Layer-by-layer Membrane Research Articles

Layer-by-layer assembled membranes from graphene oxide and polyethyleneimine for ethanol and isopropanol dehydration

Novel thin film composite membranes based on layer-by-layer (LbL) self-assembly of polyethyleneimine (PEI) and graphene oxide (GO) on chlorine-treated polyamide membranes were prepared for pervaporation dehydration of alcohols. To improve the membrane perfoarmance, the self-assembled bilayers were crosslinked with glutaraldehyde. A two-level factorial design was used to determine the effects of the main factors involved in the membrane preparation and their interactions on the permeation flux and separation factor. The impacts of the number of bilayers on the membrane performance were considered to gain an insight into the mass transfer resistance contributed by the bilayers. At 60 °C, the crosslinked (PEI/GO)7 LbL membrane showed a flux of 1770 and 1494 g/m2 h for ethanol/water and isopropanol/water mixtures, respectively, at 2 wt% water in feed, with a corresponding separation factor of 77 and 197. The long-term stability test showed the feasibility of the crosslinked membranes for alcohol dehydration.

Layer-by-layer assembly of polyethyleneimine/graphene oxide membranes for desalination of high-salinity water via pervaporation

This study reports on surface modification of thin-film-composite (TFC) polyamide membranes for desalination of high-salinity water via pervaporation. The membrane modification involves surface treatment of the polyamide membrane with chlorine, followed by layer-by-layer (LbL) deposition of positively charged polyethyleneimine (PEI) and negatively charged graphene oxide (GO). It was shown that the controlled membrane chlorination significantly increased water permeability and incorporating PEI and GO to the chlorine-treated polyamide membrane improved the salt rejection. The pure water flux through the PEI/GO LbL membrane was two times higher than that through the original membrane. The PEI/GO LbL membrane was tested for desalination of aqueous solutions containing NaCl, Na2SO4, MgSO4 andMgCl2 salts, and a water flux as high as 8 kg/m2h with a high salt rejection (>99.9%) was obtained for all the tested salts at various temperatures and feed concentrations.

A novel layer-by-layer heterogeneous cation exchange membrane for heavy metal ions removal from water

A novel layer-by-layer (LbL) cation exchange membrane was prepared for heavy metal ions removal from water via electrodialysis. LBL membranes fabricated by coating of [chitosan-co-activated carbon nanoparticles] layer on polyvinyl chloride-based heterogeneous cation exchange membrane. Betterment in adherence of layers was achieved through glutaraldehyde cross linking. FTIR, FESEM, 3D-surface images and BET analysis were used for LBL membrane characterization. Membrane surface hydrophilicity, flux, membrane potential, transport number, and their permselectivity were studied. FTIR spectra confirm LbL formation decisively. FESEM images and BET analysis demonstrated that coating of second layer on PVC membrane led to a compact structure. LbL membrane showed smoother and more hydrophilic surface compared to pristine membrane. The transport number and permselectivity increased by deposition of second layer whereas sodium flux showed up-down trend. ED experiment showed good ability in heavy metal ions removal for LBL membrane that follows (Cu2+> Ni2+> Pb2+) sequence. EDX analysis showed a competitive adsorption for heavy metal ions on LBL membrane as (Pb2+> Cu2+≥Ni2+). The effect of ultrasonic waves on regeneration of fouled membranes by heavy metals was investigated. The results showed improved performance for the regenerated membrane. Mechanical resistance also improved by utilizing of ACNs in chitosan layer.

Improved phosphoric acid recovery from sewage sludge ash using layer-by-layer modified membranes

We report an advanced treatment method for phosphoric acid recovery from leached sewage sludge ash. Layer-by-layer (LbL) polyelectrolyte deposition has been used as a tool to modify and convert a hollow ultrafiltration membrane into a nanofiltration (NF) LbL membrane for H3PO4 recovery. To build the LbL membrane, poly(styrenesulfonate) PSS was chosen as polyanion, while three different polycations were used: a permanently charged polyelectrolyte, poly(diallyldimethylammonium chloride), PDADMAC; a pH-dependent charged polyelectrolyte poly(allylamine hydrochloride), PAH; and a PAH modified with guanidinium groups (PAH-Gu). Based on detailed surface characterizations (AFM, XPS and Zeta-potential) it was concluded that both charge density and pH-responsiveness of the polycations are key parameters to control the final membrane surface structure and transport properties. The surface properties of LbL-coated membranes were correlated with the membrane filtration performance, when exposed to the real leached sewage sludge ash solution. The highest permeability was recorded for (PDADMAC/PSS)6, a result that was rationalized on its loose, and possibly less interpenetrated, structure, followed by (PAH-Gu/PSS)6 characterized by a more dense, compact layer. H3PO4 recovery was the highest in the case of (PDADMAC/PSS)6, but the retention of multivalent metals (Fe3+ and Mg2+) was low, leading to a more contaminated permeate. The opposite trend was observed for (PAH-Gu/PSS)6, resulting in a less metal-contaminated, but also a less H3PO4-concentrated permeate. Our LbL-modified membranes were found to improve the permeability and H3PO4 recovery compared to a commercially available acid-resistant NF membrane.

