Anthraquinone-modified triazine rich g-C3N4 for high efficiency photocatalytic H2O2 synthesis via promoting singlet oxygen conversion

Abstract

Photocatalytic hydrogen peroxide (H₂O₂) production via a two-electron oxygen reduction reaction (2e⁻ ORR) represents a sustainable alternative to the energy-intensive anthraquinone (AQ) process. Although graphitic carbon nitride (g-C₃N₄) demonstrates significant advantages in photocatalytic H₂O₂ synthesis, its efficiency is severely limited by rapid charge recombination and the competitive oxidation of the critical superoxide radical (·O₂⁻) intermediate to singlet oxygen (¹O₂). Herein, AQ-modified triazine rich g-C₃N₄ (AQ/CN-x%) was successfully constructed through molten salt-assisted polycondensation and amidation grafting reactions. The coexistence of triazine and heptazine units not only promotes the separation of photogenerated charges but also provides more modification sites for AQ anchoring. Due to its strong electron-withdrawing nature, the AQ modification further enhances the separation of photogenerated charge carriers. More importantly, the AQ moiety effectively converts the competitively generated ¹O₂ into H₂O₂via hydroanthraquinone intermediates, significantly improving the photocatalytic H₂O₂ synthesis efficiency in pure water. The optimized AQ/CN-70% catalyst achieved a remarkable H₂O₂ production rate of 165.3 μmol g⁻¹ h⁻¹, representing 4.6-fold and 13.8-fold enhancements over CN-70% and g-C₃N₄, respectively. This work provides a novel strategy for converting ¹O₂ into H₂O₂ by incorporating strongly electron-withdrawing AQ units into the triazine rich g-C₃N₄ framework, leading to a significant enhancement in photocatalytic H₂O₂ synthesis activity.