Abstract: Photocatalytic conversion of carbon dioxide (CO₂) into solar fuels offers a sustainable approach to mitigating carbon emissions and energy crises. However, this process remains hindered by inefficient charge separation and limited CO₂ adsorption/activation. Herein, we propose to tackle these challenges by constructing a ternary graphitic carbon nitride (g-C₃N₄)/carbon dots (CDs)/SnS₂ heterojunction via a CDs-confined self-assembly strategy. The CDs allow the uniform riveting of SnS₂ nano-islands onto ultrathin g-C₃N₄ nanosheets and prevent the aggregation of SnS₂ nanocrystals, which leads to the formation of numerous micro-scale Type-II heterojunction units. Additionally, CDs also function as charge transfer bridges to facilitate the separation of charge carriers. In gas-solid phase reactions without sacrificial agents, the optimized heterojunction can convert CO₂ to CO with a production rate of 28.32 µmol g^-1 h^-1 and a selectivity of 89 %, which is 10.85-fold higher than that of pristine g-C₃N₄. In situ X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and in situ Kelvin probe force microscopy (KPFM) collectively reveal enhanced interfacial charge transport and spatial separation. In situ Fourier transform infrared spectroscopy (FTIR) coupled with density functional theory (DFT) simulations confirms reduced energy barriers for CO₂ activation for the facile formation of critical intermediates (*COOH, *CO). This work demonstrates the potential of confinement engineering and interfacial electronic modulation for efficient solar-driven CO₂ conversion.

Key words: Photocatalysis, g-C₃N₄, Carbon dots, Heterojunction, CO₂ reduction