Dawson-type polyoxometalate-based vacancies g-C3N4 composite-nanomaterials for efficient photocatalytic nitrogen fixation

Abstract

Nitrogen (N₂) fixation is the second most vital chemical process in nature, preceded only by photosynthesis. However, the construction of efficient photocatalysts for N₂ reduction is still a significant challenge. Herein, for the first time, we report four kinds of Dawson-type polyoxometalate (POM)-based nitrogen vacancies graphitic carbon nitride (V-g-C₃N₄) (POM@V-g-C₃N₄) composite-nanomaterials, which have outstanding photocatalytic N₂ fixation activities under mild conditions. V-g-C₃N₄ can capture N₂ molecules strongly and accurately. The POMs doped into V-g-C₃N₄ play a major role in promoting the activation and dissociation of N₂ for the following three reasons: (1) a wide spectrum is established from 200–900 nm to enhance the utilization of light energy. (2) POMs are easily reduced under light conditions, with the advantage of stronger pre-reduction properties, to provide abundant electrons to activate N₂. The reduced POMs further react with oxygen returning to the original POMs, and the reaction forms a self-healing, recyclable photocatalytic N₂-fixing system. (3) The recombination of photogenerated carriers is effectively suppressed and charge-transfer resistance is weakened. Surprisingly, α₂-K₈P₂W₁₇O₆₁(Co²⁺·OH₂)·16H₂O (P₂W₁₇Co) P₂W₁₇Co@V-g-C₃N₄ shows the best photocatalytic N₂ fixation efficiency of 214.6 μmol L⁻¹ h⁻¹, which is increased by 91.05% and 95.99% as compared to that of P₂W₁₇Co and V-g-C₃N₄ only. It provides a new view toward the design of sustainable, stable and high-performance photocatalytic N₂ fixation nanomaterials.