Michael S. Wong

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Name: ?Wong, Michael

Organization: Rice University , USA

Department: Department of Chemical and Biomolecular Engineering

Title: Professor(PhD)

TOPICS

Physical Chemistry

Chemicals
References

Improved CO2 Absorption in a Gas–Liquid Countercurrent Column Using a Ceramic Foam Contactor

Co-reporter:Zhen Wang, Mayank Gupta, Sumedh S. Warudkar, Kenneth R. Cox, George J. Hirasaki, and Michael S. Wong

Industrial & Engineering Chemistry Research 2016 Volume 55(Issue 5) pp:1387-1400

Publication Date(Web):January 15, 2016

DOI:10.1021/acs.iecr.5b03600

Solid foams are porous, monolithic materials with higher specific surface areas than the random packings that are commonly used in amine-based CO2 capture processes. In this work, the hydrodynamic characteristics (e.g., pressure drop, flooding point, and liquid holdup) and CO2 absorption performance of α-Al2O3 ceramic foam packings of different porosities were investigated experimentally in a gas–liquid countercurrent column. With a 30 wt % diglycolamine (DGA) solvent as the CO2 absorbent, the foams allowed higher flow rates of gas and liquid than a random packing before undesirable flooding was reached. Ceramic foams with lower porosities have larger operating capacities than those with higher porosities. A parametric study of a one-dimensional flow model was performed by investigating the effects of gas velocity, liquid velocity, and CO2 solvent loading on the CO2 removal performance. Lower gas velocities and higher liquid velocities increased the CO2 removal efficiency. The CO2 removal efficiency decreased with increasing initial CO2 loading. The initial CO2 loading of DGA solutions is recommended to be less than 0.35 mol of CO2/mol of DGA to provide efficient CO2 removal. Ceramic foams improve CO2 absorption using liquid amines, which can lead to smaller carbon capture units.

High activity and regenerability of a palladiumgold catalyst for chloroform degradation

Co-reporter:Juan C Velázquez;Sukit Leekumjorn;Gary D Hopkins;Kimberly N Heck;Jason S McPherson;John A Wilkens;Bradley S Nave;Martin Reinhard;Michael S Wong

Journal of Chemical Technology and Biotechnology 2016 Volume 91( Issue 10) pp:2590-2596

Publication Date(Web):

DOI:10.1002/jctb.4851

Abstract

BACKGROUND

Chloroform (CF), a common groundwater contaminant, can be degraded in deionized water reductively using Pd and Pd-Au catalysts under mild conditions (room temperature, atmospheric pressure) via hydrodechlorination (HDC). However, the performance of these catalysts under field-like conditions is unknown. This study evaluates the lab-scale performance and optimal operating conditions for flow reactors using Pd/Al₂O₃ and Pd-Au/Al₂O₃.

RESULTS

Both catalysts were active for CF HDC when tested using deionized water and groundwater spiked with CF. The Pd-Au catalyst was ∼263× more active than the Pd catalyst using unbuffered deionized water (1550 mL-g_Pd⁻¹-min⁻¹ vs 5.89 mL-g_Pd⁻¹-min⁻¹), and was ∼137× more active using buffered groundwater (1030 mL-g_Pd⁻¹-min⁻¹ vs 7.53 mL-g_Pd⁻¹-min⁻¹). The buffer was a carbonate/citrate mixture optimized to prevent pH drop and scale formation from minerals present in groundwater. A catalytic flow process was designed using a buffer co-feed and daily regeneration of the catalyst bed. Pd-Au/Al₂O₃- and Pd/Al₂O₃-containing reactors exhibited CF conversions of 65% and 32.5% over 18 days operating at a weight hourly space velocity of 30 h⁻¹.

CONCLUSIONS

This study provides insights into strategies for long-term operation of catalytic flow reactors to treat CF in groundwater, and shows the higher CF HDC catalytic efficiency of Pd-Au over Pd. © 2015 Society of Chemical Industry

EXAFS Characterization of Palladium-on-Gold Catalysts Before and After Glycerol Oxidation

Co-reporter:Zhun Zhao;Jeffrey T. Miller;Tianpin Wu;Neil M. Schweitzer

Topics in Catalysis 2015 Volume 58( Issue 4-6) pp:302-313

Publication Date(Web):2015 April

DOI:10.1007/s11244-015-0371-3

Supported precious metal catalysts have been studied extensively for selective oxidation as a means to upgrade glycerol, a low-cost byproduct of biodiesel manufacture. We recently used a model bimetallic catalyst (Au nanoparticles decorated with Pd and immobilized onto carbon, “Pd-on-Au/C”) to study the metal nanostructure effects on glycerol oxidation. In this study, a detailed X-ray absorption spectroscopy analysis of Pd-on-Au catalysts before and after glycerol oxidation (60 °C, 0.1 M glycerol, 0.4 M NaOH, and constant O2 flow at 1 atm) is presented. Catalysts with two Pd surface coverages (60 and 150 sc%) with comparable turnover frequency values were studied, along with the less active 4-nm Au/C and 4-nm Pd/C as control samples. Extended X-ray absorption fine structure analysis showed that there was no change to oxidation states and coordination numbers for 60 sc% Pd-on-Au/C and Au/C catalysts after contact with the glycerol reaction medium or after 3 h of glycerol reaction. With a higher fraction of oxidized Pd (~40 %) than 60 sc% Pd-on-Au/C (~25 %), the 150 sc% catalyst showed some variation in oxidized Pd content before and after glycerol reaction. Pd/C grew in Pd particle size and became more oxidized after contacting reaction medium and after 3 h reaction, contributing to its observed catalyst deactivation. Structural stability and catalytic activity are improved for the water-phase oxidation of glycerol and likely other alcohols when Pd is supported on Au, highlighting the potential advantages of using Au as a support for other catalytically active metals.

