Near-Ambient Pressure XPS and NEXAFS Study of a Superbasic Ionic Liquid with CO2

In situ photoemission and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the interaction of CO2 with an ionic liquid thin film. A thin film of the superbasic ionic liquid (SBIL) trihexyltetradecylphosphonium benzimidazolide ([P-66614][benzim]) was prepared on a rutile TiO2 (110) surface and exposed to CO2 at near-ambient pressures. NEXAFS measurements combined with density functional theory calculations indicate a realignment of [benzim](-) anions from 27 degrees from the surface normal to 54 degrees upon exposure to CO2. Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) shows evidence of irreversible CO2 absorption in thin films of [P-66614][benzim] and a greater concentration of CO2-reacted anions in the deeper layers. These results give a new perspective on CO2 uptake in ionic liquids and fundamental interactions at the liquid-gas interface. Understanding this interfacial behavior is important for developing ILs for gas capture applications and may influence the performance of other IL-based technologies.