Photocatalytic production of H2O2 from wastewater under visible light by chlorine and ZnIn2S4 co-decorated TpPa-1

Abstract

A covalent organic framework (COF) named TpPa-1 was co-modified by chlorine grafting and ZnIn₂S₄ integration for concurrent photocatalytic H₂O₂ generation and wastewater purification under visible light. The introduction of electron-withdrawing chlorine groups on TpPa-1 decreases the density of adjacent electron clouds, which promotes the charge carrier separation and the intimate combination with ZnIn₂S₄ by Cl–Zn/Cl–In bonds, providing an appreciably enhanced photocatalytic activity. Specifically, in pure water, the optimal ZnIn₂S₄/TpPa-Cl₂ sample can achieve a H₂O₂ yield of 766 μmol L⁻¹, which is 1.5, 2, 7.8 and 5 times those of ZnIn₂S₄/TpPa-1, TpPa-Cl₂, ZnIn₂S₄ and TpPa-1, respectively. In the tetracycline solution, 95% of tetracycline was degraded and, concomitantly, H₂O₂ with a yield of 846 μmol L⁻¹ was generated. It is found that H₂O₂ generation undergoes a two-step O₂ reduction with ·O₂⁻ as the intermediate, while ·O₂⁻, holes and ·OH are the active species in tetracycline degradation. Likewise, other common pollutants like o-nitrophenol, acid golden yellow and acid red in wastewater could also be effectively degraded along with the appreciable production of H₂O₂, which realizes the so-called wastewater valorization. This study could advance COF-based photocatalysts and provide a novel insight into wastewater treatment.