Photocatalytic degradation of norfloxacin antibiotic by a novel Cu-ZnO/BiOI/Bi2WO6 double Z-type heterojunction: Performance, mechanism insight and toxicity assessment

Abstract

A novel double Z-type Cu-ZnO/BiOI/Bi₂WO₆ photocatalyst was synthesized using one-pot hydrothermal method. The effects of Bi₂WO₆ and Cu-ZnO contents, antibiotic concentration, catalyst dosage, solution pH value, coexisting ions, antibiotic types, mixed antibiotic types, water source and light source on the catalytic performance of the Cu-ZnO/BiOI/Bi₂WO₆ were investigated. Remarkably, under visible light irradiation, the removal rate of 20 mg/L norfloxacin reached 94.32 % within 120 min using the optimized Cu-ZnO/BiOI/Bi₂WO₆ photocatalyst, and its pseudo-first-order reaction rate constants were 5.63 and 1.80 times higher than those of BiOI and BiOI/Bi₂WO₆, respectively. The toxicity prediction and experimental findings indicated that the toxicity of the degraded norfloxacin (NOR) solution was notably diminished. The Cu-ZnO/BiOI/Bi₂WO₆ catalyst exhibited excellent salt tolerance, high reusability stability, universality and spectral response. Outstanding photocatalytic performance of Cu-ZnO/BiOI/Bi₂WO₆ photocatalyst is primarily due to the co-recombination of Cu-ZnO and Bi₂WO₆ on BiOI, which increases the surface area and active sites of the catalyst. More importantly, the double Z-type heterojunction, created through the intimate union of the semiconductor boundary within the composite catalyst, enhances the interface charge transport efficacy and the efficiency of separating photogenerated carriers. Finally, in conjunction with a diverse range of experimental methodologies, the degradation pathway of NOR through the Cu-ZnO/BiOI/Bi₂WO₆ composite catalyst and the electron transfer mechanism within the double Z-type heterojunction have been comprehensively elucidated. This study provides a pioneering reference for optimizing BiOI-based heterojunction catalysts and addressing antibiotic-contaminated wastewater treatment.