K+-induced crystallization of polymeric carbon nitride to boost its photocatalytic activity for H2 evolution and hydrogenation of alkenes

Crystalline semiconductors with ordered long-range structure and minimized phase defect are capable of efficient separation and diffusion of photoexcited charge carriers, which is crucial for achieving high photocatalytic performances. Here, we present a new strategy using KCl as structure inducer, where potassium ions (K+) act as a smart binder for re-ordering the structure of amorphous polymer carbon nitride (PCN) to furnish K+ implanted crystalline PCN (KPCN). The X-ray photoelectron spectroscopy depth profiling with Ar+ cluster ion sputtering illustrated that the element K is uniformly distributed in bulk of KPCN. The microstructure evolution of KPCN under elevated temperature was identified using in situ Fourier-transform infrared spectroscopy. This crystalline structure endows the ordered electronic transmission channels in KPCN, thus enhanced the efficiency of hot charge carriers separation and migration, as well as visible light capture. Therefore, the re-ordered KPCN displays nearly 20 times enhancement toward photocatalytic hydrogen evolution, and high activity in water-splitting-based alkenes hydrogenation using the in-situ photo-generated H-species from water as sustainable H-source. The present work highlights a green and reliable strategy to remodel the structure of PCN by K+ thus dramatically boosting the photocatalytic activity for hydrogen evolution as well as water-splitting-based photosynthesis of high value-added fine chemicals.