Diffusional Transport of Ions in Plasticized Anion-Exchange Membranes

Abstract

Diffusional transport properties of hydrophobic anion-exchange membranes were studied using the polymer inclusion membrane (PIM). This class of membranes is extensively used in the chemical sensor and membrane based separation processes. The samples of PIM were prepared by physical containment of the trioctylmethylammonium chloride (Aliquat-336) in the plasticized matrix of cellulose triacetate (CTA). The plasticizers 2-nitrophenyl octyl ether, dioctyl phthalate, and tris(2-ethylhexyl)phosphate having different dielectric constant and viscosity were used to vary local environment of the membrane matrix. The morphological structure of the PIM was obtained by atomic force microscopy and transmission electron microscopy (TEM). For TEM, platinum nanoparticles (Pt nps) were formed in the PIM sample. The formation of Pt nps involved in situ reduction of PtCl(6)(2-) ions with BH(4)(-) ions in the membrane matrix. Since both the species are anions, Pt nps thus formed can provide information on spatial distribution of anion-exchanging molecules (Aliquat-336) in the membrane. The glass transitions in the membrane samples were measured to study the effects of plasticizer on physical structure of the membrane. The self-diffusion coefficients (D) of the I(-) ions and water in these membranes were obtained by analyzing the experimentally measured exchange rate profiles of (131)I(-) with (nat)I(-) and tritiated water with H(2)O, respectively, between the membrane and equilibrating solution using an analytical solution of Fick's second law. The values of D(I(-)) in membrane samples with a fixed proportion of CTA, plasticizer, and Aliquat-336 were found to vary significantly depending upon the nature of the plasticizer used. The comparison of values of D with properties of the plasticizers indicated that both dielectric constant and viscosity of the plasticizer affect the self-diffusion mobility of I(-) ions in the membrane. The value of D(I(-)) in the PIM samples did not vary significantly with concentration of Aliquat-336 up to 0.5 mequiv g(-1), and thereafter D(I(-)) increased linearly with Aliquat-336 concentration in the membrane. The self-diffusion coefficients of water D(H(2)O) in PIM samples were found to be 1 order of magnitude higher than the value of D(I(-)) and varied slightly depending upon the plasticizer present in the membrane. It was observed in electrochemical impedance spectroscopic studies of the PIM samples that diffusion mobility of NO(3)(-) ions was 1.66 times higher than that of I(-) ions, and diffusion mobility of SO(4)(2-) ions was half of that for I(-) ions. The theoretical interpretation of experimental counterions exchange rate profiles in terms of the Nernst-Planck equation for interdiffusion also showed higher diffusion mobility of NO(3)(-) ions in the PIM than Cl(-), I(-), and ClO(4)(-) ions, which have comparable diffusion mobility.

A fluorophore-labelled copper complex: crystal structure, hybrid cyclic water–perchlorate cluster and biological properties

“…(2017). C73, 710-717 inorganic anions in nature and biological systems (Sodaye et al, 2006;Kumar et al, 2011). Inorganic anion-water clusters remain relatively unexplored compared to the large number of reports on water clusters (Barbour et al, 1998;Moorthy et al, 2002;Dai et al, 2008;Jin et al, 2010 (Reger et al, 2006).…”

Mathematical modeling of the extraction of uranium(VI) into a polymer inclusion membrane composed of PVC and di-(2-ethylhexyl) phosphoric acid

“…PIMs have attracted increasing interest due to their potential to reduce the chemical hazards associated with conventional solvent extraction technologies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In PIM techniques, an extraction reagent is encapsulated in a base polymer, eliminating the need for flammable and toxic solvents as diluents.…”

Determination of the initial flux of polymer inclusion membranes

“…PIMs have been developed as a safer alternative to liquid-liquid extraction techniques (commonly referred to as solvent extraction, SX), which often require large inventories of toxic, volatile and flammable chemicals. Many researchers have successfully adapted existing SX technologies to PIM systems [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], and work continues towards better understanding the fundamental processes that underpin PIM extraction and transport.…”