Extraction of Na+ ions by dibenzo-18-crown-6 in biphasic aqueous systems of ionic liquid and chloroform

Abstract

The molecular dynamics simulations were carried out to explore the extraction of Na+ ions in the ionic liquid (IL)–water, chloroform–water biphasic systems containing the crown ether: dibenzo-18-crown-6 (DB18C6) to compare organic solvents such as chloroform to ionic liquid (IL) as receiving solvent phase. The free DB18C6 was found to be highly interacted with IL as compared to chloroform. The Na+–DB18C6 complex interacts preferentially with IL at the interface. The complex has higher interaction energies with IL (-47.04 kcal/mol) as compared to chloroform (-0.11 kcal/mol). The large sharp peak height for the radial distribution function in Na+–DB18C6 complex suggests high stability and strong interaction. At the IL–water interface, it was observed that the Na+–DB18C6 complex had a lower self-diffusion coefficient (0.538 × 10−9 m2/s) than other species. The spatial distribution functions further indicated that the surfaces of Na+ were very closely distributed around the active sides of crown ether in the IL–water system whereas, in chloroform–water systems, it was distributed very far from the crown ether. The present results may help us to understand the role of solvents in heavy metal ion extraction and also in the future design of crown ethers and solvents.