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.