Preparation of poly(vinylidene fluoride-co-tetrafluoroethylene)-based polymer inclusion membrane using bifunctional ionic liquid extractant for Cr(VI) transport

A series of novel polymer inclusion membranes (PIMs) were prepared and applied in Cr(VI) transport. The PIMs were composed of bifunctional ionic liquid extractant (Bif-ILE) [trialkylmethylammonium][bis(2,4,4-trimethylpentyl) phosphinate] ([A336][C272]), [trialkylmethylammonium][di-2- ethylhexylphosphinate] ([A336][P204]), or [trialkylmethylammonium][di-(2- ethylhexyl)orthophosphinate] ([A336][P507]) as the carrier, 1-octyl-3- methylimidazolium hexafluorophosphate or tetrafluoroborate ([C ₈mim][PF ₆] or [BF ₄]) as the ionic liquid plasticizer (ILP), and poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF) as the polymer. ILP played a key role for the permeability coefficient (P). The maximum P values of [A336][C272], [A336][P204], and [A336][P507] PIMs were 1.39, 1.41, and 0.66 times higher than that without the plasticizer, respectively. The HCl concentration in the feed phase and NaOH concentration in the stripping phase had effects on the flux of Cr(VI). The maximum initial flux (J _i) was 40.08 μmol m ^-2 s ^-1 using the [A336][P204] PIM when the initial HCl concentration in the feed phase was 0.20 mol L ^-1 and the NaOH concentration in the stripping phase was 0.05 mol L ^-1. The selectivity of three PIMs followed as [A336][P204] ≈ [A336][P507] > [A336][C272]. Compared with Cyphos IL 104, the P value of Cr(VI) using [A336][C272], [A336][P204], or [A336][P507] was all higher than using Cyphos IL 104.