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.