Synthesis of Bi4O5I2 coupled with Sb2WO6 boosts the photocatalytic degradation of tetracyclines under simulated sunlight

For this study, a Sb2WO6/Bi4O5I2 composite material was successfully prepared via a precipitation-calcination method. The Sb2WO6/Bi4O5I2 heterostructure enhanced the light absorption and facilitated the separation of charge carriers. Under simulated sunlight exposure, the removal rates of tetracycline (TC) and doxycycline hyclate (DOX·HCl) reached 88.2% and 83.9%, respectively, over an optimized SWB2 composite (theoretical mole ratio of Sb2WO6: BiOI was 1.5:10). Further, the total organic carbon (TOC) removal rates were 37.6% and 33.7%, respectively. The experiments explored various parameters including catalyst dosage, initial concentrations of TC and DOX·HCl, solution pH, and common inorganic ions. The TC and DOX·HCl degradation pathways were speculated. Furthermore, SWB2 demonstrated remarkable stability and cyclability under simulated sunlight. Trapping experiments and electron paramagnetic resonance (EPR) tests revealed that •O2- played a major role as a free radical in the photocatalytic process, while h+ and •OH also had significant contributions. Based on in-situ XPS, trapping experiments, EPR test, band bending analysis, and SPV tests, the formation of S-scheme heterojunction between Sb2WO6 and Bi4O5I2 was inferred. This study provides insights into the design strategy of S-scheme heterojunctions between Aurivillius-type compounds and bismuth-rich halide bismuth oxide, which is informative for the development of advanced environmental remediation concepts.