Volcano-shape glycerol oxidation activity of palladium-decorated gold nanoparticles

Co-reporter:Zhun Zhao, Joni Arentz, Lori A. Pretzer, Pongsak Limpornpipat, James M. Clomburg, Ramon Gonzalez, Neil M. Schweitzer, Tianpin Wu, Jeffrey T. Miller and Michael S. Wong

Chemical Science 2014 vol. 5(Issue 10) pp:3715-3728

Publication Date(Web):02 Jun 2014

DOI:10.1039/C4SC01001A

Bimetallic PdAu catalysts are more active than monometallic ones for the selective oxidation of alcohols, but the reasons for improvement remain insufficiently detailed. A metal-on-metal material can probe the structure–catalysis relationship more clearly than conventionally prepared bimetallics. In this study, Pd-on-Au nanoparticles with variable Pd surface coverages (sc%) ranging from 10 to 300 sc% were synthesized and immobilized onto carbon (Pd-on-Au/C). Tested for glycerol oxidation at 60 °C, pH 13.5, and 1 atm under flowing oxygen, the series of Pd-on-Au/C materials showed volcano-shape catalytic activity dependence on Pd surface coverage. Increasing surface coverage led to higher catalytic activity, such that initial turnover frequency (TOF) reached a maximum of ∼6000 h−1 at 80 sc%. Activity decreased above 80 sc% mostly due to catalyst deactivation. Pd-on-Au/C at 80 sc% was >10 times more active than monometallic Au/C and Pd/C, with both exhibiting TOF values less than ∼500 h−1. Glyceric acid was the dominant primary reaction product for all compositions, with its zero-conversion selectivity varying monotonically as a function of Pd surface coverage. Glyceric acid yield from Pd-on-Au/C (80 sc%) was 42%, almost double the yields from Au/C and Pd/C (16% and 22%, respectively). Ex situ X-ray absorption near edge structure analysis of two Pd-on-Au/C materials with comparable activities (60 sc% and 150 sc%) showed that the former had less oxidized Pd ensembles than the latter, and that both catalysts were less oxidized compared to Pd/C. That Au stabilizes the metallic state of surface Pd atoms may be responsible for activity enhancement observed in other PdAu-catalyzed oxidation reactions. Decorating a Au surface with Pd generates a catalyst that has the deactivation resistance of Au, the higher glyceric acid selectivity of Pd, and the synergistically higher activities that neither metal has.

Supporting palladium metal on gold nanoparticles improves its catalysis for nitrite reduction

Co-reporter:Huifeng Qian, Zhun Zhao, Juan C. Velazquez, Lori A. Pretzer, Kimberly N. Heck and Michael S. Wong

Nanoscale 2014 vol. 6(Issue 1) pp:358-364

Publication Date(Web):30 Oct 2013

DOI:10.1039/C3NR04540D

Nitrate (NO3−) and nitrite (NO2−) anions are often found in groundwater and surface water as contaminants globally, especially in agricultural areas due to nitrate-rich fertilizer use. One popular approach to studying the removal of nitrite/nitrate from water has been their degradation to dinitrogen via Pd-based reduction catalysis. However, little progress has been made towards understanding how the catalyst structure can improve activity. Focusing on the catalytic reduction of nitrite in this study, we report that Au NPs supporting Pd metal ("Pd-on-Au NPs") show catalytic activity that varies with volcano-shape dependence on Pd surface coverage. At room temperature, in CO2-buffered water, and under H2 headspace, the NPs were maximally active at a Pd surface coverage of 80%, with a first-order rate constant (kcat = 576 L gPd−1 min−1) that was 15x and 7.5x higher than monometallic Pd NPs (∼4 nm; 40 L gPd−1 min−1) and Pd/Al2O3 (1 wt% Pd; 76 L gPd−1 min−1), respectively. Accounting only for surface Pd atoms, these NPs (576 L gsurface-Pd−1 min−1) were 3.6x and 1.6x higher than monometallic Pd NPs (160 L gsurface-Pd−1 min−1) and Pd/Al2O3 (361 L gsurface-Pd−1 min−1). These NPs retained ∼98% of catalytic activity at a chloride concentration of 1 mM, whereas Pd/Al2O3 lost ∼50%. The Pd-on-Au nanostructure is a promising approach to improve the catalytic reduction process for nitrite and, with further development, also for nitrate anions.

Carbon-Based Nanoreporters Designed for Subsurface Hydrogen Sulfide Detection

Co-reporter:Chih-Chau Hwang, Gedeng Ruan, Lu Wang, Haiyan Zheng, Errol L. G. Samuel, Changsheng Xiang, Wei Lu, William Kasper, Kewei Huang, Zhiwei Peng, Zachary Schaefer, Amy T. Kan, Angel A. Martí, Michael S. Wong, Mason B. Tomson, and James M. Tour

ACS Applied Materials & Interfaces 2014 Volume 6(Issue 10) pp:7652

Publication Date(Web):April 15, 2014

DOI:10.1021/am5009584

Polyvinyl alcohol functionalized carbon black with H2S-sensor moieties can be pumped through oil and water in porous rock and the H2S content can be determined based on the fluorescent enhancement of the H2S-sensor addends.Keywords: breakthrough study; carbon black; fluorescent enhancement; H2S detection; nanoparticle; polyvinyl alcohol (PVA);

Surface modification of carbon black nanoparticles by dodecylamine: Thermal stability and phase transfer in brine medium

Co-reporter:Meiriane C.F. Soares, Marcelo M. Viana, Zachary L. Schaefer, Varun S. Gangoli, Yinhong Cheng, Vinicius Caliman, Michael S. Wong, Glaura G. Silva

Carbon 2014 Volume 72() pp:287-295

Publication Date(Web):June 2014

DOI:10.1016/j.carbon.2014.02.008

Stable aqueous dispersions of carbon black (CB) nanoparticles were prepared by developing a generic bilayer approach to the CB phase-transfer method using commercial Avanel as a surfactant. CB was oxidized using ammonium persulfate, and dodecylamine (DDA) was grafted onto this carbon core using N,N-dicyclohexylcarbodiimide as a coupling agent. The covalent bond between CB and DDA was confirmed by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, and thermogravimetric analysis. The average diameter of the primary carbon nanoparticles after chemical modification increased from 15 to 20 nm, as determined by high-resolution transmission electron microscopy. Dispersions of the modified CB was stable in organic solvents and were thermally stable in saline water when Avanel was used as a surfactant. The Avanel coating on the CB particles enabled the design of carbon materials with high colloidal stability, as evidenced by dynamic light scattering measurements and the breakthrough characteristics of the coated material in sandstone rocks.

