Improving photocatalytic performance of defective titania for carbon dioxide photoreduction by Cu cocatalyst with SCN^- ion modification

Titanium dioxide (TiO₂) with defects is a promising semiconductor photocatalyst for photoreduction CO₂, due to its unique electronic properties. However, defective TiO₂ is difficult to achieve a high yield of CO₂ photoreduction, especially the high-value-added C₂₊ hydrocarbons, due to the slow transfer of multielectron/proton and sluggish C-C coupling kinetics. Here, we combine the photoinduced deposition of copper (Cu) nanoparticle on defective titania (TiO₂-SBO) with thiocyanate anion (SCN^-, KSCN) surface modification via impregnation route to prepare a series of high performance photocatalysts (SCN-Cu/TiO₂-SBO). It was found that the production rate and selectivity of C₂H₄ of CO₂ over sample SCN-Cu/TiO₂-SBO-3 as a representative are 4.7 μmol·g⁻¹·h⁻¹ and 40%, while the CO and CH₄ yields rise by 2 times and 5 times as compared with those over bare TiO₂-SBO. This is because the Cu cocatalyst can serve as the active site for C-C coupling (via intermediate *CO-COH) and the SCN-induced surface dipole effect can enhance the carrier's dynamic behavior and accelerate the multielectron transfer, while the SCN^- ions with nucleophilicity are conducive to CO₂ adsorption as well as CO hydrogenation and the multi-proton coupling process of C₂₊ products. Furthermore, first principle calculations illustrate that the Cu species can effectively reduce the reaction energy of the key intermediate *CO-COH of ethylene, and SCN^- ions benefit to the adsorption of CO₂ molecules, and thereby being favor for the generation of ethylene.