Preparation Of Ion-Selective Electrodes And Activity Coefficients Of Imidazolium-Based Ionic Liquids

Currently, ion-liquids (ILs) are introduced in various areas, such as electrochemistry, bioscience, catalysis and synthesis processes. The application of ILs will need physical chemistry data. This leads the studies about physical chemistry properties of ILs much more urgently than before. The information of thermodynamic properties like activity coefficent, Gibbs free energy and osmotic coefficent of ILs in solution are still vacant. As known, the activity coefficient is an important physical and chemical parameter to measure the degree of departure the actual behavior of solution from ideal or ideally dilute behavior. The activity coefficients of individual ions in electrolyte solutions play an important role in biological processes, geological studies, designing ion-exchange equipment and so on. As part of the National Nature Science Foundation of China (No.20673033), the major contents of the present work are as follows:1. The PVC membrane electrodes, complex of Cnmim-TBP as the active substance and DBP as plasticizer, were prepared for [Cnmim]Cl. These ion-selective electrodes (ISEs) work well over wide range of concentration (1.0×10^-61 mol·kg-1) with slopes close to the theoretical one. Electrode membranes with different proportion of Cnmim-TBP or different plasticizer were made, but slight differences were discovered on the response capability. All the electrodes provide high selectivity on simple cations.2. Obvious phenomenon are observed among the imidazole cations with similar structures: (1) the electrodes Cnmim-TBP have a high selectivity to [Cnmim]+ over [Cn–xmim]+ but low selectivity over [Cn+xmim]+; (2) for an interfering ion, the values of log Kpoti/j decrease about 0.5 while one CH2 group is added to 1-alkyl group of response ions; (3) for a response ion but different interfering ions, the log Kpoti/j values increase about 0.5 while one CH2 group is added to 1-alkyl of interfering ions. This is due to the difference in working mechanism of the electrods and the properties of the active substances Cnmim?TBP. The change in these selectivity coefficients shows that there are specific interactions between 1-alkyl chain of ILs and the active substances Cnmim?TBP.3. The structures of crystals of Cnmim?TBP were analysised and their melting points were also measured. Results showed that their melting points are low and decrease with increasing the carbon chain. So, the substances composing of imidazole as cation and TBP? as anion can be considered as a new type of ion-liquids.4. The mean ionic activity coefficientγ, excess Gibbs energy GE and osmotic coefficientφwere determined at different temperatures. Results showed that: (1) the activity coefficients, excess Gibbs energy of [Cnmim]Cl as the temperature (308.15 K?328.15 K) nearly change, and the osmotic coefficient of [Cnmim]Cl slightly increase with increasing the temperature (308.15 K?328.15 K); (2) for each given temperature the activity coefficients of [Cnmim]Cl decrease with increasing the concentrations; (3) theγ, GE andφvalues for [C4mim]Cl, [C6mim] and [C8mim]Cl at 298.15 K show the same order: Y[C4mim]Cl > Y[C6mim]Cl > Y[C8mim]Cl (Y standsγ, GE, andφ).5. The activity coefficents for individual ions at different temperature were also determined. Results showed that: (1) both theγ+ andγ? decrease with increasing the concentration; (2) all the values ofγCl? are decrease with increasing the temperature; (3) at the same temperature, both theγ+ andγ? follow the same order: Y[C4mim]Cl > Y[C6mim]Cl > Y[C8mim]Cl.6. Activity coefficients for the ternery systerm ([C4mim]Cl + NaCl + water) were determined. Rusults showed that: (1) both the NaCl and [C4mim]Cl in the NaCl +[C4mim]Cl +water system obey"Harned's Rule"; (2) the values of activity activity coefficients can be represented by different modols, Such as Scatchard, Pitzer, Lim-HOLL and so on; (3) the activity coefficients of [C4mim]Cl were calculated by the Friedman mixing parameters fitted by logγ(NaCl), the values are in agreement with those determined by [C4mim]?ISE .7. Mean activity coefficient for entire ions in solution containing two or more electrolytes as a new concept was proposed firstly and was commented.