Salt- and temperature-stable quantum dot nanoparticles for porous media flow

Co-reporter:Gautam C. Kini, Jie Yu, Lu Wang, Amy T. Kan, Sibani L. Biswal, James M. Tour, Mason B. Tomson, Michael S. Wong

Colloids and Surfaces A: Physicochemical and Engineering Aspects 2014 Volume 443() pp:492-500

Publication Date(Web):20 February 2014

DOI:10.1016/j.colsurfa.2013.11.042

•Cadmium selenide nanoparticles (NPs) are colloidally stable in 1 M NaCl brine solution.•A nonionic ethoxylated alcohol surfactant (Neodol) provides this salt stability.•NPs are colloidally stable up to 70 °C, near the surfactant cloud point temperature.•NPs can travel through crushed calcite and sandstone and through a sandstone core.•NP adsorption during porous media flow can occur due to surfactant clouding.The transport of colloidal nanoparticles (NPs) through porous media is a well-studied phenomenon at ambient temperature and in low-to-zero salinity water found in aquatic systems. Little is known at much higher temperatures and salinities such as conditions found in petroleum reservoirs, thus limiting the possible use of NPs in downhole oilfield applications. Using 3-nm CdSe quantum dots (QDs) as a model material, we report that NPs can be prepared with excellent colloidal stability at high ionic strengths and elevated temperatures. QDs with an outer coating of a nonionic ethoxylated alcohol surfactant showed little aggregation in synthetic seawater with ionic strength of 0.55 M and 1 M NaCl brine solution based on dynamic light scattering analysis. They showed colloidal stability up to 70 °C, close to the cloud point temperature of the nonionic surfactant. They further showed nearly unimpeded flow behavior when carried in high-salinity water through a packed column of crushed calcite or sandstone mineral at room temperature. QDs were successfully passed through a medium-permeability Berea sandstone core (100 mDa) at 17 atm, 25 °C, and 8 mL/h. The preparation strategy for salt- and temperature-stable QDs is applicable to a wide range of particle sizes and compositions, toward the general handling and use of functional NPs in high-salinity environments.

Using Catalytic and Surface-Enhanced Raman Spectroscopy-Active Gold Nanoshells to Understand the Role of Basicity in Glycerol Oxidation

Co-reporter:Kimberly N. Heck, Benjamin G. Janesko, Gustavo E. Scuseria, Naomi J. Halas, and Michael S. Wong

ACS Catalysis 2013 Volume 3(Issue 11) pp:2430

Publication Date(Web):September 10, 2013

DOI:10.1021/cs400643f

The origin of oxidation activity of gold catalysts has been a subject of great interest, particularly with the discovery of selective glycerol oxidation under water-phase alkaline conditions, for which neither small gold nanoparticles nor a catalyst support is necessary for activity. Little is known about the interactions among the catalyst surface, reactant, and hydroxyl species, which have never been examined spectroscopically because of a lack of developed in situ methods. In this work, we studied the room-temperature, water-phase reaction of glycerol oxidation using gold nanoshells (Au NSs), in which the gold substrate was active for surface-enhanced Raman spectroscopy (SERS) and catalysis. Analysis of glycerol solutions at high pH values and with oxygen content indicated that glycerol and glycerolate species did not bind directly to the catalyst surface in the absence of oxygen. However, glycerate surface species formed very rapidly when oxygen was present, suggesting an Eley–Rideal-type reaction mechanism with O2 (and/or O2-activated OH–) as the adsorbed species. SERS analysis of carbon monoxide chemisorption on Au NSs indicated that higher pH values progressively weakened the C–O bond as the Au negative charge increased. The importance of high alkalinity to Au-catalyzed alcohol oxidation may result from both the activation of glycerol via deprotonation and the weakening of the adsorbed O2 double bond via induced Au negative charge.Keywords: catalysis; glycerol oxidation; gold; nanoshells; surface-enhanced Raman spectroscopy

Gold nanoparticles for cleaning contaminated water

Co-reporter:Huifeng Qian;Lori A. Pretzer;Juan C. Velazquez;Zhun Zhao

Journal of Chemical Technology and Biotechnology 2013 Volume 88( Issue 5) pp:735-741

Publication Date(Web):

DOI:10.1002/jctb.4030

Abstract

Pollutants in the form of heavy metals, fertilizers, detergents, and pesticides have seriously reduced the supply of pure drinking water and usable water. Gold metal has intriguing potential to deal with the water pollution problem, as recent research on several fronts is advancing the concept of nanoscale gold as the basis for cost-effective nanotechnology-based water treatment. Nano-gold has special properties, such as enhanced catalytic activity, visible surface plasmon resonance color changes, and chemical stability, that make it more useful than other materials. This Perspective article highlights the current use of gold nanoparticles for the efficient removal and the selective and sensitive detection of a variety of pollutants in water. The challenges in further developing nano-gold to address water contamination are discussed, which should stimulate future research into improved removal and detection of undesirable chemical compounds. © 2013 Society of Chemical Industry

Light-Triggered Biocatalysis Using Thermophilic Enzyme–Gold Nanoparticle Complexes

Co-reporter:Matthew D. Blankschien, Lori A. Pretzer, Ryan Huschka, Naomi J. Halas, Ramon Gonzalez, and Michael S. Wong

ACS Nano 2013 Volume 7(Issue 1) pp:654

Publication Date(Web):December 13, 2012

DOI:10.1021/nn3048445

The use of plasmonic nanoparticle complexes for biomedical applications such as imaging, gene therapy, and cancer treatment is a rapidly emerging field expected to significantly improve conventional medical practices. In contrast, the use of these types of nanoparticles to noninvasively trigger biochemical pathways has been largely unexplored. Here we report the light-induced activation of the thermophilic enzyme Aeropyrum pernix glucokinase, a key enzyme for the decomposition of glucose via the glycolysis pathway, increasing its rate of reaction 60% with light by conjugating the enzyme onto Au nanorods. The observed increase in enzyme activity corresponded to a local temperature increase within a calcium alginate encapsulate of ∼20 °C when compared to the bulk medium maintained at standard, nonthermophilic temperatures. The encapsulated nanocomplexes were reusable and stable for several days, making them potentially useful in industrial applications. This approach could significantly improve how biochemical pathways are controlled for in vitro and, quite possibly, in vivo use.Keywords: alginate; nanorod; thermophilic enzyme; thermophilic enzyme−photothermal gold nanoparticles

Water-Phase Synthesis of Cationic Silica/Polyamine Nanoparticles

Co-reporter:Quang X. Nguyen, T. Grant Belgard, John J. Taylor, Vinit S. Murthy, Naomi J. Halas, and Michael S. Wong