Layer by Layer Assembly of Poly (Allylamine Hydrochloride)/Phosphate Ions and Poly (Sodium 4-Styrene Sulfonate) Membrane for Forward Osmosis Application

Based on the layer by layer (LbL) assembly technology, the nano-scale composite membrane with excellent structure can be prepared by changing the polyelectrolyte and controlling the deposition conditions. Polyamines and phosphate ions (Pi) can be self-organized to form supramolecular systems which could be exploited to stabilize the interfacial architecture. The LbL membrane was made of the positively charged poly (allylamine hydrochloride) (PAH) self-organized with Pi and the negatively charged poly (sodium 4-styrene sulfonate) (PSS) alternatively on top of a poly (acrylonitrile) (PAN) substrate. Compared to the membrane without Pi, the membrane assembled by PAH/Pi improved forward of flux and reduced flux of salt. The concentration of PAH and PSS, deposition time, pH and number of layers showed significant influences on the performance of the membrane. In this experiment, we systematically investigated the preparation conditions and under the optimized conditions the prepared membrane exhibited high water fluxes of 13.5 Lm-2 h-1 with corresponding salt to water flux, Js/Jv, ratio of 0.07 gL-1 tested by forward osmosis when DI water as feed solution and 2 mol L-1 MgCl2 as draw solution.

Characterization of Bovine Serum Albumin and (-)-Epigallocatechin Gallate/3,4- O-Dicaffeoylquinic Acid/Tannic Acid Layer by Layer Assembled Microcapsule for Protecting Immunoglobulin G in Stomach Digestion and Release in Small Intestinal Tract.

The protein-polyphenol layer by layer (LbL) assembled polymer composite microcapsule is a considerable delivery system that can be used to improve the bioactive stability and effectiveness of natural compounds in various applications. In the present study, three kinds of polyphenols were loaded in the sequence of (-)-epigallocatechin gallate (EGCG), 3,4- O-dicaffeoylquinic acid (3,4-diCQA), and tannin acid (TA) to prepare a BSA-polyphenol LbL membrane. The composition of IgG-(BSA-EGCG/3,4-diCQA/TA) n microcapsules and their stability and releasing ability in the gastrointestinal tract were evaluated. In addition, by binding of these three kinds of polyphenols to BSA, the thermal denaturation temperature and ordered secondary structure of the BSA-polyphenol microcapsules were increased, and the time of scavenging activity on 2,2'-azinobis(3-ethylbenzothiazolin-6-sulfonic acid) free radicals was significantly prolonged. These findings suggest that (BSA-EGCG/3,4-diCQA/TA) n microcapsules can not only protect IgG in food processing and stomach digestion but also release it in the small intestinal tract for bioactive delivery.

Stable and effective proton exchange membrane formation via cross-linking the polymeric proton donor and proton acceptor in a layer-by-layer structure

Systematic arrangement of the proton donor and acceptor as a layer-by-layer (LbL) structure is one of the simplest surface modification methods to improve the proton conductivity of a proton exchange membrane. In general, LbL assembly occurs via physical or chemical interaction between each deposited layer. Here, the stabilization of the proton donor and acceptor polymers by cross-linking those two layers together was applied as a concept. The challenge was the molecular design of the proton donor and accepter polymer species to each have compatible cross-linkable functional groups as well as proton transfer species in the molecules. Poly(acrylic acid) decorated with different amounts of thiol groups (PAA-M) was synthesized, while benzimidazole decorated branching polyethyleneimine was functionalized with maleimide groups (BIm-PEI-MI). The cross-linkable proton donor and acceptor were alternately LbL deposited on a sulfonated poly(ether ether ketone) (SPEEK) surface. The LbL membrane with an optimum crosslink level showed a proton conductivity of up to 2 orders of magnitude higher than that of the pure SPEEK membrane even at a temperature as high as 170 °C.

