The oxidation of aqueous ammonia over a platinum-loaded TiO2 photocatalyst was investigated for purification of wastewater. The reaction rate for the decomposition of aqueous ammonia was significantly increased by the addition of oxygen to the reaction system. The enhancement of charge separation efficiency due to consumption of photogenerated electrons by oxygen increased the decomposition rate. For dissolved oxygen (DO) concentrations below 0.09 mM, the initial decomposition rate and the selectivity for nitrite and nitrate increased as DO concentration increased. Although the selectivity for nitrite and nitrate was over 90% for the initial concentration of ammonia ([NH3](i))=5.0 mM under an air flow, the selectivity was suppressed as the initial concentration of ammonia was increased, e.g., 43% for [NH3](j), = 100 mM. (C) 2013 Elsevier B.V. All rights reserved.