Extraction of metal ions from water using a novel liquid membrane containing ZIF-8 nanoparticles, an ionic liquid, and benzo-18-crown-6

Abstract

As a promising type of separation membrane, liquid membranes have been broadly studied. Developing and designing a liquid membrane that shows high performance and stability for ion removal is a challenge that needs to be addressed. Here, to demonstrate the effectiveness and generalization of our method, a novel polymer inclusion membrane (PIM) was developed as a liquid membrane to separate Ca²⁺. The PIM contains three major components: green polyol (GPO) as the base polymer, 1-butyl-3-methylimidazolium chloride (BMIMCl) as the plasticizer, and benzo-18-crown-6 as the carrier. Due to interesting characteristics of metal–organic frameworks (MOFs), such as their highly porous structure, they have attracted attention for separating metal ions. In this work, zeolitic imidazolate framework (ZIF) nanoparticles having a highly porous structure were used to improve the flux of Ca²⁺ through the PIM. The impact of each constituting component of the membrane was studied. The best membrane, which resulted in optimal flux, consisted of 1 g GPO, 1.5 g ionic liquid, 0.75 g crown ether, and 0.15 g ZIF-8 (a subclass of ZIF). Additionally, the employed membrane shows a higher flux compared with other similar studies. Efficaciously separating Ca²⁺ can imply that any ions can be separated using our approach while tailored compositions are provided.