Chemistry of Materials 2012 Volume 24(Issue 8) pp:1426

Publication Date(Web):April 3, 2012

DOI:10.1021/cm203132m

Silica particles are commonly functionalized with amine groups on their surface through the hydrolytic condensation of aminotrialkoxysilanes for use in bioimaging, enzyme immobilization, and other applications. Eliminating this aminotrialkoxysilane condensation step could simplify and improve the efficiency of the synthesis of amine-functionalized silica. Here, we describe a one-pot, ambient-condition, water-phase method to synthesize silica-based nanoparticles (NPs) that present surface amine groups. The formation mechanism involves the electrostatic cross-linking of cationic polyallylamine hydrochloride by citrate anions and the infusion of the resulting polymer/salt aggregates by silicic acid. The particles were unimodal with average diameters in the range of 40 to 100 nm, as determined by the size of the templating polymer-salt aggregates. Colorimetric analysis using Coomassie brilliant blue and zeta potential measurements confirmed the presence of surface amine groups on the hybrid silica/polymer NPs. The point of zero-charge value for these NPs was ∼5, between the corresponding values of unfunctionalized and aminopropyltriethoxysilane-functionalized silica particles (∼2 and ∼10, respectively). Surface charge calculations indicated the hybrid NPs had a lower amine surface density than aminopropyltriethoxysilane-functionalized silica (0.057 #/nm2 vs 0.169 #/nm2 at pH 7). The polymer-salt aggregate synthesis chemistry is a new approach toward controlling the amine surface density and point of zero-charge of hybrid silica/polymer NPs.Keywords: citrate; composite; hybrid; nanoparticles; PAH; polymer; silica;

Understanding the Solvent Polarity Effects on Surfactant-Capped Nanoparticles

Co-reporter:Sukit Leekumjorn, Sravani Gullapalli, and Michael S. Wong

The Journal of Physical Chemistry B 2012 Volume 116(Issue 43) pp:13063-13070

Publication Date(Web):October 22, 2012

DOI:10.1021/jp307985c

Understanding the molecular interactions between suspended nanoparticles (NPs) and the suspending solvent fluid may provide a useful avenue to create and to study exotic NP ensembles. This study focused on using a coarse-grained computational model to investigate the molecular interactions between oleate-capped NPs in various solvents, and to relate the results to experimental features of solvent-suspended, oleate-capped CdSe quantum dots (QDs). The QDs were modeled as a closed-shell fullerene molecule with an oleate-like ligand attached to each vertex. Solvent polarity was found to correlate to the simulation and experimental results more strongly than either dielectric constant or dipole moment. Computational results showed that the nonpolar solvents of hexane, toluene, and benzene (polarity index ETN < 0.120) kept NPs in suspension and solvated the oleate chains such that the oleate layer swelled to full extension. In contrast, as the most polar solvent tested (ETN = 1.000), water caused NPs to aggregate and precipitate. It partially solvated the oleate chains and compressed the layer to 86% of full extension. For solvents of intermediate polarity like ethanol, acetone, and chloroform, the oleate layer swelled with decreasing polarity index values, with rapid swelling occurring close to ETN = 0.307 (∼50:50 vol % chloroform/acetone) below which QDs were colloidally stable. This study represents the first attempt to delineate the solvent effect on surfactant-coated NP hydrodynamic size, colloidal stability, and aggregation behavior.

Solvothermal Synthesis of Ultrasmall Tungsten Oxide Nanoparticles

Co-reporter:Nikolaos Soultanidis, Wu Zhou, Christopher J. Kiely, and Michael S. Wong

Langmuir 2012 Volume 28(Issue 51) pp:17771-17777

Publication Date(Web):December 11, 2012

DOI:10.1021/la3029462

The synthesis of catalytically useful, ultrasmall oxide nanoparticles (NPs) of group 5 and 6 metals is not readily achievable through reported methods. In this work, we introduce a one-pot, two-precursor synthesis route to <2 nm MOx NPs in which a polyoxometalate salt is decomposed thermally in a high-boiling organic solvent oleylamine. The use of ammonium metatungstate resulted in oleylamine-coated, crystalline WOx NPs at consistently high yields of 92 ± 5%. The semicrystalline NPs contained 20–36 WOx structural units per particle, as determined from aberration-corrected high-resolution scanning transmission electron microscopy, and an organic coating of 16–20 oleylamine molecules, as determined by thermogravimetric analysis. The NPs had a mean size of 1.6 ± 0.3 nm, as estimated from atomic force microscopy and small-angle X-ray scattering measurements. Carrying out the synthesis in the presence of organic oxidant trimethylamine N-oxide led to smaller WOx NPs (1.0 ± 0.4 nm), whereas the reductant 1,12-dodecanediol led to WOx nanorods (4 ± 1 nm × 20 ± 5 nm). These findings provide a new method to control the size and shape of transition metal oxide NPs, which will be especially useful in catalysis.

Engineered nanoparticles for hydrocarbon detection in oil-field rocks

Co-reporter:Jacob M. Berlin, Jie Yu, Wei Lu, Erin E. Walsh, Lunliang Zhang, Ping Zhang, Wei Chen, Amy T. Kan, Michael S. Wong, Mason B. Tomson and James M. Tour

Energy & Environmental Science 2011 vol. 4(Issue 2) pp:505-509

Publication Date(Web):03 Dec 2010

DOI:10.1039/C0EE00237B

Polyvinyl alcohol functionalized oxidized carbon black efficiently carries a hydrophobic compound through a variety of oil-field rock types and releases the compound when the rock contains hydrocarbons.

Kinetics Analysis of Palladium/Gold Nanoparticles as Colloidal Hydrodechlorination Catalysts

Co-reporter:Yu-Lun Fang, Kimberly N. Heck, Pedro J. J. Alvarez, and Michael S. Wong

ACS Catalysis 2011 Volume 1(Issue 2) pp:128

Publication Date(Web):January 18, 2011

DOI:10.1021/cs100067k

The aqueous-phase hydrodechlorination (HDC) of trichloroethene (TCE) is an important chemical reaction for water pollution control, for which unsupported palladium-on-gold and palladium nanoparticles (Pd/Au and Pd NPs) definitively show the beneficial effects of gold on palladium catalysis. The observed batch reactor kinetics can be erroneously oversimplified when concentration and mass transfer effects are neglected. A comprehensive treatment of NP catalysis is presented here using Pd-based NPs as the catalytic colloid and TCE HDC as the model reaction. Mass transfer effects were quantified for three specific compositions (Pd/Au NPs with 30% and 60% Pd surface coverages, and pure Pd NPs) by analyzing the observed reaction rates as functions of stirring rate and initial catalyst charge. The largest effect on observed reaction rates came from gas−liquid mass transfer. The TCE HDC reaction was modeled as a Langmuir−Hinshelwood mechanism involving competitive chemisorption of dihydrogen and TCE for all three NP compositions. Differences in adsorption affinities of the reactant molecules for the Pd/Au and Pd surfaces are suggested as responsible for the observed difference in TCE reaction order at high TCE concentrations; that is, first-order for Pd/Au NPs and non-first-order for Pd NPs.Keywords (keywords): gold; hydrodechlorination; kinetics; Langmuir−Hinshelwood; mass transfer; nanoparticle catalysis; palladium; trichloroethene

