Abstracts for Publications 41-60
57. W. Zhou, E. I. Ross-Medgaarden, W. V. Knowles, M. S. Wong, I. E. Wachs
and C. J. Kiely, "Identification of active Zr–WOx clusters on a
ZrO2 support for solid acid catalysts," Nature Chem. (online) (2009). DOI:10.1038/NCHEM.433 Tungstated zirconia is a robust solid acid catalyst for light alkane (C4–C8) isomerization. Several structural models for catalytically active sites have been proposed, but the topic remains controversial, partly because of the absence of direct structural imaging information on the various supported WOx species. High-angle annular dark-field imaging of WO3/ZrO2 catalysts in an aberration-corrected analytical electron microscope allows, for the first time, direct imaging of the various species present. Comparison of the relative distribution of these WOx species in materials showing low and high catalytic activities has allowed the deduction of the likely identity of the catalytic active site—namely, subnanometre Zr–WOx clusters. This information has subsequently been used in the design of new catalysts, in which the activity of a poor catalyst has been increased by two orders of magnitude using a synthesis procedure that deliberately increases the number density of catalytically relevant active species. |
56. S. E. Plush, M. Woods, Y. Zhou, S. B. Kadali, M. S. Wong and A. D. Sherry, "Nanoassembled Capsules as Delivery Vehicles for Large Payloads of High Relaxivity Gd3+ Agents,"J. Am. Chem. Soc., 131(43), 15918–15923 (2009). DOI:10.1021/ja906981w
Nanoassembled capsules (NACs) that incorporate a polymer aggregate inside a silica shell may be loaded with agents that are of particular interest for therapeutic or diagnostic applications. NACs formed using the MRI contrast agent GdDOTP5− in the internal polymer aggregate are reported herein, the smaller of which show promise as potential MRI contrast agents. Unlike many other nanoencapsulated systems, water access to the inner core of these NACs does not appear to be limited and consequently the water relaxivity per Gd3+ agent can reach as high as 24 mM−1 s−1. Robust, spherical capsules were formed using polyallylamine or poly-l-lysine ranging from 0.2 to 5 μm in diameter. The greatest gains in relaxivity were observed for smaller NACs, for which water accessibility remained high but molecular rotation of the Gd3+ chelate was effectively restricted. Larger NACs did not afford such large gains in relaxivity, the result of poorer water accessibility combined with less-effective rotational restriction. |
55. M. A. Yaseen, J. Yu, B. Jung, M. S. Wong, and B. Anvari, "Biodistribution of Encapsulated
Indocyanine green (ICG) is a fluorescent probe used in various optically mediated diagnostic and therapeutic applications. However, utility of ICG remains limited by its unstable optical properties and nonspecific localization. We have encapsulated ICG within electrostatically assembled mesocapsules (MCs) to explore its potential for targeted optical imaging and therapy. In this study, we investigate how the surface coating and size of the MCs influences ICG’s biodistribution in vivo. ICG was administered intravenously to Swiss Webster mice as a free solution or encapsulated within either 100 nm diameter MCs coated with dextran; 500 nm diameter MCs coated with dextran; or 100 nm diameter MCs coated with 10 nm ferromagnetic iron oxide nanoparticles, themselves coated with polyethylene glycol. ICG was extracted from harvested blood and organs at various times and its amount quantified with fluorescence measurements. MCs containing ICG accumulated in organs of the reticuloendothelial system, namely, the liver and spleen, as well as the lungs. The circulation kinetics of ICG appeared unaffected by encapsulation; however, the deposition within organs other than the liver suggests a different biodistribution mechanism. Results suggest that the capsules’ coating influences their biodistribution to a greater extent than their size. The MC encapsulation system allows for delivery of ICG to organs other than the liver, enabling the potential development of new optical imaging and therapeutic strategies. |
54. K. N. Heck, M. O. Nutt, P. Alvarez, and M. S. Wong, "Deactivation Resistance of Pd/Au 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 catalyst 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. Graphical Abstract: 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.
