Novel RM based S-scheme heterojunction Bi2WO6/Fe2O3 as an effective activator for peroxydisulfate in the degradation of tetracycline hydrochloride under visible light: Preparation, application, and degradation mechanism

Abstract

In this work, utilizing industrial waste red mud (RM) as raw material, a novel RM-based S-scheme heterojunction Bi₂WO₆-Fe₂O₃ (Bi₂WO₆/Fe₂O₃) photocatalyst was synthesized by solvothermal-calcination method and served as an activator for peroxydisulfate (PDS) to efficiently degrade tetracycline hydrochloride (TCH) in water body under visible light. A series of characterization results showed that Bi₂WO₆/Fe₂O₃ successfully formed an S-scheme heterojunction structure, and the specific surface area and defective structures were significantly improved. The optimum application conditions were as follows: Bi₂WO₆/Fe₂O₃ dosage of 0.33 g/L, PDS concentration of 3 mmol/L, and initial pH of 5.58. Under the optimum application conditions, the removal ratio of TCH (30 mg/L) could reach 84.8 % after 0.5 h of reaction time. In addition, the results of the response surface methodology (RSM) indicated that the effect of experimental parameters on the degradation of TCH was as follows: PDS concentration > Bi₂WO₆/Fe₂O₃ dosage >initial pH. Based on a series of characterization results, a possible photocatalytic mechanism for the degradation of TCH in the Bi₂WO₆/Fe₂O₃+PDS+Vis system was proposed. Furthermore, DFT calculations and LC-MS were employed to gain the potential degradation pathways of TCH. The biological toxic experiment proved that the toxicity of TCH solution was effectively reduced after treatment by the Bi₂WO₆/Fe₂O₃+PDS+Vis system. Recycling experiments proved that Bi₂WO₆/Fe₂O₃ had good stability. The work not only presents a green and economical approach to degrade TCH in water body but also opens up a new insight of utilizing RM to synthesize S-scheme heterojunction of Bi₂WO₆/Fe₂O₃.