Carbon doping and bridging oxygen benefit for g-C3N4 to photocatalytic H2 production from methanol/water splitting: Experiments and theoretical calculations

Abstract

Water-based homogeneous pre-assembly and thermal polycondensation were used to prepare carbon-doped oxygen-bridged layer-twisted graphite carbon nitride (g-C₃N₄) heterojunction for highly efficient photocatalytic hydrogen evolution (PHE). Despite the narrow band gap of around 0.91 eV, g-C₃N₄ heterojunction exhibited an excellent hydrogen evolution rate (563.87 μmolg⁻¹h⁻¹) in 30 % methanol/water solution without precious metal assisting catalysts, 36.85 times higher than g-C₃N₄. C doping in heptazine ring and bridging O caused the adjacent layer of g-C₃N₄ to twist by 11° in three-dimensional space. Noticeably, carbon doping in triazine ring was favorable to the establishment of build-in electric field between adjacent layers owing to the delocalized large π bonds. Bridging oxygen acted as a conversion switch for electron storage and transport of photogenerated charge from innerlayer (unmodified layer) with high Fermi level to outlayer (modified layer) with low Fermi level. This work provided an insightful guidance to novel layer-twisted g–C₃N₄–based photocatalysts for efficient H₂ production.