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

Abstract

Nanofiltration (NF) membrane processes are attractive to remove multivalent ions. As ion retention in NF membranes is determined by both size and charge exclusion, negatively charged membranes are required to reject negatively charged ions. Layer‐by‐layer assembly of alternating polycation (PC) and polyanion layers on top of a support is a versatile method to produce membranes. Especially the polyelectrolyte (PE) couple polydiallyldimethylammoniumchloride and poly(sodium‐4‐styrenesulfonate) (PDADMAC/PSS) is extensively investigated. This PE couple cannot form highly negatively charged membrane surfaces, due to interdiffusion and charge overcompensation of PDADMAC into the PSS layers, which limits the operational window to tailor membrane properties. We propose the use of asymmetric layer formation and show how combining two charge densities of one PC can produce negatively charged NF membranes. Starting from hollow fiber ultrafiltration supports coated with base layers of PDADMAC/PSS, they are coated with PDADMAC/PSS or poly(acrylamide‐co‐diallyldimethylammoniumchloride), P(AM‐co‐DADMAC)/PSS layers. P(AM‐co‐DADMAC) has a charge density of only 32% compared to 100% for PDADMAC. The particular novel membranes coated with P(AM‐co‐DADMAC) have a highly negatively charged surface and high permeabilities (7–19 L/[m2hbar]), with high retentions for Na2SO4 of up to 95%. These values position the developed membranes in the top range compared to commercial and other layer‐by‐layer membranes.

Preparation of cationic cotton through reaction with different polyelectrolytes

“…The application of PAcD has become a research focus due to several advantages, such as high positive charge density, safety, and stability of the cation unit (Lian et al 2016 ). Recently, PAcD has been researched for the development of drug carriers nanogels and nanofiltration membranes (Sana et al 2019 ; Scheepers et al 2021 ). Qi et al ( 2018 ) prepared hydrogel using PAcD to adsorption of methyl orange dye in aqueous solutions, for wastewater treatment.…”

Lowering the fresh water footprint of cooling towers: A treatment-train for the reuse of discharged water consisting of constructed wetlands, nanofiltration, electrochemical oxidation and reverse osmosis

“…The NF-membrane used in the present study does not retain enough monovalent ions to reach the desired product quality. However, ongoing developments in the field of membrane fabrication resulted in the development of for instance layer-by-layer membranes with alternating charge densities that increase the retention of monovalent ions (Scheepers et al, 2020(Scheepers et al, , 2021 which can eventually result in reaching the desired product quality with only NF. The application of only one…”

“…Water Nexus combines the development of digital tools for mapping, management and control of fresh water resources with the development of innovative water treatment technology for saline industrial wastewater. A substantial part of Water Nexus is dedicated to developing green and grey technologies that facilitate the reuse of CTW, such as constructed wetlands (CWs) (Wagner et al, 2020b(Wagner et al, , 2020c(Wagner et al, , 2021, advanced oxidation processes for the electrochemical degradation of organics (Bruninghoff et al, 2019(Bruninghoff et al, , 2021Saha et al, 2020a) and nanofiltration (NF) with novel layer-by-layer membranes that allow ion-specific removal (Scheepers et al, 2020(Scheepers et al, , 2021. Recently, the use of hybrid pre-treatment and desalination systems for seawater desalination has shown to increase the water recovery and lower the energy requirements for treatment (Pan et al, 2018b).…”

Addressing Specific (Poly)ion Effects for Layer-by-Layer Membranes

“…On the other hand, although the PDADMAC/PSS couple delivers membranes with better permeabilities, their performances are highly dependent on the nature of the terminating layer, resulting in extreme differences in retention behaviors. 41 PAMA is a PAH derivative (partially) consisting of quaternary ammonium ions (Figure 1a) that in terms of CD and chaotropicity perfectly lays in between those of PDADMAC and PAH, making it an interesting PE for membrane preparation when good rejection (like PAH) and improved water permeability (like PDADMAC) could be combined. PAMA as a fully methylated derivative was already synthesized by Wytrwal et al for use in biotechnological applications but has not yet been used for the preparation of LbL membranes.…”

“…At the same time, in LbL membranes, these PEs give rise to relatively low water permeabilities, which is obviously undesired. On the other hand, although the PDADMAC/PSS couple delivers membranes with better permeabilities, their performances are highly dependent on the nature of the terminating layer, resulting in extreme differences in retention behaviors …”