Hierarchical Composite Membranes with Robust Omniphobic Surface Using Layer-By-Layer Assembly Technique

In this study, composite membranes were fabricated via layer-by-layer (LBL) assembly of negatively charged silica aerogel (SiA) and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FTCS) on a polyvinylidene fluoride phase inversion membrane and interconnecting them with positively charged poly(diallyldimethylammonium chloride) (PDDA) via electrostatic interaction. The results showed that the PDDA-SiA-FTCS coated membrane had significantly enhanced the membrane structure and properties. New trifluoromethyl and tetrafluoroethylene bonds appeared at the surface of the coated membrane, which led to lower surface free energy of the composite membrane. Additionally, the LBL membrane showed increased surface roughness. The improved structure and property gave the LBL membrane an omniphobic property, as indicated by its good wetting resistance. The membrane performed a stable air gap membrane distillation (AGMD) flux of 11.22 L/m2 h with very high salt rejection using reverse osmosis brine from coal seam gas produced water as feed with the addition of up to 0.5 mM SDS solution. This performance was much better compared to those of the neat membrane. The present study suggests that the enhanced membrane properties with good omniphobicity via LBL assembly make the porous membranes suitable for long-term AGMD operation with stable permeation flux when treating challenging saline wastewater containing low surface tension organic contaminants.

Enhanced performance of DMFC prepared by 10Cu/CeO2 catalyst and nanocomposite SPVA membranes with layer-by-layer coating of polyacrylic acid and chitosan

In the present study, TiO2 nanoparticles are used as inorganic nanofiller material to prepare nanocomposite proton exchange membrane (PEM). Sulfonated polyvinyl alcohol (SPVA) is synthesized by 4-formylbenzene-1,3-disulfonic acid disodium salt hydrate and water. The cross-linking reaction is performed by glutaraldehyde. These membranes were then dip coated with polyacrylic acid and chitosan alternately and one layer-by-layer (LBL), two LBL and three LBL membranes were prepared. The chemical structure evaluation of SPVA membrane is performed using FTIR. The direct methanol fuel cell (DMFC) catalysts of 10Cu/CeO2 and 10 Pt-10 CeO2/C were prepared by reduction reaction and hydrothermal technique. Thus obtained material was spin coated on 2 × 2 cm2 carbon paper to prepare catalyst anode/cathode. The morphology, size, and purity of catalyst particles are analysed by SEM, UV–visible spectroscopy, FTIR and EDS. Electrochemical analysis is also done to test the performance. Results show that Cu/CeO2 catalyst shows excellent catalysis towards methanol oxidation, which is better than 10 Pt-10 CeO2/C particles. The 10Cu/CeO2 catalyst gives peak voltage of 915 mV for infinite resistance, which is higher than the reported value of the conventional 20 Pt/C catalyst (810 mV).

Anti-fouling and high water permeable forward osmosis membrane fabricated via layer by layer assembly of chitosan/graphene oxide

To date, forward osmosis (FO) has received considerable attention due to its potential application in seawater desalination. FO does not require external hydraulic pressure and consequently is believed to have a low fouling propensity. Despite the numerous privileges of FO process, a major challenge ahead for its development is the lack of high performance membranes. In this study, we fabricated a novel highly-efficient FO membrane using layer-by-layer (LbL) assembly of positive chitosan (CS) and negative graphene oxide (GO) nanosheets via electrostatic interaction on a porous support layer. The support layer was prepared by blending hydrophilic sulfonated polyethersulfone (SPES) into polyethersulfone (PES) matrix using wet phase inversion process. Various characterization techniques were used to confirm successful fabrication of LbL membrane. The number of layers formed on the SPES-PES support layer was easily adjusted by repeating the CS and GO deposition cycles. Thin film composite (TFC) membrane was also prepared by the same SPES-PES support layer and polyamide (PA) active layer to compare membranes performances. The water permeability and salt rejection of the fabricated membranes were obtained by two kinds of draw solutions (including Na2SO4 and sucrose) under two different membrane orientations. The results showed that membrane coated by a CS/GO bilayers had water flux of 2–4 orders of magnitude higher than the TFC one. By increasing the number of CS/GO bilayers, the selectivity of the LbL membrane was improved. The novel fabricated LbL membrane showed better fouling resistance than the TFC one in the feed solution containing 200ppm of sodium alginate as a foulant model.

