Understanding the Interplay Between Pore Structure and Ionic Liquid Interaction on the Gas Uptake of Microporous Carbons

Interfaces formed between porous carbon materials and ionic liquids (ILs) play an essential role in catalysis as well as in electrochemical energy storage and energy conversion. Profound knowledge about the formed local structures on a molecular level is essential to create the desired physicochemical environments and to control the (remaining) porosity of the involved carbon materials. In the present study, the interplay between pore structure and ionic liquid (IL) loading in CO₂-activated microporous carbons is investigated with a special focus on the gas adsorption properties of the remaining hybrid materials. Two activated carbon materials with distinct micropore sizes (AC30 and AC120) are loaded with two hydrophobic ILs, namely 1-ethyl-3-methylimidazolium-bis(trifluormethylsulfonyl)imid (EMIM TFSI) and tributyloctyl phosphonium-tris(pentafluoroethyl) trifluorophosphate (P₄₄₄₈ eFAP), at varying contents. The results reveal that IL configuration within the pores is crucial for gas uptake: EMIM TFSI maintains open porosity in larger micropores (AC120) but completely fills the smaller ones (AC30), whereas P₄₄₄₈ eFAP forms closed porosity by covering pore openings, enhancing gas uptake in residual pores (e.g., for CO₂ at 273 K). N₂ sorption at 298 K highlights the pronounced confinement effect of EMIM TFSI in smaller pores, leading to significant gas uptake. X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC) analyses confirm these configurations and show that high IL loading induces bulk-like behavior. These findings demonstrate how ionic liquids can be used to steplessly modify pore structures and influence solid-liquid-gas interfaces, providing insights into tailoring properties such as gas uptakes, hydrophobicity, and other physicochemical characteristics by their interaction with porous carbon materials.