Investigation of confined ionic liquid in nanostructured materials by a combination of SANS, contrast-matching SANS, and nitrogen adsorption.

Small-angle neutron scattering (SANS), contrast-matching SANS, and nitrogen adsorption have been utilized to investigate the confined ionic liquid (IL) [bmim][PF(6)] phase in ordered mesoporous silica MCM-41 and SBA-15. The results suggest that the pores of SBA-15 are completely filled with IL whereas a small fraction of the pore volume, the pore "core", of MCM-41 is empty. The contrast-matching SANS measurements confirm the enhanced solubility of water in IL. In addition, they provide strong evidence that water does not enter the empty pore core of MCM-41, possibly because of the preferred orientation of the IL molecules in the adsorbed layer.

Grafting of imidazolium based ionic liquid on the pore surface of nanoporous materials--study of physicochemical and thermodynamic properties.

Supported ionic liquid phase (SILP) systems were prepared by immobilizing a methylimidazolium cation based ionic liquid onto the pore surface of two types of support, MCM-41 and Vycor. The "grafting to" method was applied, involving (3-chloropropyl)-trialkoxysilane anchoring on the supports' silanol groups, followed by treatment with 1-methylimidazole and ion exchange with PF(6)(-). Optimum surface pretreatment procedures and reaction conditions for enhanced ionic liquid (IL) loading were properly defined and applied for all modifications. A study on the effect of different pore sizes on the physical state of the grafted 1-(silylpropyl)-3-methylimidazolium-hexafluorophosphate ([spmim][PF(6)(-)]) was also conducted. The [spmim][PF(6)(-)] crystallinity under extreme confinement in the pores was investigated by modulated differential scanning calorimetry (DSC) and X-ray diffraction (XRD) and was further related to the capacity of the developed SILP to preferentially adsorb CO(2) over CO. For this purpose, CO(2) and CO absorption measurements of the bulk ionic liquid [bmim][PF(6)(-)] and the synthesized alkoxysilyl-IL were initially performed at several temperatures. The results showed an enhancement of the bulk IL performance to preferentially adsorb CO(2) at 273 K. The DSC analysis of the SILPs revealed transition of the melting point of the grafted alkoxysilyl-IL to higher temperatures when the support pore size was below 4 nm. The 2.3 nm MCM-41 SILP system exhibited infinite CO(2)/CO separation capacity at temperatures below and above the melting point of the bulk IL phase, adsorbing in parallel significant amounts of CO(2) in a reversible manner. These properties make the developed material an excellent candidate for CO(2)/CO separation with pressure swing adsorption (PSA) techniques.