Photo-Fenton treatment of emerging pollutants in municipal wastewater using nanocatalysts: A sustainable approach

Municipal wastewater is an intricate matrix containing pharmaceuticals, pesticides, personal care products, endocrine disruptors, antibiotics, and microplastics, which persist owing to low biodegradability and resistance against conventional treatment processes such as sedimentation, biological oxidation, and coagulation. Advanced oxidation processes are promising alternatives, the photo-Fenton reaction being a green option as it can generate hydroxyl radicals under UV or solar irradiation. Recent progress in nanotechnology has improved the activity, stability, and recyclability of nanostructured catalysts in photo-Fenton systems by designing them with greater activity, stability, and recyclability. This review critically discusses nanostructured catalysts like doped and hybrid metal oxides, carbon-based composites, and magnetic nanoparticles, and their mechanisms, selectivity toward pollutants, and efficiency in municipal wastewater treatment. Specific focus is laid on solar-powered systems and multiconstituent nanocatalysts, reducing energy costs and making recovery accessible for reuse. Photo-Fenton nanocatalysis, being applied in wastewater treatment, is aligned with global sustainability objectives, namely SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production). Some of the challenges, however, are in the spotlight, like deactivation of the catalysts, secondary toxicity, cost considerations, and regulatory authorization. The future involves direction in the form of bio-inspired catalyst design, hybridization with membrane or bioprocess, and digital optimisation technology adoption for enhanced efficiency. By merging material innovation with sustainable engineering, nanocatalyst-enhanced photo-Fenton treatment is a paradigm shift for municipal wastewater treatment.