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

Abstract

The weak visible light harvesting and high charge recombination are two main problems that lead to a low photocatalytic H 2 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 increased H 2 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. By consequence, a remarkably improved photocatalytic performance was realized under visible light irradiation, with a H 2 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. The n-π* electronic transition engineered p -CN can simultaneously realize the extended light absorption and reduced charge recombination, thereby giving rise to a significantly increased photocatalytic H 2 generation. 1. The n-π* transition can extend light absorption and reduce charge recombination. 2. Microwave thermolysis of molecule self-assembly aggregates is a general route to activate n-π* transition. 3. The n-π* transition significantly increased photocatalytic performance of H 2 generation.