Solar-Driven Rhodamine B Degradation Using Biogenically Recovered Mixed Metal(Loid) Sulfides Derived from Metallurgical Waste

Biogenically recovered mixed metal(loid) sulfides (BPS) obtained from metallurgical effluents were evaluated as sustainable photocatalysts for the solar-driven degradation of Rhodamine B (RhB). The material, recovered using biogenic sulfide produced by sulfate-reducing bacteria in an upflow anaerobic sludge bed reactor, was mainly composed of Sb2S3 and Bi-containing sulfide phases and exhibited a fibrous morphology and a narrow direct band gap of 1.306 eV. Under solar irradiation, BPS achieved RhB degradation efficiencies above 98% under the evaluated conditions (0.8 g L−1 catalyst and 5 mg L−1 dye), consistently outperforming reagent-grade Sb2S3. Photocatalytic degradation followed pseudo-first-order kinetics (R2 > 0.90), and the apparent reaction rate constant was more than five times higher than that of the reference material under the best-performing conditions. A preliminary reusability assessment and post-reaction characterization after three photocatalytic cycles revealed no significant morphological or compositional changes in BPS. These results demonstrate that waste-derived metal(loid) sulfides recovered through a biogenic process can serve as effective solar photocatalysts, highlighting a promising circular-economy strategy for transforming metallurgical residues into value-added materials for water remediation.