Preparation of PVDF-based polymer inclusion membrane using ionic liquid plasticizer and Cyphos IL 104 carrier for Cr(VI) transport

A new type of polymer inclusion membrane (PIM) was prepared and applied in Cr(VI) transport. The novel PIMs are composed of three main components: poly(vinylidene fluoride) (PVDF) as support, 1-alkyl-3-methylimidazolium hexafluorophosphate or tetrafluoroborate ([Cnmim][PF6] or [BF4] (n = 4,8)) as ionic liquid plasticizers (ILPs) and phosphonium IL trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos IL 104) as carrier. The effective contact area of membrane for Cr(VI) transport was increased due to the enhanced surface roughness and the contact angle by using ILPs, which also led to the permeability coefficient (P) increasing four times faster than that without ILPs. It was found that [C8mim][BF4] as plasticizer had the maximum P value 19.64 μm s−1. The flux of Cr(VI) was affected by both HCl concentration in feed phase and NaOH concentration in stripping phase. The P of membrane with Cyphos IL 104 as carrier was 13 times faster than that of Aliquat 336. Compared with supported liquid membrane (SLM) and other PIMs, longer reusability and larger flux were found for the new prepared PIMs.

Research highlights
► In this paper, imidazolium ionic liquids (ILs) [C4mim][PF6], [C8mim][PF6], [C8mim][BF4] and [C8mim][NTf2] were first used as membrane plasticizers instead of molecular plasticizers in polymer inclusion membrane (PIM).
► A new type of PIM was prepared and applied in Cr(VI) transportation. Compared with supported liquid membranes and other PIMs, there were some advantages of the novel PIMs such as longer reusability and larger flux.
► The structure of membrane was changed with ILs added. 1-Alkyl-3-methylimidazolium ILs in PIMs enhanced the surface roughness and the contact angle hence they enlarge the effective contact area of membrane for Cr(VI) separation.