Introduction of a Hydroxyl Self-Sacrificing Surface\non Ultrathin Poly(heptazine imide) Nanosheets by KCl Grafting: A New\nStrategy to Improve the Photocatalytic Production of H<sub>2</sub>O<sub>2</sub>

The generation of\nH<sub>2</sub>O<sub>2</sub> through photocatalysis\nis increasingly recognized as a viable approach for addressing the\nenergy and environmental challenges encountered in industrial production\nprocesses. In this research, we synthesized ultrathin (1 nm) poly(heptazine\nimide) (PHI) nanosheets as a photocatalyst by a one-step KCl molten\nsalt process. The utilization of Fourier transform infrared and X-ray\nphotoelectron spectroscopy substantiated that the interlayer-bonded\npotassium atoms induce polarization in water molecules, facilitating\nthe attachment of hydroxyl groups on the surfaces of nanosheets. These\ngroups serve as self-sacrificing entities, promoting the reaction\nthat leads to the generation of H<sub>2</sub>O<sub>2</sub>. The preparation\ntemperature and KCl doping amount factors for the H<sub>2</sub>O<sub>2</sub> generation rate were investigated, and the mechanism of the\nKCl-bonded structure on photogeneration charge separation transport\nwas analyzed. Owing to the elevated crystallization and the presence\nof surface self-sacrificing hydroxyl groups, the rate of H<sub>2</sub>O<sub>2</sub> production reaches 6117.5 and 308.35 μmol·g<sup>–1</sup>·h<sup>–1</sup> under visible-light irradiation\n(λ ≥ 420 nm) in isopropanol solution and pure water,\nrespectively. These rates are 30 and 18.7 times higher than those\nobserved for bulk g-C<sub>3</sub>N<sub>4</sub>, respectively. The\nphotocatalytic kinetic processes for H<sub>2</sub>O<sub>2</sub> formation\nand decomposition were also calculated to investigate the catalyst\nactivities.