Efficient charge carrier separation over carbon-rich graphitic carbon nitride for remarkably improved photocatalytic performance in emerging organic micropollutant degradation and H₂ production

Graphitic carbon nitride (g-C3N4) shows great potentials in visible-light-driven catalytic oxidation of organic micropollutants to harmless products and reduction of water to H-2 but suffers from drawback of sluggish charge carrier separation and transfer dynamics. To overcome this drawback, here a novel point defect engineering strategy, by a nicotinic acid or barbituric acid-assisted supramolecule self-assembly of dicyandiamide followed by thermal polymerization, is designed to prepare pyridine unit-incorporated g-C3N4 (C-Pyr-CNx) and carbon atom self-doped g-C3N4 (C-CNx). The strategy leads to well-regulated chemical structures of C-Pyr-CNx and C-CNx and thus the precisely controlled electronic structures. The C-Pyr-CNx and C-CNx both exhibit remarkably improved visible-light photocatalytic activity in degradation of emerging organic micropollutants (methylparaben, acetaminophen and bisphenol A) and water-splitting to H-2 production in comparison of bulk g-C3N4 and carbon-rich g-C3N4 prepared by a direct thermal copolymerization of nicotinic acid or barbituric acid with dicyandiamide, and their photocatalytic redox activity depends on carbon doping level. Experimental results combined with theoretical simulations reveal that the superior photocatalytic redox performance of C-Pyr-CNx and C-CNx is mainly dominated by the significantly boosted charge carrier separation and transfer dynamics driven by carbon doping induced-local electric field and -midgap states, which finally generates abundant reactive oxidation species including center dot O-2(-) anion radicals, center dot OH radicals and O-1(2) for the deep oxidation of target organic micropollutants to significantly reduce their ecotoxicity; additionally, such efficient charge carrier separation and transfer also favors high mobility for free electron-involved photocatalytic H-2 evolution reaction.