Photoelectrochemical advanced oxidation processes for removal of azo dye from water: emerging aspects and oxidation products

Abstract Azo dyes are one of the large classes of water soluble synthetic dyes with a wide range of colors and can be released into the environment when used. Azo dyes belong to one of the most numerous groups of synthetic dyes and are characterized by the presence of an azo group (-N=N-) with two or more symmetrical or asymmetrical aromatic radicals. Processes of photoelectrochemical oxidation using various approaches have been developed for the removal of azo dyes from wastewater. The fundamentals of different photoelectrochemical oxidation processes for azo dyes, such as photoelectrocatalytic oxidation (PEC), photoelectro-Fenton (PEF), and solar photoelectro-Fenton (SPEF) processes, are discussed. The use of different semiconductor materials as electrode materials in photoelectrocatalysis and PEF for azo dye removal, the influence of different parameters on the removal of azo dyes from wastewater, reactor design, combined photoelectrochemical oxidation, including the use of fuel cells, are also considered. The anodic, electrochemical, and photoelectrochemical oxidation processes for azo dye removal is compared. Also shows what products are mainly formed during photoelectrochemical oxidation of azo dyes and how photoelectrochemical oxidation affects the toxicity of azo dye solutions under different conditions.