Unique roles of exfoliated bentonite in S-scheme BiOBr/Bi2MoO6 heterojunction for boosted ciprofloxacin degradation

Abstract

S-scheme heterojunction retained the strong redox potential of catalysts, yet confronting severe photocorrosion and particle agglomeration, resulting in poor stability. Herein, the dual Bi-based S-scheme heterojunction supported by exfoliated bentonite (BiOBr/Bi2MoO6/BTex) was fabricated via a facile microwave hydrothermal strategy. BTex could promote the dispersion of photocatalysts and reinforce heterojunction stability through intensive surface interaction, thus reducing leakage of metal ions. The optimal BiOBr/10% Bi2MoO6/BTex exhibited excellent visible light photocatalytic performance and 94% ciprofloxacin (CIP) could be degraded within 120 min. Furthermore, the high catalytic efficiency could be maintained within the pH range from 5 to 9, and efficient degradation of tetracycline and dyes could also be achieved. Basing the analysis of band structures and determination of active species, enhanced separation and migration efficiency of photogenerated carriers could be ascribed to the synergistic effect of internal electron field (IEF) from heterojunction and surface charge repulsion from BTex. Additionally, the susceptible sites of CIP were obtained by density functional theory calculations, and three possible degradation pathways, including breakage of the quinolone ring, oxidation of the piperazine ring and defluorination were speculated combined with HPLC-MS results. With prolonging photocatalysis time, the diminished toxicity of intermediates was confirmed. This study supplied new insights to improve performance and control morphology of S-scheme heterojunctions by introducing cost-effective nature bentonite.