The synergistic mechanism of free radicals between graphene oxide (GO) and hydrogen peroxide (H2O2) under visible light†

Graphene oxide (GO) is a promising metal-free photocatalyst for the degradation of organic pollutants. In particular, GO and H₂O₂ exhibit a synergistic effect that significantly enhances the degradation efficiency of organic pollutants. However, the mechanism of reactive oxygen species (ROS) generation and transformation in the GO and H₂O₂ system (GO/H₂O₂) has not been reported. In this study, we prepared GO with photocatalytic activity under visible light. When targeting the reactive red X-3B (X-3B) as a pollutant, the synergistic efficiency of the GO/H₂O₂ was enhanced by 85.56%. We employed electron paramagnetic resonance (EPR) and free radical probe to conduct both qualitative and quantitative analyses of ROS. The results show that ·OH, ·O₂⁻ and ¹O₂ were produced in the GO, H₂O₂, and GO/H₂O₂ systems. The synergistic effect was mainly driven by the reaction of H₂O₂ and h⁺ produced by GO under visible light. h⁺ is the engine of the synergistic effect between GO and H₂O₂. The transformation relationships among ·OH, ·O₂⁻ and ¹O₂ in the GO, H₂O₂ and GO/H₂O₂ systems were investigated. The main free radicals in the degradation process were ¹O₂ and ·O₂⁻. The influencing factors of the GO/H₂O₂ system were investigated, covering GO concentration, H₂O₂ concentration, pH value, X-3B concentration, and common water matrices. Notably, GO demonstrates excellent durability and mineralization capacity, maintaining superior photocatalytic performance even after 6 cycles. Moreover, during its application, the number of defects in GO increases, which improves the photocatalytic performance. This work clarified the underlying synergistic mechanism of ROS in GO/H₂O₂.