatic framework (PAF) was surface-functionalized with poly(acrylonitrile) through atom-transfer radical polymerization (ATRP). Batches of this adsorbent were conditioned with potassium hydroxide (KOH) at room temperature or 80 °C prior to contact with a uranium-spiked seawater simulant, with minimal differences in uptake observed as a function of conditioning temperature. A maximum capacity of 4.81 g-U/kg-ads was obtained following 42 days contact with uranium-spiked filtered environmental seawater, which demonstrates a comparable adsorption rate. A kinetic investigation revealed extremely rapid uranyl uptake, with more than 80% saturation reached within 14 days. Relying on the semiordered structure of the PAF adsorbent, density functional theory (DFT) calculations reveal cooperative interactions between multiple adsorbent groups yield a strong driving force for uranium binding.
Co-reporter:Ziqi Tian; Sheng Dai
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 13) pp:2568-2572
Publication Date(Web):June 19, 2016
DOI:10.1021/acs.jpclett.6b01141
We propose the concept of site partition to explain the role of guest molecules in increasing CO2 uptake in metal–organic frameworks and to design new covalent porous materials for CO2 capture. From grand canonical Monte Carlo simulations of CO2 sorption in the recently synthesized CPM-33 MOFs, we show that guest insertion divides one open metal site into two relatively strong binding sites, hence dramatically increasing CO2 uptake. Further, we extend the site partition concept to covalent organic frameworks with large free volume. After insertion of a designed geometry-matching guest, we show that the volumetric uptake of CO2 doubles. Therefore, the concept of site partition can be used to engineer the pore space of nanoporous materials for higher gas uptake.
Co-reporter:Cheng Zhan, Pengfei Zhang, Sheng Dai, and De-en Jiang
ACS Energy Letters - New in 2016 2016 Volume 1(Issue 6) pp:
Publication Date(Web):November 16, 2016
DOI:10.1021/acsenergylett.6b00483
Supercapacitors based on the electric double-layer mechanism use porous carbons or graphene as electrodes. To move beyond this paradigm, we propose boron supercapacitors to leverage two-dimensional (2D) boron sheets’ metallicity and low weight. Six 2D boron sheets from both previous theoretical design and experimental growth are chosen as test electrodes. By applying joint density functional theory (JDFT) to the electrode–electrolyte system, we examine how the 2D boron sheets charge up against applied potential. JDFT predicts that these 2D boron sheets exhibit specific capacitance on the order of 400 F/g, about four times that of graphene. Our work suggests that 2D boron sheets are promising electrodes for supercapacitor applications.
Co-reporter:Cheng Zhan
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 5) pp:789-794
Publication Date(Web):February 17, 2016
DOI:10.1021/acs.jpclett.6b00047
We apply joint density functional theory (JDFT), which treats the electrode/electrolyte interface self-consistently, to an electric double-layer capacitor (EDLC) based on few-layer graphene electrodes. The JDFT approach allows us to quantify a third contribution to the total capacitance beyond quantum capacitance (CQ) and EDL capacitance (CEDL). This contribution arises from the dielectric screening of the electric field by the surface of the few-layer graphene electrode, and we therefore term it the dielectric capacitance (CDielec). We find that CDielec becomes significant in affecting the total capacitance when the number of graphene layers in the electrode is more than three. Our investigation sheds new light on the significance of the electrode dielectric screening on the capacitance of few-layer graphene electrodes.
