Performance Study On Aqueous Two-Phase Systems Composed Of Piperazinium-Based Ionic Liquids And Surfactants

In this work, six piperazinium-based ionic liquids (ILs) have been synthesized and characterized. The density, viscosity and conductivity data for the binary system of one IL,(N-(2-hydroxyethyl)piperazinium propionate), with three molecular solvents, water, methanol and ethanol, are determined to provide fundmental data for applications.The ILs and several surfactants have been investigated to find novel IL-based aqueous two-phase systems (ATPS). On the basis of the phase behavior observations for a variety of systems of ionic liquid+surfactant+water, two specific systems of N-ethylpiperazinium tetrafluroborate ([C2pi][BF4])+sodium dodecyl sulfate (SDS)+H2O and N-phenylpiperazinium tetrafluroborate ([Phpi][BF4])+sodium dodecyl benzene sulfonate (SDBS)+H2O with appropriate compositions are found to have the abilities to generate ATPS. The ATPS regions in the ternary phase diagrams are then determined. The macroscopic properties are investigated from the observation and analysis of phase volume ratio and density. The phase compositions and microstructures are observed by UV,1H NMR, DLS and TEM. It is indicated that the ILs and surfactants are concentrated in the lower phase for both of the systems. The density difference between the upper and the lower phases in [C2pi][BF4]+SDS+H2O system is about0.003g-cm-3, which is one magnitude smaller than that in [Phpi][BF4]+SDBS+H2O system. As a result, it takes a longer phase separation time for the former system than for the latter system. Self-assembled vesicles with the diameter of hundred nanometres are found for the ATPS of [C2Pi][BF4]+SDS+water. The [C2pi]+cations of the piperazinium-based IL are mainly packed inside the vesicles through significant interactions between [C2pi]+and [C12OSO3]-. The packing effect contributes to the self-assembly of vesicles and further results in the slow phase separation. However, the phase separation for the ATPS of [Phpi][BF4]+SDBS+H2O is resulted from the salting-out effect, the IL and surfactant are mainly concentrated in the lower phase, and only micelles are found, which are disordered in appearance and are much small in size. Furthermore, these two kinds of ATPS have been used to extract dyes, crystal violet and malachite green. The content of dye is determined by UV-Vis spectrophotometer. The influences of mass ratio of surfactant/ionic liquid and concentration of dye on the extraction performance are discussed in detail. The experimental results show that both of the [C2pi][BF4]+SDS+H2O and [Phpi][BF4]+SDBS+H2O systems have much high extraction efficiencies of the dyes. The extraction ratios in the ATPS of [C2pi][BF4]+SDS+H2O can be higher than99%in the experimental dye concentration range from10-6to10-3mol·L-1.