W and Cu double cationic vacancies on S-scheme Bi2WO6/CuS heterojunction induced spin polarization and facilitated magnetic enhancement of photocatalytic activity toward levofloxacin degradation

•W and Cu cationic vacancies on Bi2WO6/CuS heterojunction induced spin polarization.•Spin polarization promoted carrier separation on the Vw-BWO/Cu1-xS.•The presence of W, Cu vacancies on the Vw-BWO/Cu1-xS could increase active sites.•Application of an external magnetic field for Vw-BWO/Cu1-xS enhanced LEV degradation.•LEV degradation pathways and ecotoxicity changes were studied. In this research, the Bi2WO6/CuS heterojunctions (Vw-BWO/Cu1-xS) with Cu vacancies and W vacancies were fabricated via hydrothermal and post-etching methods towards levofloxacin (LEV) degradation. Multiple characterizations and tests verified the presence of W and Cu vacancies, and the Vw-BWO/Cu1-xS 10:1 heterojunction exhibited favorable optical properties. Density function theory (DFT) calculations revealed that W, Cu cation vacancies induced electron spin polarization on the Vw-BWO/Cu1-xS, facilitating carrier separation, and allowing more holes to be participated in photocatalytic reaction. Moreover, the presence of W, Cu vacancies could increase active sites, facilitating LEV absorption and activation. The Vw-BWO/Cu1-xS 10:1 composite achieved the highest LEV removal of 90.61 % within 60 min of light exposure, which was 1.24 times of the BWO. Notably, application of an external magnetic field (20 mT) to the Vw-BWO/Cu1-xS 10:1 could enhance photocatalytic degradation of LEV, which was 1.46 times of that without external magnetic field. Additionally, possible degradation routes of LEV and ecotoxicity of degradation intermediate products were determined. This study opens up a feasible approach for introduction of cationic vacancies and spin polarization on heterojunctions to improve photocatalytic activity.