Photooxidation of organic wastes using semiconductor nanoclusters. 1997 annual progress report
'The photooxidation of toxic organic chemicals to carbon dioxide and dilute mineral acids using sunlight as an energy source and nanosize semiconductors to catalyze the process. The authors efforts in the first year of this program focused on demonstration of three important attributes of nanosize: MoS{sub 2} as used to photocatalyze the oxidation of organics in solution: (1) Ability to utilize visible light to initiate photo-redox reactions in solution. (2) Successful oxidative destruc-tion of organic pollutants. (3) Structural and chemical integrity during and after the removal of organic pollutants (i.e. no photochemical degradation of the catalyst). To these ends the authors have used nanosize MoS{sub 2} of three dif-ferent sizes and associated band gaps, and studied photoredox reactions catalyzed with nanosize MoS{sub 2} that had been both dispersed in solution and supported on a macroscopic powder. The latter would be the method of choice for use in practical photocatalytic applications. As they emphasized in the original proposal, MoS{sub 2} in nanosize form can be tuned to absorb various amounts of the solar spectrum. In figure 1 they show the relationship of the absorption edge of the various materials studied as photocatalysts relative to the natural solar spectrum. Their have demonstrated electron and hole transfer from nanosize MoS{sub 2} using visible light. In order to oxidize organic impurities using this part of the spectrum they needed to add an agent, bypyridine (bpy), which could accept an electron and be reduced. In actual applications they anticipate the de of sacrificial electron acceptor played by the byp could be played by soluble heavy metal ion pollutants, (e.g. Pb, Cd) which, when reduced, would precipitate out of solution, thus purifying the water and driving the reaction. Using liquid chromatography analysis they have demonstrated that bypridine binds strongly to nanosize MoS{sub 2} and acts like an electron transfer relay to effect charge separation. The hole left behind on MoS{sub 2} is then used to oxidize the organic im-purities. In its reduced form bypridine complexes to the oxidized organic impurity and precipitates out of solution. The authors studied the chemistry of this process by high pressure liquid chromatography which separates each of the chemicals in the solution from the MoS{sub 2} photocatalyst. The results of this experiment are shown in figure 2. The initially present organic impurity peak at t-5.2 minutes (an organic chloride) is destroyed as more bypridine is added until it cannot be detected. However, the amount of nanosize MoS{sub 2} remains un-changed, as measured by the area under the MoS{sub 2} elation peak. Another, broader, organic peak observed in this figure at t4.7 minutes also is destroyed by the MoS{sub 2} as additional bpy is added, and, at higher levels of bpy (not shown) this chemical is completely oxidized and precipitated out of solution as well. The white precipitate which forms can be removed from the solvent.'
- 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:
- 13679
- Report Number(s):
- EMSP-55387-97; ON: DE00013679
- Country of Publication:
- United States
- Language:
- English
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