[Zurück]

L. Viau, M.-A. Néouze, C. Biolley, S. Volland, D. Brevet, P. Gaveau, P. Dieudonné, A. Galarneau, A. Vioux:
"Ionic liquid mediated sol-gel synthesis in the presence of water or formic acid: which synthesis for which material?";
Chemistry of Materials, 24 (2012), 16; S. 3128 - 3134.

Sol-gel syntheses involving either neutral water or formic acid (FA) as a reactant have been investigated (1) to determine the best conditions to confine a maximum of ionic liquid (IL) inside silica-based matrices and (2) to reach the highest porosity after removing the IL from the ionogels. Several sets of ionogels were prepared from various 1-butyl-3-methylimidazolium ILs and various silica or organosilica sources as tetramethoxysilane (TMOS), a mixture of TMOS and methyltrimethoxysilane (MTMS) or a mixture of TMOS and an organically bridged precursor as 1,2-bis(triethoxysilyl)ethane (BTESE) and 1,4-bis(triethoxysilyl)benzene (BTESB). The study disclosed the critical effect of the anion on the morphology (monolith, powder) and texture of the resulting ionogels. Particularly, tetrafluoroborate anion led to monolith ionogels by a simple hydrolytic way, affording highly condensed mesoporous silicas with some fluorinated surface sites, which had never been reported before and was evidenced by ¹⁹F NMR. On the other hand, FA solvolysis turned out to be the only way to get non-exuding crack-free monoliths from ILs containing bis(trifluoromethylsulfonyl)imide [NTf₂] anion, which opens the route for applications needing transparent monolithic devices, as photochemistry or photosensing. With bulkier imidazolium and pyridinium cations, highly porous silicas have been synthesized after removing the IL by solvent extraction, which featured pore diameter and pore volume as high as 10-15 nm and 3 cm³ g^-1, respectively, and could be efficient supports for immobilizing bulky molecules (porphyrins, enzymes, organometallics etc.).

Ionic Liquids, Non-aqueous Sol-Gel, Organic-Inorganic Hybrid Materials, Mesoporous Silica

http://dx.doi.org/10.1021/cm301083r