Incorporating p-Phenylene as an Electron-Donating Group into Graphitic Carbon Nitride for Efficient Charge Separation

Low charge-separation transport efficiency resulting from structural defects largely limits photocatalytic hydrogen production over polymeric graphitic carbon nitride (PCN) photocatalyst. Herein, an electron-donating group, namely p-phenylene, is incorporated into PCN by a polycondensation reaction between carbon nitride and p-phenylenediamine (or p-benzoquinone) to repair the structural defects. The p-phenylene-modified PCN exhibits an almost fivefold increase in H₂ evolution, a threefold increase in photocurrent density, and higher nonradiative rate (0.285 ns^-1 ). Spectroscopic studies confirm that p-phenylene tends to bridge the heptazine-based oligomers through a polycondensation reaction. Theoretical calculations reveal that anchoring of the heptazine units by p-phenylene induces localization of h⁺ and e^- on the phenylene and melem moieties, respectively, which effectively separates the charge carriers. This strategy provides an opportunity to overcome structural defects in carbon nitride for efficient photocatalytic solar energy conversion.