Metal-ion-assisted construction of cyano group defects in g-C3N4 to simultaneously degrade wastewater and produce hydrogen

Converting inexhaustible solar energy into chemical energy for environmental contaminant control and fossil fuel substitution has been considered a sustainable and promising strategy. In this paper, an easy-to-operate salt-assisted method is used to synthesize a bifunctional graphitic carbon nitride (BaCN-C3N4) co-decorated with Ba2+ doping and cyano defects. This novel BaCN-C3N4 is applied to produce hydrogen from organic wastewater efficiently and stably. Experimental characterization and DFT calculation suggest that Ba2+ is trapped in the carbon nitride intra-layer ring cavity through ion–dipole interaction, meanwhile the presence of Ba2+ promotes the production of cyano defects by partial heptazine ring opening. The mechanism of the excellent photocatalytic activity of BaCN-C3N4 is that the synergistic action of Ba2+ and cyano group promotes stronger visible light absorption, narrower band gap and higher photogenerated electron-hole separation. As a consequence, BaCN-C3N4 achieves an outstanding hydrogen production rate (10316 μmol/g/h) from wastewater, which is nearly 5.5 times that of the pristine g-C3N4. This investigation cleverly used the salt-assisted method to construct cation and cyano defects co-modified carbon nitride, achieving the goal of coinstantaneous pollutant degradation and energy development, and providing a new strategy for semiconductor photocatalysts to convert solar energy.