Photocatalytic oxidation of ammonia using copper-mediated phosphotungstic acid intercalated sulfonated bentonite for sustainable eutrophication control: A case study from Lake Qarun.

This study introduces a novel photocatalyst-copper-mediated phosphotungstic acid intercalated acidified bentonite (Cu@PTA/SB)-for the efficient oxidation of ammonia in both synthetic aqueous solutions and eutrophic natural waters. The catalyst was synthesized by sulfonating carbonaceous bentonite, followed by intercalation of phosphotungstic acid and in situ deposition of copper nanoparticles. Physicochemical characterization confirmed a stable mesoporous structure with a surface area of 72.26 m/g and average pore diameter of 8.25 nm, enhancing adsorption capacity and redox activity. In synthetic ammonium solutions, the catalyst demonstrated significant efficiency, achieving ammonia removal rates of 88.4 %, 81.3 %, 70.5 %, and 58.3 % for 10-30 mg/L concentrations using 0.02 g under visible light. Increasing the dosage to 0.04 g enabled complete removal (100 %) of 10 and 15 mg/L ammonia within 120 min at pH 9. Kinetic analysis showed that the oxidation followed pseudo-first-order kinetics at lower concentrations (R = 0.996, k = 0.01823 min), while higher concentrations followed pseudo-second-order behavior due to surface saturation. Quantum yield declined with increasing ammonia, confirming optimal photonic efficiency under moderate loading. In real water from eutrophic Lake Qarun (NH = 5.6 mg/L, pH 8.5), the catalyst achieved 65.6 % removal in the first cycle and 98.3 % cumulative reduction after two cycles, reaching a final concentration of 0.03 mg/L-well below WHO and EPA thresholds. The synergistic redox behavior of cupper and tungsten enhanced oxidizing species generation, while the sulfonated bentonite ensured pollutant accessibility and catalyst dispersion. These results demonstrate the catalyst's practical potential for sustainable, low-cost nutrient removal, offering an effective approach for eutrophication mitigation, aquatic life protection, and water quality restoration in polluted freshwater systems.