Solar-Enhanced Photocatalytic Degradation of Pharmaceutical Residues in Wastewater Using Fe-, Cu-, and Zn- Doped TiO₂ Nanomaterials

Pharmaceutical residues are increasingly recognised as critical emerging contaminants due to their persistence, bioactivity, and incomplete removal in conventional wastewater treatment systems. In this study, TiO₂ nanomaterials doped with Fe, Cu, and Zn were synthesised via a sol–gel route and comprehensively characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and UV–Vis diffuse reflectance spectroscopy (DRS). Their photocatalytic performance was evaluated under solar-simulated irradiation for the degradation of diclofenac, paracetamol, and sulfamethoxazole. High-performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis were employed to quantify pollutant degradation and mineralisation, respectively. Metal doping reduced crystallite size, enhanced surface area, and narrowed the TiO₂ bandgap, thereby extending visible-light absorption. Among the catalysts, Fe–TiO₂ at 5% doping exhibited the highest activity, achieving >90% degradation of all three pharmaceuticals and >70% TOC removal within 120 minutes. Kinetic analysis confirmed pseudo-first-order behaviour (R² > 0.95), with Fe–TiO₂ showing the fastest rate constants (0.024–0.030 min⁻¹). Scavenger experiments identified hydroxyl (•OH) and superoxide (O₂•⁻) radicals as the primary reactive species. These findings highlight the promise of solar-assisted photocatalysis with metal-doped TiO₂ as a sustainable and efficient strategy for removing pharmaceutical residues from wastewater, with strong potential for practical application in regions with abundant solar resources.