Construction of Ag3PO4/NiWO4 S-scheme heterojunction with enhanced sonocatalytic performance for the removal of tetracycline: Characterization, sonocatalytic mechanism and degradation pathways

In this study, Ag3PO4/NiWO4 (AN) composites were synthesized by a two-step method. The sonocatalytic properties of Ag3PO4/NiWO4 composites were investigated using tetracycline (TET) as a contaminant model, and the best sonocatalytic performance was obtained for AN-30. The removal of TET at pH= 8 with an initial concentration of 20 mg/L could reach 98.16 +/- 0.37 % after sonication at 500 W for 5 min with 2 g/L of AN-30 and 3 mmol/L of K2S2O8 added. Combined with the experimental results of active species capture and X-ray photoelectron spectroscopy, it was demonstrated that Ag3PO4 formed an S-scheme heterojunction with NiWO4, which promoted the separation of electron-hole pairs and thus improved the sonocatalytic performance of NiWO4. The cycling experiments showed that the Ag3PO4/NiWO4 catalysts also had good reusability and stability. Several transformation pathways of TET were deduced by liquid chromatography-mass spectrometry analysis. The biotoxicity test confirmed that the sonocatalytic technique could degrade TET into less toxic substances. This study would provide a research basis for the design and development of novel sonocatalysts for the sonocatalytic removal of pharmaceutical wastewater.