Significantly narrowed bandgap and enhanced charge separation in porous, nitrogen-vacancy red g-C3N4 for visible light photocatalytic H2 production

[Display omitted] •Porous g-C3N4 with tunable N-vacancies was prepared at more gentle HPHT conditions.•The N-vacancies extended visible light absorption beyond 660 nm (band gap ~1.88 eV).•N-vacancies and porous structure promoted charge separation and transfer.•The PNCN-2 exhibited 13.5 times enhancement in H2 evolution rate compared with BCN. Porous graphitic carbon nitride (g-C3N4) with tunable nitrogen vacancies was prepared by a high pressure and high temperature (HPHT) process combined with hard template method. The concentrations of two-coordinated nitrogen vacancy can be tuned by temperatures that are much gentler than those required at ambient pressure. Such produced samples after HPHT treatment show decreased interlayer distance, up-shift in valance band (VB) and down-shift in conduction band (CB), and thus exhibit narrowed bandgap down to 1.88 eV, as well as increased efficiency of charge carrier separation and transfer. Consequently, the porous vacancy-rich g-C3N4 with increased specific surface area exhibits 13.5 times enhancement in photocatalytic H2 evolution compared to the bulk g-C3N4. The underlying mechanism for the significantly enhanced photocatalytic H2 production is further proposed. This process is efficient for defects engineering of carbon nitride materials with simultaneous realization of porous structure, which might be extended to other materials for superior performance.