Comparative study on the deposition of enzyme-entrapped membranes with spatial homogeneity for bioimaging

The output characteristics of potentiometric biosensor arrays having 128×128 elements with an area of 37.30μm×37.30μm were investigated. For the sensing of adenosine-5′-triphosphate (ATP) as a target molecule, apyrase was immobilized in poly-ion complex (PIC) membranes deposited on sensor surfaces. Two different methods for the deposition of PIC membranes, a conventional layer-by-layer (LBL) method and a novel mixed layer (ML) method, were compared to characterize the spatial homogeneity of the sensor output. It was revealed that the standard deviation of the output distribution was smaller for the ML membrane than that for the LBL membrane. Furthermore, the ML membrane exhibited a superior detection limit of 100μM ATP, compared with 300μM for the LBL membrane, indicating the promising properties of the ML membrane for imaging applications. The factors causing the distribution of the output were also discussed.

Constructing polymeric proton donor and proton acceptor in layer-by-layer structure for efficient proton transfer in PEMFC

Heterocyclic compounds are known as proton transfer species for anhydrous polymer electrolyte membrane (PEM), for which efficient proton conductivity at high operating temperature has yet to be found. The present work proposes an approach to enhance the proton transfer of the membrane by combining the concept of proton donor and acceptor with an ordered structure, i.e. layer-by-layer (LbL). By simply applying poly(acrylic acid) (PAA) as a polymeric proton donor and benzimidazole (BIm) conjugated on branching poly(ethyleneimine) as a polymeric proton acceptor and alternately coating the sulfonated poly(ether ether ketone) (SPEEK), a LbL membrane can be obtained. The proton transfer can be fine-tuned by the number of bilayers, and at that time, the 20-bilayered SPEEK/BIm-PEI/PAA is an optimal condition, which achieves a balance between the hydrogen bond and chain mobility under LbL packing that allows a 1.5 higher order of magnitude conductivity than an as-prepared SPEEK membrane even at a high operating temperature range (90–170 °C). The present work, for the first time, shows how a simple LbL technique is practical for constructing high-ordered structure of proton donor and acceptor species on the membrane surface for the efficient proton transfer in a PEM.

Self-assembly of graphene oxide/polyaniline multilayer counter electrodes for efficient dye-sensitized solar cells

Layer-by-layer (LbL) assembly provides a facile approach in fabricating well-defined nanoarchitectures with electrical and electrochemical properties. Research on electrical and electrochemical performances of the LbL membranes from graphene oxide would be profound in modern photovoltaic nanodevices. We demonstrate here the LbL self-assembly of polyaniline-(graphene oxide/polyaniline)n [PANi-(GO/PANi)n] (n represents the deposition cycle) multilayer films with good electrical and electrochemical behaviors and employment as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The resulting multilayer films give a linear growth in bulk conductivity and increased electrocatalytic activity toward triiodides. Careful examination of data and characterizations indicates that the electrical and electrochemical properties are impressive to fulfill the task of PANi-(GO/PANi)n CEs. A promising power conversion efficiency of 7.41% (measured under standard AM1.5 test conditions) is obtained in PANi-(GO/PANi)4 CE in comparison with 6.37% from PANi-(GO/PANi)1 CE. This strategy provides new opportunity for the fabrication of efficient DSSCs, and the efficiency record is expected to be surpassed by scalable technique and components.

Stabilization of layer-by-layer assembled nanofiltration membranes by crosslinking via amide bond formation and siloxane bond formation

Two crosslinking methods for layer-by-layer (LbL)-assembled nanofiltration membranes were developed to improve the stability of the membrane under high ionic strength conditions and chlorine treatment. In the first method, an amine coupling reaction was applied between amino groups on cationic polyelectrolytes and carboxyl groups on anionic polyelectrolytes. The amine coupling reaction was carried out by an active ester method using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, and crosslinked LbL membranes via amide bond formation. The crosslinking by amine coupling reaction improved the stability of the membrane performance under high ionic strength conditions. However, it was not effective under chlorine treatment. As a next challenge, we crosslinked LbL membranes by a silane coupling reaction between oppositely charged polyelectrolytes modified with reactive silane groups. Cationic and anionic polyelectrolytes modified with reactive silane groups were synthesized, and the synthesis of the polyelectrolytes was confirmed by Fourier transform infrared spectroscopy. The LbL membranes were fabricated with the synthesized polyelectrolytes and crosslinked via siloxane bond formation between oppositely charged polyelectrolytes. The silane coupling reaction improved the separation performance of the membranes, and the siloxane-crosslinked membranes were found to be highly stable under both high ionic strength conditions and chlorine treatment.

