Room-temperature development of thin film composite reverse osmosis membranes from cellulose acetate with antibacterial properties

• Generation of nanoporous cellulose acetate thin film composites via spin-coating.
• Transformation of membranes to RO performance through water-swelling-induced healing.
• Membrane treatment with Ag nanoparticles leads to 4-log reduction in biofouling.

A cellulose acetate thin film composite (CA TFC) membrane was developed by direct casting of CA onto an ultrafiltration membrane support. The flux through the CA TFC membrane was, as expected, inversely proportional to the selective layer thickness. The membrane with the lowest thickness of the CA film (217 nm) initially had poor salt rejection (~55%) but relatively high permeability (~0.5 l m−2 h−1 bar−1). In contrast to asymmetric CA reverse osmosis membranes that are developed in 4 °C water baths, the CA TFC membranes were developed by subsequent swelling in room temperature water baths, thermal annealing at 81 °C, and with room-temperature incorporation of silver nanoparticles onto CA TFC surfaces by chemical reduction. The change in the physical properties as a result of the swelling process was examined with ellipsometry, grazing incidence X-ray scattering and contact angle measurements. A combined swelling and annealing treatment was found to improve salt rejection to an acceptable reverse osmosis salt rejection level (~94%) without significant deterioration of flux. The swelling time was found to generally improve the membrane performance in terms of flux and surface roughness whilst the silver nanoparticle treatment reduced bacterial surface coverage by four orders of magnitude.

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