Microwave awakening the n-π* electronic transition in highly crystalline polymeric carbon nitride nanosheets for photocatalytic hydrogen generation

The n-π* electronic transition in polymeric carbon nitride (PCN) can remarkably harvest visible light, which thus potentially promotes the photocatalytic hydrogen H 2 generation. However, awaking the n-π* electronic transition has proven to be a grand challenge. Herein, we reported on the awakening of n-π* electronic transition by microwave thermolysis of urea pellet, which yielded the PCN with absorption edge of 600 nm, near 140 nm red-shift from 460 nm of pristine PCN. The n-π* electronic transition endows PCN with an increased photocatalytic H 2 generation, with a highest H 2 rate of 61.7 μmol h −1 under visible light exposure, which is near 6 times higher than that by using the PCN from the thermolysis of urea pellets in an electric furnace (10.6 μmol h −1 ). Furthermore, the n-π* transition in PCN leads to the longest wavelength of 535 nm that can initiate H 2 generation, remarkably longer than the absorption edge of pristine PCN (460 nm). This work manifests the advantages of microwave sintering route to awaken the n-π* electronic transition in PCN for an increased photocatalytic performance.