Shell Thickness Control of Nanoparticle/Polymer Assembled Microcapsules

Co-reporter:Hitesh G. Bagaria, Shyam B. Kadali, and Michael S. Wong

Chemistry of Materials 2011 Volume 23(Issue 2) pp:301

Publication Date(Web):December 29, 2010

DOI:10.1021/cm102472h

Organic/inorganic composite microcapsules can be produced in water through a two-step charge-driven assembly of polyallylamine, citrate anions, and 13 nm silica nanoparticles. The shell is composed of nanoparticles intermixed with polymer, and is thick enough (100s of nm) to provide structural stability before or after drying. Controlling shell thickness, however, is currently difficult to perform. Presented here is a new method in which the shell wall can be thickened by contacting the as-synthesized capsules with silicic acid. This shell thickening was observed and quantified for a moderately broad, unimodal size distribution of capsular particles, through a combination of transmission electron and confocal fluorescence microscopies. Thermogravimetric analysis confirmed the deposition of additional silica, and Coulter counter measurements showed the mean capsule diameter of ∼4.5 ± 2.2 μm changed negligibly with silicic acid treatment. The shell-thickening process occurred in an inward direction, in which the nanosized silicic acid oligomers most likely diffused through the permeable capsule wall and deposited within the wall and on the inner shell wall surface. Adjustable shell wall thicknesses in hybrid microcapsules provide enhanced capability for chemical encapsulation, storage, and release applications.

Polyamine–salt aggregate assembly of capsules as responsive drug delivery vehicles

Co-reporter:Hitesh G. Bagaria and Michael S. Wong

Journal of Materials Chemistry A 2011 vol. 21(Issue 26) pp:9454-9466

Publication Date(Web):24 May 2011

DOI:10.1039/C1JM10712G

Responsive capsular delivery systems that can partly mimic the complexity of cellular systems hold great promise for the future of medicine. Simple self-assembled systems like liposomes are already in clinical use and others like polymeric micelles are under clinical trials. Unlike these self-assembled systems, the greater flexibility and versatility offered by template-based routes will likely drive the development of sophisticated capsules. The focus of this review is to introduce one such template-based route, which is based on polyamine–salt aggregate or ‘PSA’ assembly. The basic synthesis premise involves the assembly of cationic polymer (like poly-L-lysine) by ionic crosslinking with multivalent anionic salts (like citrate) into metastable templates for cargo encapsulation and shell material deposition. The technique offers several benefits: (i) the synthesis procedure involves simple mixing at ambient conditions, (ii) the capsule size is easy to control in the sub-100 nm to micron range, and (iii) a wide range of formulations is readily available with the use of different polymer, salt, cargo, and shell-forming precursors. In this review, the current state of this technique, the materials chemistry of the capsule assembly, and the demonstrated applications, including photothermal therapy, MRI contrast agent development and protease-responsive NIR imaging, will be discussed.

Self-Assembly and Nanotechnology: Real-Time, Hands-On, and Safe Experiments for K-12 Students

Co-reporter:Hitesh G. Bagaria, Michelle R. Dean, Carolyn A. Nichol, and Michael S. Wong

Journal of Chemical Education 2011 Volume 88(Issue 5) pp:609-614

Publication Date(Web):March 14, 2011

DOI:10.1021/ed100598y

What students and teachers often ask is, how are nano-sized materials made when they are so small? One answer is through the process of self-assembly in which molecules, polymers, and nanoparticles connect to form larger objects of a defined structure and shape. Two hands-on experiments are presented in which students prepare capsules in real time using simple and safe ingredients and study the materials for encapsulation and release of food coloring dye. These experiments are visual and interactive demonstrations of self-assembly (as a synthesis tool) and nanotechnology (in which nanomaterial can be made to perform useful functions), and build on the concepts of acid−base chemistry and electrostatic interaction.Keywords: Acids/Bases; Dyes/Pigments; Elementary/Middle School Science; First-Year Undergraduate/General; Hands-On Learning/Manipulatives; High School/Introductory Chemistry; Laboratory Instruction; Materials Science; Nanotechnology; Noncovalent Interactions; Physical Chemistry;

Self-Assembly Synthesis, Tumor Cell Targeting, and Photothermal Capabilities of Antibody-Coated Indocyanine Green Nanocapsules

Co-reporter:Jie Yu ; David Javier ; Mohammad A. Yaseen ; Nitin Nitin ; Rebecca Richards-Kortum ; Bahman Anvari

Journal of the American Chemical Society 2010 Volume 132(Issue 6) pp:1929-1938

Publication Date(Web):January 21, 2010

DOI:10.1021/ja908139y

New colloidal materials that can generate heat upon irradiation are being explored for photothermal therapy as a minimally invasive approach to cancer treatment. The near-infrared dye indocyanine green (ICG) could serve as a basis for such a material, but its encapsulation and subsequent use are difficult to carry out. We report the three-step room-temperature synthesis of ∼120-nm capsules loaded with ICG within salt-cross-linked polyallylamine aggregates, and coated with antiepidermal growth factor receptor (anti-EGFR) antibodies for tumor cell targeting capability. We studied the synthesis conditions such as temperature and water dilution to control the capsule size and characterized the size distribution via dynamic light scattering and scanning electron microscopy. We further studied the specificity of tumor cell targeting using three carcinoma cell lines with different levels of EGFR expression and investigated the photothermal effects of ICG containing nanocapsules on EGFR-rich tumor cells. Significant thermal toxicity was observed for encapsulated ICG as compared to free ICG at 808 nm laser irradiation with radiant exposure of 6 W/cm2. These results illustrate the ability to design a colloidal material with cell targeting and heat generating capabilities using noncovalent chemistry.