Micro-morphology and formation of layer-by-layer membranes and their performance in osmotically driven processes

We have fabricated novel multilayer membranes for forward osmosis (FO) processes by layer-by-layer (LbL) assembly of polyelectrolytes and examined the fundamentals of LbL membrane formation and microstructure. The LbL membrane was made of a positively charged poly(allylamine hydrochloride) (PAH) and a negatively charged blend of poly(acrylic acid) (PAA) and poly(sodium 4-styrene sulfonate) (PSS) at a weight ratio of 1:1 on top of hyperbranched polyethyleneimine (PEI) modified Torlon substrates and then crosslinked by glutaraldehyde (GA). The newly developed 3-bilayer membrane has an impressive water flux of 28LMH (Lm−2h−1) and reverse salt flux of 1.97gMH (gm−2h−1) using 0.5M MgCl2 as the draw solution. Positron annihilation spectroscopy (PAS) analyses reveal that PEI densified the upper layer of the substrate while GA crosslinked the selective layer as well as part of the PEI modified substrate. PAS experiments also indicated that growth in membrane thickness was non-linear and became insignificant after around 6-bilayer of deposition. An immobilized osmotic pressure was observed due to the ion adsorption on the LbL layer. FO results show that the pH and salt concentration of polyelectrolytes play important roles on membrane morphology and FO performance. Both water flux and reverse salt flux were strongly influenced by polyelectrolytes’ charge density and the degree of chain coils. Due to strong charge density and chain packing when pH values of PAH and PAA–PSS are 5 and 3–5, respectively, the resultant LbL membranes show both low water flux and low reverse salt flux. The addition of NaCl in polyelectrolyte solutions may facilitate chain coils, rearrange coil size, affect chain packing and create defects depending on NaCl concentration. A relatively high NaCl concentration tends to decompose the coils and weaken the LbL structure, thus increase the water flux but reduce the reverse salt flux.

A layer-by-layer self-assembly approach to developing an aquaporin-embedded mixed matrix membrane

Aquaporin (AQP) is a water channel protein in biological membranes that possesses exceptional water selectivity and permeability. The AQP-embedded biomimetic membrane can be potentially used in water purification and pharmaceutical separation. A practical and stable design of AQP-embedded mixed matrix membrane has been revealed in this work using the multilayer polyelectrolyte adsorption method. By encapsulating AQP-incorporated vesicles with positively charged poly-L-lysine molecules, the vesicles could be adsorbed onto polyanion films. AFM and FESEM studies showed that the amount of adsorbed vesicles was proportional to the percentage of charged lipids that was present in the liposomes. The AQP embedded layer-by-layer (LbL) membrane demonstrated a water permeability of 6 L m−2 h−1 bar−1 and MgCl2 rejection greater than 95%. In comparison with the control LbL membrane without embedding any liposomes, the newly designed mixed matrix membrane improved the water permeability by 60% because of the presence of AQPs. The AQPZ-incorporated membrane was also tested for glutathione separation at various pH levels. The rejection rate of glutathione was greater than 93% at pH values ranging from 4 to 9. Since the LbL approach provides the AQP embedded biomimetic membrane with satisfactory stability and separation performance, it makes the large scale fabrication of AQPZ-incorporated membranes feasible and practical.

Insights on the accumulation of charge carriers for enhanced electrical and photoelectric behaviors in conducting multilayer films

Layer-by-layer (LbL) assembly provides a facile approach for fabricating organized nanoscale structures with outstanding mechanical, electrical, optical, electrochemical, and photoelectric properties. Revelation of electrical and photoelectric performance of LbL membranes made from graphene oxide would be profound for modern nanodevices. Herein, we demonstrate the LbL self-assembly of conducting [poly(diallyldimethylammonium chloride)/graphene oxide]n [(PDDA/GO)n] multilayer films with extraordinary electrical and photoelectric behaviors. The resulting multilayer films demonstrate linear growth in their bulk conductivity and maximum photocurrent density. Careful examination of the characterization and electrochemical data indicates that the fantastic effects upon the electrical conduction and photocurrent are due to the accumulation of electrons that have tunneled across PDDA from the bottom layer of GO to the top. This profound phenomenon, along with the simple fabrication method and well-defined architecture, makes these conducting multilayers promising candidates for use in electric and photovoltaic devices.

