Two birds with one stone: Engineering polymeric carbon nitride with n-π∗ electronic transition for extending light absorption and reducing charge recombination

The weak visible light harvesting and high charge recombination are two main problems that lead to a low photocatalytic H₂ generation of polymeric carbon nitride (p-CN). To date, the approaches that are extensively invoked to address this problem mainly rely on heteroatom-doping and heterostructures, and it remains a grand challenge in regulating dopant-free p-CN for increasing H₂ generation. Here, we report utilizing the inherent n-π∗ electronic transition to simultaneously realize extended light absorption and reduced charge recombination on p-CN nanosheets. Such n-π∗ electronic transition yields a new absorption peak of 490 ​nm, which extends the light absorption edge of p-CN to approximately 590 ​nm. Meanwhile, as revealed by the photoluminescence (PL) spectra of p-CN at the single-particle level, the n-π∗ electronic transition gives rise to an almost quenched PL signal at room temperature, unravelling a dramatically reduced charge recombination. As a consequence, a remarkably improved photocatalytic performance is realized under visible light irradiation, with a H₂ generation rate of 5553 ​μmol ​g⁻¹∙h⁻¹, ∼ 12 times higher than that of pristine p-CN (460 ​μmol∙g⁻¹∙h⁻¹) in the absence of the n-π∗ transition. This work illustrates the highlights of using the inherent n-π∗ electronic transition to improve the photocatalytic performance of dopant-free carbon nitrides.