Detoxification of organic pollutants using a double S-scheme TiO_2-x/Co₃S₄-CoS nanocomposites under visible light

The uncontrolled release of antibiotics and organic dyes into aquatic environments has raised serious concerns about human health and natural ecosystems. In this research, a novel ternary heterostructure photocatalyst composed of oxygen–vacancy rich TiO₂ (denoted as TiO_2-X), Co₃S₄, and CoS was fabricated using a hydrothermal route to improve the oxidation efficiency of an antibiotic (Tetracycline hydrochloride: TCH) along with four dye pollutants (Malachite green: MG, Fuchsine: FS, Rhodamine B: RhB, and Methylene blue: MB) when exposed to visible light. The TiO_2-X/Co₃S₄–CoS-2 nanocomposite showed better photocatalytic activity than the TiO_2-X and Co₃S₄-CoS photocatalysts against the degradation of FS (99.4% in 120 min), MB (98% in 210 min), RhB (99.3% in 120 min), MG (99% in 150 min) and TCH (99% in 75 min) under visible light. Furthermore, phytotoxicity assessment using lentil seed growth confirmed the biocompatibility of the treated water. This superior performance can be attributed to the synergistic effects of Co₃S₄–CoS and TiO_2-X, efficient charge transfer through a probable double S-scheme mechanism, increased surface area, rapid photocharge transfer, and the generation of active species. Also, the spherical structure of the photocatalyst may enhance the adsorption of pollutants. These findings demonstrate the innovation and high efficiency of the spherical TiO_2-X/Co₃S₄–CoS-2 heterostructures as environmentally friendly, non-toxic, effective, and reusable photocatalysts for the treatment of antibiotic-contaminated water.