Functionalizing g-C 3 N 4 with Mn 0.5 Cd 0.5 S toward a visible-light-driven heterojunction photocatalyst for rapid antibiotic degradation

The removal of persistent antibiotic pollutants such as tetracycline (TC) from wastewater remains a significant challenge. To address the inherent limitations of graphitic carbon nitride (g-C3N4)—namely its restricted visible-light absorption and rapid charge recombination—this study constructed a novel Mn0.5Cd0.5S/g-C3N4 heterojunction photocatalyst via a combined calcination-hydrothermal strategy. Comprehensive characterization confirmed the successful integration of Mn0.5Cd0.5S nanoparticles with g-C3N4 nanosheets, which extended the visible-light response and facilitated interfacial charge transfer. The optimal composite exhibited remarkably enhanced photocatalytic activity, degrading 92.94% of TC within 60 min under visible light. The apparent rate constant (k) calculated from pseudo-first-order kinetics was 0.02366 min−1, which is 14.8 and 6.1 times higher than that of pristine g-C3N4 and Mn0.5Cd0.5S, respectively. Radical trapping and spectroscopic analyses revealed that the boosted performance originates from efficient spatial separation of charge carriers via a type-II heterojunction mechanism, where superoxide radicals (•O2−) and holes (h+) serve as the primary active species. The composite also demonstrated excellent stability over four consecutive cycles. This work provides an effective strategy for modifying g-C3N4-based materials and offers insight into the design of high-performance heterojunction photocatalysts for environmental remediation.