In situ formation of TiS₂-decorated anatase TiO₂ via sulfate-derived synthesis for enhanced photocatalytic degradation of acetaminophen.

Titanium dioxide (TiO₂) remains one of the most investigated photocatalysts for environmental remediation; however, its practical application under visible light is still limited by its wide band gap and rapid electron-hole recombination. In this work, TiO₂ nanoparticles were synthesized by a modified polymeric precursor method using different citric acid/metal ratios, leading to materials with distinct structural and surface properties. Structural analyses confirmed the formation of anatase TiO₂ with nanometric crystallite sizes and high specific surface area. Spectroscopic and EPR analyses revealed the presence of oxygen vacancies, Ti³⁺ species, and sulfur-related surface defects, which contributed to enhanced visible-light absorption and charge separation. Among the synthesized materials, the M1C15 sample exhibited the best photocatalytic performance toward acetaminophen degradation, achieving complete removal under UV irradiation. LC-MS analyses confirmed the disappearance of acetaminophen signals after treatment and revealed the formation of intermediate compounds associated with oxidative degradation pathways and radical coupling reactions. EPR spin-trapping experiments demonstrated the generation of hydroxyl radicals (•OH), supporting the proposed photocatalytic mechanism. Under visible-light irradiation, the M1C15 sample achieved 18.2% paracetamol removal, indicating photocatalytic activity beyond the UV region. DRS, FTIR, EPR, and XPS analyses suggested that this behavior is associated with the formation of TiS₂ species on the surface of M1C15. These findings show that the proposed low-cost synthesis route produces promising photocatalysts for the treatment of pharmaceutical-contaminated wastewater under natural or artificial irradiation conditions with reduced energy demand.