Reductively-induced carbon vacancies facilitate visible light-driven hydrogen evolution enhancement of g-C3N4

Graphite nitrogen carbide (g-C3N4, GCN) has attracted extensive attention. Herein, the g-C3N4 precursor was obtained through a conventional pyrolysis condensation path employing melamine as raw material. The g-C3N4 with abundant C vacancies was prepared with sodium borohydride (NaBH4) as reductant in different concentrations. Under visible light irradiation, the 3NBCN catalyst treated with 3 mol L−1 NaBH4 solution reveals outstanding photocatalytic hydrogen production activity, reaching 1764.9 μmol g−1 h−1, which is 7.56 folds higher than that of the reference GCN (206.3 μmol g−1 h−1). The 3NBCN also exhibits remarkable stability in the photocatalytic cyclic hydrogen production experiment. As a control experiment, Cr(VI) reduction further attests that g-C3N4 reduced by NaBH4 has an increased photocatalytic performance. The reduction rate of Cr(VI) over 3NBCN is 3.38 folds higher than that over the reference GCN. Multiple characterization results and density functional theory (DFT) calculations prove that the boosted photocatalytic activity benefits from the successful introduction of C defects, which promotes that photoexcited charges separate and transfer considerably faster and more efficiently. Considering all our results, a hypothesis for the mechanism of enhancement in photocatalytic performance is presented.