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Synthesis and Application of Nanosize Semiconductors for Photooxidation of Toxic Organic Chemicals
Jess P. Wilcoxon, T.R. Thurston, P. Provencio, G.A.
Samara, Organization 1122, Sandia National Laboratories, Albuquerque, N.M. 87185-1421

Photooxidation of organic chemicals in water using semiconductors has been investigated for over 15 years, but has been mainly limited to one material, TiO2. I will discuss the synthesis and characterization of new types of nanoparticle semiconductors such as MoS2 and WS2 using the inverse micelle method. These layered, very chemically stable, dichalcogenides are widely employed as thermal desulfurization catalysts in crude oil refining but have, until recently, never been exploited as photocatalysts. In bulk form these black colored semiconductors have near infared bandgaps and thus hole energies which are insufficient to photooxidize organic molecules. We have demonstrated that quantum confinement of the photogenerated carriers in nanosize semiconductor MoS2 shifts these energies substantially as demonstrated a blue shift of the absorbance edge and PL emission into the visible.[1] Using liquid chromatographic (LC) analysis to follow the photooxidation process, we have shown that the photogenerated carriers in nanosize MoS2 are sufficiently energetic to completely photooxidize otherwise stable, toxic organics such as phenol and pentachlorophenol to CO2 and HCl.[2-4] LC was also used to monitor the stability and optical properties of the nanosize MoS2. We discuss both the size-dependent reaction kinetics of dispersed and supported MoS2 and compare our observations with those obtained for commercial nanomaterials such as deGussa TiO2 as well as nanosize TiO2 and SnO2. Future directions for research in this area as well as the possibility of other useful photochemical reactions such as H2S splitting using nanoclusters will be mentioned.

[1] J.P. Wilcoxon, P. Provencio, G.A. Samara, J. Appl. Phys., 81,
[2] T.R. Thurston and J.P. Wilcoxon, J. Phys. Chem., 103, 11, 1998.
[3] J.P. Wilcoxon, J. Phys. Chem., 104, 7334, 2000.
[4] J. P. Wilcoxon, "Photooxidation Method Using MoS2 Nanocluster Materials", U.S. Patent # 6,245,200, issued June 12, 2001.

Acknowledgment: This work was supported by the Division of Materials Science and Engineering, Office of Science, US Department of Energy under contract
DE-AC04-AL8500. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the US Department of Energy.

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