Immobilization and melting point depression of imidazolium ionic liquids on the surface of nano-SiOx particles.

Four kinds of imidazolium-based ionic liquids (ILs) were immobilized onto the surface of nano-SiO(x) particles (d approximately 20 nm) by grinding in an agate mortar to produce a series of weight ratios of ionic liquid to nanoparticles. The physicochemical properties of immobilized ILs were investigated by differential scanning calorimetry, powder X-ray diffraction and Raman spectroscopy. It was found that the melting points (T(m)) of the immobilized ILs depressed significantly in comparison with the bulk ionic liquids. The T(m) depressions are 10, 12, 13 and 41 degrees C for [EMIM][PF(6)], [PMIM][PF(6)], [PHMIM][BF(4)] and [EMIM][I], respectively, for a loading amount of 35 wt% ionic liquid. The T(m) depression of [EMIM][PF(6)] was independent of the weight proportion of immobilized ionic liquid up to 50 wt%, indicating that nano-SiO(x) has a large capacity for immobilized ILs. The T(m) depression of [EMIM][I] is particularly significant because the H-bonding interactions of iodine anions with surface silanol groups of nano-SiO(x) particles is much weaker than that of fluorine anions with silanol groups of other investigated ionic liquids.