Application of Modified Metal Oxide Electrodes in Photoelectrochemical Removal of Organic Pollutants from Wastewater

The scarcity of clean water due to the increase in ground and surface water pollution by numerous pollutants from municipal, industrial, and agricultural sources is considered to be the most pressing environmental problem and a threat to the survival of humans. Among the methods being tested for the sustainable removal of these pollutants from water before use or disposed into the environment is photoelectrochemical degradation. This technique is a combination of electrochemical oxidation and heterogeneous photocatalytic degradation and involves the use of metal oxide semiconductor-based electrodes in the presence of light. This process begins with the generation of electrons by the metal oxide semiconductors which react with oxygen and water molecules to produce oxidants including superoxide and hydroxyl radicals which are responsible for the degradation of the pollutants. The efficacy of this process is, however, hampered by the high rate at which the electrons recombine with the co-generated holes and the poor visible light activity of the semiconductors due to their wide band gaps. A number of modifications have been made to the semiconductors to resolve the above-mentioned problems and improve on the efficiency of the photoelectrochemical degradation process. This chapter dwells mainly on the various modifications that have been made to the metal oxides including the use of carbon-based and polymeric materials, doping with metal, doping with non-metals, co-doping with metals and non-metals and formation of mixed metal oxide/heterostructures.