Photoelectrocatalytic technologies for environmental applications

This paper summarizes recent research works dealing with the development of photoelectrocatalytic oxidation technologies combining both electrolytic and photocatalytic processes. Photoelectrocatalytic technologies have received particular attention due to their potential and effectiveness in the photodegradation of refractory organic and microbial pollutants present in water and wastewater. Here, titanium dioxide (TiO2) plays the most important role compared to other semiconductor photocatalysts (CdS, ZnO, SnO2, etc.) due to its excellent chemical and physical properties. The recombination of the photogenerated electrons and holes is the main factor that generally limits the application of photocatalytic processes (PCPs) in the environmental field. Considerable efforts have been made to increase the photocatalytic efficiency and decrease the charge recombination by means of photoelectrocatalytic processes (PECPs), also referred to as electrochemically assisted photocatalytic processes, which consists of applying an external potential on photocatalysts. This paper deals with the mechanism of photoelectrocatalytic processes, the characteristics and methods for preparing a TiO2 electrode, the irradiation sources, and the types of reactors used. Moreover, the key factors affecting the photoelectrocatalytic oxidation efficiency are discussed, including the applied electrical potential, light intensity, pH, dissolved oxygen concentration, electrolyte concentration, and temperature. Finally, the paper emphasizes the recent applications of photoelectrocatalytic processes and suggests new research directions for the development of this promising technology.