CdWO₄ Sub-1 nm Nanowires for Visible-Light CO₂ Photoreduction

Quantum size effect usually causes energy level splitting and band broadening as material size decreases. However, this may change again by the surface adsorbents, doping and defects, which rarely attracts much attention. Herein, CdWO₄ sub-1 nm nanowires (SNWs) with oleylamine adsorption, PO₄ ^3--doping and oxygen defects are synthesized by combining Cd(CH₃COO)₂, H₃PW₁₂O₄₀ (PW₁₂) and oleylamine (abbreviated as PO₄ ^3--CdWO₄-X SNWs). Compared with bulk CdWO₄, they exhibit unexpected absorption spectra (extended from 292 nm to 453 nm) and band gap (reduced from 4.25 eV to 2.74 eV), thus bringing remarkable visible-light CO₂ photoreduction activity. Under 410 nm LED light irradiation, PO₄ ^3--CdWO₄-40 SNWs exhibit the highest photocatalytic performance with a CO₂-to-CO generation rate of 1685 μmol g^-1 h^-1. Density functional theory (DFT) calculations demonstrate the adsorbed oleylamine raises the valence band and enhances the adsorption of reaction substrate and intermediates, thus decreasing their reduction energy barriers. Furthermore, PO₄ ^3--doping and oxygen defects will generate defect energy band below the conduction band of PO₄ ^3--CdWO₄-40 SNWs, resulting in remarkable visible light absorption and superior photocatalytic CO₂ reduction performance. This work highlights the significant impacts of surface adsorbents, doping and defects on the physicochemical and catalytic properties of sub-nano materials.