Design and synthesis of piperazine-based task-specific ionic liquids for liquid-liquid extraction of Cu, Ni, and Co from water

The novel synthesis of task-specific ionic liquids (TSILs) introducing piperazine substructures was described. Piperazine functional groups were easily grafted onto an imidazolium cationic derivative via a simple four-step process starting from available materials such as imidazole, ethylene glycol, and 1-butylamine or 3-dimethylaminopropylamine. Effects of pH, temperature, and structure of functional groups on the performance of liquid-liquid extraction of Cu, Ni, and Co from water were investigated. It was found that TSILs were efficient for removal of these metal ions in mild acid solutions. The TSIL with an extra nitrogen atom showed a higher capability to separate metal ions, especially for Cu. This may be ascribed to the intrinsic structure of the functional groups - the more coordination sites, the higher the affinity for the metal ions. Furthermore, the thermodynamics indicated that the extraction process was exothermic and spontaneous in nature.