Co-reporter:Weihong Wu, Chad Priest, Jingwei Zhou, Changjun Peng, Honglai Liu, and De-en Jiang
The Journal of Physical Chemistry B 2016 Volume 120(Issue 29) pp:7227-7233
Publication Date(Web):July 5, 2016
DOI:10.1021/acs.jpcb.6b05452
Uranium from the sea provides a long-time supply guarantee of nuclear fuels for centuries to come, and the neutral Ca2UO2(CO3)3 complex has been shown to be the dominant species of uranium in seawater. However, the solvation and structure of the Ca2UO2(CO3)3 complex in seawater have been unclear. Herein we simulate the Ca2UO2(CO3)3 complex in a model seawater solution via classical molecular dynamics. We find that Na+ and Cl– ions interact very differently with the neutral Ca2UO2(CO3)3 complex in seawater. Especially, one Na+ ion is closely associated with the Ca2UO2(CO3)3 complex, thereby effectively making the complex have a +1 charge, while Cl– ions are much farther away. Hence, this work reveals the important role of Na+ ions in affecting the solvation of the Ca2UO2(CO3)3 complex in seawater, which has implications in designing ligands to attract the Ca2UO2(CO3)3 complex to the sorbent.
Co-reporter:Robert C. Haddon, Ziqi Tian, and De-en Jiang
The Journal of Organic Chemistry 2016 Volume 81(Issue 9) pp:3648-3653
Publication Date(Web):April 11, 2016
DOI:10.1021/acs.joc.6b00298
The Hammond Postulate and the Leffler analysis have provided a cornerstone in the understanding of reaction processes in organic chemistry for over 60 years, yet quantitative applications of these methodologies over the range of reactions envisaged in the original works remain elusive. In the present paper, we analyze a series of SN2 reactions in three solvents that lead to endothermic and exothermic reaction processes, and we show that within the hybridization reaction coordinate the SN2 reaction is fully consistent with both treatments. We give new presentations of the reaction energies as a function of reaction progress, which allow the generation of unified reaction coordinate diagrams that show a linear relationship between the hybridization metric of reaction progress and the relative energies of the stationary points on the potential surface as a function of structure and solvent as originally envisaged by Leffler and Hammond.
Co-reporter:Kyuju Kwak; Qing Tang; Minseok Kim; De-en Jiang;Dongil Lee
Journal of the American Chemical Society 2015 Volume 137(Issue 33) pp:10833-10840
Publication Date(Web):July 29, 2015
DOI:10.1021/jacs.5b06946
The exceptional stability of thiolate-protected Au25 clusters, [Au25(SR)18]−, arises from the closure of superatomic electron shells, leading to a noble-gas-like 8-electron configuration (1S21P6). Here we present that replacing the core Au atom with Pd or Pt results in stable [MAu24(SR)18]0 clusters (M = Pd, Pt) having a superatomic 6-electron configuration (1S21P4). Voltammetric studies of [PdAu24(SR)18]0 and [PtAu24(SR)18]0 reveal that the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps of these clusters are 0.32 and 0.29 eV, respectively, indicating their electronic structures are drastically altered upon doping of the foreign metal. Density functional investigations confirm that the HOMO–LUMO gaps of these clusters are indeed smaller, respectively 0.33 and 0.32 eV, than that of [Au25(SR)18]− (1.35 eV). Analysis of the optimized geometries for the 6-electron [MAu24(SR)18]0 clusters shows that the MAu12 core is slightly flattened to yield an oblate ellipsoid. The drastically decreased HOMO–LUMO gaps observed are therefore the result of Jahn–Teller-like distortion of the 6-electron [MAu24(SR)18]0 clusters, accompanying splitting of the 1P orbitals. These clusters become 8-electron [MAu24(SR)18]2– clusters upon electronic charging, demonstrating reversible interconversion between the 6-electron and 8-electron configurations of MAu24(SR)18.
Co-reporter:Qing Tang and De-en Jiang
Chemistry of Materials 2015 Volume 27(Issue 10) pp:3743
Publication Date(Web):May 1, 2015
DOI:10.1021/acs.chemmater.5b00986
The MoS2 monolayer is the second most studied two-dimensional material after graphene. However, the covalent chemistry through the S layers has not been fully explored for controlling the properties of the MoS2 monolayer. Herein we probe the potential of chemical functionalization of monolayer MoS2 in tuning its electronic properties by first-principles density functional theory. We find that the chemical bonding of the functional groups (H, CH3, CF3, OCH3, NH2) is anomalously strong (4–5 eV) on the 1T phase (in low-coverage regimes) but very weak on the 2H phase. This strong affinity of 1T-MoS2 for functional groups is closely related to its metallicity and partially filled Mo 4d states. More interestingly, 1T-MoS2, which is metastable when unfunctionalized, becomes the stable phase after a crossover coverage of functionalization. Surface functionalization also results in dramatic changes to the electronic properties of 1T-MoS2. We find that the band gap of the 1T-MoS2 monolayer strongly depends on the functional group type and its coverage and can be tuned from zero to ∼1 eV. This work demonstrates the great potential of controlling monolayer MoS2’s phase stability and electronic properties by covalent functionalization.
