Abstract: The d-band states of catalytic materials participate in adsorbing reactive intermediate species and deter-mine the catalytic behaviors in CO₂ reduction reactions. However, surface d-band states relating to the photocatalytic CO₂ reduction reactions behaviors are rarely concerned. Herein, a slightly amount of Cd²⁺ is decorated on the surface of (CuGa)_xZn_1-2xGa₂S₄ material (Cd²⁺/(CuGa)_xZn_1-2xGa₂S₄) to tune the sur-face d-band states for improved CO₂ reduction reactions. The Cd²⁺/(CuGa)_xZn_1-2xGa₂S₄ is fabricated via the facile ions-exchange method to make that slightly Zn²⁺ is substituted by Cd²⁺. The Cd²⁺/(CuGa)_xZn_1-2xGa₂S₄ exhibits much enhanced photocatalytic activity in CO₂ reduction reactions to produce CO and water splitting to produce H₂. Physical characterizations show that the energy band structure is not changed obviously. Density functional theory reveals that Cd²⁺/(CuGa)_xZn_1-2xGa₂S₄ possesses a closer shift of d-band center to Fermi level than (CuGa)_xZn_1-2xGa₂S₄, suggesting easier adsorption of CO₂ reduc-tion reactive intermediates after Cd²⁺ decoration. Further calculations confirm that a relatively reduced adsorption Gibbs energy of reactive intermediates in CO₂ reduction reaction is required on Zn atoms in Cd²⁺/(CuGa)_xZn_1-2xGa₂S₄ material, benefiting the photocatalytic CO₂ reduction reactions. This work engi-neers surface d-band states by surface Cd²⁺ decoration, which gives an effective strategy to design highly efficient photocatalysts for syngas production.

Key words: Photocatalysis, d-band state, Density functional theory, Sulfide semiconductor, Surface modification