Effect of F− on photocatalytic H2O2 evolution activity of g-C3N4 nanotubes and fs-TAS mechanism study

Hydrogen peroxide (H₂O₂) is extensively used in medical disinfection, water treatment, and environmental protection. To achieve the green synthesis of H₂O₂, g-C₃N₄-based photocatalysis is an effective strategy and shows great potential. Nonetheless, single g-C₃N₄ exhibits poor photocatalytic properties due to severe photogenerated charge recombination. To solve this challenge, this work enables F^–adsorption on the surface of g-C₃N₄ nanotubes in solution driven by Coulomb forces through pH adjustment and the addition of NH₄F. The photocatalytic H₂O₂ production rate of the optimal F^–-decorated g-C₃N₄ is three times higher than that of pure g-C₃N₄, attributing to the synergistic effect of F^–and H⁺. Quenching experiments verify that the photocatalytic H₂O₂ production process of CNF is a two-electron oxygen reduction process. Electron quenching dynamics of g-C₃N₄ and CNF are revealed by femtosecond transient absorption spectroscopy (fs-TAS). Compared to pure g-C₃N₄, CNF has an additional ultrashort lifetime (3.1 ps) representing the interfacial electron transfer from the conduction band of g-C₃N₄ to F^–. In situ fs-TAS results show that the interfacial electron transfer rate and electron utilization efficiency are respectively increased from 1.5×10⁸ s^–1 and 19% in air to 5.0×10⁸ s^–1 and 45% in O₂ atmosphere with ethanol sacrificial agent. Hence, the O₂, H⁺, and photogenerated electrons are key substances in the H₂O₂ evolution. This work has elucidated the dynamics mechanism of enhanced photocatalytic performance of F^–-modified g-C₃N₄ and provides inspiration for the design and synthesis of efficient g-C₃N₄-based photocatalysts.