N-doped carbon quantum dot-induced cyano-enrichment enhances K-doped C3N4 for efficient photocatalytic H2O2 production

Photocatalytic hydrogen peroxide (H₂O₂) production represents a clean and sustainable synthesis method. In this work, a synergistic dual-strategy modification was developed to achieve cascade effects for enhancing the photocatalytic activity of bulk carbon nitride. The primary modification involved innovative incorporation of nitrogen-doped carbon quantum dots (NCQS) to facilitate potassium doping. The NCQS serve a dual function. On the one hand, they act as cyano-group inducers, promoting ring-opening within the potassium-doped carbon nitride structure to form cyano groups and thereby facilitate cyano functionality enrichment. On the other hand, the NCQS act as a surface modifier that synergized with K⁺ to directly enhance charge carrier migration across interlayers and surfaces. The secondary modification employed alkaline hydrothermal treatment to introduce nitrogen vacancies (NVs). Combining the experimental results and DFT calculation, it can be seen that the enriched cyano groups and NVs modify the electronic structure of carbon nitride, which promotes the separation and transport of charge carriers while providing abundant cyano-active reaction sites for the oxygen reduction reaction. Benefiting from the modification, The KCNC5–K achieves an outstanding H₂O₂ production rate of 12,366 μmol g⁻¹ h⁻¹ (a 107.2-fold enhancement over g-C₃N₄) with a remarkable H₂O₂ selectivity of 80 %. This study not only proposes a novel approach for modulating the cyano groups on the surface of carbon nitride via incorporation of carbon quantum dots, but also offers valuable insights for the development of high-performance carbon nitride-based photocatalysts for hydrogen peroxide production.