Ag Nanoparticles Composited Ni(II)-MOF for Enhancing Photocatalytic CO₂ Reduction to CO

A series of Ag@NiX composite photocatalysts were successfully constructed via a chemical reduction strategy and applied to gas-solid phase photocatalytic CO₂ reduction without additional photosensitizer using H₂O as sacrificial agent. The introduction of Ag nanoparticles (Ag NPs) on a Ni-MOF, namely [Ni₂(tipe)(cca)₂(H₂O)₂] ·2DMF·2H₂O (NiX) (tipe = 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethene, H₂cca = 4-carboxycinnamic acid), effectively enhanced visible-light absorption capability of the composites and promoted separation and migration of photogenerated charge carriers. Among the prepared samples, Ag@NiX-2 exhibited optimal photocatalytic performance and achieved a CO production rate of 14.7 μmol g^-1 in 5 h. In situ FT-IR measurements revealed the formation of key intermediate *COOH during the CO₂ photoreduction process, thereby elucidating the reaction pathway. Theoretical calculations showed that an interfacial charge transfer occurs between Ag NPs and NiX in the Ag@NiX composite, thus reducing the reaction Gibbs free energy. This study offers a feasible approach for rational development of MOF-based composite photocatalysts toward efficient photocatalytic CO₂ reduction.