Solar-driven S-scheme magnetic CoFe2O4/CdO@bentonite heterostructure for concurrent Cr(VI) reduction and cefixime degradation: mechanistic insights, kinetics, and real wastewater validation

Abstract

A novel solar-responsive magnetic CoFe2O4/CdO@bentonite (CF-CdO@B) heterostructure was rationally engineered. The incorporation of bentonite as a support matrix enabled improved dispersion, enhanced interfacial contact, and increased adsorption capacity, while the integration of CoFe2O4 and CdO facilitated efficient charge separation. Comprehensive structural, optical, and electrochemical characterizations confirmed the successful formation of a tightly coupled heterointerface. Under sunlight irradiation, the optimized photocatalyst achieved rapid and complete removal of Cr(VI) and cefixime within 25 and 60 min, respectively. Kinetic analysis revealed pseudofirst- order behavior with significantly enhanced rate constants (0.6447 min-1 for Cr(VI) and 0.2686 min-1 for cefixime), outperforming the individual components by an order of magnitude. Mechanistic investigations demonstrated that the superior photocatalytic activity originates from an S-scheme charge transfer pathway. The catalyst exhibited excellent magnetic recoverability, structural stability, and reusability over multiple cycles. Importantly, its practical applicability was validated in complex real water matrices, achieving high cefixime removal efficiencies (94% in tap water, 91% in river water, and 85% in hospital wastewater) and complete Cr(VI) reduction even in industrial effluents. This study provides a robust and sustainable strategy for dual-function photocatalysis, offering new insights into S-scheme heterojunction design and highlighting the potential of CF-CdO@B as an efficient candidate for real-world wastewater remediation.