Carbon nitride quantum dots decorated with cyano groups for boosting photocatalytic hydrogen peroxide production

The photocatalytic hydrogen peroxide (H₂O₂) production by graphitic carbon nitride is a sustainable and environment-benign alternative approach of conventional anthraquinone autoxidation technology, but it is great challenges to promote two-electron O₂ reduction and water oxidation. Herein, we present the well-dispersed graphitic carbon nitride quantum dots decorated with cyano groups (Na-CNQD and K-CNQD) by thermal polymerization of melamine in the presence of metal fluoride. The quantum confinement and edge effect have endowed the photocatalysts with rich active sites, wide light absorption range and the inhibited charge recombination. The cyano moieties function as O₂ reduction centers to accept the photogenerated electrons and facilitate their rapid transfer to O₂ molecules. This process enables the selective two-electron reduction of O₂, leading to the production of H₂O₂. Concurrently, the valence band holes on the heptazine moiety oxidize water into H₂O₂. These synergistic effects promote photocatalytic H₂O₂ production from O₂ and H₂O without the need for additional photosensitizers, organic scavengers and co-catalysts. In contrast, pristine carbon nitride nanosheets remain inactive under the same conditions. This study offers new strategies for rational design of carbon-based materials for solar-to-chemical energy conversion.