Carbon quantum dots nano-island with atomically dispersed copper for efficient carbon dioxide photoreduction.

In this study, a novel hierarchical photocatalyst was successfully developed by coupling nitrogen‑oxygen co-doped carbon quantum dots (N,O-CQDs) confined copper single-atom nano-islands (Cu SA-NOC) anchored on g-C3N4 (CuCCN) for efficient CO2 photoreduction. The CuCCN catalyst delivers an outstanding CO evolution rate of 17.42 μmol g-1 h-1, surpassing that of pristine g-C3N4 by 10.4 times, while maintaining a high CO selectivity of 93.0%. Comprehensive characterizations confirm the atomically dispersed Cu species anchored within the N,O-CQDs nano-islands and the formation of a well-defined Cu-N2OC coordination structure. Transient absorption spectroscopy (TAS) and photoelectrochemical measurements reveal that the unique architecture of CuCCN significantly facilitates charge separation and suppresses carrier recombination. In-situ Fourier transform infrared spectroscopy (IS-FTIR) and density functional theory (DFT) calculations were employed to elucidate the reaction pathway. The results indicate that the synergistic interaction among the Cu SA sites, N,O-CQDs bridges, and g-C3N4 substrate promotes CO2 adsorption and activation, as well as reduces the energy barrier for the formation of the key *COOH intermediate, thereby enhancing both activity and selectivity. This work not only provides an effective nano-island confinement strategy for constructing stable and high-performance single-atom photocatalysts but also offers deep insights into the charge transport and synergistic catalytic mechanisms in composite photocatalytic systems.