Dual-defect engineered LaOCl@CdS heterostructures for enhanced photocatalytic ciprofloxacin degradation: Mechanistic insights and reaction pathways

• Co vacancy on CoWO 4 was loaded onto Cu 2 O to form Co x WO 4 @Cu 2 O Z-scheme heterojunction. • By introducing Co vacancies, regulation of BIEF in Co x WO 4 @Cu 2 O heterojunction was achieved. • The removal of 15 mg/L catechol by 10 mg Co x WO 4 @Cu 2 O can reach 91 % after 1 hour of reaction. • Detailed discussions were conducted on the thermodynamics, kinetics, and reusability. • Mechanism of Co vacancies enhancing BIEF strength of Co x WO 4 @Cu 2 O is discussed. Defect engineering and heterostructure construction are important strategies to enhance the photocatalytic performance of single-phase materials. In this study, an O- and Cd-dual-defect-modified LaOCl@CdS heterojunction (Ov-L@Cdv-C) was successfully constructed. Under visible light irradiation, using the typical fluoroquinolone antibiotic ciprofloxacin (CIP) as the target pollutant, Ov-L@Cdv-C exhibited superior photocatalytic degradation performance compared to Ov-LaOCl and Ov-L@CdS. Under optimal conditions (0.5 g/L catalyst, 0.010 g/L initial CIP concentration, pH = 5), the degradation efficiency of CIP reached 84.79 % within 150 min, significantly higher than that of Ov-LaOCl (48.73 %) and Ov-L@CdS (71.96 %). XPS and EPR characterizations confirmed the presence of abundant O and Cd dual defects in the Ov-L@Cdv-C heterojunction. ESR and free radical quenching experiments revealed that the main reactive species during the degradation process were ·O 2 − and h⁺. Based on work function calculations and built-in electric field analysis, a Z-scheme photocatalytic mechanism for the Ov-L@Cdv-C dual-defect heterojunction was proposed. Furthermore, LC-MS analysis identified the degradation intermediates and proposed three possible degradation pathways. In addition, T.E.S.T. predictions indicated that the toxicity of CIP gradually decreased during the photocatalytic degradation process.