Engineering nitrogen-deficient K-doped g-C3N4 for enhanced H2O2 photosynthesis and concurrent alcohol-to-aldehyde conversion under visible light

Abstract

The strategic coupling of photocatalytic H2O2 production with the selective oxidation of alcohols to value-added aldehydes represents a transformative approach toward maximizing solar-to-chemical energy conversion. To realize such a dual-function system, potassium-doped graphitic carbon nitride containing nitrogen vacancies (KCN-Nv) has been synthesized via a molten-salt-assisted KOH-etching strategy. The optimized photocatalyst exhibits a high selectivity of approximately 99% for the oxidation of 4-methoxybenzyl alcohol to anisaldehyde, along with a high H2O2 production rate of 8789 μmol g−1 h−1. It also achieves an apparent quantum yield of 4.97%, significantly outperforming most previously reported g-C3N4-based photocatalysts under similar conditions. The superior performance of KCN-Nv arises synergistically from the structural and electronic modifications introduced during synthesis. KCl–LiCl molten-salt treatment introduces interlayer K+ ions and cyano groups, which enhance the separation and transport of photoinduced charge carriers while also promoting proton capture during the reaction. Meanwhile, KOH etching generates nitrogen vacancies, which strengthen O2 adsorption and further improve intralayer charge mobility. Notably, the proximity of cyano groups and nitrogen vacancies creates a proton- and oxygen-enriched microenvironment, significantly accelerating H2O2 formation. This study demonstrates that the synergistic co-engineering of K doping, cyano functionalization, and nitrogen vacancies in g-C3N4 provides a potent strategy for designing dual-function photocatalysts capable of integrated H2O2 photosynthesis and selective alcohol oxidation under visible light.