Donnan Exclusion Research Articles

Steering the Selectivity of CORR from Acetate to Ethanol via Tailoring the Thermodynamic Activity of Water

AbstractThe electrochemical conversion of carbon monoxide (CO) into oxygenated C2+ products at high rates and selectivity offers a promising approach for the two‐step conversion of carbon dioxide (CO2). However, a major drawback of the CO electrochemical reduction in alkaline electrolyte is the preference for the acetate pathway over the more valuable ethanol pathway. Recent research has shed light on the significant impact of thermodynamic water activity on the electrochemical CO2 reduction reaction pathways, but less is understood for the electrochemical reduction of CO. In this study, we investigated how the water activity at the electrified interface can be enhanced to adjust the selectivity between acetate and ethanol. We employed an ionomer modifier to lower the local concentration of alkali ions (via Donnan exclusion), successfully enhancing ethanol production while suppressing acetate formation. We observed a remarkable improvement in the Faradaic efficiency of ethanol and alcohol (i. e. ethanol, propanol etc), which reached 42.5 % and 55.1 %, respectively, at a current density of 700 mA cm−2. The partial current densities of ethanol and alcohol reached 698 and 942 mA cm−2 at 2000 mA cm−2. Furthermore, we achieved a 3.7‐fold increase in the ethanol/acetate ratio, providing clear evidence of our successful modulation of product selectivity.

Supramolecular-Coordinated Nanofiltration Membranes with Quaternary-Ammonium Cyclen for Efficient Lithium Extraction from High Magnesium/Lithium Ratio Brine

Ion-selective membranes (ISM) with sub-nanosized pore channels hold significant potential for applications in saline wastewater treatment and resource recovery. Herein, novel synergistic ion channels featuring bi-periodic structures were constructed through the coordination of functional Cyclen (quaternary_1,4,7,10-tetraazacyclododecane, Q_Cyclen) and Cu2+-m-Phenylenediamine (Cu2+-MPD) to develop supramolecular membranes for lithium extraction. The exterior quaternary ammonium-rich sites exhibit a significant Donnan exclusion effect, resulting in tremendous mono/divalent (Li+/Mg2+) ion selectivity; while the interior regular-confined channels of Cyclen yield a fast vehicular pathway, facilitating water molecules and Li+ ion-selective transport. The optimized membrane exhibited an increased water permeance of 19.2 L·m-2·h-1·bar-1 and simultaneously promoted Li+/Mg2+ selectivity (achieving a selectivity of 18.5 under a Mg2+/Li+ mass ratio of 30), surpassing the trade-off limit of conventional nanofiltration membranes. Due to the acquired excellent Li+/Mg2+ selectivity, lithium extraction from simulated salt-lake brines was successfully achieved through a two-stage nanofiltration process, reducing the Mg2+/Li+ mass ratio from 40 to 1.1. This work validates the applicability of macrocyclic with intrinsic sub-nanosized channels and desired multifunctionality for developing high-performance ISM for efficient lithium separation and beyond.

Reconstructing Electrically Conductive Nanofiltration Membranes with an Aniline-Functionalized Carbon Nanotubes Interlayer for Highly Effective Toxic Organic Treatment.

Conductive nanofiltration (CNF) membranes hold great promise for removing small organic pollutants from water through enhanced Donnan exclusion and electrocatalytic degradation. However, current CNF membranes face limitations in conductivity, structural stability, and nanochannel control strategies. This work addresses these challenges by introducing aniline-functionalized carbon nanotubes (NH2-CNTs) as an interlayer. NH2-CNTs enhance the dispersibility and adhesion of pristine carbon nanotubes, leading to a more conductive and stable composite nanofiltration membrane. The redesigned NH2-CNTs interlayered conductive nanofiltration (NICNF) membrane exhibits a 10-fold increase in conductivity and a high response degree (80%) with excellent cyclic stability, surpassing existing CNF membranes. The synergistic effects of enhanced Donnan exclusion, voltage switching, and electrocatalysis enable the NICNF membrane to achieve selective recovery of mixed dyes, 98.97% removal of residual wastewater toxicity, and a 5.2-fold increase in permeance compared to the commercial NF270 membrane. This research paves the way for next-generation multifunctional membranes capable of the efficient recovery and degradation of toxic organic pollutants in wastewater.

