Photo-removal of 2,2′4,4′-tetrabromodiphenyl ether in liquid medium by reduced graphene oxide bridged artificial Z-scheme system of Ag@Ag3PO4/g-C3N4

Abstract

2,2′,4,4′-Tetrabrominateddiphenyl ether (BDE-47), as one of polybrominated diphenyl ethers (PBDEs), has been proven to be global contaminant owing to widespread utilization as flame retardant. Herein, a novel visible-light-driven (VLD) artificial indirect Z-scheme system of Ag@Ag3PO4/g-C3N4/rGO is finely designed for BDE-47 removal assisted with abundant solar energy. The novel hybrid composite exhibits an enhanced reductive debromination activity with removal efficiency of 93.4% under visible light irradiation (λ > 420 nm) for 120 min, which is 173.65 times higher than pristine g-C3N4 catalyst. A series of experiments in terms of the environmental effects of initial concentration, pH, solvent and light source are performed to optimize the photocatalytic performance. The presence of rGO as an excellent storing and shuttling medium, can further facilitate the charge carrier separation in the indirect Z-scheme system for the enhanced photo-reduction debromination performance. The accumulated electrons on the solid catalyst can attack the ortho-Br of BDE-47 to formation of BDE-28, and then so on. The protons (H+) can be reduced to atomic hydrogen (H°), which can greatly weaken para-Br of BDE-47 to generation of BDE-17. Furthermore, the remaining holes can react with CH3OH to generate CH2OH radical, and then further directly produce electron for debromination process. A possible debromination pathway for BDE-47 was proposed. This work provides a green and promising strategy utilizing solar energy to remove BDE-47 in the liquid medium by virtue of VLD composite.