Dual-Charged Hollow Fiber Membranes for Low-Pressure Nanofiltration Based on Polyelectrolyte Complexes: One-Step Fabrication with Tailored Functionalities

Abstract

A new nanofiltration (NF) hollow fiber membrane is developed by using two oppositely charged polyelectrolytes coagulating into a polyelectrolyte complex (PEC) onto polyether sulfone base polymer. The particular membrane architecture emerges during a single-step procedure, allowing setting both the porous negatively charged support of the hollow fiber and the separation layer containing also the positive polyelectrolyte (PEI/PDADMAC) through a single layer dry-jet wet spinning process. The novelty is two-pronged: the composition of the hollow fiber membrane itself and its fabrication procedure (one-step fabrication of membranes employing polyelectrolytes). These result in highly permeable hollow fiber membranes with a stable separation layer and performance at par with the membranes reported in literature obtained by multistep processes. More importantly, the membranes are obtained through a simple, very fast (one-step), and less expensive procedure. The best performance among these newly obtained hollow-fiber membranes is achieved by PD5% hollow fiber (MWCO of 300 Da), which showed 7.6 L/m(2)·h·bar permeability and ∼90% rejection of MgCl2, MgSO4, and Na2SO4 at 2 bar pressure. Thus, the resulting membranes not only have the advantages of the hollow-fiber configuration, but perform very well at extremely low pressures (the lowest reported in the literature). The broad impact of the results presented in this Article lies in the potential to dramatically reduce both the fabrication (duration and complexity) and the price and desalination costs of highly performing NF hollow fiber membranes. These might result in interesting potential applications and open new directions toward designing efficient functional NF hollow fibers for water desalination.

Microstructure–performance relationships of hollow‐fiber membranes with highly efficient separation of oil‐in‐water emulsions

“…However, the hollow‐fiber membranes used in this study still had great advantages in terms of oil rejection and water flux compared with other hollow‐fiber membranes previously reported for emulsion separation . Therefore, in the light of these results, we consider that a membrane should have a suitable microstructure to allow an excellent mass‐transfer capacity per unit and efficient separation to be in line those reported by other research groups …”

Forward Osmosis: A Critical Review

“…The resulting membranes from this simultaneous spinning/cross-linking process had a molecular weight cut-off in the range of 2.5-3.5 kDa, which means that further improvements are needed before they can be suitable for FO applications, though the reproducibility and simplicity of this one-step method are advantageous. Another simultaneous (single-step) method for forming a dense selective layer was developed by Gherasim et al [179], who managed to form a polyelectrolyte-complex layer in the lumen part of hollow fibers by using a polyanion in the dope and a polycation in the bore liquid. The resulting fibers had a cut-off in the range of that of nanofiltration membranes [179].…”

“…Another simultaneous (single-step) method for forming a dense selective layer was developed by Gherasim et al [179], who managed to form a polyelectrolyte-complex layer in the lumen part of hollow fibers by using a polyanion in the dope and a polycation in the bore liquid. The resulting fibers had a cut-off in the range of that of nanofiltration membranes [179]. This needs to be improved before they can become suitable for FO, but in this case too, the reproducibility and ease of this method are advantages.…”

Direktes Herstellungsverfahren von Komposit‐Hohlfasermembranen mit sinusförmiger Geometrie

“…Mit dem direkten Spinnverfahren, dass zusätzlich auf einer chemischen Reaktion in der Spinndüse basiert, kann eine oberflächenmodifizierte Hohlfasermembran in einem Prozessschritt hergestellt werden , . Bei der ersten Anwendung dieses Konzepts wurde ein reaktives Polymer verwendet, das durch Phaseninversion in eine poröse Trägerstruktur umgewandelt wird und gleichzeitig mit einem Reaktanten aus der Lumenflüssigkeit reagiert .…”

“…Das inerte Polymer fällt aus und wird zur porösen Trägerstruktur während die Vernetzungsreaktion die gewünschte dichte Trennschicht auf der Lumenseite bildet. Gherasim et al haben das Layer‐by‐Layer‐Konzept für die nachträgliche Membranbeschichtung auf das Prinzip des direkten Spinnens von Komposit‐Hohlfasermembranen übertragen. Dabei findet eine ionische Vernetzungsreaktion zwischen entgegengesetzt geladenen Polyelektrolyten in der Polymerlösung und Lumenflüssigkeit statt.…”