Dual-site and carbon-ring moiety modulation of polymeric carbon nitride for improved cooperative photocatalysis.

Abstract

The conjugated structure of graphitic polymeric carbon nitrides (GPCNs) has low efficiency in the photocatalytic hydrogen peroxide (H₂O₂) production, due to the electronic properties, band structure, and surface-active-sites. Herein, boron and carbon-ring modified GPCNs were synthesized with via a thermal condensation method, using melamine and phenylboronic acid as raw materials. The introduced boron atom, conjugated to the carbon atom in the heptazine moiety, and the adjacent nitrogen vacancy (V_N) formed a dual-site, which not only modified the electronic properties but also promoted the adsorption and activation of molecular dioxygen; The carbon-ring introduced altered the band structure and electron distribution, which was proved by density functional theory (DFT) calculations. The co-modification promoted the conversion of dioxygen molecule to H₂O₂, coupled with oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). The optimal activity was achieved over CN-B₃ (1.87 mmol/(g·h)), which was about 4-fold higher than that of PCN (0.49 mmol/(g·h)). More interestingly, mechanism study revealed that the photocatalytic H₂O₂ generation was realized via a photon energy transfer route, that is, O₂ molecule firstly was converted to a highly active singlet oxygen (¹O₂) intermediate, which was reduced by electrons to superoxide anions (O₂^-) and coupled with proton to form H₂O₂. This method provides a novel strategy to improve photocatalytic H₂O₂ and high value-added chemical production by regulating the microstructure and electronic structure of GPCNs through heteroatom and moiety co-modification.