Co-reporter:Ziqi Tian, Sheng Dai, and De-en Jiang
Chemistry of Materials 2015 Volume 27(Issue 16) pp:5775
Publication Date(Web):August 3, 2015
DOI:10.1021/acs.chemmater.5b02370
Nitrogen doping is an important strategy in tuning the properties and functions of carbonaceous materials. But the chemical speciation of the nitrogen groups in the sp2-carbon framework has not been firmly established. Here we address two important questions in nitrogen doping of carbonaceous materials from a computational approach: the relative stability of different nitrogen groups and their X-ray photoelectron spectrum (XPS) signatures of the core-level (N 1s) electron binding energies. Four types of nitrogen groups (graphitic, pyrrolic, aza-pyrrolic, and pyridinic) in 69 model compounds have been examined. Computed formation energies indicate that pyrrolic and pyridinic nitrogens are significantly more stable (by about 110 kJ/mol) than graphitic and aza-pyrrolic nitrogens. This stability trend can be understood from the Clar’s sextet rule. Predicted N 1s binding energies show relatively high consistency among each dopant type, thereby offering a guide to identify nitrogen groups. The relative stability coupled with predicted N 1s binding energies can explain the temperature-dependent change in the experimental XPS spectra. The present work therefore provides fundamental insights into nitrogen dopants in carbonaceous materials, which will be useful in understanding the applications of nitrogen-doped carbons in electric energy storage, electrocatalysis, and carbon capture.
Co-reporter:Runhai Ouyang and De-en Jiang
ACS Catalysis 2015 Volume 5(Issue 11) pp:6624
Publication Date(Web):October 1, 2015
DOI:10.1021/acscatal.5b01521
The Au25(SR)18 cluster can catalyze 100% selective hydrogenation of α,β-unsaturated ketones to unsaturated alcohols. However, the mechanism remains a mystery. Here we unravel the underlying mechanism by using first-principles density functional theory calculations with benzalacetone as a substrate. We find that the Au25(SR)18 cluster cannot directly activate either H2 or benzalacetone separately. Instead, starting with coadsorption of H2 and benzalacetone on Au25(SR)18, H2 heterolytically cleaves to the substrate and to a surface Au atom of the cluster, followed by the facile transfer of H from the Au atom to the partially hydrogenated substrate. In this mechanism, C═O and C═C hydrogenations have barriers of 0.99 and 1.12 eV, respectively, in agreement with the experimentally observed selectivity toward unsaturated alcohol. In addition, we show that the ethanol solvent can further stabilize the partially hydrogenated intermediate of C═O hydrogenation via a hydrogen bond, leading to a smaller H2 cleavage energy (0.90 eV). Hence, the heterolytic cleavage of H2 on the Au25 nanocluster favors the more polar C═O bond of benzalacetone, leading to selective formation of unsaturated alcohol. This work reveals that the weak interaction between H2 and the Au cluster, the formation of a Au hydride, and the polar solvent are responsible for the high selectivity of the α,β-unsaturated ketone hydrogenation to the corresponding unsaturated alcohol over the Au25 nanocluster.Keywords: benzalacetone; density functional theory; gold nanocluster; hydrogenation; solvent effects
Co-reporter:Runhai Ouyang, Yu Xie and De-en Jiang
Nanoscale 2015 vol. 7(Issue 36) pp:14817-14821
Publication Date(Web):19 Aug 2015
DOI:10.1039/C5NR03903G
Neural network potentials trained by first-principles density functional theory total energies were applied to search for global minima of gold nanoclusters within the basin-hopping method. Using Au58 as an example, we found a new putative global minimum which has a core–shell structure of Au10@Au48 and C4 symmetry. This new structure of Au58 is 0.24 eV per formula more stable than the best previous model that has C1 symmetry. This work demonstrates that neural network potentials combined with the basin-hopping method could be very useful in global minimization for medium-sized metal clusters which might be computationally prohibitive for first principles density functional theory.
