Acidic ionic liquid immobilized on magnetic mesoporous silica: Preparation and catalytic performance in esterification

Magnetic mesoporous silica (SCF) with cobalt ferrite nanoparticles embedded in silica, exhibiting a mesoporous structure, high magnetic responsivity and paramagnetism, was prepared using a reverse microemulsion-mediated sol-gel method and then modified with 3-mercaptopropyl trimethoxysilane to achieve sulfhydryl-group-modified SCF (MPS-SCF). 1-Allyl-3-(butyl-4-sulfonyl) imidazolium trifluoromethanesulfonate ([BsAIm][OTf]) was immobilized on MPS-SCF via free radical addition. The obtained MPS-SCF and [BsAIm][OTf]/SCF were characterized by FT-IR, XRD, TEM, VSM, elemental analysis and N₂ adsorption-desorption measurements. The immobilization of [BsAIm][OTf] on MPS-SCF and the relationship between the sulfhydryl group (SH) loading of MPS-SCF and the ionic liquid loading of [BsAIm][OTf]/SCF were studied. The catalytic activities of [BsAIm][OTf]/SCF were evaluated through the esterification of oleic acid with straight-chain alcohols. The results showed that more modifications corresponded to an increase in the SH loading of MPS-SCF and a decrease in the average pore diameter and specific surface area of MPS-SCF. The more SH groups that were supported on MPS-SCF, the less ionic liquid was immobilized on [BsAIm][OTf]/SCF due to its smaller pore diameter, which hindered the diffusion and immobilization of [BsAIm][OTf]. Moreover, when the carbon number of the straight-chain alcohol increased, the mass-transfer resistance in [BsAIm][OTf]/SCF rapidly increased and the conversion of oleic acid significantly decreased under the same reaction conditions.