Ionic Liquids as homogeneous photocatalyst for CO2 reduction in protic solvents

Abstract

The study focuses on the photocatalytic reduction of CO2 in protic solvents such as iPrOH or H2O and in the presence of different imidazolium-based ionic liquids (IL). Under UV–vis irradiation, the dilute IL solution adsorbs light, which allows the generation of radical species via electrons produced at the IL, and thus the reduction of CO2. The nature of the solvent impacts the strength of the interaction between the anion and the cation in the IL. The cation functions as an activated species that produces electrons to give the CO2•− radical, and the anion activates the solvent in a way that weakens the HOR bond. All of this contributes to (i) providing protons needed for CO2 reduction, (ii) reducing the energy barrier to CO2 reduction, and ultimately (iii) promoting its efficiency. The important factors we explored are the light adsorption capacity and the value of the Kamlet-Taft (K-T) β parameter, which both have a synergistic effect on the CO2 reduction efficiency. Finally, in aqueous media, the influence of pH was also studied on the selectivity.

Keywords

• Ionic Liquid
• Photocatalytic CO2 reduction
• UV–vis adsorption
• Kamlet-Taft (K-T) β parameter
• Protic solvent
• pH impact