Photoreduction and Photodegradation of Inorganic Pollutants: II. Selective Reduction and Recovery of Au, Pt, Pd, Rh, Hg, and Pb

Toxic metals in their various oxidation states can neither be biodegraded, nor can they be “chemically decontaminated”. Environmental pollution by toxic metals is a function of the form of the metals and not necessarily a function of their bulk concentration. In recent years much concern has been expressed about the state of our chemical environment. Contamination seems to have no boundaries. Experiments with semiconductor materials, coupled or uncoupled to suitable redox catalysts, have demonstrated the feasibility of carrying out several reactions induced by light. Amongst these reactions is the attractive potential to utilize and develop a technology based on semiconductors that will mediate either the reduction of metals, toxic to the environment or of strategic and economic importance, or the oxidation of organic products that are harmful to the environment (for example, pesticides, herbicides, etc…). This lecture summarizes, albeit not exhaustively, metals pollution and their toxic nature, the traditional technologies employed to detoxify aqueous effluents. Finally, it discusses at some length recent work on a new developing technology, based principally on semiconductor materials (TiO2, WO3, ZnO, among others) irradiated by light of suitable energy. The results seem encouraging!