Photooxidation of organic wastes using semiconductor nanoclusters. 1998 annual progress report
'This report summarizes work after 1.5 years of a 3-year project. The authors efforts have focused on demonstration of photocatalysis of organic pollutants using nanosize MoS{sub 2}. They investigated the effects of (1) bandgap, valence and conduction band energies; (2) surface modification of MoS{sub 2} by deposition of metal and metal oxide islands to enhance electron transfer; and (3) use of semi-conductor semi-conductor composites to achieve improved charge separation and thus photooxidation of pollutants. They synthesized and studied nanosize MoS{sub 2} of three different sizes and associated bandgaps and studied photoredox reactions of nanosize MoS{sub 2} dispersed in solution and supported on a macroscopic powder. The latter would be the method of choice for use as a practical photocatalyst for water purification. As they emphasized in the original proposal, MoS{sub 2} in nanosize form can be tuned to absorb various amounts of the solar spectrum. They discovered there is an optimal choice of absorbance characteristics and valence and conduction band levels which allow the rapid photo-oxidation of a chosen organic molecule. The advantages of having a photostable material with a tunable bandgap were demonstrated in an experiment where phenol destruction with visible (> 450 nm) light occurred at a dramatically faster rate with nanoscale MoS{sub 2} catalysts compared to the best available previous material TiO{sub 2}. This was the first demonstration of rapid photooxidation of an organic molecule using a completely photostable catalyst and only visible light. The possibility of transferring electrons or holes between nanoscale MoS{sub 2} and other semiconductor materials in order to increase electron/hole lifetimes were explored. It was shown that small amounts (<5 weight %) of nanoscale MoS{sub 2} deposited on to TiO{sub 2} can lead to significant ({approximately}2) enhancements of phenol destruction rates. A number of different chemicals were photocatalyzed sucessfully to CO{sub 2}, but most of the work centered on the destruction of phenol. This particular organic was chosen for its ease of detection and relative resistance to oxidation, and because its photo-oxidation has been studied extensively by many previous researchers. No attempts were made to find the absolute quantum yield of the photo-oxidation process. Rather, following the approach of Serpone and coworkers they compared the relative activity of nanoscale MoS{sub 2} to a well studied photocatalyst, Degussa P25 TiO{sub 2}. Chemical analysis was done with high pressure liquid chromatography (HPLC) using a reverse phase column, Hewlett-Packard 1050 diode array detector, and Hewlett-Packard 1046A fluorescence detector. The fluorescence detector allowed detection of phenol to {approximately} 10 ppb without preconcentration. They were typically able to destroy phenol and certain cholorinated hydrocarbons such as pentachlorophenol (a common wood preservative) to undetectable levels in less than 2--3 hours of treatment.'
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
- OSTI ID:
- 13680
- Report Number(s):
- EMSP-55387-98; ON: DE00013680
- Country of Publication:
- United States
- Language:
- English
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