A High-Pressure Study of the Effects of TiO(2) Nanoparticles on the Structural Organization of Ionic Liquids

Abstract

The local structures between nano-TiO(2) and 1-ethyl-3-methylimidazolium trifluorornethanesulfonate (EMI(+)TFS(-) ) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMI(+)TES(-)) were investigated using high-pressure infrared spectroscopy. No significant changes in C-H spectral features of EMI(+)TFS(-) were observed in the presence of nano-TiO(2) under ambient pressure. As the EMI(+)TES(-)/nano-TiO(2) mixture was compressed to 0.3 GPa, the imidazolium C-H absorptions became two sharp bands at 3108 and 3168 cm(-1), respectively, and the alkyl C-H stretching absorption exhibits a new band at 3010 cm(-1) associated with a weaker band at 3028 cm(-1). It appears that pressure stabilizes the isolated conformations due to pressure-enhanced imidazolium C-H-nano-TiO(2) interactions. Our results also reveal that alkyl C-H groups play non-negligible roles at the conditions of high pressures. The results of BMI(+)TFS(-)/nano-TiO(2) are remarkably different from what is revealed for EMI(+)TFS(-)/nano-TiO(2). The spectral features and band frequencies of BMI(+)TFS(-)/nano-TiO(2) are almost identical to those of pure BMI(+)TES(-) under various pressures. This study demonstrates that changes to the alkyl chain length of the cation could be made to control the order and strength of ionic liquid/nano-TiO(2) interactions.