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