Efficient degradation of metronidazole antibiotic by TiO2/Ag3PO4/g–C3N4 ternary composite photocatalyst in a continuous flow-loop photoreactor

Abstract

Developing photocatalytic systems by major design to achieve deep degradation of contaminants such as antibiotics to improve environmental conditions is highly desirable. Herein, we reported a facile method to fabrication of composite consisting of g-C3N4 layers and TiO2/Ag3PO4 nanoparticles (TiO2/Ag3PO4/g–C3N4) through calcination and precipitation methods. The as-prepared photocatalyst was used for the photodegradation of metronidazole (MNZ) in a designed continuous flow-loop photoreactor which is equipped with blue light-emitting diodes (LEDs) irradiation based on central composite design (CCD). According to the desirability function, the degradation efficiency of MNZ was also reported to be 97.18% under optimal conditions. The experiments indicated the photocatalytic degradation of MNZ by the as-prepared samples were in the order of TiO2/Ag3PO4/g-C3N4 > TiO2/g-C3N4 > TiO2/Ag3PO4 > TiO2. The strengthened visible-light-driven photocatalytic performance can be assigned to the formation of a Z-scheme system, surface plasmon resonance (SPR) effect, and high charge separation compared to pure and binary samples for degradation of MNZ. Based on trapping results, hydroxyl radicals were the major active radicals in the degradation of MNZ. Besides, the photodegradation pathway of MNZ was clarified via the analysis of intermediate products, and a mechanism of charge-carrier separation for MNZ photodegradation via TiO2/Ag3PO4/g–C3N4 was proposed.