Highly crosslinked layer-by-layer polyelectrolyte FO membranes: Understanding effects of salt concentration and deposition time on FO performance

Layer-by-layer (LbL) deposition of polyelectrolytes onto a negative charge membrane has been investigated under a highly crosslinking condition for forward osmosis (FO). The influence of salt concentration and deposition time on LbL FO membranes performance has been investigated in order to optimize the deposition process, followed by the investigation of polyelectrolyte layer's crosslinking. In the crosslinking steps, polycation layers of the three bilayer LbL membrane were firstly crosslinked using glutaraldehyde (GA) as the crosslinker. Compared to a non-crosslinked membrane, the reverse salt fluxes were reduced by 63% and 58% under the PRO (pressure retarded osmosis) testing mode using 0.5M MgCl2 and 0.5M NaCl as draw solutions, respectively. Subsequently, the polyanion layer of that membrane was photo-crosslinked under ultraviolent (UV) at the wavelength of 254nm. The reverse salt flux of the resulting membrane was further reduced by 55% and 53% under the PRO testing mode using 0.5M MgCl2 and 0.5M NaCl as draw solutions, respectively. Specially, the LbL membrane with only one bilayer after cross-linking by both GA and 4h-UV could achieve a water flux of about 11LMH and a reverse flux of 8gMH under the PRO test using 0.3M NaCl as a draw solution. This is the first time, a LbL polyelectrolyte membrane has been successfully demonstrated as a FO membrane with good rejection toward NaCl while none of previously reported LbL polyelectrolyte membranes have achieved based on the best of our knowledge.

Preparation and performance of dynamic layer-by-layer PDADMAC/PSS nanofiltration membrane

Dynamic layer-by-layer (LBL) self-assembly technology was used to prepare as few as three to five bilayers of poly(diallyl-dimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) on negatively charged polysulfone (PS) ultrafiltration (UF) membranes of 50kDa MWCO and compared with those of the static assembly membranes. The prepared dynamic assembly (PDADMAC/PSS)4 nanofiltration (NF) membrane showed a permeation flux of 60Lm−2h−1 at 1.0MPa, much higher than that of the commercial DL membrane (GE Osmonics, USA), but with a rejection of about 90% of SO42− which is relatively less than that of the DL membrane. The rejection performance showed that the dynamic–static assembly was more effective than others. Using dynamic–static assembly preparation, the rejection of (PDADMAC/PSS)3 membrane was about 90%, while the flux was about 55Lm−2h−1 at 1.0MPa. The surface morphology of the prepared LBL membranes were characterized by SEM and AFM, and no defect was found. The surface morphology of the membrane prepared by dynamic–static assembly was almost the same as the commercial membranes. The analysis of filtration resistance indicated that the deposition of the first and second bilayer was crucial during the whole preparation process.

Synthesis of high flux forward osmosis membranes by chemically crosslinked layer-by-layer polyelectrolytes

Forward osmosis (FO) membranes were successfully fabricated using layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene-sulfonate) (PSS) on a porous polyacrylonitrile (PAN) substrate. In addition, chemical crosslinking of LbL polyelectrolyte layers was performed with glutaraldehyde (GA). The resultant crosslinked (the xLbL series) and non-crosslinked (the LbL series) membranes were characterized in terms of the substrate morphology and structure, the separation layer water permeability and salt rejection, and the FO water flux and solute flux performance. Both LbL and xLbL membranes had relatively high water permeability (∼ or >7.0 L/m 2 h bar). On the other hand, the crosslinked xLbL membranes showed better and more stable MgCl 2 rejection, leading to a relatively low FO solute reverse transport (the solute flux over water flux ratio < 6 mM regardless of draw solution (DS) concentration and membrane orientation). High FO water fluxes were achieved for both crosslinked and non-crosslinked membranes, where a thin substrate with finger-like pores were adopted to minimize internal concentration polarization in the porous support layer. The crosslinked membrane xLbL3 (with 3 PAH/PSS deposition layers) had an FO water flux of ∼100 L/m 2 h in the active-layer-facing-DS orientation using a 2 or 3 M MgCl 2 draw solution and distilled water as the feed water, which clearly demonstrates the potential of LbL membranes for high flux FO applications.