Graphene-polyelectrolyte multilayer membranes with tunable structure and internal charge

Abstract

One great advantage of graphene-polyelectrolyte multilayer (GPM) membranes is their tunable structure and internal charge for improved separation performance. In this study, we synthesized GO-dominant GPM membrane with internal negatively-charged domains, polyethyleneimine (PEI)-dominant GPM membrane with internal positively-charged domains and charged-balanced dense/loose GPM membranes by simply adjusting the ionic strength and pH of the GO and PEI solutions used in layer-by-layer membrane synthesis. A combined system of quartz crystal microbalance with dissipation (QCM-D) and ellipsometry was used to analyze the mass deposition, film thickness, and layer density of the GPM membranes. The performance of the GPM membranes were compared in terms of both permeability and selectivity to determine the optimal membrane structure and synthesis strategy. One effective strategy to improve the GPM membrane permeability-selectivity tradeoff is to assemble charged-balanced dense membranes under weak electrostatic interactions. This balanced membrane exhibits the highest MgCl 2 selectivity (~86%). Another effective strategy for improved cation removal is to create PEI-dominant membranes that provide internal positively-charged barrier to enhance cation selectivity without sacrificing water permeability. These findings shine lights on the development of a systematic approach to push the boundary of permeabilityselectivity tradeoff for GPM membranes.

Ultrastable Nanofiltration Membranes Engineered by Polydopamine-Assisted Polyelectrolyte Layer-by-Layer Assembly for Water Reclamation

“…Comparisons of (a) Na 2 SO 4 and (b) MgSO 4 separation performances of various LBL-based NF membranes in the literature. (PEI 1.5 /GO 0.3 /PEI 3.0 )/hPAN from ref , (PDDA/GO) 4.0 from ref , PS/PDA/CS/SiO 2 from ref , (CS/PAA) 4 and (CS/PAA) 4 CS from ref , LBL-cPP and LBL-cPP from ref , and (PEI/GO) 3 from ref . PEI, polyethylenimine; GO, graphene oxide; PDDA, poly­(diallyldimethyl ammonium chloride); PS, polysulfone; PDA, polydopamine; CS, chitosan; PAA, poly­(acrylic acid); hPAN, hydrolyzed PAN.…”

“…9−12 Recently, layer-by-layer (LBL) assembly has gained immense popularity for fabricating high-performance NF membranes because it is facile, scalable, cost-effective, and environmentally friendly. 13 By alternative adsorption of two polyelectrolytes with opposite charge properties onto porous substrates, high-performance NF membranes with a flexible charged selective layer, desired water permeability, and satisfied salt rejection have been successfully developed. 14−16 For example, Liu et al developed a hollow fiber NF membrane based on LBL depositions of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) followed by glutaraldehyde (GA) cross-linking.…”

Partially Reduced Graphene Oxide Membranes Crosslinked by an Anionic Porphyrin: Green Fabrication for High‐Performance Ion Sieving

“…Crosslinking between GO layers is the most commonly used method to fabricate GO membranes with uniform channel size because of the swelling behavior of these membranes in water being suppressed [14,17–25] . Up to now, this kind of method is easy to implement via intercalating some cross‐linkers with diameter around 1 nm such as covalent bonding agents, [17–22] inorganic salt ions, [23–24] planar cations [14] and polycations [25] . Among them, covalent bonding agents have the advantages of high stability and controllable cross‐linking size.…”

Mechanism of Permselectivity Enhancement in Polyelectrolyte-Dense Nanofiltration Membranes via Surfactant-Assembly Intercalation

“…The irreversible LbL deposition of polyelectrolytes is mainly driven by electrostatic attractions between the oppositely charged polyelectrolytes. − With this approach, the LNF membranes are commonly fabricated using at least one weak polyelectrolyte (e.g., one strong and one weak polyelectrolyte or two weak polyelectrolytes), ,,− whereas DNF membranes are typically fabricated using two strong polyelectrolytes. − Several critical membrane properties, such as the pore size distribution, surface charge, and active layer thickness, are affected by multiple factors in the LbL deposition process, such as the type of polyelectrolytes, , polyelectrolyte concentration, ionic strength of the polyelectrolyte solution, − pH, − and temperature. , Adjusting these parameters provides avenues to control the membrane permeance and ion selectivity. Beyond these parameters, integrating various types of additives (e.g., nanomaterials) into the PEM is also a widely explored approach to enhance the permselectivity. , …”

“…Beyond these parameters, integrating various types of additives (e.g., nanomaterials) into the PEM is also a widely explored approach to enhance the permselectivity. 49,50 In our recent studies, we reported a novel and cost-effective approach to dramatically enhance the permeance of loose NF membranes for removing macromolecules (e.g., humic acid and dyes). 16,32 This approach is based on the intercalation of surfactant bilayers between weak polycations (polyethylenimine, PEI) and strong polyanions (polystyrene sulfonate, PSS) and has been demonstrated to be capable of enhancing the performance by multiple folds without compromising the rejection of macromolecules.…”