UiO-66-NH2 modified thin film nanocomposite (TFN) membranes for selective separation of Li+/Co2+ in a flow electrode capacitive deionization system

Abstract

As key metal elements in lithium-ion batteries (LIBs), the recovery of lithium (Li) and cobalt (Co) showed both economic and environmental benefits. In this study, a thin-film nanocomposite (TFN) membrane with high selectivity was fabricated based on nanoscale UiO-66-NH2 particles, and the modified membranes were applied in the flow-electrode capacitive deionization device (FCDI) for the separation of monovalent and divalent cations. UiO-66-NH2 provided hydrophilic water channels and increased the permeability of Li+. TFN exhibited a rejection rate of Co2+ over 95%, and the separation factor of Li+/Co2+ was 27.44 during the operation of 150 min in FCDI with the addition of 10 mg UiO-66-NH2, which was about 1.52 times greater than that of the commercial cation-selective membrane (CSO). The size repulsion effect caused by size difference between hydrated ions and membrane pores and Donnan electrostatic repulsion force generated by positively charged membranes were evaluated to be the main basis for the ion separation of prepared membranes. The novel system using TFN membrane in FCDI had a better ability to resist Co2+ fouling and a good Li+/Co2+ separation effect. We believe these modified membranes have promising potential for the selective separation of heavy metal ions and the recycling of metal resources.