Plasmon-driven N-2 photofixation in pure water over MoO3-x nanosheets under visible to NIR excitation

Photochemical N-2 fixation offers a promising route for the activation and transformation of inert nitrogen molecules to generate useful chemicals under mild conditions by using solar energy. Plasmonic nanostructures, characterized by their ability to harvest broad spectrum sunlight to enable energetic hot electron-driven chemical reactions, provide a unique platform for the high-efficiency utilization of solar energy. Herein, we report the realization of plasmon-driven photochemical N-2 fixation by semiconducting plasmonic MoO3-x nanosheets. Specifically, the co-existence of the low valence state of Mo with the oxygen vacancy enables a perfect functional combination of rich active sites for nitrogen absorption with broad spectrum plasmon-induced hot electrons within a single MoO3-x nanosheet, which facilitates the photochemical N-2 transformation without any other co-catalyst. Under irradiation with a broad region from visible to NIR, N-2 can be reduced to ammonia in pure water. The apparent quantum efficiency under NIR excitation at 808 and 905 nm reaches 0.31% and 0.22%, respectively, which are the highest for N-2 photofixation under NIR excitation ever reported. The plasmon excited hot electron-driven N-2 reduction has been demonstrated to be responsible for the photochemical N-2 fixation. This work provides a new route for the design and fabrication of functional plasmonic semiconductor nanomaterials towards the wide-band utilization of solar energy.