Photocatalytic Degradation of Persistent Organic Pollutants in Nigerian Industrial Wastewater Using Visible-Light-Active Composite Nanomaterials

This dissertation investigates the synthesis, characterisation, and application of visible-light-active composite nanomaterials for the photocatalytic degradation of persistent organic pollutants in industrial wastewater from Nigerian textile, pharmaceutical, and petrochemical sectors. Persistent organic pollutants including azo dyes, pharmaceutical residues, and polycyclic aromatic hydrocarbons resist conventional biological treatment and pose long-term environmental and health risks in receiving water bodies. Visible-light-active photocatalysis using solar radiation represents a potentially transformative treatment approach for Nigerian industrial facilities given the country's high solar irradiance, but nanomaterial systems optimised for the specific pollutant profiles, water quality matrices, and solar spectral distribution of Nigerian wastewater environments have not been developed. The dissertation makes original contributions in three interconnected domains: synthesis and characterisation of nitrogen-doped titanium dioxide and graphitic carbon nitride composite nanomaterials with optimised visible light absorption and quantum yield through a systematic experimental design programme; mechanistic investigation of reactive oxygen species generation and pollutant degradation pathways in the specific wastewater matrices of Nigerian industrial effluents, using electron paramagnetic resonance spectroscopy and isotopic labelling to confirm degradation mechanisms; and scale-up engineering of a solar photocatalytic reactor prototype tested under controlled outdoor conditions in Abuja, evaluating treatment kinetics, catalyst stability, and energy efficiency relative to advanced oxidation alternatives. The dissertation produces original theoretical insights into synergistic photocatalytic mechanism enhancements from the composite structure and provides a performance database for engineering design of solar photocatalytic treatment systems in Nigerian industrial applications. Keywords: photocatalysis, persistent organic pollutants, nanomaterials, industrial wastewater, solar treatment.