Relating n-Pentane Isomerization Activity to the Tungsten Surface Density of WOx/ZrO2

Co-reporter:Nikolaos Soultanidis ; Wu Zhou ; Antonis C. Psarras ; Alejandro J. Gonzalez ; Eleni F. Iliopoulou ; Christopher J. Kiely ; Israel E. Wachs

Journal of the American Chemical Society 2010 Volume 132(Issue 38) pp:13462-13471

Publication Date(Web):September 3, 2010

DOI:10.1021/ja105519y

Zirconia-supported tungsten oxide (WOx/ZrO2) is considered an important supported metal oxide model acid catalyst, for which structure−property relationships have been studied for numerous acid-catalyzed reactions. The catalytic activity for xylene isomerization, alcohol dehydration, and aromatic acylation follows a volcano-shape dependence on tungsten surface density. However, WOx/ZrO2 has not been studied for more acid-demanding reactions, like n-pentane isomerization, with regard to surface density dependence. In this work, WOx/ZrO2 was synthesized using commercially available amorphous ZrOx(OH)4−2x and model crystalline ZrO2 as support precursors. They were analyzed for n-pentane isomerization activity and selectivity as a function of tungsten surface density, catalyst support type, and calcination temperature. Amorphous ZrOx(OH)4−2x led to WOx/ZrO2 (WZrOH) that exhibited maximum isomerization activity at ∼5.2 W·nm−2, and the crystalline ZrO2 led to a material (WZrO2) nearly inactive at all surface densities. Increasing the calcination temperature from 773 to 973 K increased the formation of 0.8−1 nm Zr-WOx clusters detected through direct imaging on an aberration-corrected high-resolution scanning transmission electron microscope (STEM). Calcination temperature further increased catalytic activity by at least two times. Brønsted acidity was not affected but Lewis acidity decreased in number, as quantified via pyridine adsorption infrared spectroscopy. WOx/ZrO2 exhibited isomerization activity that peaked within the first 2 h time-on-stream, which may be due to Zr-WOx clusters undergoing an activation process.

CdSe tetrapod synthesis using cetyltrimethylammonium bromide and heat transfer fluids

Co-reporter:Wen Yin Lynn Ko, Hitesh G. Bagaria, Subashini Asokan, Kuan-Jiuh Lin and Michael S. Wong

Journal of Materials Chemistry A 2010 vol. 20(Issue 12) pp:2474-2478

Publication Date(Web):11 Feb 2010

DOI:10.1039/B922145J

The synthesis of CdSe tetrapod-shaped quantum dots using phenyl-based heat transfer fluids as inexpensive alternatives to octadecene solvent was studied. The CdSe tetrapods were synthesized using the hot-injection method, in which the trioctylphosphine selenide precursor and the shape-inducing cetyltrimethylammonium bromide surfactant were injected into a cadmium oleate-containing solvent at 190 °C. At a synthesis temperature of 160 °C, the resulting quantum dot particles were found to grow more slowly in heat transfer fluids and pure phenyl-type solvents than in octadecene. With synthesis time, the selectivity to tetrapods increased, and the arms grew proportionally in width and length. The use of heat transfer fluids provides a convenient means to control growth of shaped nanoparticles.

Microfluidic Formation of Ionically Cross-Linked Polyamine Gels

Co-reporter:Gautam C. Kini, Justin Lai, Michael S. Wong and Sibani Lisa Biswal

Langmuir 2010 Volume 26(Issue 9) pp:6650-6656

Publication Date(Web):January 15, 2010

DOI:10.1021/la903983y

In this article, we discuss in situ polymer gelation in microfluidic channels from electrostatically mediated interactions when reactant streams of a linear cationic polymer (poly(allylamine hydrochloride, PAH) and a multivalent anion (sodium citrate) are subjected to shear flow. We find that the polyamine exhibits shear-thickening behavior as it is ionically cross-linked by citrate ions to form viscoelastic gel phases. These gels form at room temperature and remain stable and intact after the cessation of flow. Gelation is found to occur in the polymer stream and not the citrate stream because of an appreciably higher diffusivity of citrate ions when compared to the gel and PAH and because of laminar flow conditions in the microfluidic environment. Gel formation occurred when the pH of the PAH stream was below the PAH pKa value of 8.38 and when citrate was either in a disodium or trisodium state. The formation of aggregates, gels, and droplets was found to depend strongly on the charge ratio and flow conditions. The gelation of PAH begins with the formation of colloidal aggregates of PAH and citrate, which then combine under shear flow to form noncontinuous or continuous gels. Droplets of citrate can form within regions of continuous gels as excess citrate anions diffuse into the gel stream.

Controlled Growth of Sub-10 nm Gold Nanoparticles Using Carbon Monoxide Reductant

Co-reporter:Lori A. Pretzer ; Quang X. Nguyen

The Journal of Physical Chemistry C 2010 Volume 114(Issue 49) pp:21226-21233

Publication Date(Web):November 16, 2010

DOI:10.1021/jp107945d

There is a need to develop aqueous-phase synthesis methods of sub-10-nm Au nanoparticles (NPs), given their many exciting possibilities in catalysis, sensing, biomedical, and other water-based applications. Synthesizing Au NPs by reducing Au salt onto preformed NPs as seeds is a useful approach because final particle size can be finely predicted and controlled, though few studies have reported successful synthesis of Au NPs in the 1 and 10 nm size range. Here we report that water-suspended Au particles with a diameter ∼2.8 nm can be grown as large as ∼12 nm with sub-nanometer control, as verified through detailed ultraviolet−visible spectroscopy, small-angle X-ray scattering, and transmission electron microscopy measurements. With carbon monoxide as the reducing agent, this seeded-growth method results in colloidally stable Au sols. The reaction mechanism most likely involves the catalyzed oxidation of CO into CO2 accompanied by electron transfer to the gold hydroxide-chloride ionic species through the growing particle.

Electrolyte Solutions Improve Nanoparticle Transfer from Oil to Water

Co-reporter:Hitesh G. Bagaria, Gautam C. Kini, and Michael S. Wong

The Journal of Physical Chemistry C 2010 Volume 114(Issue 47) pp:19901-19907

Publication Date(Web):November 5, 2010

DOI:10.1021/jp106140j

Many techniques to transfer NPs from the oil phase into the water phase have been developed, but all have limitations that remain to be addressed, specifically low transfer yields and partial NP aggregation. One of the transfer processes involves emulsifying an oil suspension of NPs in water with surfactants, followed by evaporation of the oil to produce water suspensions of surfactant-encapsulated NPs. We show here that using salt solutions instead of deionized water significantly improves this emulsion-based transfer process. With oleate-coated CdSe quantum dots as a model NP system, hexane as the oil phase, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as the emulsifying surfactant, and NaCl solution as the water phase, the resultant aqueous suspensions exhibit months-long photoluminescence stability, near 100% phase-transfer yield, and nonaggregation. These benefits are attributed to a more laterally packed AOT layer surrounding the NP, as supported by zeta-potential measurements, surface-charge calculations, thermogravimetry, and Nile Red fluorescence analysis. The new phase-transfer method is general for a variety of NP, surfactant, and salt types.

