Synthesis, Characterisation, and Photocatalytic Activity of Zinc Oxide Nanostructures Doped with Nitrogen for Degradation of Pharmaceutical Contaminants in Hospital Wastewater in Oyo State

Pharmaceutical contaminants including antibiotics and analgesics are increasingly detected in hospital effluents in Nigeria, presenting ecotoxicological risks given their persistence and bioactivity at sub-therapeutic concentrations. This study synthesises nitrogen-doped zinc oxide nanostructures and evaluates their photocatalytic efficiency for degradation of ciprofloxacin and diclofenac in real hospital wastewater from a tertiary care facility in Oyo State, South West Nigeria. Nitrogen-doped ZnO nanoparticles were synthesised by co-precipitation using urea as a nitrogen source and characterised by X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, BET surface area analysis, and X-ray photoelectron spectroscopy. Photocatalytic degradation experiments were conducted under visible light irradiation, with pharmaceutical concentrations monitored by ultra-high-performance liquid chromatography. Degradation kinetics, reactive oxygen species identification, and mineralisation efficiency were investigated. Effects of catalyst loading, initial pharmaceutical concentration, pH, and inorganic ion interference on degradation efficiency were systematically examined. Nitrogen doping reduced the band gap from 3.37 to 2.84 electronvolts, enabling visible-light activity. Ciprofloxacin and diclofenac degradation efficiencies of 96 and 89 percent respectively were achieved after 120 minutes of solar irradiation. Mineralisation as assessed by total organic carbon reduction was 78 percent. The catalyst retained 91 percent activity after five regeneration cycles. The study demonstrates a viable solar-driven photocatalytic strategy for pharmaceutical wastewater treatment relevant to hospital waste management in South West Nigeria. Keywords: zinc oxide nanoparticles, photocatalysis, pharmaceutical contaminants, hospital wastewater, Oyo State