High-Efficiency "Working-in-Tandem" Nitrogen Photofixation Achieved by Assembling Plasmonic Gold Nanocrystals on Ultrathin Titania Nanosheets.

The fixation of atmospheric N2 to NH3 is an essential process for sustaining life. One grand challenge is to develop efficient catalysts to photofix N2 under ambient conditions. Herein we report an all-inorganic catalyst, Au nanocrystals anchored on ultrathin TiO2 nanosheets with oxygen vacancies. It can accomplish photodriven N2 fixation in the "working-in-tandem" pathway at room temperature and atmospheric pressure. The oxygen vacancies on the TiO2 nanosheets chemisorb and activate N2 molecules, which are subsequently reduced to NH3 by hot electrons generated from plasmon excitation of the Au nanocrystals. The apparent quantum efficiency of 0.82% at 550 nm for the conversion of incident photons to NH3 is higher than those reported so far. Optimizing the absorption across the overall visible range with the mixture of Au nanospheres and nanorods further enhances the N2 photofixation rate by 66.2% in comparison with Au nanospheres used alone. This work offers a new approach for the rational design of efficient catalysts toward sustainable N2 fixation through a less energy-demanding photochemical process compared to the industrial Haber-Bosch process.