Tailored Exfoliation of Polymeric Carbon Nitride for Photocatalytic H₂O₂ Production and CH₄ Valorization Mediated by O₂ Activation

Abstract

The exfoliation of bulk C₃N₄ (BCN) into ultrathin layered structure is an effective strategy to boost photocatalytic efficiency by exposing interior active sites and accelerating charge separation and transportation. Herein, we report a novel nitrate anion intercalation-decomposition (NID) strategy that is effective in peeling off BCN into few-layer C₃N₄ (fl-CN) with tailored thickness down to bi-layer. This strategy only involves hydrothermal treatment of BCN in diluted HNO₃ aqueous solution, followed by pyrolysis at various temperatures. The decomposition of the nitrate anions not only exfoliates BCN and changes the band structure, but also incorporates oxygen species onto fl-CN, which is conducive to O₂ adsorption and hence relevant chemical processes. In photocatalytic O₂ reduction under visible light irradiation, the H₂O₂ production rate over the optimal fl-CN-530 catalyst is 952 μmol g^-1 h^-1, which is 8.8 times that over BCN. More importantly, under full arc irradiation and in the absence of hole scavenger, CH₄ can be photocatalytically oxidized by on-site formed H₂O₂ and active oxygen species to generate value-added C1 oxygenates with high selectivity of 99.2 % and record-high production rate of 1893 μmol g^-1 h^-1 among the metal-free C₃N₄-based photocatalysts.