Study by impedance spectroscopy of polymeric membranes modified by adsorption of anthraquinone-type redox mediators and conductive polymers

The objective of this work was to study, by impedance spectroscopy, polymer membranes modified by adsorption of anthraquinone-type redox mediators and conductive polymers. For that, asymmetric cellulose membranes were modified by adsorption of a textile dye (acid blue 129 or AQN-129) and a conductive polymer (poly(anilinesulfonic acid) or PASA). Membrane modification was performed by adsorption of AQN-129/PASA system from aqueous solution at different levels of ionic strength (low, half, and high). Later, interaction with divalent metal ions was analyzed by diafiltration experiments and electrochemical impedance spectroscopy using the single-sine technique. Results suggest that AQN-129 adsorption was enhanced with the increase of ionic strength (7.7, 13.8, and 16.2 % for low, half, and high ionic strength, respectively), average permeability coefficients for modified membranes decreased from 7.5 × 10⁻¹⁰ to 2.3 × 10⁻¹⁰ m³/m²sPa. In addition, for modified membranes, divalent metal ion retention increased in the following order Pb²⁺ > Cu²⁺ > Zn² > Cd²⁺ > Co²⁺ > Ni²⁺. It is concluded that asymmetric cellulose membrane can change strongly their dielectric response by adsorption of conductive polymer. It was observed that changes in dielectric response can be modulated by adsorption of small amounts of AQN-129. Finally, results suggest that novel membranes could be developed by an adequate control of AQN-129 and PASA adsorption for different applications based on their dielectric response.