Conduction Properties of Polyethersulfone/Carbon Nanotubes (CNTs)-Based Membranes for Water Treatment: Forecast By Electrochemical Impedance Spectroscopy
Authors: Ngaboyamahina Edgard , Bossa Nathan , Glass Jeffrey T. , Wiesner Mark R. 
Published: February 2020

Pressure-driven membrane processes such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) are widely used for water treatment1-2. Recently, attention has been focused on the use of carbon nanotubes (CNTs) electrical and chemical properties to produce conductive membranes with the goals of preventing membrane fouling and enhancing mechanical properties3-4.

Fouling is one of the main issues causing the decline of filtration performance over time. The application of an external electric field on or near the membrane has been used to reduce fouling5. This may produce back transport phenomena that reduce the accumulation of foulants near the membrane, produce reactive oxidant species that may inhibit the development of biofilms and/or remove biofilms and adsorbed organic matter on membrane surfaces. These latter processes may be enhanced by formulating electrically conductive membranes. A strategy to design such membranes requires insight into the physico-chemical properties and electrochemical characterization that are relevant to forecasting filtration performance. The application of an electrical potential across membranes may also be used to characterize membranes and diagnose membrane fouling.

In this work, structural and physico-chemical characteristics of polyethersuflone-based membranes were studied where electrically conductive carbon nanotubes (CNTs) were added to the polymer. Among other characterization techniques, electrochemical impedance spectroscopy (EIS) was used to gain insight into the membrane properties. Resistance, diffusion and pore accessibility were systematically analyzed for different electrolyte concentrations. Results indicate that the addition of CNTs into the polymeric membrane changes the electronic conductivity and the ion transport within the porous structure, in part due the enhanced hydrophilicity provided by the CNTs. From the perspective of generating reactive oxidant species at the membrane interface or within the membrane matrix, charge transfer properties were also studied in the presence of a redox probe.

References

1. She, Q.; Wang, R.; Fane, A. G.; Tang, C. Y., Membrane Fouling in Osmotically Driven Membrane Processes: A Review. Journal of Membrane Science
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2. Tul Muntha, S.; Kausar, A.; Siddiq, M., Advances in Polymeric Nano-Filtration Membrane: A Review. Polymer-Plastics Technology and Engineering
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3. Shawky, H. A.; Chae, S.-R.; Lin, S.; Wiesner, M. R., Synthesis and Characterization of a Carbon Nanotube/Polymer Nanocomposite Membrane for Water Treatment. Desalination
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4. Song, R.; Yang, D.; He, L., Preparation of Semi-Aromatic Polyamide(Pa)/Multi-Wall Carbon Nanotube (Mwcnt) Composites and Its Dynamic Mechanical Properties. Journal of Materials Science
2008, 43, 1205-1213.

5. Huotari, H. M.; Trägårdh, G.; Huisman, I. H., Crossflow Membrane Filtration Enhanced by an External Dc Electric Field: A Review. Chemical Engineering Research and Design
1999, 77, 461-468.

Figure 1