Co-reporter:Qing Tang, Runhai Ouyang, Ziqi Tian and De-en Jiang
Nanoscale 2015 vol. 7(Issue 6) pp:2225-2229
Publication Date(Web):18 Dec 2014
DOI:10.1039/C4NR05826G
A key challenge in nanocluster research in particular and nanoscience in general is structure prediction for known compositions. Usually a simple ligand such as a methyl group is used to replace complex ligands in structure prediction of ligand-protected nanoclusters. However, how ligands dictate the energy landscape of such a cluster remains unclear. Here we elucidate the role of the ligand effect on the isomer stability of Au24(SR)20 nanoclusters by computing the relative energy of two isomers (one from the experiment, denoted as the “J” isomer; the other is the best theoretical model, denoted as the “P” isomer) of Au24(SR)20 with dispersion-corrected density functional theory. We find that when R = –CH3, the two isomers are equally stable (within 0.13 eV), but for R = –CH2CH2Ph the P isomer is more stable by 1.6 eV and for R = –CH2Ph-tBu the J isomer is more stable by 1.0 eV. Partition of the total energy into DFT and vdW contributions indicates that the higher stability of the P isomer in the case of R = –CH2CH2Ph stems from the stronger vdW interactions among –CH2CH2Ph groups, while the higher stability of the J isomer in the case of R = –CH2Ph-tBu is due to its better capacity to respond to the steric effect of the larger –CH2Ph-tBu groups. This finding confirms that the ligand plays a crucial role in dictating the isomer stability.
Co-reporter:Ziqi Tian, Sheng Dai, and De-en Jiang
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 23) pp:13073
Publication Date(Web):May 19, 2015
DOI:10.1021/acsami.5b03275
Porphyrin-based two-dimensional polymers have uniform micropores and close to atom-thin thicknesses, but they have not been explored for gas separation. Herein we design various expanded porphyrin derivatives for their potential application in membrane gas separation, using CO2/N2 as an example. Pore sizes are determined based on both van der Waals radii and electron density distribution. Potential energy curves for CO2 and N2 passing through are mapped by dispersion-corrected density functional theory calculations. The passing-through barriers are used to evaluate CO2/N2 separation selectivity. Promising subunits for CO2 separation have been selected from the selectivity estimates. 2D membranes composed of amethyrin derivatives are shown to have high ideal selectivity on the order of 106 for CO2/N2 separation. Classical molecular dynamics simulation yields a permeance of 104–105 GPU for CO2 through extended 2D membranes based on amethyrin derivatives. This work demonstrates that porphyrin systems could offer an attractive bottom-up approach for 2D porous membranes.Keywords: 2-dimensional polymer; CO2 capture; dispersion-corrected DFT; gas separation; ultrathin membrane;
Co-reporter:Zhao Yuan;Qing Tang;Kesavapillai Sreenath;J. Tyler Simmons;Ali H. Younes;Lei Zhu
Photochemistry and Photobiology 2015 Volume 91( Issue 3) pp:586-598
Publication Date(Web):
DOI:10.1111/php.12393
Abstract
2-(2′-Hydroxyphenyl)benzoxazole (HBO) is known for undergoing intramolecular proton transfer in the excited state to result in the emission of its tautomer. A minor long-wavelength absorption band in the range 370–420 nm has been reported in highly polar solvents such as dimethylsulfoxide (DMSO). However, the nature of this species has not been entirely clarified. In this work, we provide evidence that this long-wavelength absorption band might have been caused by base or metal salt impurities that are introduced into the spectral sample during solvent transport using glass Pasteur pipettes. The contamination by base or metal salt could be avoided by using borosilicate glass syringes or nonglass pipettes in sample handling. Quantum chemical calculations conclude that solvent-mediated deprotonation is too energetically costly to occur without the aid of a base of an adequate strength. In the presence of such a base, the deprotonation of HBO and its effect on emission are investigated in dichloromethane and DMSO, the latter of which facilitates deprotonation much more readily than the former. Finally, the absorption and emission spectra of HBO in 13 solvents are reported, from which it is concluded that ESIPT is hindered in polar solvents that are also strong hydrogen bond acceptors.
