| Abstract [eng] |
Ionic liquids (ILs) is an extremely attractive study material in spectroscopy due to their variable abilities and wide range of applications. Most notably, ionic liquids are great designer solvents, as their abilities can be tuned to match a specific solute and negligible vapor pressure let them serve as "green" solvents by replacing volatile and toxic industrial solvents. On the other hand, synthesis of imidazolium-based ILs require much of traditional solvents for preparation and purification. Water can drastically change the properties of ionic liquids, therefore it is crucial to study the effects of water on ionic liquids. The main goal of this work was to investigate effect of imidazolium ring containing ILs, namely 1-butyl-3-methylimidazolium iodide, -bromide, -chloride and -nitrate, on -[O–H] stretch band using Raman spectroscopy. To achieve the goal, following objectives were established: to study -[O–H] bands integral intensities dependencies on water concentration in the mixture and investigate the possible structural changes in both ILs and water; to determine depolarization ratios for the -[O–H] bands, assess and study their dependence on water concentration. Conclusions: Upon increasing the water molar fraction in the mixtures with ILs containing halide anions, a blue shift of ν3270 and ν3450 -[O–H] bands and a red shift of ν3650 -[O–H] band were detected in the Raman spectra. The -[O–H] bands shifts correlate well with two-dimensional analysis results. It could be a sign to the weaking of hydrogen bonds. Furthermore, two critical slope change points at XH2O≈0,4 and ≈0,7 were determined in the S3270/(S3270+S3450+S3650) integral intensity ratio. The most prominent changes in slopes for all of the studied ILs are at the ≈0,7 molar fraction of water, varying slightly for each IL. The points could be sorted out in this particular manner: XH2O=0,75±0,02 for [Cl]- anion, XH2O=0,69±0,02 for [Br]-, XH2O=0,66±0,02 for [I]- and XH2O=0,56±0,02 for [NO3]-. Lastly, polarized Raman spectra of the ILs aqueous solutions were measured and depolarization ratios for ν3270 and ν3450 -[O–H] bands were determined. For the ν3270 band the depolarization ratio decreases slightly throughout the whole concentration range, reaching 0,2±0,08 value, whereas ν3450 band's depolarization ratio decreases from 0,40±0,08 to 0,20±0,08. Only in the case of [BMIM][NO3]- the ν3450 band's depolarization ratio slightly, suggesting the symmetry of -[O–H] bands is decreasing. |
