Carbon Vacancy-Modified Carbon Nitride Allotropic Composite for Solar Hydrogen Generation Coupled with Selective Oxidation of 5-Hydroxymethylfurfural

A melon-poly(heptazine imide) (PHI) carbon nitride allotropic composite is constructed by partial phase conversion of melon-based carbon nitride through hydrothermal treatment using pure water. Solid-state nuclear magnetic resonance characterization reveals the existence of the intrinsic defects of carbon vacancies in the melon-PHI carbon nitride allotropic composite. In the presence of the Pt nanoparticle cocatalyst and the hole scavenger of triethanolamine, the carbon vacancy-modified melon-PHI allotropic composite exhibits superior photocatalytic performance for hydrogen production compared to the pristine melon-based carbon nitride. Moreover, the simultaneous H2 evolution from water splitting coupled with selective oxidation of 5-(hydroxymethyl) furfural to 2,5-diformylfuran is achieved over the carbon vacancy-modified melon-PHI allotropic composite photocatalyst with activities of 41 and 49 μmol g–1 h–1 under AM 1.5G (100 mW cm–2) illumination with a UV filter. Density functional theory calculations suggest that the defective heptazine rings with carbon vacancies locate in the PHI portion and contribute to the major charge density of the highest occupied molecular orbital in the PHI portion of the the allotropic composite. This intrinsic defect allows the improvement of photocharge separation and the creation of additional active sites in the carbon nitride photocatalyst to boost the performances of photocatalytic redox reactions.