Boron-doped polymeric carbon nitride co-modified with carbon-ring and carboxyl for efficient photocatalytic overall water-splitting

The photocatalytic overall water-splitting to generation hydrogen and oxygen over polymeric carbon nitrides is highly crucial in green energy usages and industry applications. To promote the separation efficiency of photoinduced charge carriers and adjust the band structure of polymeric carbon nitrides (PCNs), boron doped PCN modified with carbon-ring (CR) and carbonyl was synthesized via a polymerization of melamine with boric acid and benzoic acid. The combination of doped boron atom into the heptazine structure by displacing a carbon atom with the introduction of CR conjugated to the carbon atom in heptazine unit regulated the band structure, electronic structure, and delocalized the distribution of electrons, leading to improved separation and transfer of charge carriers photoinduced. Moreover, experimental results combined with density functional theory (DFT) calculations proved that the introduced polar groups, carboxyl, facilitated the adsorption of water molecules and promoted the photocatalytic hydrogen evolution. Importantly, the CR in-situ formed promoted the photocatalytic dioxygen evolution. The combined effect of doped boron, CR modification and carboxyl group endowed the improved the photocatalytic overall water-splitting activity. This work provides an avenue for the synthesis of metal-free photocatalysts with improved overall water-splitting activity via the combination of heterogeneous atom doping and construction of delocalized π-conjugated structures and polar group modification.