Double vacancies synergistically enhanced photocatalytic activity of S-Scheme VO,S-Bi2WO6/L-CoIn2S4 heterojunction for degradation of co-existing antibiotics

Abstract

In this study, the VO,S-Bi2WO6/L-CoIn2S4 heterojunction photocatalysts enriched with O and S double vacancies were prepared by L-cysteine self-doping strategy for efficient degradation of antibiotics. Results of X-ray photoelectron spectroscopy and electronic paramagnetic resonance (EPR) analysis demonstrated the existence of O and S vacancies in photocatalysts. Results of band structure analysis, electron spin resonance (ESR) and free radical capture experiments indicated that charges transfer pathway of the VO,S-Bi2WO6/L-CoIn2S4 heterojunction conformed to S-scheme mechanism. Benefiting from the synergistic effects of O, S double defects, active sites of the heterojunction were increased, and separation of photogenerated carriers was promoted. The VO,S-Bi2WO6/L-CoIn2S4 heterojunction achieved degradation efficiencies of 92.7%, 83.7%, and 40.7% for tetracycline (TC), Chlortetracycline (CTC), and Levofloxacin (LEV) within 100 min, respectively, with ·O2− as the dominated reactive species contributing to antibiotics degradation. The VO,S-Bi2WO6/L-CoIn2S4 exhibited the highest kinetic constant, which was 1.73 and 1.33 times of those of the Bi2WO6 and L-CoIn2S4. Surprisingly, when TC and CTC were coexisted, the removal of TC decreased from 92.7% to 81%, while the removal of CTC increased to 88%, showing competitive effect. Possible degradation pathways of TC and CTC were proposed according to their degradation intermediates. Ecotoxicity of the main degradation intermediates were alomost lower than TC and CTC. This work provides a reference for developing efficient S-Scheme heterojunctions with dual-vacancy for efficient degradation of organic contaminants.