Methods of evaluating pore morphology in hybrid organic-inorganic porous materials

Hybrid materials were prepared by immobilizing ionic liquid (IL), based on grafting methylimidazolium cation on the internal surface of porous Vycor (R). The extent of the initial silane grafting, expressed as the fraction of the occupied Vycor (R) silanol groups was determined by the analysis water vapor adsorption-desorption isotherms. Chloroform was shown to be the most appropriate solvent, giving silanol occupation degree of the order of 80%. Moreover, the pretreatment of Vycor (R) at 430 K under high vacuum conditions, enhanced the monolayer grafting and this can be attributed to avoidance of silane polymerization on the Vycor (R) surface and expanded the degree of chloroform coverage up to 96%. Combination of nitrogen physisorption with SAXS led to the elucidation of the morphology of the internal surface after grafting. It was concluded that the adsorbed water on the Vycor (R) surface, in combination with the presence of residual water in the solvent, facilitated the formation of bulky, but not continuous organosilane entities, which were generated by the silane polymerization. The grafted samples were further treated with 1-methylimidazole at 358 K for 48 hours following ion exchange with the PF6-. A new methodology was developed aiming at the determination of the w/w% percentage of IL loading on the grafted materials. The method is based on appropriate analysis of the transient data of CO2 adsorption isotherms and the results were in good agreement with the analysis of the TGA measurements. (C) 2008 Elsevier Inc. All rights reserved.