Chemical Modification of a Sulfonated Membrane with a Cationic Polyaniline Layer to Improve its Permselectivity

The surface of a cation-exchange membrane (Neosepta) bearing sulfonate groups was modified by a thin polyaniline layer to produce a thin positively charged layer at its surface. This modification induces a slight modification of the surface morphology as evidenced by scanning electron microscopy and a decrease in ion exchange capacity. The presence of the polyaniline layer was confirmed by X-ray photoelectron spectroscopy. The selectivity of the modified and unmodified membranes toward protons vs. metallic cations such as and were determined after electrodialysis in a two-compartment electrochemical cell. The data indicate that the transport of the metallic cations is decreased significantly following the modification of the membrane with the cationic polyaniline layer. The latter allows the transport of protons from the catholyte to the anolyte compartment with a much improved selectivity since the divalent cations are excluded from the membrane due to the electrostatic barrier created by the thin protonated polyaniline layer.