Co-reporter:Xian-Kai Wan;Shang-Fu Yuan;Dr. Qing Tang;Dr. De-en Jiang;Dr. Quan-Ming Wang
Angewandte Chemie International Edition 2015 Volume 54( Issue 20) pp:5977-5980
Publication Date(Web):
DOI:10.1002/anie.201500590
Abstract
A 23-gold-atom nanocluster was prepared by NaBH4-mediated reduction of a solution of PhCCAu and Ph3PAuSbF6 in CH2Cl2. The cluster composition was determined to be [Au23(PhCC)9(Ph3P)6]2+ and single-crystal X-ray diffraction revealed that the cluster has an unprecedented Au17 kernel protected by three PhC2-Au-C2(Ph)-Au-C2Ph motifs and six Ph3P groups. The Au17 core can be viewed as the fusion of two Au10 units sharing a Au3 triangle. Electronic structure analysis from DFT calculations suggests that the stability of this unusual 12-electron cluster is a result of the splitting of the superatomic 1D orbitals under D3h symmetry of the Au17 kernel. The discovery and determination of the structure of the Au23 cluster demonstrates the versatility of the alkynyl ligand in leading to the formation of new cluster compounds.
Co-reporter:Chad Priest, Qing Tang, and De-en Jiang
The Journal of Physical Chemistry A 2015 Volume 119(Issue 33) pp:8892-8897
Publication Date(Web):July 21, 2015
DOI:10.1021/acs.jpca.5b04015
We explore the structural evolution of Tcn (n = 4–20) clusters using a first-principles global minimization technique, namely, basin-hopping from density functional theory geometry optimization (BH-DFT). Significantly more stable structures have been found in comparison with previous models, indicating the power of DFT-based basin hopping in finding new structures for clusters. The growth sequence and pattern for n from 4 to 20 are analyzed from the perspective of geometric shell formation. The binding energy per atom, relative stability, and magnetic moments are examined as a function of the cluster size. Several magic sizes of higher stability and symmetry are discovered. In particular, we find that Tc19 prefers an Oh symmetry structure, resembling a piece of a face-centered-cubic metal, and its electrostatic potential map shows interesting features that indicate special reactivity of the corner atoms.
Co-reporter:Ziqi Tian, Tomonori Saito, and De-en Jiang
The Journal of Physical Chemistry A 2015 Volume 119(Issue 16) pp:3848-3852
Publication Date(Web):March 31, 2015
DOI:10.1021/acs.jpca.5b01892
Ab initio calculations were used to identify CO2-philic groups. Over 55 neutral molecules were screened for CO2 affinity via binding energetics. It is found that poly(ethylene oxide)s (PEO) oligomers with more than three repeating units are good CO2-binding groups, consistent with the high-performance of PEO-based materials for CO2/N2 separation. More interestingly, two triazole groups linked with a methylene chain are also excellent for CO2 binding with a favorable interaction of more than 28 kJ/mol, indicating that polymers or covalent-organic frameworks (COFs) with triazoles may be utilized for CO2 capture. This work provides a useful guide to introduce promising organic groups into polymeric membranes and COFs for CO2/N2 separation media.
