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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 %.

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Hydrogels with ion exchange properties were synthesized from compounds derived from wood biopolymer hemicellulose and from commercial vinyl monomers to be tested as active materials for the removal of Cu(II), Cr(VI), and As(V) ions. The hemicellulose O-acetyl galactoglucomannan (GGM) was used as the precursor material, and through a transesterification reaction, GGM was converted into a macromonomer GGM–glycidyl methacrylate (GGM-GMA). Subsequently, the GGM-GMA macromonomer, containing more than one methacrylate group, was used as a crosslinking agent in the synthesis of hydrogels through free-radical polymerization reactions in combination with a 2-acrylamido-2-methyl-1-propanesulfonic acid monomer to produce a cation exchange hydrogel. Also, (3-acrylamidopropyl)trimethylammonium chloride monomer was applied together with the GGM-GMA to form hydrogels that can be used as anion exchange hydrogel. The hydrogels were characterized by Fourier transform-infrared (FT-IR), 1H-NMR spectroscopy, and thermogravimetric analysis (TGA), as well as derivative thermogravimetry (DTG). The microstructure of the hydrogels was characterized by scanning electron microscopy (SEM) analysis with X-ray microanalysis energy-dispersive spectroscopy (EDS). The results obtained regarding the absorption capacity of the Cu(II), Cr(VI), and As(V) ions were studied as a function of the pH value and the initial concentration of the metal ions in the solutions. Absorption was carried out in consecutive batches, and it was found that the poly(GGM-GMA/AMPSH) hydrogel reached an absorption capacity of 90 mg g–1 for Cu(II). The poly(GGM-GMA/APTACl) hydrogel reached values of 69 and 60 mg g–1 for Cr(VI) and As(V) oxyanions, respectively. Tests with polymer blends (mixtures of anionic and cationic hydrogels) were also carried out to remove Cu(II), Cr(VI), and As(V) ions from multi-ionic solutions, obtaining satisfactory results.

Polypropylene (PP) membranes incorporating poly [(ar-vinylbenzyl) trimethylammonium chloride] P(ClVBTA), and poly[sodium (styrene sulfonate)] P(SSNa) were modified via an "in situ" radical polymerization synthesis. Two methods were used for impregnation of the reactive solution: pressure injection and plasma superficial activation with argon gas. The following conditions were varied: the monomer concentrations, number of injections, and cross-linked concentration. The modified polypropylene membranes were then characterized using scanning electron microscopy/energy dispersive X-ray spectroscopy, Fourier transform-infrared spectroscopy, electrokinetic potential, and Donnan dialysis for the chromium ions transport. The modified membranes exhibited a hydrophilic character with a water uptake capacity between 15% and 20% and a percent modification between 2.5% and 4.0%. This was compared with the results of an unmodified polypropylene membrane as the blank and the mentioned polypropylene membrane has not the capacity to uptake water because this kind of material is highly hydrophobic. Hexavalent chromium ions were efficiently transported by the modified membranes containing P(ClVBTA) via a plasma method and it achieved 59.2% extraction at pH 9.0 using a 1-mol L 21 NaCl extraction agent. Therefore, unmodified polypropylene membrane shows an extraction percentage close to 10% from the hexavalent chromium ions at pH 9.0. In the same way, the trivalent chromium transport using membranes modified with P(SSNa) achieved 49.0% extraction at pH 2.0 using 1 3 10 21 mol L 21 HNO 3 and 1 mol L 21 NaCl as the extraction agents. Moreover, the unmodified polypropylene membrane reached a value close to 10% from the trivalent chromium ions using 1 3 10 21 mol L 21 HNO 3 and 1 mol L 21 NaCl.