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

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-Cl-2 sample can achieve a H2O2 yield of 766 mu mol L-1, which is 1.5, 2, 7.8 and 5 times those of ZnIn2S4/TpPa-1, TpPa-Cl-2, ZnIn2S4 and TpPa-1, respectively. In the tetracycline solution, 95% of tetracycline was degraded and, concomitantly, H2O2 with a yield of 846 mu mol L-1 was generated. It is found that H2O2 generation undergoes a two-step O-2 reduction with O-2(-) as the intermediate, while O-2(-), 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.