Gas/solid/liquid triphase interface of carbon nitride for efficient photocatalytic H2O2 production†

Abstract

Photocatalytic two-electron oxygen reduction offers a sustainable method to produce hydrogen peroxide (H₂O₂). However, the efficiency of carbon nitride (CN) in this process is hindered by serious charge recombination and slow diffusion of oxygen. This work reports the thermal vapor-assisted surface chemical modification of CN by 4-aminobenzoyl groups (PABA/CN), which alters the conjugation system, extends the light absorption range, and enhances charge separation and electron transfer. Besides, it tunes the CN surface to be hydrophobic, which forms a gas/solid/liquid triphase interface in photocatalytic H₂O₂ production, and thus significantly improves O₂ diffusion and proton supply for photosynthesis of H₂O₂. Photocatalytic experiments revealed that PABA/CN delivered an H₂O₂ yield of up to 745 μmol g⁻¹ h⁻¹ in pure water, 8 times that of pristine CN, ranking among the top performances of CN-based photocatalysts. Moreover, its selectivity reached 70%. Mechanism studies identified a two-step one-electron oxygen reduction reaction pathway for H₂O₂ photoproduction. Overall, this work simultaneously addresses the issues of mass transfer of O₂, light harvesting, and charge separation of CN in photosynthesis of H₂O₂via surface chemical modification with 4-aminobenzoyl moieties, which extends π-conjugation and imparts surface hydrophobicity.