Reduced State of the Graphene Oxide@Polyoxometalate Nanocatalyst Achieving High-Efficiency Nitrogen Fixation under Light Driving Conditions

The nitrogen (N-2) reduction to generate ammonia (NH3) is a prerequisite for inputting fixed nitrogen (N) into a global biogeochemical cycle. Developing highly efficient photocatalysts for N-2 fixation under mild conditions is still a challenge. Herein, we first report three kinds of reduction states of graphene oxide (GO)@polyoxometalate (POM) composite nanomaterials, which have outstanding photocatalytic N-2 fixation activities in pure water without any other electronic sacrificial agents and cocatalysts at atmospheric pressure and room temperature. A lot of experiments show that the remarkable photocatalytic N-2 fixation performance of these three nanocatalysts is due to three factors that doping the reduced POMs (also called heteropoly blues) into the reduce GO (rGO) reduces the aggregation state of rGO (from 5 to 2 rim), resulting in rGO exposing many active sites to enhance the N-2 adsorption amount, these nanocatalysts possess a wide absorption spectrum and strong reducibility, which facilitate absorb light energy exciting abundant photoelectrons to activate N-2, and rGO can effectively suppress the electrons recombination and rapidly transfer electrons to the absorbed N-2 to accelerate NH3 production. Among them, r-GO@H-5[PMo10V2O40] (PMo10V2) exhibits the highest NH3 generation efficiency of 130.3 mu mol L-1 h(-1), which is improved by 65.9 and 97.3% compared to the reduced PMo10V2 (rPMo(10)V(2)) and PMo10V2. Introduction of POMs provides a new perspective in the design of high-performance photocatalytic N-2 fixation nanomaterials.