Covalently Linked Porphyrin-g-C3N4 Nanosheet with Intrinsically Integrated Catalytic Sites Promoting Efficient Photocatalytic H2 Evolution

Abstract Graphitic carbon nitride (g-C3N4 and g-CN) is a promising metal-free semiconductor for photocatalytic solar energy conversion, yet its practical application is hindered by high charge recombination rates, limited visible light absorption, and lack of catalytic centers. Molecular doping offers an effective strategy to address these limitations by incorporating functional molecular fragments within the CN nanosheet, enhancing charge separation and electronic properties without the interfacial losses typical of heterojunctions. In this work, we report the rational design of an integrated porphyrin-CN covalent hybrid catalyst via a molecular doping approach. A meso-tetrakis(4-cyanophenyl)porphyrin derivative is functionalized to form polymerizable 2,4-diamino-1,3,5-triazine (DAT) domains, enabling copolymerization with melamine. The resulting porphyrin-doped CN hybrids with intrinsic catalytic centers exhibited extended light absorption and suppressed radiative recombination. Post-synthetic metalation at intrinsically integrated catalytic sites with Ni2+ or Co2+ ions yields efficient solar-driven H2 Evolution. This strategy demonstrates a versatile platform for constructing multifunctional molecular CN hybrids tailored for solar-energy applications. Under photocatalytic conditions using visible light, the Ni- and Co-based porphyrin-modified CN hybrids show a hydrogen evolution reaction (HER) rate of 640 μmol·g−1 h−1 and 720 μmol·g−1 h−1, respectively, in the presence of ascorbic acid as a sacrificial agent.