Nitrogen-doped carbon quantum dots bridging α-Fe₂O₃@g-C₃N₄ to promote photocarrier separation for efficient photocatalytic hydrogen production

Utilizing the upconversion fluorescence (UCFL) property of nitrogen-doped carbon dots (NCDs), they were incorporated into a nano α-Fe₂O₃@g-C₃N₄ composite to enhance its performance in the hydrogen evolution reaction.Through the coupling reaction between the carboxyl groups on the surface of nitrogen-doped carbon quantum dots (NCDs) and the amino groups on the surface of α-Fe₂O₃@g-C₃N₄ (FO@CN), a core-shell structured NCDs-α-Fe₂O₃@g-C₃N₄ (NCD-FO@CN) nanocomposite was successfully prepared. Its morphology, composition, and structure were characterized using HRTEM, XRD, N₂ adsorption-desorption isotherms, FTIR, and XPS. The results indicate that NCD-FO@CN possesses a suitable band structure that meets the thermodynamic requirements for water reduction to produce hydrogen. The introduction of NCDs effectively enhances the separation and migration efficiency of photogenerated charge carriers. Based on a comprehensive analysis of the band structure, electron transfer, and work function of NCD-FO@CN, an S-scheme heterojunction charge transfer mechanism was confirmed. The NCDs act as electron mediators and photosensitizers. Leveraging their upconversion fluorescence properties, electrons (e⁻) accumulate in the conduction band of C₃N₄, while holes (h⁺) accumulate in the valence band of α-Fe₂O₃. Experimental and theoretical calculation results demonstrate that the photogenerated electrons from the NCD-FO@CN system reduce water molecules to H₂. Using triethanolamine as a sacrificial agent at pH=8, the hydrogen production rate of NCD-FO@CN reaches 2156.5 μmol· g⁻¹·h⁻¹, which is 9.09 times higher than that of pure α-Fe₂O₃.When using tap water, lake water, seawater, and wastewater as reaction mediums, the NCD-FO@CN photocatalytic system exhibits hydrogen production rates of 2006.6, 1959.8, 1876.5, and 1651.3 μmol·g⁻¹·h⁻¹, respectively, demonstrating excellent photocatalytic hydrogen evolution performance and promising application prospects.