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

Abstract

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.