Cooperation of oxygen doping and nitrogen vacancies in graphitic carbon nitride via high-pressure and high-temperature strategy for enhanced photocatalytic H 2 evolution

The efficacy of single-site defect engineering in graphitic carbon nitride (g-C₃N₄) is often compromised by the inevitable creation of charge recombination centers. To overcome this limitation, we propose a synergistic dual-site defect strategy and develop a high-pressure and high-temperature (HPHT) method to concurrently introduce oxygen dopants and nitrogen vacancies into g-C₃N₄. During HPHT treatment, adsorbed oxygen atoms are embedded into the lattice, while adjacent nitrogen atoms are expelled to form vacancies. Such dual-defects induce slight band-gap narrowing of g-C₃N₄ while significantly promote charge transfer and separation, thereby boosting photocatalytic hydrogen evolution. Theoretical calculations confirm that the oxygen dopants (p-type doping) and nitrogen vacancies (n-type doping) act as donor-acceptor pairs. This charge compensation effect prevents the formation of localized impurity states in the gap but instead modifies the band edges to enhance the oxidation capability and facilitate the spatial separation of electron and hole carriers. Benefiting from these advantages, the optimized g-C₃N₄ exhibits a twofold enhancement in photocatalytic activity, accompanied by a marked increase in carrier concentration. This work provides a novel strategy and fundamental insights for synthesizing highly efficient defect-engineered photocatalysts.