Polyamine-Guided Synthesis of Anisotropic, Multicompartment Microparticles

Co-reporter:Vinit S. Murthy, Shyam B. Kadali and Michael S. Wong

ACS Applied Materials & Interfaces 2009 Volume 1(Issue 3) pp:590

Publication Date(Web):February 20, 2009

DOI:10.1021/am8001499

Colloidal particles that have nonuniform bulk or surface compositions are of emerging interest because of their potential applications involving advanced chemical storage and delivery and the self-assembly of novel functional materials. Experimental realization of anisotropic particles is much more difficult than that for particles with uniform bulk and surface composition, however. A new wet-chemical synthesis method to anisotropic microparticles is presented. This approach makes convenient use of the unusual observation of a salt-triggered separation of two water-solubilized polyamines into colloidal aggregates with nonuniform polymer composition. The anisotropic structure of these ionically cross-linked aggregates is explained by the difference in surface tensions of the contained single-polymer domains. Contacting the polymer aggregates with silicic acid or 13-nm silica nanoparticles leads to the charge-driven formation of solid or hollow microspheres, respectively. Depending on the poly(lysine)/poly(allylamine) ratio, the nonuniformity of the polymer aggregates translates to surface patches or internal compartments found in the resultant silica/polymer microparticles. Such hybrid materials with their unique structure could serve as a new basis for targeted chemical delivery and controlled release for potential applications in medicine, food, and cosmetics.Keywords: assembly; carbon/silicon/oxides; colloidal; hybrid; materials; nanoparticles; polymers; silica

Cleaner water using bimetallic nanoparticle catalysts

Co-reporter:Michael S. Wong;Pedro J. J. Alvarez;Yu-lun Fang;Nurgül Akçin;Michael O. Nutt;Jeffrey T. Miller;Kimberly N. Heck

Journal of Chemical Technology and Biotechnology 2009 Volume 84( Issue 2) pp:158-166

Publication Date(Web):

DOI:10.1002/jctb.2002

Abstract

Groundwater contaminated by hazardous chlorinated compounds, especially chlorinated ethenes, continues to be a significant environmental problem in industrialized nations. The conventional treatment methods of activated carbon adsorption and air-stripping successfully remove these compounds by way of transferring them from the water phase into the solid or gas phase. Catalysis is a promising approach to remove chlorinated compounds completely from the environment, by converting them into safer, non-chlorinated compounds. Palladium-based materials have been shown to be very effective as hydrodechlorination catalysts for the removal of chlorinated ethenes and other related compounds. However, relatively low catalytic activity and a propensity for deactivation are significant issues that prevent their widespread use in groundwater remediation. Palladium-on-gold bimetallic nanoparticles, in contrast, were recently discovered to exhibit superior catalyst activity and improved deactivation resistance. This new type of material is a significant next-step in the development of a viable hydrodechlorination catalysis technology. Copyright © 2008 Society of Chemical Industry

Assembling Colloidal Silica into Porous Hollow Microspheres

Co-reporter:Shyam B. Kadali;Nikolaos Soultanidis

Topics in Catalysis 2008 Volume 49( Issue 3-4) pp:251-258

Publication Date(Web):2008 August

DOI:10.1007/s11244-008-9079-y

A non-surfactant-based synthesis approach to mesoporous hollow spheres through the use of colloidal silica is presented. Based on nanoparticle assembly chemistry developed previously for silica/polymer hybrid microcapsules, the room-temperature preparation follows a two-step sequence: (1) the electrostatic reaction of cationic polymer with an anionic salt solution, resulting in a suspension of salt-bridged polymer aggregates; and (2) the electrostatic reaction between this suspension and an aqueous suspension of nanoparticles (NPs). As a specific example, 13-nm silica particles, combined with polyallylamine and sodium citrate, gave silica/polymer hollow spheres with a mean diameter of 2.1 μm and a BET surface area of 4 m2/g. After calcination at 600 °C, the resulting silica-only microcapsules had a BET surface area of 259 m2/g, a modal pore size of 4.0 nm, and a pore volume of 0.38 cc/g, values that exceeded those of calcined silica NPs. This colloidal silica-based material is an example of the simultaneous control of pore size (at the nanometer scale) and particle morphology (at the micrometer scale) that is possible through charge-driven NP assembly.

Towards an in vivo biologically inspired nanofactory

Co-reporter:

Nature Nanotechnology 2007 2(1) pp:

Publication Date(Web):2007-01-01

DOI:10.1038/nnano.2006.180

Nanotechnology is having a major impact on medicine and the treatment of disease, notably in imaging and targeted drug delivery. It may, however, be possible to go even further and design 'pseudo-cell' nanofactories that work with molecules already in the body to fight disease.

Synthesis of nanoparticle-assembled tin oxide/polymer microcapsules

Co-reporter:Jie Yu, Vinit S. Murthy, Rohit K. Rana and Michael S. Wong

Chemical Communications 2006 (Issue 10) pp:1097-1099

Publication Date(Web):30 Jan 2006

DOI:10.1039/B513901E

Tin oxide nanoparticles can be assembled into micron-sized hollow capsule structures through a simple mixing procedure based on charge-mediated polymer aggregate templating.

Nanoparticle Self-Assembly of Hierarchically Ordered Microcapsule Structures

Co-reporter:R. K. Rana;V. S. Murthy;J. Yu;M. S. Wong

Advanced Materials 2005 Volume 17(Issue 9) pp:

Publication Date(Web):25 APR 2005

DOI:10.1002/adma.200401612

Microcapsules with multilayer-thick shells are synthesized by depositing negatively charged nanoparticles around cationic polyamine aggregates crosslinked by multivalent counteranions (see Figure and inside cover). Unique among hollow-sphere preparative routes, this rapid and green synthesis leads to a robust organic/inorganic hybrid structure, applies to a wide spectrum of colloidal species, and permits the non-destructive encapsulation of water-soluble compounds.