Co-reporter:Runhai Ouyang
The Journal of Physical Chemistry C 2015 Volume 119(Issue 37) pp:21555-21560
Publication Date(Web):August 28, 2015
DOI:10.1021/acs.jpcc.5b06994
Although several thiolate-protected Au nanoclusters have yielded to total-structure determination, the ligand-conformation energy landscapes and how they affect the relative stability of the whole clusters are not well understood. In this work, we employ a force-field-based approach to perform the ligand-conformation search for isolated thiolate-protected Au nanoclusters using Au25(SR)18 (R = C2H4Ph) as an example. We find that the ligand-conformation energy landscape of Au25(SC2H4Ph)18 comprises multiple low-energy funnels of similar stability instead of a single global minimum. In fact, we find slightly more stable conformations of isolated Au25(SC2H4Ph)18 than those observed in the experiment from a crystalline state, indicating that specific environments such as crystal packing and solvents may all affect the ligand conformation. This work reveals the role of ligand conformation in the cluster energy landscape.
Co-reporter:Cheng Zhan
The Journal of Physical Chemistry C 2015 Volume 119(Issue 39) pp:22297-22303
Publication Date(Web):September 8, 2015
DOI:10.1021/acs.jpcc.5b05930
Quantum capacitance has been recently measured for electric double layers (EDL) at electrolyte/graphene interfaces. However, the importance of quantum capacitance in realistic carbon electrodes is not clear. Toward understanding that from a theoretical perspective, here we studied the quantum capacitance and total capacitance of graphene electrodes as a function of the number of graphene layers. The quantum capacitance was obtained from electronic density functional theory based on fixed band approximation with an implicit solvation model, while the EDL capacitances were from classical density functional theory. We found that quantum capacitance plays a dominant role in total capacitance of the single-layer graphene both in aqueous and ionic-liquid electrolytes but the contribution decreases as the number of graphene layers increases. The total integral capacitance roughly levels off and is dominated by the EDL capacitance beyond about four graphene layers. Because many porous carbons have nanopores with stacked graphene layers at the surface, this research provides a good estimate of the effect of quantum capacitance on their electrochemical performance.
Co-reporter:Qing Tang
The Journal of Physical Chemistry C 2015 Volume 119(Issue 5) pp:2904-2909
Publication Date(Web):January 16, 2015
DOI:10.1021/jp5123695
Au18(SR)14 (−SR being a thiolate group) is a small, stable thiolated gold nanocluster experimentally identified in 2005, but its structure remains elusive. A previously proposed model for Au18(SR)14 based on density functional theory (DFT) structural optimization consists of a Au8 core protected by two −RS–Au–SR–Au–SR– (dimer) and two −RS–Au–SR–Au–SR–Au–SR– (trimer) motifs. Here we revisit structure prediction for Au18(SR)14 from extensive exploration of the possible isomers for Au18(SCH3)14 by applying structural hypotheses based on both “staple motifs” and “ring and staple motifs”. Three isomers based on the staple motifs are found to be more stable than the best previous model. The two lowest-energy Au18(SCH3)14 isomers (I and II) also have a Au8 core protected by two dimer and two trimer motifs, but the core geometry and electronic properties are different. The third lowest-energy isomer (III) consists of a Au8 core protected by two −RS–Au–SR– (monomer) and two −RS–Au–SR–Au–SR–Au–SR–Au–SR– (tetramer) motifs. By changing R from CH3 to the experimentally used cyclohexanyl group (C6H11), we found that isomer III is the most stable for Au18(SC6H11)14. The computed X-ray diffraction (XRD) pattern and optical spectrum of isomer III are in good agreement with the experimental data. This work suggests that Au18(SR)14 may have monomer and tetramer motifs in the protective layer.