Understanding copper corrosion in bentonite-enriched environments: Insights from the point defect model

The study simulated copper corrosion in a bentonite/groundwater solution, analyzing the kinetics of metal passivation through potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy experiments. Morphological characterization provided insights into corrosion development patterns, and the mechanisms by which bentonite affects copper corrosion were comprehensively elucidated based on the point defect model. The findings revealed that bentonite affects copper corrosion resistance through Donnan exclusion, cation adsorption, and hydrolysis salt effects. At lower potentials, bentonite aids in inhibiting anodic dissolution, reducing the polarization current by approximately 75 % under certain conditions. With increasing bentonite content, the induction time for stable pitting corrosion shortens significantly, down to 10 %, the current surge before breakdown intensifies, and the breakdown potential decreases. When the bentonite volume ratio exceeds 0.5/0.1, the breakdown potential of OFP-Cu/OF-Cu markedly decreases and stabilizes at 0.1/0 VSCE. The microscopic mechanism of pitting corrosion induced by bentonite hydrolysis salts was elucidated using the point defect model, calculating the polarizability of the passive layer/outer layer interface as α = 0.1. The reliability of the cation adsorption and adsorption-desorption mechanisms was confirmed through experimental data fitting, point defect model fitting, and theoretical analysis.

The Hidden Role of the Dielectric Effect in Nanofiltration: A Novel Perspective to Unravel New Ion Separation Mechanisms.

Nanofiltration (NF) membranes play a critical role in separation processes, necessitating an in-depth understanding of their selective mechanisms. Existing NF models predominantly include steric and Donnan mechanisms as primary mechanisms. However, these models often fail in elucidating the NF selectivity between ions of similar dimensions and the same valence. To address this gap, an innovative methodology was proposed to unravel new selective mechanisms by quantifying the nominal dielectric effect isolated from steric and Donnan exclusion through fitted pore dielectric constants by regression analysis. We demonstrated that the nominal dielectric effect encompassed unidentified selective mechanisms of significant relevance by establishing the correlation between the fitted pore dielectric constants and these hindrance factors. Our findings revealed that dehydration-induced ion-membrane interaction, rather than ion dehydration, played a pivotal role in ion partitioning within NF membranes. This interaction was closely linked to the nondeformable fraction of hydrated ions. Further delineation of the dielectric effect showed that favorable interactions between ions and membrane functional groups contributed to entropy-driven selectivity, which is a key factor in explaining ion selectivity differences between ions sharing the same size and valence. This study deepens our understanding of NF selectivity and sheds light on the design of highly selective membranes for water and wastewater treatment.

Steering the Selectivity of CORR from Acetate to Ethanol via Tailoring the Thermodynamic Activity of Water.

The electrochemical conversion of carbon monoxide (CO) into oxygenated C2+ products at high rates and selectivity offers a promising approach for the two-step conversion of carbon dioxide (CO2). However, a major drawback of the CO electrochemical reduction in alkaline electrolyte is the preference for the acetate pathway over the more valuable ethanol pathway. Recent research has shed light on the significant impact of thermodynamic water activity on the electrochemical CO2 reduction reaction pathways, but less is understood for the electrochemical reduction of CO. In this study, we investigated how the water activity at the electrified interface can be enhanced to adjust the selectivity between acetate and ethanol. We employed an ionomer modifier to lower the local concentration of alkali ions (via Donnan exclusion), successfully enhancing ethanol production while suppressing acetate formation. We observed a remarkable improvement in the Faradaic efficiency of ethanol and alcohol (i.e. ethanol, propanol etc), which reached 42.5% and 55.1%, respectively, at a current density of 700 mA cm-2. The partial current densities of ethanol and alcohol reached 698 and 942 mA cm-2 at 2000 mA cm-2. Furthermore, we achieved a 3.7-fold increase in the ethanol/acetate ratio, providing clear evidence of our successful modulation of product selectivity.

