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

Abstract The n-π* electronic transition in polymeric carbon nitride (PCN) can remarkably harvest visible light, which thus potentially promotes the photocatalytic hydrogen H2 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 H2 generation, with a highest H2 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 H2 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.