Co-reporter:Qing Tang
The Journal of Physical Chemistry C 2015 Volume 119(Issue 20) pp:10804-10810
Publication Date(Web):October 1, 2014
DOI:10.1021/jp508883v
The phenylethynyl group (PhC≡C—) has attracted attention recently as a new way to passivate gold surfaces, but little is known of the interfacial structure and bonding. Here we employ density functional theory to investigate the organogold interfaces between PhC≡C— and the flat Au(111) surface as well as between PhC≡C— and a model gold nanocluster (Au20). Although isolated PhC≡C— prefers the three-coordinate hollow site on the perfect Au(111) surface, formation of the PhCC—Auadatom—CCPh motif becomes energetically preferred when the Au adatom is present, resembling the RS—Au—SR motif on Au(111). However, distinct from the thiolate/Au interface, the PhCC—Auadatom–CCPh staple motif features π-bonding of the C≡C bond to the substrate Au atom in addition to the σ-bonding of the terminal carbon to the gold adatom (or the staple gold atom). Geometry optimization and simulated annealing further show that this new type of staple motif is also the preferred bonding mode of the PhC≡C— groups on the Au20 cluster. The novel PhC≡C—Au—C≡CPh motif with π-bonding to the Au substrate is expected to be a key feature of the PhC≡C/Au interface for gold clusters, nanoparticles, and surfaces. This insight will help structural elucidation and chemical understanding of both self-assembled monolayers of PhC≡C— groups on gold surfaces and PhC≡C— protected gold nanosystems.
Co-reporter:Xian-Kai Wan;Shang-Fu Yuan;Dr. Qing Tang;Dr. De-en Jiang;Dr. Quan-Ming Wang
Angewandte Chemie 2015 Volume 127( Issue 20) pp:6075-6078
Publication Date(Web):
DOI:10.1002/ange.201500590
Abstract
A 23-gold-atom nanocluster was prepared by NaBH4-mediated reduction of a solution of PhCCAu and Ph3PAuSbF6 in CH2Cl2. The cluster composition was determined to be [Au23(PhCC)9(Ph3P)6]2+ and single-crystal X-ray diffraction revealed that the cluster has an unprecedented Au17 kernel protected by three PhC2-Au-C2(Ph)-Au-C2Ph motifs and six Ph3P groups. The Au17 core can be viewed as the fusion of two Au10 units sharing a Au3 triangle. Electronic structure analysis from DFT calculations suggests that the stability of this unusual 12-electron cluster is a result of the splitting of the superatomic 1D orbitals under D3h symmetry of the Au17 kernel. The discovery and determination of the structure of the Au23 cluster demonstrates the versatility of the alkynyl ligand in leading to the formation of new cluster compounds.
Co-reporter:Xian-Kai Wan; Qing Tang; Shang-Fu Yuan; De-en Jiang;Quan-Ming Wang
Journal of the American Chemical Society 2014 Volume 137(Issue 2) pp:652-655
Publication Date(Web):December 29, 2014
DOI:10.1021/ja512133a
A novel Au19 nanocluster with a composition of [Au19(PhC≡C)9(Hdppa)3](SbF6)2 was synthesized (Hdppa = N,N-bis(diphenylphosphino)amine). Single crystal X-ray structural analysis reveals that the cluster comprises a centered icosahedral Au13 core hugged by three V-shaped PhC≡C–Au–C≡C(Ph)–Au–C≡CPh motifs. Such motif is observed for the first time in an alkynyl-protected gold nanocluster. The Au19 cluster shows two main optical-absorption bands at 1.25 and 2.25 eV, confirmed by time-dependent density functional theory. Orbital analysis indicates that PhC≡C– groups can actively participate in the frontier orbitals of the whole cluster. The new Au19 cluster and the novel alkynyl–gold motif open the door to understanding the alkynyl–gold interface and discovering many potential members of this new class of gold clusters.
