The structure of water in dilute aqueous solutions of ionic liquids: IR and NMR study

Two kinds of ionic liquids (ILs) (including n-butylammonium nitrate C4H9NH3NO3 and 1-ethyl-3-methylimidazolium tetrafluoroborate EmimBF4) are involved here to study their impacts on the H-bonding structure of water in dilute aqueous solutions using 1H NMR and IR spectra. It has been found that in water-rich region, the chemical shifts of water δ(H2O) in C4H9NH3NO3/water and EmimBF4/water systems decreased with increasing ILs, indicating that the structure of water could be broken by the ILs, which was consistent with IR experimental evidence. In order to uncover the differences amongst ILs, organic compounds and inorganic salts, 1H NMR and IR spectra of KNO3/water and N-methylimidazole/water in dilute aqueous solutions have also been measured. The results demonstrated that KNO3 acted similarly to ILs in breaking the water structure, but that those of N-methylimidazole had the opposite effect.