In photocatalytic oxidation a semiconductor, upon absorption of a photon, acts as a catalyst in producing reactive radicals, mainly hydroxyl radicals. These radicals, in turn, can oxidize organic compounds and completely mineralize them. In this way, organic molecules are decomposed to form carbon dioxide, water, and mineral acids as final products. Conventional treatment methods, in contrast, simply transfer the pollutants from one medium to another. The oxidative power of the hydroxyl radical is more than twice that of chlorine, thus its potential for oxidizing pollutants that normally are hard to destroy, like halogenated organics, surfactants, herbicides, and pesticides, to carbon dioxide.

Designs of solar photocatalytic reactors have followed those of solar thermal collectors, including concentrating reactors, such as those that use parabolic troughs, and nonconcentrating ones such as flat-plate designs. Nonconcentrating reactors have an advantage because they can use the diffuse part of solar UV radiation in addition to the beam part.

Solar photocatalytic detoxification technology has shown great potential for the treatment of groundwater and soils contaminated with toxic organic chemicals and for treating certain industrial wastewaters, as well as for gas-phase detoxification and for disinfection of water and air.

D. Yogi Goswami is Professor of Mechanical Engineering and Director of the Solar Energy and Energy Conversion Laboratory at the University of Florida in Gainesville, and Daniel M. Blake is Principal Scientist at the National Renewable Energy Laboratory in Golden, Colo.

The above was adapted from an article in the August issue of Mechanical Engineering magazine. To obtain a copy of this issue, click here.

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