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

Wataru Hiramatsu; Yasuhiro Shiraishi; Satoshi Ichikawa; Shunsuke Tanaka; Yasuo Kawada; Chihiro Hiraiwa; Takayuki Hirai

doi:10.1021/jacs.4c14804

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

J Am Chem Soc. 2025 Jan 15;147(2):1968-1979. doi: 10.1021/jacs.4c14804. Epub 2024 Dec 29.

Authors

Wataru Hiramatsu¹, Yasuhiro Shiraishi^{1

2}, Satoshi Ichikawa³, Shunsuke Tanaka⁴, Yasuo Kawada⁵, Chihiro Hiraiwa⁵, Takayuki Hirai¹

Affiliations

¹ Research Center for Solar Energy Chemistry and Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan.
² Innovative Catalysis Science Division, Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI), Osaka University, Suita 565-0871, Japan.
³ Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Ibaraki 567-0047, Japan.
⁴ Department of Chemical, Energy, and Environmental Engineering, Kansai University, Suita 564-8680, Japan.
⁵ Hydrogen Business Strategy Division, The Kansai Electric Power Co., Inc., Kita-ku, Osaka 530-8270, Japan.

PMID: 39812080
DOI: 10.1021/jacs.4c14804

Abstract

Photocatalytic transformation of nitrate (NO₃^-) in wastewater into ammonia (NH₃) 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-TiO₂) powders, prepared via the sol-gel method and subsequent calcination, promote NO₃^--to-NH₃ reduction in water. The Cu²⁺ doping into TiO₂ creates a large number of surface oxygen vacancies (OV_surf), which are stable even under aerated conditions. The Ti³⁺ and Cu²⁺ atoms adjacent to OV_surf behave as active sites for the NO₃^--to-NH₃ reduction. Doping with an appropriate amount of Cu²⁺ 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.