Plasmon-driven N2 photofixation in pure water over MoO3−x nanosheets under visible to NIR excitation

Abstract

Photochemical N₂ 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 N₂ fixation by semiconducting plasmonic MoO_3−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 MoO_3−x nanosheet, which facilitates the photochemical N₂ transformation without any other co-catalyst. Under irradiation with a broad region from visible to NIR, N₂ 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 N₂ photofixation under NIR excitation ever reported. The plasmon excited hot electron-driven N₂ reduction has been demonstrated to be responsible for the photochemical N₂ 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.