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

Photocatalytic transformation of nitrate (NO) in wastewater into ammonia (NH) 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) powders, prepared via the sol-gel method and subsequent calcination, promote NO-to-NH reduction in water. The Cu doping into TiO creates a large number of surface oxygen vacancies (OV), which are stable even under aerated conditions. The Ti and Cu atoms adjacent to OV behave as active sites for the NO-to-NH reduction. Doping with an appropriate amount of Cu and calcination at an appropriate temperature produce the catalysts with a large number of OV, while maintaining a high conductivity, and exhibit a high photocatalytic activity.