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53. S. Leekumjorn and M. S. Wong, "Self-assembly of Nanoparticle Building Blocks," in Sukit Leekumjorn and Michael S. Wong This chapter provides an overview of recent experimental and simulations work in the self-assembly of nanoparticles into structured materials. The self-assembly of nanoparticle building blocks through substrate assembly, interfacial assembly, and template-assisted assembly is discussed. Nanoparticle-assembled capsules are highlighted as an example of template-assisted assembly. The effects of nanoparticle dimensionality, shape, and composition are discussed, with quantum dot tetrapods as a material of interest. The computational approach to nanoparticle self-assembly is reviewed and assessed. |
52. E. Muñoz Tavera, S. B. Kadali, H. G. Bagaria, A. W. Liu,and M. S. Wong ,"Experimental and Modeling Analysis of Diffusive Release from Single-shell Microcapsules," AIChE J. DOI:10.1002/aic.11914 |
51. V.S. Murthy, S.B. Kadali, and M.S. Wong, "Polyamine-Guided
Synthesis of Anisotropic, Multicompartment Microparticles," Appl. Mater. Interfac., 1, 590-596 (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. |
50. E. I. Ross-Medgaarden, I. E. Wachs, W. V. Knowles, A. Burrows,
C. J. Kiely, and M. S. Wong, "Tuning the Electronic and Molecular
Structure of Catalytic Active Sites with Titania Nanoligands," J. Am. Chem. Soc.,
131, 680-687 (2009). DOI:10.1021/ja711456c A series of supported 1−60% TiO2/SiO2 catalysts were synthesized and subsequently used to anchor surface VOx redox and surface WOx acid sites. The supported TiOx, VOx, and WOx phases were physically characterized with TEM, in situ Raman and UV−vis spectroscopy, and chemically probed with in situ CH3OH-IR, CH3OH-TPSR and steady-state CH3OH dehydration. The CH3OH chemical probe studies revealed that the surface VOx sites are redox in nature and the surface WOx sites contain acidic character. The specific catalytic activity of surface redox (VO4) and acidic (WO5) sites coordinated to the titania nanoligands are extremely sensitive to the degree of electron delocalization of the titania nanoligands. With decreasing titania domain size, <10 nm, acidic activity increases and redox activity decreases due to their inverse electronic requirements. This is the first systematic study to demonstrate the ability of oxide nanoligands to tune the electronic structure and reactivity of surface metal oxide catalytic active sites. |
49. M.S. Wong, P. J.J. Alvarez, Y.L. Fang, N. Akcin, M. O. Nutt,
J. T. Miller, and K. N. Heck, "Cleaner Water using Bimetallic Nanoparticle
Catalysts" J.
Chem. Tech. & Biotech, 84, 158-166 (2009). DOI:10.1002/jctb.2002 |
48. Q. Li, M. B. Tomson, M. S. Wong, and P. J. J. Alvarez, "Nanotechnology: A Source for No abstract yet. |
47. M.A. Yaseen, J. Yu, M.S. Wong and B. Anvari, "In-vivo
Fluorescence Imaging of Mammalian Organs using Charge-assembled Mesocapsule
Constructs Containing Indocyanine Green" Optics
Express, 16 (25), 20577-20587 (2008). DOI:10.1364/OE.16.020577 |
46. K.N. Heck, B.G. Janesko, G.E. Scuseria, N.J. Halas and M.S.Wong,
"Observing Metal-Catalyzed Chemical Reactions in Situ Using Surface-Enhanced
Raman Spectroscopy on Pd-Au Nanoshells" J. Am. Chem. Soc. , 130 (49), 16592–16600 (2008). DOI:10.1021/ja803556k Insight into the nature of transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chemical reactions is obtainable from a number of surface spectroscopic techniques. Carrying out these investigations under actual reaction conditions is preferred but remains challenging, especially for catalytic reactions that occur in water. Here, we report the direct spectroscopic study of the catalytic hydrodechlorination of 1,1-dichloroethene in H2O using surface-enhanced Raman spectroscopy (SERS). With Pd islands grown on Au nanoshell films, this reaction can be followed in situ using SERS, exploiting the high enhancements and large active area of Au nanoshell SERS substrates, the transparency of Raman spectroscopy to aqueous solvents, and the catalytic activity enhancement of Pd by the underlying Au metal. The formation and subsequent transformation of several adsorbate species was observed. These results provide the first direct evidence of the room-temperature catalytic hydrodechlorination of a chlorinated solvent, a potentially important pathway for groundwater cleanup, as a sequence of dechlorination and hydrogenation steps. More broadly, the results highlight the exciting prospects of studying catalytic processes in water in situ, like those involved in biomass conversion and proton-exchange membrane fuel cells. |
45. M. S. Wong, Book review of Nanoparticles and Catalysis D. Astruc, Ed.; Angew.
Chem. 47, 7795-7796 (2008). DOI:10.1002/anie.200785570 |
44. V. S. Murthy and M. S. Wong, "Enzyme Encapsulation
using Nanoparticle-assembled Capsules," in Nanoscale Science
and Technology in Biomolecular Catalysis; J. B. Kim, S. H. Kim,
and P. Wang, Eds., American Chemical Society: Washington, D.C.; Chapter
13, 214-232 (2008) |
43. E. I. Ross-Medgaarden, W. V. Knowles, T. Kim, M. S. Wong,
W. Zhou, C. J. Kiely, and I. E. Wachs, "New Insights into the Nature
of the Acidic Catalytic Active Sites Present in ZrO2-supported Tungsten
Oxide Catalysts," J.
Catal. 256, 108-125 (2008) DOI:10.1016/j.jcat.2008.03.003 |
42. S. B. Kadali, N. Soultanidis, and M. S. Wong, "Assembling
Colloidal Silica into Porous Hollow Microspheres," Topic.
Catal., 49 (3-4), 251-258 (2008) DOI:10.1007/s11244-008-9079-y |
41. M. A. Yaseen, J. Yu, M. S. Wong, and B. Anvari, "Laser-Induced
Heating of Dextran-Coated Mesocapsules Containing Indocyanine Green," Biotechnol.
Prog., 23 (6), 1431-1440 (2007). |
