Surface modification of thin film composite membrane support layers with polydopamine: enabling use of reverse osmosis membranes in pressure retarded osmosis

Previous investigations of forward osmosis and pressure retarded osmosis identified asymmetric membrane support layer hydrophilicity as critical to obtain high water flux. In this study, the support layers of two commercially available thin film composite reverse osmosis membranes were modified to enhance their hydrophilicity. The membrane support layers were coated with polydopamine, a novel bio-inspired hydrophilic polymer. This resulted in increased hydrophilicity and a corresponding increase in 'wetted porosity' and reduced internal concentration polarization. The modified membranes were then characterized for contact angle, salt rejection, hydraulic permeability, salt flux, and osmotic flux. The results were promising, indicating that the modified reverse osmosis membranes exhibited an eight to fifteen fold increase in flux performance under test conditions when compared to baseline control data. This modification method, which is scalable, has the potential to enable the use of existing thin film composite membranes for all engineered osmosis applications.