Fouling control in reverse osmosis membranes through modification with conductive carbon nanostructures

A conductive form of networked cellulose, prepared by incorporating carbon nanotubes, has been used in polyvinyl alcohol (PVA) membranes for reverse osmosis. The use of networked cellulose and carbon nanostructures (CNS) not only helps control the thermal, mechanical and electrical properties of the membrane, but also enhances RO performance and allows the membrane surface to be cleaned electrolytically. High surface area multi-walled CNTs become trapped in the structure of networked cellulose. The modified material has greater tensile strength and elastic modulus, indicating an improvement in the mechanical properties of the membrane. Membranes with CNS demonstrate enhanced electrocatalytic activity when tested for hydrogen evolution in an acidic medium. The membranes are successfully applied to reverse osmosis using a feed of 25,000 ppm NaCl, where the membranes with 7 wt% CNS exhibited a 93% increase in flux compared to PVA-NC with no CNS, due to the nanotubes disrupting the compression of polymer chains under pressure. The membrane surface was recovered after fouling via electrolytic cleaning where the membrane was used as the cathode and a potential of −5 V was applied for 20 min. All membranes retained a high salt rejection above 99.8%.