Elucidation of mechanisms, pathways, and toxicity of fabricated Z-scheme KNbO3/ZnIn2S4 hollow core–shell composites for enhanced ciprofloxacin photodegradation

Semiconductor photocatalysis technology for environmental remediation faces primary challenges, such as charge-carrier recombination and interfacial charge transfer inhibition, which affect its degradation efficiency in removing organic contaminants. In this work, we successfully synthesized a unique Z-scheme KNbO3/ZnIn2S4 hollow core–shell microsphere via a combined hard template, thermal treatment, and hydrothermal processes as the photocatalyst for ciprofloxacin (CIP), oxytetracycline hydrochloride (OTCH), and rhodamine B (RhB) remediation under sunlight irradiation. Compared to the pure KNbO3 and ZnIn2S4, our optimized 15-KNbO3/ZnIn2S4 composite exhibited enhanced photodegradation performance with up to 99.8 %, 96.8 % and 97.5 % for CIP, OTCH, and RhB removal within 110 min, respectively. At the KNbO3/ZnIn2S4 heterojunction interface, the composite developed its internal electric field and enhanced its photoabsorption under visible light region, thus boosting its charge separation. Subsequently, we evaluate the removal of total organic carbon (TOC) concentration and the influence of different ions on CIP degradation. In addition, we systematically investigated the Z-scheme charge migration process within the heterojunction with a series of experiments. Our results indicated that the hydroxyl and superoxide radicals were the dominant active species during photocatalysis. The composite also could achieve excellent stability and adaptability. We also managed to identify the CIP-degraded intermediates and deduce their possible degradation pathways. Lastly, our toxicity analysis revealed that CIP toxicity could decrease gradually during photocatalysis. In this work, we presented a unique method for preparing inexpensive and highly efficient Z-scheme hollow core–shell structure photocatalysts with excellent antibiotic remediation in water under simulated sunlight illumination.