Fe/S-Modified MIL-125 for Efficient Photocatalytic Degradation of Antibiotics: Performance and Mechanism

Antibiotics have been extensively used in medicine and aquaculture, leading to severe environmental contamination. Among them, chlortetracycline (CTC) has attracted considerable attention due to its large consumption and high residual risk. MIL-125(Ti), as a representative titanium-based metal–organic framework, exhibits good structural stability and tunability; however, its intrinsically weak visible-light response and rapid charge recombination limit further photocatalytic applications. To improve its photocatalytic performance, MIL-125 was first synthesized via a hydrothermal method, and then Fe and S species were introduced through a combination of in situ coprecipitation and mild sulfuration, yielding an Fe/S-modified MIL-125 photocatalyst. The introduction of Na2S induced defect sites and coordinatively unsaturated centers on the MIL-125 surface, while the cooperative participation of Fe species further regulated the surface electronic structure and active-site distribution, thereby enhancing visible-light absorption and interfacial charge transfer. Under AM 1.5 irradiation, the optimized Fe/S-MIL-125 achieved a CTC degradation efficiency of 98.6% within 120 min at an initial concentration of 40 mg L−1. In addition, the material exhibited broad applicability toward multiple antibiotics, with degradation efficiencies exceeding 87% for ciprofloxacin (CIP) and clindamycin (CLI). Cycling tests demonstrated that the catalyst retained high activity after five successive runs, indicating excellent stability. Radical scavenging experiments and ESR analyses revealed that superoxide radicals (·O2−) were the dominant reactive species. Overall, the Fe/S-modified strategy significantly enhanced the photocatalytic performance of MIL-125 through defect engineering and interfacial charge regulation, offering a promising approach for the design of MOF-based materials for antibiotic removal.