Thermal Stability Limits of Imidazolium Ionic Liquids Immobilized on Metal-Oxides

Abstract

Thermal stability limits of 33 imidazolium ionic liquids (ILs) immobilized on three of the most commonly used high surface area metal-oxides, SiO2, γ-Al2O3, and MgO, were investigated. ILs were chosen from a family of 13 cations and 18 anions. Results show that the acidity of C2H of an imidazolium ring is one of the key factors controlling the thermal stability. An increase in C2H bonding strength of ILs leads to an increase in their stability limits accompanied by a decrease in interionic energy. Systematic changes in IL structure, such as changes in electronic structure and size of anion/cation, methylation on C2 site, and substitution of alkyl groups on the imidazolium ring with functional groups have significant effects on thermal stability limits. Furthermore, thermal stability limits of ILs are influenced strongly by acidic character of the metal-oxide surface. Generally, as the point of zero charge (PZC) of the metal-oxide increases from SiO2 to MgO, the interactions of IL and metal-oxide dominate over interionic interactions, and metal-oxide becomes the significant factor controlling the stability limits. However, thermal stability limits of some ILs show the opposite trend, as the chemical activities of the cation functional group or the electron donating properties of the anion alter IL/metal-oxide interactions. Results presented here can help in choosing the most suitable ILs for materials involving ILs supported on metal-oxides, such as for supported ionic liquid membranes (SILM) in separation applications or for solid catalyst with ionic liquid layer (SCILL) and supported ionic liquid phase (SILP) catalysts in catalysis.

Development of flame retardant cotton fabric based on ionic liquids via sol-gel technique.

“…As previously reported, ILs have a good thermal stability and flame retardant properties [11,12,13]. In the present work, ionic liquids combined with silica precursor showed a good resistance to a direct flame.…”

Improving Gas Separation Performance of ZIF-8 by [BMIM][BF4] Incorporation: Interactions and Their Consequences on Performance

“…However, based on the findings of a previous study, 30 we interpret the interactions of ZIF-8 with the IL as described in the following: Due to the presence of imidazolium ring in ZIF-8, anion of IL interacts with MOF and receives electrons.This interaction lead to an increase in inner B−F bond strength, indicated by blue shifts in ν(BF 4 ) asym . As anion prefers to interact more with the MOF, its interionic interactions weakens consistently with an increase in C2−H stretching in imidazolium ring [43][44]. This change also leads to an increase in the electron density of cation and corresponding strengthening of the inner bonds in imidazolium ring.…”

Halogen free 1,2,3- and 1,2,4-triazolide based ionic liquids: synthesis and properties

“…Importantly, the T dec value of IL-1 is higher than those for some of the known imidazolium ILs with organic anions. 27,28 The Interestingly, the introduction of a nitro group into the triazole ring did not destabilize the respective anion significantly. IL-3 starts decomposing at 234 1C and loses 90% of the initial mass at 300 1C.…”