One-pot solvothermal synthesis of Bi/Bi2S3/Bi2WO6 S-scheme heterojunction with enhanced photoactivity towards antibiotic oxytetracycline degradation under visible light

A novel noble-metal-free ternary Bi/Bi2S3/Bi2WO6 S-scheme heterojunction and Schottky junction was successfully synthesized by one-pot solvothermal method. UV-Vis spectroscopy showed improved light absorption in the ternary composite structure. Electrochemical impedance spectroscopy and photoluminescence spectroscopy confirmed the reduced interfacial resistivity and photogenerated charge recombination rate of the composites. Using oxytetracycline (OTC) as model pollutant, Bi/Bi2S3/Bi2WO6 presented high photocatalytic activity towards OTC degradation, where the removal rate of Bi/Bi2S3/Bi2WO6 was 1.3 and 4.1 times higher than that of Bi2WO6 and Bi2S3 under visible light irradiation in 15 min, respectively. The excellent visible photocatalysis activity was attributed to the SPR effect of metal Bi and the direct S-scheme heterojunction of Bi2S3 and Bi2WO6 with the matched energy band structure, which led to the increased electron transfer rate and high separation efficiency of the photogenerated election-hole pairs. After seven cycles, the degradation efficiency for 30 ppm OTC with Bi/Bi2S3/Bi2WO6 only decreased 20.4%. In the degradation solution, the composite photocatalyst leached only 16 ng/L Bi and 26 ng/L W of metal with high photocatalytic stability. Moreover, free radical quenching experiment and electron spin-resonance spectroscopy experiment revealed that ·O2-, 1O2, h+ and ·OH played crucial roles in the photocatalytic degradation of OTC. Based on the analysis of high performance liquid chromatography-mass spectrometry for the intermediates in the degradation process, the degradation pathway was provided. Finally, combined with ecotoxicological effect analysis, the decreased toxicity of OTC after degradation towards rice seedlings was confirmed.