Facilitated transport of europium(III) ions across fixed-site membrane

Abstract

Fixed-site membranes were prepared by UV initiated in situ polymerization of the functional monomers in pores of the poly(propylene) host membranes for the facilitated transport studies. The crosslinker N-N-methylene-bis-acrylamide (5 mol.%) was used to produce the crosslinked stable gel in pores of host poly(propylene) membrane. The ethylene glycol methacrylate phosphate (EGMP) was selected as a functional monomer due to its phosphate group that has strong complexing ability towards lanthanides/actinides ions. However, the transport rate of Eu 3+ ions across the EGMP membrane separating feed and receiver compartments of a permeation cell was quite slow due to strong binding of ions with fixed phosphate sites in the membrane. In order to enhance the transport rate of Eu 3+ ions across the fixed-site membrane, the EGMP was polymerized along with a co-monomer like 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), acrylic acid (AA), and methylmethacrylate (MM). It was observed that the presence of sulfonic acid groups (AMPS) along with phosphate groups (EGMP) in 1:1 proportion in the membrane enhanced transport rate of Eu 3+ ions significantly. The variation of uptake of Eu 3+ ions as a function of feed acidity indicated that the equilibrium selectivity of the fixed-site membrane was not affected by the presence of strong acidic group. The permeability coefficient of Eu 3+ ions across the water swollen EGMP + AMPS membrane was found to be 2.69 × 10 −3 cm s −1, which is comparable to that reported for carrier facilitated transport of trivalent ions across supported liquid membrane. The perm-selectivity of Eu 3+ over Zn 2+ ions across EGMP + AMPS membrane from feed containing 0.2 mol L −1 HNO 3 was not as high as expected from the uptake studies. For example, the uptake of Zn 2+ was only 10% as compared to 93% for Eu 3+ ions from 0.2 mol L −1 HNO 3 but the permeability coefficient of Eu 3+ ions was only three times higher than that for Zn 2+ ions across water swollen EGMP + AMPS membrane. The perm-selectivity of Eu 3+ ions over Zn 2+ ions could be improved to some extent by incorporating plasticizer in the EGMP + AMPS membrane.