Cesium Salts as Mild Chemical Scissors To Trim Carbon Nitride for Photocatalytic H2 Evolution

Carbon nitride (CN) is considered to be one of the most promising materials for solar photocatalytic hydrogen evolution. However, its low crystallinity degree, to some extent, limited its photocatalytic activity. Unlike previous reports, we developed a feasible method to improve the crystallinity of carbon nitride using unmelted CsCl as mild chemical scissors to trim pristine carbon nitride instead of its precursor or the intermediates with incomplete structure. As a result, the regular poly(heptazine imides) structures with higher pi conjugation were exposed to the surface, wherein the bonded Cs+ ions on the surface of carbon nitride changed the charge distribution. The high regular structure can wipe out the defect sites, reducing recombined sites of electron and hole, and poly(heptazine imides) structure can greatly reserve the visible light absorption ability from pristine carbon nitride. Benefiting from these excellent features, the resultant product exhibits excellent photocatalytic hydrogen evolution activity, which is about 23 times higher than that of bulk carbon nitride.