Recent advances of photocatalytic degradation for BTEX: Materials, operation, and mechanism

BTEX with benzene ring and different groups (methyl and ethyl) have aroused enormous concern due to their wide sources and large contribution to photochemical reactions and ozone pollution. This paper systematically reviewed the photodegradation of BTEX including materials, operating parameters, and reaction mechanisms. The photocatalytic materials including monadic or binary metal oxides, hydroxides, and metal-free materials were broadened the optical absorption range and enhanced the absorption capacity by modifying, thus greatly improving the photocatalytic performance. The most effective strategy is forming the heterojunction with built-in fields, which enhances the light absorption capacity and leads lower recombination rate of photocarrier to generate more active oxygen species. The parameters of operating mode, initial concentration, flow rate, temperature, relative humidity and light play important roles in photocatalytic degradation of BTEX. Furthermore, this work highlights that the process of photo-oxidizing BTEX overwhelmingly follows the Langmuir-Hinshelwood model. The mechanisms including adsorption and surface reaction are described using the density functional theory calculations. The review reveals that BTEX are oxidized to the aldehyde and organic acids and opened the ring by active species, eventually mineralized to CO2 and H2O. Moreover, the different degradation pathways of BTEX are studied with the differences of position and number of methyl and ethyl groups. The technique combination is mostly used in the removal of BTEX due to complex working conditions in practical application. The challenge of catalyst inactivation can be regenerated by heating and UV cleaning.