Titania and zirconia ceramic nanofiltration membrane fabrication by coating method on mullite and mullite-alumina microfiltration supports for industrial wastewater treatment

Industrial wastewater treatment increasingly relies on membrane separation, with ceramic membranes offering many advantages such as thermal stability and pH resistance. The resistance of ceramic membranes to extreme pH conditions indicates their ability to maintain structure and performance when exposed to highly acidic or alkaline environments. A high-permeability ceramic nanofiltration membrane was developed, boasting excellent rejection rates through a multilayer asymmetric design. Initially, two tubular porous supports, mullite and mullite-alumina, with a weight percent of 50, were fabricated using the extrusion method. Subsequently, a colloidal sol of titania (TiO2) and titania-zirconia (TiO2- ZrO2) was prepared via the sol–gel method and coated on the ceramic supports using the dip-coating method. After analyzing the membrane microstructure using SEM, XRD, and BET, the efficiency of the membranes in treating synthetic oily wastewater was evaluated. The results underscore the significant impact of the Donnan exclusion mechanism on the rejection of nanofiltration (NF) membranes. An increase in pressure led to a rise in rejection rates up to 7 bars. The Chemical Oxygen Demand (COD) rejection for mullite-titania zirconia (MTZ) and mullite-alumina-titania zirconia (MATZ) membranes was 98.65 % and 98 %, respectively. The pure water permeability test results for mullite and mullite-alumina supports, as well as MTZ and MATZ membranes, were recorded as 254, 382, 70, and 89 L bar-1m-2h−1, respectively.

Rational construction of positively charged polyamide nanofiltration membranes for precision cation separations

Nanofiltration has gained extensive attention in various energetically efficient separations towards a sustainable water–energy nexus. However, state-of-the-art polyamide nanofiltration membranes are constrained by the inherent trade-off between water permeance and solute selectivity, and a remarkable improvement in membrane permselectivity remains a big challenge. Here we conceived a density functional theory (DFT) assisted surface modification approach using triaminoguanidine hydrochloride (TGH) as the functional modifier to fabricate polyamide membranes with extremely high surface electropositivity and well-defined nanopores to overcome this challenge. Experimental data and DFT simulation results show that TGH surface modification can significantly manipulate surface charges and polarity to facilitate water permeation and enhance Donnan exclusion selectivity. Compared with the pristine benchmark membrane, the TGH-modified membrane exhibited a 4-fold increase in water permeance and a 6-fold increase in salt rejection, which successfully breaks the trade-off, excellent monovalent/divalent cation selectivity, and superior operational stability over a wide range of testing pressure, feed pH, and operation time, outperforming state-of-the-art membranes with similar chemistry. Taken together, this study demonstrates a feasible and reliable method combining DFT and experiments to rationally tailor the membrane characteristics at the molecular level, enabling the successful fabrication of effective polyamide nanofiltration membranes with precisely regulated structural and surface properties for water purification and precision ion separations.

Direct recovery of high-purity lithium via nanofiltration membranes from leaching solution of spent lithium batteries

The recycling of spent ternary lithium batteries (T-LIBs) promises scarce strategic resource recovery, however, efficient and selective recovery of Li+ from T-LIBs leaching solution with complex components is still a considerable challenge. Herein, we present a polyamide nanofiltration membrane based on the positively charged nanoscale dispersion interlayer for the first application in recycling lithium from the leaching solution of spent T-LIBs. The electronegativity is weakened by positive charge within the interlayer, which enhance the effect of Donnan exclusion. The pos-TFNi membrane can effectively permeate Li+ while the interfering divalent ions are almost completely separated, achieving the high purity (separation factor ≥ 93.5) and high recovery rate (79.2%) of Li+ from leaching solution simultaneously, with a 6.2-fold improvement in the separation factor over the pristine TFC membrane, and outperformed the majority of the NF membranes. This work represents a reference for the recycling of the massive accumulation of spent T-LIBs worldwide.

Purification of Eucalyptus globulus steam explosion hydrolysates via nanofiltration to recover xylooligosaccharides

Nanofiltration was applied to purify steam explosion hydrolysates obtained from Eucalyptus globulus woodchips. The complex hydrolysate comprised xylooligosaccharides, monosaccharides, glucuronic acid (GluA), and degradation products, including acetic acid, furfural, and 5-hydroxymethylfurfural (HMF). Membranes with 750 and 200 Da molecular weight cut-offs were assessed for their ability to retain oligosaccharides while allowing degradation products to permeate. Using the 750 Da membrane, the average compound retention order was: acetic acid (9.8 %) < furfural (10.8 %) < HMF (31.4 %) ≪ arabinose (52.5 %) < xylose (63.8 %) < glucose (76.0 %) < GluA (90.6 %). The separation mechanism for neutral saccharides and furans was primarily molecular sieving, while Donnan exclusion was the primary retention mechanism responsible for GluA. Separation factors obtained for acetic acid and furfural over xylotriose and xylobiose exceeded 10 and 3, respectively, for both membranes, showing that desired compounds were predominantly retained. Permeability loss during nanofiltration was fully restored after implementing cleaning-in-place for both membranes.

