K-Doping of Graphitic Carbon Nitride: A Pathway for Highly Efficient Photocatalytic Synthesis of Hydrogen Peroxide

The photocatalytic synthesis of hydrogen peroxide (H₂O₂) has emerged as a promising alternative to the energy-intensive anthraquinone process. Among various photocatalysts, graphitic carbon nitride (g-C₃N₄), as a metal-free semiconductor with visible-light responsiveness, has demonstrated exceptional potential for the selective production of H₂O₂. In this work, a K-modified g-C₃N₄ photocatalyst (KCN) was facilely synthesized via a secondary calcination method using potassium chloride (KCl) as the doping precursor. The optimized sample KCN-6 exhibited remarkable H₂O₂ generation activity, achieving a production rate of 409.4 μmol·g^–1·h^–1 in a 10% ethanol solution, an 8-fold enhancement compared to that of pristine g-C₃N₄. Subsequently, a cyclic test was conducted, and its performance remained at 90% after five cycles. At the same time, the H₂O₂ yield further increased to 818.9 μmol·g^–1·h^–1 under sunlight irradiation, highlighting its practical applicability. The superior performance stems from the synergistic effect of K incorporation and modification of cyano groups, which narrows the band gap, broadens light absorption, and facilitates charge-carrier separation. Based on the detection of active species, a plausible mechanism involving a two-step single-electron-transfer pathway was proposed. This study elucidates that K incorporation can modulate the photophysical properties and charge-transfer dynamics, offering valuable insights for designing high-performance, solar-driven photocatalytic systems for sustainable H₂O₂ production.