Nanostructures of Ionic Liquids Confined in Pores of SBA-15: Insights from Experimental Studies and Mean-Field Density Functional Theory

Abstract

The arrangement of ionic liquids (ILs) within mesoporous ordered silica SBA-15 is revealed from nitrogen physisorption experiments combined with non-local density functional theory analysis of the pore structure and mean-field density functional theory (MFDFT). Using MFDFT on simple lattice models, we outline possible scenarios for IL distributions within the pores and conditions under which they originate. MFDFT predictions for nitrogen adsorption on these models of pore structures modified with ILs are in qualitative agreement with the experimental results. They demonstrate that the distribution of the ILs inside the pores of SBA-15 is sensitive to solid–fluid interactions, leading to different structures as a function of loading. This study also recommends the MFDFT and lattice models as a powerful framework for the interpretation of nitrogen sorption behavior, which complements the existing theoretical and experimental techniques to characterize the structure of supported ILs.

Lattice Model of Fluid Transport in Mixed Matrix Membranes

“…In recent years, significant contributions have been made to the development of this approach to study adsorption hysteresis, capillary condensation phenomena, and diffusion processes in porous materials. [ 47–67 ]…”

How 2D Nanoflakes Improve Transport in Mixed Matrix Membranes: Insights from a Simple Lattice Model and Dynamic Mean Field Theory

“…These nonequilibrium conditions imitate conditions across a membrane. This method has been applied extensively to study the adsorption/desorption hysteresis, capillary condensation, and diffusion in porous materials. − Previously, we have demonstrated the utility of the DMFT in studies of single component fluid transport in simple slit pores, and complex, heterogeneous media . In a follow-up study, we investigated two-component systems to explain separation phenomena in sorption-driven membrane processes …”

Effect of Pore Confinement of Ionic Liquids on Solute Diffusion within Mesoporous Silica Microparticles

“…18 Other techniques to probe the interactions between ILs and pore walls in confined systems include solid-state NMR 19 and FTIR. 17 through charge interactions, 14,20,21 from which changes in the physical properties are inferred. ILs confined in mesoporous silica have been investigated as catalysts for asymmetric catalysis, Friedel−Crafts isopropylation, and trimerization reactions.…”

“…Several factors limit the use of ILs as bulk phase solvents: their cost, their viscosity and corresponding low mass transfer rate, , and their potential toxicity, emphasizing the importance of recovering ILs even in dilute solutions. Immobilization of ILs on surfaces or their confinement in a porous matrix with submicrometer pathlength takes advantage of their favorable solvent properties while mitigating the limitations of transport and solvent recovery in bulk phases. ,− …”

“…Other techniques to probe the interactions between ILs and pore walls in confined systems include solid-state NMR and FTIR . Molecular dynamics has been extensively used to study the layering of the ionic liquid cation with the pore walls through charge interactions, ,, from which changes in the physical properties are inferred. ILs confined in mesoporous silica have been investigated as catalysts for asymmetric catalysis, Friedel–Crafts isopropylation, and trimerization reactions. − Confined ILs are also promising candidates for gas adsorption.…”