Co-reporter:Guoxiang Hu, Qing Tang and De-en Jiang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 34) pp:NaN23871-23871
Publication Date(Web):2016/08/10
DOI:10.1039/C6CP04011J
Cobalt phosphide (CoP) is one of the most promising, earth-abundant electrocatalysts discovered to date for hydrogen evolution reaction (HER), yet the mechanism is not well understood. Since hydrogen adsorption is a key factor of HER activity, here we examine the adsorption of atomic hydrogen on the low-Miller-index surfaces of CoP, including (111), (110), (100), and (011), by using periodic density functional theory. From the calculated Gibbs free energy of adsorption, we predict that (111), (110), and (011) surfaces will have good catalytic activities for HER. From ab initio atomistic thermodynamics, we find that the stabilities of the surfaces at 1 atm H2 and 300 K follow the trend of (111) > (100) ∼ (110) ≫ (011). On the most stable (111) surface, both Co bridge sites and P top sites are found to be able to adsorb hydrogen with a close-to-zero free energy change and the synergy of proximal Co and P atoms on the surface results in a better HER activity. Our work provides important insights into CoP's excellent HER activity and a basis for further mechanistic understanding of HER on CoP and other transition-metal phosphides.
Co-reporter:Victor Fung, Franklin (Feng) Tao and De-en Jiang
Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 18) pp:NaN6869-6869
Publication Date(Web):2016/05/20
DOI:10.1039/C6CY00749J
Co3O4 is a metal oxide catalyst with weak, tunable M–O bonds promising for catalysis. Here, density functional theory (DFT) is used to study the oxidative dehydrogenation (ODH) of ethane on Co3O4 nanorods based on the preferred surface orientation (111) from the experimental electron-microscopy image. The pathway and energetics of the full catalytic cycle including the first and second C–H bond cleavages, hydroxyl clustering, water formation, and oxygen-site regeneration are determined. We find that both lattice O and Co may participate as active sites in the dehydrogenation, with the lattice-O pathway being favored. We identify the best ethane ODH pathway based on the overall energy profiles of several routes. We identify that water formation from the lattice oxygen has the highest energy barrier and is likely a rate-determining step. This work of the complete catalytic cycle of ethane ODH will allow further study into tuning the surface chemistry of Co3O4 nanorods for high selectivity of alkane ODH reactions.
Co-reporter:Chad Priest, Ziqi Tian and De-en Jiang
Dalton Transactions 2016 - vol. 45(Issue 24) pp:NaN9819-9819
Publication Date(Web):2016/01/22
DOI:10.1039/C5DT04576B
Recent experiments have shown that the neutral Ca2UO2(CO3)3 complex is the dominant species of uranium in many uranyl-containing streams. However, the structure and solvation of such a species in water has not been investigated from first principles. Herein we present a first principles molecular dynamics perspective of the Ca2UO2(CO3)3 complex in water based on density functional theory and Born–Oppenheimer approximation. We find that the Ca2UO2(CO3)3 complex is very stable in our simulation timeframe for three different concentrations considered and that the key distances from our simulation are in good agreement with the experimental data from extended X-ray absorption fine structure (EXAFS) spectroscopy. More important, we find that the two Ca ions bind differently in the complex, as a result of the hydrogen-bonding network around the whole complex. This finding invites confirmation from time-resolved EXAFS and has implications in understanding the dissociative equilibrium of the Ca2UO2(CO3)3 complex in water.
Co-reporter:Cheng Zhan, Yu Zhang, Peter T. Cummings and De-en Jiang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 6) pp:NaN4674-4674
Publication Date(Web):2016/01/08
DOI:10.1039/C5CP06952A
Recent experiments have shown that nitrogen doping enhances capacitance in carbon electrode supercapacitors. However, a detailed study of the effect of N-doping on capacitance is still lacking. In this paper, we study the doping concentration and the configuration effect on the electric double-layer (EDL) capacitance, quantum capacitance, and total capacitance. It is found that pyridinic and graphitic nitrogens can increase the total capacitance by increasing quantum capacitance, but pyrrolic configuration limits the total capacitance due to its much lower quantum capacitance than the other two configurations. We also find that, unlike the graphitic and pyridinic nitrogens, the pyrrolic configuration's quantum capacitance does not depend on the nitrogen concentration, which may explain why some capacitance versus voltage measurements of N-doped graphene exhibit a V-shaped curve similar to that of undoped graphene. Our investigation provides a deeper understanding of the capacitance enhancement of the N-doping effect in carbon electrodes and suggests a potentially effective way to optimize the capacitance by controlling the type of N-doping.
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