KNO3-Assisted incorporation of K dopants and N defects into g-C3N4 with enhanced visible light driven photocatalytic H2O2 production

Doping with heteroatoms and introducing defects are efficient protocols to enhance the photocatalytic performance of graphitic carbon nitride (g-C3N4) for H2O2 production. Herein, a facile one-pot KNO3-assisted thermal polymerization of thiourea and urea was reported for the modification of g-C3N4 with K dopants and N defects (denoted as M-CN-K-1). As a visible light photocatalyst with isopropanol as an electron donor, the obtained M-CN-K-1 sample exhibited an excellent H2O2 production activity of 2.92 mmol g(-1) g-C3N4 h(-1), which was 15.6, 5.8 and 2.2 times that of pristine g-C3N4 samples derived from urea, thiourea, and a mixture of thiourea and urea, respectively. The outstanding performance of the KNO3-modified g-C3N4 is attributed to the controllable introduction of cyano groups on the opened s-triazine heterocycle and K insertion into the g-C3N4 layers, which are conducive to regulating the morphology, electronic structure, and electron withdrawing and transfer capability. The KNO3-modified g-C3N4 possesses a lamellar structure with a high surface area, smaller energy gap for broadened visible light absorption, more negative conduction band position with stronger reduction ability, suppressed recombination of electron-hole pairs, and enhanced electron transfer, which exert a synergistic effect on the photocatalytic H2O2 production. The H2O2 formation in M-CN-K-1 undergoes the pathway of two-step one-electron indirect O-2 reduction (O-2 -> O-(2)-> H2O2). This study provides a facile and promising strategy for the modification of g-C3N4 to boost the photocatalytic H2O2 production activity.