Carboxyl groups as active sites for H2O2 decomposition in photodegradation over graphene oxide/polythiophene composites

Abstract Graphene oxide (GO) or reduced graphene oxide (RGO) is an excellent promoter to improve the photodegradation activity of a hybridized photocatalyst in advanced oxidation processes (AOPs). However, the identification of active sites remains a challenge due to the complexity of GO surface with different oxygen functionalities and defects coexisted. In this work, we synthesized different GO/polythiophene (GO/PTh) composites via in-situ polymerization of thiophene monomers on different GO supports with controlled content of oxygen functionalities such as carboxyl, hydroxyl and epoxide bonds. GO-COOH/PTh shows the highest performance in the degradation of methylene blue (MB) and phenol under visible light among all GO/PTh catalysts. We find the degradation rate is determined by the amount of hydroxyl free radicals (•OH) via the reaction of photoelectrons with H2O2. Different oxygen groups on GO surface results in different photoelectron conversion efficiency (η, the ratio of degradation rate to photocurrent). More importantly, we find that η correlates linearly with the amount of COOH in the catalysts, indicating COOH groups act as active sites for •OH generation during photodegradation. This study provides a deep understanding of active sites for H2O2 decomposition in photo-assisted Fenton-like systems over GO containing photocatalysts.