Improved photocatalytic conversion of high-concentration ammonia in water by low-cost Cu/TiO₂ and its mechanism study

Platinized TiO₂ (Pt/TiO₂) as a benchmark photocatalyst shows superior photocatalytic performance in environmental remediation. In order to reduce the cost of photocatalyst for practical use, a series of cooper loaded TiO₂ (Cu/TiO₂) photocatalysts were prepared by photoreduction method and compared with pure TiO₂ and Pt/TiO₂ in terms of overall ammonia conversion efficiency and selective oxidation. The as-prepared Cu/TiO₂ samples were characterized and analyzed by physicochemical instrumental measurements. The results show that about 60% Cu²⁺ ions in suspension can be photodeposited onto the surface of TiO₂ under UV light irradiation, and is mainly composed by a mixture of Cu/Cu⁺. The Cu/P25 (0.3 wt% Cu) sample was screened out as the optimal photocatalyst, via photoilluminance spectra analysis and photocatalytic oxidation of ammonia. It shows even better performance compared to Pt/TiO₂ in the oxidation of high concentration of ammonia, due to the strong coordination effect by Cu(NH₃)_n complex formation. Through Electron Spin Resonance (EPR) analysis, and free radical suppression experiments, the active oxidative species account for ammonia oxidation and selective product generation were analyzed, and the possible reaction mechanisms involving photocatalytic ammonia conversion were proposed. ^●OH has been identified as the main oxidant that affects the removal efficiency of ammonia nitrogen, whereas O₂^●- mainly affects the production of N₂ and h⁺ is mainly responsible for the production of NO₃^-. These results indicate that Cu/TiO₂ could be used as a low-cost and efficient photocatalyst in pretreatment process for conversion of high concentration of ammonia in wastewater.