Reverse osmosis membranes functionalized with polyglycidol decorated hyperbranched copolymer exhibits superior filtration performance and improved fouling resistance

In this work, we report the surface modification of commercial reverse osmosis membranes with polyglycidol functionalized cross-linked hyperbranched Polyethyleneimine-polydopamine. The polymer was synthesized in a one-pot, two-step synthesis methodology and then dip-coated onto the membranes. The coated and uncoated membranes were characterized for relevant surface characteristics i.e., surface wettability, morphology, and chemistry. Contact angle measurements showed a significant reduction in CA (from ∼90-20°), implying a transformation from hydrophobic to the hydrophilic character. The major functional groups of the polymer were identified on the modified membrane surface by Fourier Transform Infra-Red (FTIR) spectroscopy. Film deposition decreased the membrane surface roughness as confirmed by Scanning Electron (FESEM) & Atomic Force Microscopy (AFM) images with the copolymer depositing in the valleys of the polyamide layer. Surface modification of the membrane with the polymer not only reduced the adhesion but also interfered with the biological activity of a gram-positive species bacteria, B. subtilis, under static conditions. The uncoated membrane had large bacterial colonies as well as thick continuous biomass; in contrast, the coated ones had a sporadic presence of individual cells and very small patches of biofilm. Filtration experiments with DI water, a synthetic 35 g/L NaCl feed and actual seawater at normal RO operating pressures (∼55 bars), showed a significant improvement in both permeate water flux as well as salt rejection: the flux increased by 30 - 50%, whereas the rejection by 10 - 15%. Long-term biofouling and subsequent cleaning of the membranes showed the fouling on the modified membranes to be largely reversible with the flux recovery > 80%.