Preparation of multifunctional hollow fiber nanofiltration membranes by dynamic assembly of weak polyelectrolyte multilayers

In this work, we investigate the effect of preparation conditions for dynamic layer-by-layer (LbL) coating, to prepare multifunctional hollow fiber nanofiltration (NF) membranes. Dynamic coating was performed at constant pressure and at variable cross flow speeds. In this way, polyelectrolyte multilayers (PEMs) were formed of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH), on a negatively charged polyethersulfone ultrafiltration (UF) support. The resulting membrane performance was investigated and compared to membranes prepared by different methods (dip coating and dead end filtration), and it was found to be comparable. It was shown that PAH/PAA multilayers can be fabricated reproducibly and homogenously using optimised dynamic LbL deposition conditions on single fibre module (surface area of 6.2 cm2) as well as on a module of 15 fibres (surface area of 67 cm2). Moreover, the approach of dynamic coating could be easily up scaled to coat existing UF modules. The prepared membranes reject the solutes on the basis of size exclusion and Donnan exclusion, retaining small organic solutes and divalent ions. Membranes terminated with PAA exhibit a low fouling tendency compared to membranes terminated with PAH and compared to the UF support membrane. Moreover, if severe membrane fouling would occur after prolonged use, the PEM coating, including any attached foulants can be removed by rinsing with a solution that combines a low pH and a high salinity (pH 3, 3 M). The surface of bovine serum albumin (BSA) fouled membranes were successfully cleaned at least twice, after which a new PEM coating could be re-applied by active coating.