Multistrategy Optimization of Benzothiadiazole-Based Ln-MOF Composites for Enhanced Photocatalytic Degradation of Tetracycline

Abstract Tetracycline hydrochloride is a common aquatic contaminant and poses significant risks to environmental and human health. However, developing high-performance removal materials with good recyclability remains a challenge. The electron-deficient benzothiadiazole linker endowed these frameworks with visible-light absorption capability, while lanthanide nodes regulated ligand–metal electronic coupling and graphene oxide-mediated interfacial charge transfer, creating efficient photocatalyst composites (Ln-MOFs/GO) for TC degradation. The graphene oxide loading was optimized to obtain Ho/10-GO, which achieved 84.6% degradation of 10 ppm tetracycline (TC) hydrochloride within 40 min under visible-light irradiation after dark adsorption equilibrium had been reached. Encapsulating the composite in sodium alginate gel maintained a high pollutant removal rate over 15 catalytic cycles and enabled simple material recovery. Mechanistic studies combining radical-trapping tests and DMPO-based EPR measurements confirmed the generation of •O2– and indicated that the O2/electron-mediated pathway plays a key role in TC degradation. Structure–property analysis showed that the photocatalytic performance results from the visible-light-responsive benzothiadiazole units and the formation of type II heterojunctions, which improve photogenerated carrier separation. Ho/10-GO@Alg was also applied to visible-light-driven condensation–cyclization synthesis of benzothiazole derivatives. This research provides an effective strategy for TC degradation and offers insights into treating TC contaminants in aquatic environments.