Extractive insights in the cesium ion partitioning with bis(2-propyloxy)-calix [4]crown-6 and dicyclohexano-18-crown-6 in ionic liquid-water biphasic systems

Abstract

We report the molecular dynamics studies on the interfacial behavior of cesium (Cs+) extraction by bis(2-propyloxy)calix [4]crown-6 (BPC6) and dicyclohexano-18-crown-6 (DCH18C6). For the benchmarking study, the phase separation for [BMIM][Tf2N]-water was validated. Thereafter, to understand the mechanism of complexation and the behavior of the crown ether ligand, crown ether (CE) molecules and Cs+NO3− ions were inserted randomly in the ionic liquid (IL)–water biphasic system. It was observed that the 2:1 Cs+-BPC6 complex formed during the simulation was more stable at the interface and was found to diffuse slowly to the IL side of the interface. On the contrary the 1:1 Cs+-DCH18C6 complex was found to be fully solvated in the bulk IL phase. The [BMIM]+ cation was found to partition to the aqueous phase and exchange with Cs+ ion in presence or absence of CE. The solubility, density plots and the snapshots of the [BMIM]+ cation at the IL–water interface indicates the dual cationic exchange. A comparison of the interfacial behavior of Cs+-BPC6 complex and Cs+-DCH18C6 complex in IL–water preformed interface system, depicted that the Cs+-BPC6 complex was stable at the interface till the end of the simulation. One the other hand, the uncomplexed DCH18C6 resided at the interface, while the Cs+ ion diffused to the bulk aqueous phase. The calculated interaction energy of Cs+-BPC6 was found to higher as compared to Cs+-DCH18C6. These results display the importance of the dual cationic exchange properties of IL and the extraction efficiency of CE for extraction of metal ions.