Achieving near-infrared photocatalytic overall water splitting with singular crystalline C3N4 from semi-molten-salt treatment

Developing singular semiconductor photocatalyst for overall water splitting (OWS) is of significance for commercialization of solar-fuel-production technologies but is critically challenging due to the rigorous requirements for band structure and charge-utilization capability, especially under long-wavelength light. Herein, we report the development of a highly crystalline C3N4 photocatalyst for efficient OWS under near-infrared (NIR) irradiation (lambda >700 nm). An effective semi-molten-salt approach with solid/liquid medium was used to treat the oxygen-containing precursor and to minimize undesired nitrogen defects that the traditional strategies always suffer from. The fully condensed structure with high crystallinity was therefore achieved for oxygen-incorporated C3N4 with NIR absorption. Benefiting from simultaneous realization of high crystallinity for efficient charge separation/migration and narrowed bandgap for broad light harvesting, synthesized singular C3N4 presented unprecedented OWS performances with hydrogen/oxygen evolution amount of 1.2/0.6 mu mol over 30 h under NIR irradiation. This work provides a conceptual strategy for the design of advanced OWS-active photocatalysts.