Comparative study of metal oxides and phosphate modification with different mechanisms over g‐C ₃ N ₄ for visible‐light photocatalytic degradation of metribuzin

Abstract

Abstract In this work, a comparative study of three frequently employed modification techniques to g‐C 3 N 4 (CN) nanosheets for the photocatalytic degradation of metribuzin (MET) under visible‐light irradiation has been carried out in detail. The modification methods were coupling TiO 2 nanoparticles (TO) as electron acceptors, nano‐sized Fe 2 O 3 (FO) to construct a Z‐scheme nanocomposite, and phosphate (HP) modification to promote O 2 adsorption. The steady‐state and transient‐state surface photovoltage spectra and transient photoluminescence (PL) spectra confirmed that all the three modification techniques enhanced the charge separation with prolonged lifetimes and presented degradation activities in the order of TO/CN > FO/CN > HP/CN. The TO/CN nanocomposite showed the highest photocatalytic activity for MET degradation, with a sixfold higher rate than bulk CN. Liquid chromatography–tandem mass spectrometry and radical trapping experiments indicated that the increased activity was related to the synergetic effect of two radicals (·O 2 − and ·OH) involved in the photocatalytic degradation pathway, which was different from the ·OH radical‐dominated pathway of bulk CN. This work reveals the importance of charge separation and the influence of the radical pathway and provides guidance for the design of high‐efficiency photocatalysts.