Surface Oxygen Vacancies on Copper-Doped Titanium Dioxide for Photocatalytic Nitrate-to-Ammonia Reduction

Photocatalytic transformation of nitrate (NO 3 – ) in wastewater into ammonia (NH 3 ) is a challenge in the detoxification and recycling of limited nitrogen resources. In particular, previously reported photocatalysts cannot promote the reaction using water as an electron donor. Herein, we report that copper-doped titanium dioxide (Cu-TiO 2 ) powders, prepared via the sol–gel method and subsequent calcination, promote NO 3 – -to-NH 3 reduction in water. The Cu 2+ doping into TiO 2 creates a large number of surface oxygen vacancies (OV surf ), which are stable even under aerated conditions. The Ti 3+ and Cu 2+ atoms adjacent to OV surf behave as active sites for the NO 3 – -to-NH 3 reduction. Doping with an appropriate amount of Cu 2+ and calcination at an appropriate temperature produce the catalysts with a large number of OV surf, while maintaining a high conductivity, and exhibit a high photocatalytic activity.