Conductive CuO-CNT/PES membranes for electrochemical membrane filtration and advanced wastewater treatment

The prevalence of recalcitrant contaminants in wastewater, including organic dyes and pharmaceuticals poses serious threat to the environment owing to its complex structures and low degradability. Herein, we developed a covalently bonded CuO-CNT/polyethersulfone (PES) membrane by decorating CuO nanoparticles directly on CNT strands, followed by layer-by-layer depositions using a spray dispenser for advancing water treatment and fouling mitigation. Membrane performances were systematically evaluated using model organic compounds: the anionic Congo Red (CR), the cationic Methylene Blue (MB), and neutral antibiotic Sulfamethoxazole (SMX). At optimum external voltage (2.0 V), the organic removal efficiency was increased by 3, 4 and 5 times for CR, MB and SMX, respectively, compared to them observed without electric field. The corresponding flux recovery was improved by 59 %, 21 % and 14 % for CR, MB and SMX, respectively, exhibiting superior antifouling abilities. The performances of CuO-CNT/PES membrane under the electric field were attributed to the synergistic effects of electrostatic repulsion and indirect oxidation facilitated by hydroxyl radicals (^●OH) produced. The presence of OH radicals and short-lived Cu⁺ generated by redox conversion of Cu⁺² into Cu⁺ electrochemically was validated by X-ray photoelectron spectroscopy (XPS). Furthermore, the CuO-CNT/PES membranes demonstrated exceptional stability with high conductivity under both cathodic and anodic potentials. The degradation of organic dye can be explained by first-order reaction rate with a K₀ value of 0.0175 s⁻¹ as rate constant. Furthermore, the synthesized membrane can separate binary mixtures selectively, highlighting the potential for applying it with real wastewater treatment.