Pore-functionalized polymer membranes for preconcentration of heavy metal ions

Functionalized membranes containing carboxylate, phosphate and sulfonate groups were prepared by UV-initiator induced graft polymerization of the functional monomer (acrylic acid, ethylene glycol methacrylate phosphate (EGMP) and 2-acrylamido-2-methyl-1-propane sulfonic acid) with a crosslinker (methylenebisacrylamide) in the pores of poly(propylene) host membranes. The functionalized membranes thus obtained were characterized by gravimetry, FTIR spectroscopy, radiotracers and scanning electron microscopy for the degree of grafting and water uptake, presence of functional groups, ion-exchange capacity, and physical structure of the membranes, respectively. The uptakes of Cs+, Ag+, Sr2+, Cd2+, Hg2+, Zn2+, Eu3+, Am3+, Hf4+ and Pu4+ ions in the functionalized membranes were studied as a function of acidity of the equilibrating aqueous solution. Among the functionalized membranes prepared in the present work, the EGMP-grafted membrane (with phosphate groups) showed acid concentration dependent selectivity towards multivalent metal ions like Eu3+, Am3+, Hf4+ and Pu4+. The solvent extraction studies of EGMP monomer in methyl isobutyl ketone (MIBK) solvent indicated that divalent and trivalent metal ions form complexes with EGMP in 1:2 proportion, but the distribution coefficients of trivalent metal ions were significantly higher that for the divalent ions. The uptakes of Eu3+ ions in monomeric EGMP (dissolved in MIBK) and polymeric EGMP (in the forms of crosslinked gel and membrane) were studied as a function of concentration of H+ ions in the equilibrating solution. This study indicated that polymeric EGMP has better binding ability towards Eu3+ as compared to monomeric EGMP. The variation of distribution coefficients of Eu3+/Am3+ in gel and membrane as a function of H+ ion concentration in the equilibrating aqueous solution indicated that ionic species held in the membrane and gel were not same. These results indicated that proximity of functional groups (phosphate) plays an important role in metal ion binding with polymeric EGMP.