Preparation of new hybrid materials based on polymeric membranes and polarized electrodes for Cu2+ and Pb2+ photo reduction

Abstract

A new system combining ionic membranes–semiconductors is studied for the photo-reduction of metallic ions M²⁺ (Pb²⁺ and Cu²⁺) from water. For this purpose, a novel class of cellulose triacetate (CTA) membranes was developed; they were modified by polyanethol-sulfonic acid (PATSA), polyethylene glycol (PEG), polyethylenimine (PEI), polyvinyl pyrrolidone (PVP) incorporation that are selectively permeable to metallic ions. The synthesized membranes were plasticized by nitro-phenyl pentyl ether (NPPE) to improve the physical and mechanical properties. The elaborated membranes were characterized by thermal analysis (TGA), FTIR spectroscopy and Scanning Electron Microscopy (SEM). In parallel, two semi-conductors namely p-CuO and n-ZnO were prepared by precipitation in alkaline medium and characterized physically and electrochemically. The optical gaps of CuO (1.30 eV) and ZnO (3.25 eV) were obtained from the diffuse reflectance. The activation energies were deduced from the slope of the plots log (conductivity) vs. 1000/T. The electrochemical characterization was undertaken to establish the energy diagram of the system “p-CuO / water / M²⁺ electrolyte membranes/ water/ n-ZnO”, a preamble of the M²⁺ photo-electrodeposition. The conduction band of CuO (−0.11 V_SCE) is cathodic enough for the reduction of metal ions. As application the photo-electro-dialysis was successfully exploited to reduce the cations M²⁺ (Pb²⁺, Cu²⁺) under visible light. The results indicated that the combined system enhances considerably the electrons transfer and the diffusion flux of M²⁺ ions, thus giving appreciable percentages of M²⁺ reduction to elemental state. Abatements of 82 and 25 % were reached respectively for Pb²⁺ and Cu²⁺ upon visible light irradiation.