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

Abstract

A B S T R A C TIn 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 fiber module (surface area of 6.2 cm 2 ) as well as on a module of 15 fibers (surface area of 67 cm 2 ). 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.

End-of-life RO membranes recycling: Reuse as NF membranes by polyelectrolyte layer-by-layer deposition

“…In another study, Jin et al [27] In several studies, polyelectrolyte LbL deposition was used to reduce molecular weight cutoffs (MWCO) of porous membranes for fabricating tight UF membranes [34,35]. Use of polyelectrolyte multilayers as membrane surface modification has received a lot of attention also in most recent studies [36][37][38][39][40][41][42][43][44][45][46].…”

High Selectivities among Monovalent Cations in Dialysis through Cation-Exchange Membranes Coated with Polyelectrolyte Multilayers

“…Recently, several papers reported remarkable selectivities between monovalent and divalent cations or anions when coating ion-exchange membranes with polyelectrolyte multilayers (PEMs). − For example, White and co-workers demonstrated K + /Mg 2+ electrodialysis (ED) selectivities >1000, and Zhao et al found Cl – /SO 4 2– selectivities as high as 47 . PEM coatings also enhance ion separations with nanofiltration membranes. − However, no studies reported high selectivities among monovalent ions. Recent crown ether-containing membranes show K + /Li + and Cs + /Na + selectivities around 4, , and metal–organic framework membranes exhibit a Li + /K + selectivity of 2.2 …”

Asymmetric layer‐by‐layer polyelectrolyte nanofiltration membranes with tunable retention

“…As ion retention in NF membranes is determined by both size exclusion as well as charge exclusion, the introduction of negative membrane charges increases the repulsion of negatively charged ions 8–12 . Moreover, negatively charged NF membranes are also key to reduce fouling since several organic foulants are negatively charged (e.g., humic acid, sodium dodecylbenzene sulfonate) 13–15 …”

“…[8][9][10][11][12] Moreover, negatively charged NF membranes are also key to reduce fouling since several organic foulants are negatively charged (e.g., humic acid, sodium dodecylbenzene sulfonate). [13][14][15] One of the upcoming methods to fabricate NF membranes is layer-by-layer (LbL) coating. [16][17][18] Here, alternating layers of oppositely charged polyelectrolytes (PEs) are adsorbed on a porous support forming a PE multilayer NF membrane.…”