Inside Front Cover: Nanoparticle Self-Assembly of Hierarchically Ordered Microcapsule Structures (Adv. Mater. 9/2005)

Co-reporter:R. K. Rana;V. S. Murthy;J. Yu;M. S. Wong

Advanced Materials 2005 Volume 17(Issue 9) pp:

Publication Date(Web):25 APR 2005

DOI:10.1002/adma.200590047

Nanoparticle (NP)-assembled microcapsules represent a new class of hollow-sphere material, in which materials properties can be ‘programmed’ by way of NP and polymer compositions. Synthesis is based on a sequential self-assembly of NPs and polymer macromolecules. Reported by Wong and co-workers on p. 1145, this rapid, green synthesis technique applies to a wide spectrum of colloidal species and permits non-destructive encapsulation of water-soluble compounds. The inside cover shows a confocal microscopy image of water-filled microcapsules composed of silica NPs and a fluorescence-labelled polymer. The scale bar is 20 μm. The inset shows a simplified illustration of the microcapsule assembly process.

Hydrodechlorination catalysis of Pd-on-Au nanoparticles varies with particle size

Co-reporter:Lori A. Pretzer, Hyun J. Song, Yu-Lun Fang, Zhun Zhao, Neng Guo, Tianpin Wu, Ilke Arslan, Jeffrey T. Miller, Michael S. Wong

Journal of Catalysis (February 2013) Volume 298() pp:206-217

Publication Date(Web):1 February 2013

DOI:10.1016/j.jcat.2012.11.005

Trichloroethene (TCE), a common carcinogen and groundwater contaminant in industrialized nations, can be catalytically degraded by Au nanoparticles partially coated with Pd (“Pd-on-Au NPs”). In this work, we synthesized Pd-on-Au NPs using 3, 7, and 10 nm Au NPs with Pd surface coverages between 0–150% and studied how particle size and composition influenced their TCE hydrodechlorination (HDC) activity. We observed volcano-shape dependence on both Au particle size and Pd surface coverage, with 7 nm Au NPs with Pd coverages of 60–70% having maximum activity. Using extended X-ray absorption fine-structure spectroscopy, we found a strong correlation between catalytic activity and the presence of 2-D Pd ensembles (as small as 2–3 atoms). Aberration-corrected scanning transmission electron microscopy further confirmed the presence of Pd ensembles. The Pd dispersion and oxidation state generally changed from isolated, metallic Pd atoms to metallic 2-D Pd ensembles of varying sizes, and to partially oxidized 3-D Pd ensembles, as Pd surface coverage increased. These changes occurred at different surface coverages for different Au particle sizes. These findings highlight the importance of controlling particle size and surface coverage in bimetallic catalysts.Graphical abstractThe groundwater clean-up reaction of trichloroethene hydrodechlorination, catalyzed by Pd-on-Au nanoparticles, varies with volcano-shape dependence on both Au particle size and Pd surface coverage. Pd takes several forms on the nanoparticle surface, with metallic two-dimensional ensembles found in the most active catalyst compositions.Download high-res image (82KB)Download full-size imageHighlights► Aqueous trichloroethene hydrodechlorination is most rapid with 7 nm Pd-on-Au particles. ► Catalysis of palladium-on-gold nanoparticles changes with Au particle size. ► Volcano-shape dependence on both Au particle size and Pd surface coverage is seen. ► Metallic two-dimensional Pd ensembles correlate with high catalytic activity.

Deactivation resistance of Pd/Au nanoparticle catalysts for water-phase hydrodechlorination

Co-reporter:Kimberly N. Heck, Michael O. Nutt, Pedro Alvarez, Michael S. Wong

Journal of Catalysis (25 October 2009) Volume 267(Issue 2) pp:97-104

Publication Date(Web):25 October 2009

DOI:10.1016/j.jcat.2009.07.015

Palladium-decorated gold nanoparticles (Pd/Au NPs) have recently been shown to be highly efficient for trichloroethene hydrodechlorination, as a new approach in the treatment of groundwater contaminated with chlorinated solvents. Problematically, natural groundwater can contain chloride and sulfide ions, which are known poisons in Pd-based catalysis. In this study, the effects of chloride and sulfide on the trichloroethene hydrodechlorination catalytic activity were examined for non-supported Pd/Au NPs and Pd NPs, and alumina-supported Pd (Pd/Al2O3). Over the concentration range of 0–0.02 M NaCl, the catalytic activity of Pd/Au NPs was unaffected, while the activities of both the Pd NPs and Pd/Al2O3 catalysts dropped by ∼70%. Pd/Au NPs were found to be highly resistant to sulfide poisoning, deactivating completely at a ratio of sulfide to surface Pd atom (S:Pdsurf) of at least 1, compared to Pd NPs deactivating completely at a ratio of 0.5. Pd/Al2O3 retained activity at a ratio of 0.5, pointing to a beneficial role of the Al2O3 support. Sulfide poisoning of Pd/Au NPs with different Pd surface coverages provided a way to assess the nature of active sites. The gold component was found to enhance both Pd catalytic activity and poisoning resistance for room-temperature, water-phase trichloroethene hydrodechlorination.The effects of chloride and sulfide on water-phase trichloroethene hydrodechlorination using Pd-on-Au nanoparticles (Pd/Au NPs), Pd NPs, and alumina-supported Pd were studied. Pd/Au NPs were resistant to chloride poisoning unlike monometallic Pd, and they showed greater resistance to sulfide poisoning than monometallic Pd. Lower Pd content surface coverages led to less activity but resistance to sulfide poisoning.Download high-res image (94KB)Download full-size image

CdSe tetrapod synthesis using cetyltrimethylammonium bromide and heat transfer fluids

Co-reporter:Wen Yin Lynn Ko, Hitesh G. Bagaria, Subashini Asokan, Kuan-Jiuh Lin and Michael S. Wong

Journal of Materials Chemistry A 2010 - vol. 20(Issue 12) pp:NaN2478-2478

Publication Date(Web):2010/02/11

DOI:10.1039/B922145J

Polyamine–salt aggregate assembly of capsules as responsive drug delivery vehicles

Co-reporter:Hitesh G. Bagaria and Michael S. Wong

Journal of Materials Chemistry A 2011 - vol. 21(Issue 26) pp:NaN9466-9466

Publication Date(Web):2011/05/24

DOI:10.1039/C1JM10712G

Volcano-shape glycerol oxidation activity of palladium-decorated gold nanoparticles

Co-reporter:Zhun Zhao, Joni Arentz, Lori A. Pretzer, Pongsak Limpornpipat, James M. Clomburg, Ramon Gonzalez, Neil M. Schweitzer, Tianpin Wu, Jeffrey T. Miller and Michael S. Wong

Chemical Science (2010-Present) 2014 - vol. 5(Issue 10) pp:NaN3728-3728

Publication Date(Web):2014/06/02

DOI:10.1039/C4SC01001A