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

Abstract

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 O₂ reduction (O₂ → ˙O⁻₂→ H₂O₂). This study provides a facile and promising strategy for the modification of g-C₃N₄ to boost the photocatalytic H₂O₂ production activity.