Photocatalytic Detoxification of Polluted Waters

During the past 15 years research and development in the area of photocatalysis have been tremendous. The present review describes the basic principles of photocatalysis, focusing in particular on important mechanistic and kinetic aspects. The properties and requirements for efficient photocatalysts are discussed in detail. A few representative model compounds have been selected to illustrate the major reaction pathways in photocatalytic degradation processes. While tetrachloromethane has been chosen as a typical example for a reductive pathway, the degradation of 4-chlorophenol and naphthalene are described in detail with special emphasis on possible and often undesired intermediates. The couple benzoquinone/ hydroquinone is presented to elucidate an electron-shuttle mechanism which results in an undesirable short-circuiting of the photocatalyst. Crucial reaction parameters such as pH, temperature, solute concentration and light intensity, are given together with current theoretical models to explain their effects on the overall process efficiency. Various solar reactors for photocatalytic water treatment are described in detail including the comparison of their overall performance. Finally, several examples for the treatment of real wastewater are presented together with some initial economic considerations.