Ion-selective interpenetrating polymer networks supported inside polypropylene microporous membranes for the removal of chromium ions from aqueous media

The ion-exchange properties of interpenetrating polymer networks (IPNs) have been studied to provide metal-ion transport with high selectivity. Polypropylene (PP) membranes incorporating poly[(ar-vinylbenzyl) trimethylammonium chloride], P(ClVBTA), poly[2-(acryloyloxy)ethyl]trimethylammonium chloride] P(ClAETA), poly(acrylic acid) P(AA), poly(2-acrylamidoglycolic acid) P(AGA), poly(glycidylmethacrylate-N-methyl-d-glucamine) P(GMA-NMG), poly(2-acrylamido-2-methyl-1-propane sulfonic acid) P(AMPS), and poly[sodium (styrene sulfonate)], P(SSNa) were modified via an "in situ" radical-polymerization. The surface of PP was activated by a hydrophilic grafted polyelectrolyte and then pressure injection was used for impregnation of the reactive solution in the membrane. The following conditions were varied: the functional monomer, grafted polyelectrolyte, and cross-linked concentration. The modified PP membranes were characterized using SEM/EDS, FT-IR, electrokinetic potential, and Donnan dialysis for the chromium ion transport. The modified membranes exhibited hydrophilic character with a water-uptake capacity between 15 and 40 % and a percentage of modification between 2.5 and 5.5 % in comparison with the behavior of the unmodified polypropylene membrane as the blank probe. Hexavalent chromium ions were efficiently transported by the modified membranes containing P(ClVBTA) (61.2 %) and only 5.8 % of trivalent chromium were extracted at pH 3.0 using a 1 mol/L NaCl solution as the extraction reagent. Similarly, Cr(III) transport using membranes modified with P(SSNa) achieved 42.1 % extraction at pH 3.0 using 1 mol/L NaCl as the extraction reagent and 2.5 % extraction was achieved for Cr(VI). Unmodified PP membrane shows Cr(VI) extraction percentage between 1.6 and 3.1 %, and Cr(III)extraction percentage between 2.3 and 2.6 %.