The stability of emulsion liquid membranes (ELMs) and their ability to extract Cr(VI) were investigated. The objective of this study is to compare different ELM formulations using combinations of two hydrophilic (Tween 20 and Tween 80) and two lipophilic (polyglycerol polyricinoleate (PGPR) and Span 80) emulsifiers. TOPO (tri-n-octylphosphine oxide) as a carrier and a green solvent (sunflower oil) were used to provide high extraction efficiency of Cr(VI). All these double emulsions were characterized in droplet size distribution, zeta potential, visual inspection with a microscope, and stability. The best formulation was obtained with PGPR as the inner stabilizer and Tween 80 as the outer stabilizer, leading to Cr(VI) ion removal efficiency of up to 96%.

Novel hybrid polymer inclusion membranes (PIMs) based on poly(vinylidene fluoride) (PVDF) (polymer matrix) and Aliquat 336 (ion carrier) and containing native sodium (Cloisite Na⁺ (CNa)) and organo-modified (Cloisite 30B (C30B)) Montmorillonites were elaborated and tested for the removal of toxic Cr(VI) ions from the aqueous solution. The influence of the nanoclay incorporation on the physicochemical properties of PVDF-based PIMs was studied and the resulting membrane transport properties of the Cr(VI) ions were investigated in detail. The water contact angle measurements reveal that the incorporation of the CNa nanofiller affects the membrane wettability as less hydrophilic surface is obtained in this case—~47° in the presence of CNa as compared with ~15° for PIMs with C30B. The membrane rigidity is found to be dependent on the type and size of the used Montmorillonite. The increase of Young’s modulus is higher when CNa is incorporated in comparison with C30B. The stiffness of the PIM is strongly increased with CNa amount (four times higher with 30 wt %) which is not the case for C30B (only 1.5 times). Higher Cr(VI) permeation flux is obtained for PIMs containing CNa (~2.7 µmol/(m²·s)) owing to their porous structure as compared with membranes loaded with C30B and those without filler (~2 µmol/(m²·s) in both cases). The PIM with 20 wt % of native sodium Montmorillonite revealed satisfactory stability during five cycles of the Cr(VI) transport due to the high membrane rigidity and hydrophobicity. Much lower macromolecular chain mobility in this case allows limiting the carrier loss, thus increasing the membrane stability. On the contrary, a deterioration of the transport performance is recorded for the membrane filled with C30B and that without filler. The obtained results showed the possibility to extend the PIM lifetime through the incorporation of nanoparticles that diminish the carrier loss (Aliquat 336) from the membrane into the aqueous phase by limiting its mobility within the membrane by tortuosity effect and membrane stiffening without losing its permselective properties.

In this study, polymer inclusion membranes (PIMs) consisting of cellulose triacetate (CTA) as the base polymer, 2-nitrophenyl octyl ether as plasticizer, and tricaprylmethylammonium chloride (Aliquat 336) as carrier are used for removing the acid dye (red bordeaux acid and yellow erionyl) from aqueous solution. Extraction efficiency was studied under various experimental conditions, such as pH (2–9) of the aqueous solution, the concentration of extractant in the membrane (5–30 μmol/cm²), initial dye concentration (50–250 ppm), and the stirring speed (250–400 rpm). Under the optimized experimental conditions, 99% of dyes were extracted. The Langmuir, Freundlich, and Temkin isotherm models were used to study the equilibrium extraction data. The Langmuir equations have better regression coefficient (0.95, 0.95) than Freundlich (0.96, 0.904) and Temkin (0.873, 0.909) equation describing the acid dye extraction by the matrix CTA-Aliquat 336. The kinetic data were evaluated using pseudo-first-order, pseudo-second-order and intra-particle diffusion model. The kinetic study’s results indicate that the process of removing acid dye by PIMs is described by pseudo-second-order model.