Self-doped TiO2 nanotubes with surface modification by ionic liquids for enhanced photoreduction of CO2 to acetic acid

The photocatalytic reduction of CO2 to high-value hydrocarbons can both solve environmental problems and alleviate the energy crisis. As a room-temperature molten salt with designable anions and cations, ionic liquids are very popular in the field of CO2 capture. If combining ionic liquids with photocatalysts, simultaneous capture and conversion of CO2 are expected to be achieved. In this study, a [bmim][Tf2N] loaded self-doped TiO2 nanotubes (ILs-RTNTs) composite photocatalyst was developed for the photoreduction of CO2 to acetic acid. The acetic acid yield of ILs-RTNTs reached as high as 88.1 μmol gcat−1h−1, and there was no decrease after six cycles. Both the defects constructed by self-doping and the surface modification by ionic liquids strengthened the light utilization ability of the photocatalyst and enhanced the separation of photoinduced electron-hole pairs. Density-functional theory (DFT) calculations further revealed that the surface loading of ionic liquids introduced more active sites, strengthened the adsorption of CO2, changed the electronic structure, and lowered the energy barrier for electron transfer of the photocatalyst. This study will promote the versatile application of ionic liquids in the field of simultaneous capture and photoreduction of CO2.