Tailor-Made Heterocharged Covalent Organic Framework Membrane for Efficient Ion Separation.

Pore size sieving, Donnan exclusion, and their combined effects seriously affect ion separation of membrane processes. However, traditional polymer-based membranes face some challenges in precisely controlling both charge distribution and pore size on the membrane surface, which hinders the ion separation performance, such as heavy metal ion removal. Herein, the heterocharged covalent organic framework (COF) membrane is reported by assembling two kinds of ionic COF nanosheets with opposite charges and different pore sizes. By manipulating the stacking quantity and sequence of two kinds of nanosheets, the impact of membrane surface charge and pore size on the separation performance of monovalent and multivalent ions is investigated. For the separation of anions, the effect of pore size sieving is dominant, while for the separation of cations, the effect of Donnan exclusion is dominant. The heterocharged TpEBr/TpPa-SO3H membrane with a positively charged upper layer and a negatively charged bottom layer exhibits excellent rejection of multivalent anions and cations (Ni2+, Cd2+, Cr2+, CrO4 2-, SeO3 2-, etc). The strategy provides not only high-performance COF membranes for ion separation but also an inspiration for the engineering of heterocharged membranes.

Harnessing the power of hollow Zein nanoparticles for enhanced antifouling and heavy metal removal of polyethersulfone membranes

This study explores the physicochemical characteristics of an innovative mixed matrix membrane made from polyethersulfone (PES) and hollow Zein nanoparticles (HZNs), which are derived from the corn storage protein, Zein. HZNs, with a mean diameter of 40 nm, were applied to address the challenges associated with metal and inorganic nanoparticles, such as their tendency to accumulate unevenly on the membrane surface. The membranes were fabricated by incorporating varying concentrations of HZNs into the PES casting solution through the nonsolvent phase separation method. The addition of HZNs enhanced the hydrophilicity and pure water flux of the membranes. It also modified the membrane structure, morphology, pore size, molecular weight cut-off (MWCO), and porosity. Increasing the HZN concentration up to 5 wt% proportionally improved the surface hydrophilicity and roughness of the membranes. Furthermore, the modified membranes exhibited excellent performance in rejecting heavy metals at an acidic pH of 4, with the 5 %-HZNs/PES membrane achieving a 100 % rejection rate without significantly affecting water flux due to Donnan exclusion. Additionally, the 5 %-HZNs/PES membrane showed a minimal irreversible fouling resistance (Rir) of 17.9 % and a fouling resistance ratio (FRR) of 82.1 %. These results indicate that the developed mixed matrix membrane holds significant promise for applications in water purification processes.

Controlled Localized Metal-Organic Framework Synthesis on Anion Exchange Membranes.

Metal-organic framework (MOF) films can be used in various applications. In this work, we propose a method that can be used to synthesize MOF films localized on a single side of an anion exchange membrane, preventing the transport of the metal precursor via Donnan exclusion. This is advantageous compared to the related contra-diffusion method that results in the growth of a MOF film on both sides of the support, differing in quality on both sides. Our proposed method has the advantage that the synthesis conditions can potentially be tuned to create the optimal conditions for crystal growth on a single side. The localized growth of the MOF is governed by Donnan exclusion of the anion exchange membrane, preventing metal ions from passing to the other compartment, and this leads to a local control of the precursor stoichiometry. In this work, we show that our method can localize the growth of both Cu-BTC and ZIF-8 in water and in methanol, respectively, highlighting that this method can used for preparing a variety of MOF films with varying characteristics using soluble precursors at room temperature.

Ultrahighly Li-selective nanofiltration membranes prepared via tailored interfacial polymerization

Nanofiltration (NF) membrane-based separation has gained significant attention as an efficient technology for recovering lithium (Li) from salt-lake brines. However, many previously developed NF membranes are not commercially feasible because they lack sufficient Li selectivity and require the use of new monomers/chemicals or complicated fabrication processes. Herein, we propose a commercially viable method to fabricate ultrahighly Li-selective polyamide (PA) membranes by carefully tailoring a conventional interfacial polymerization process using an established piperazine (PIP)/trimesoyl chloride monomer system. The use of excess PIP endowed the fabricated membrane with enhanced PA crosslinking density and a positive surface charge, reinforcing both its size and Donnan exclusion mechanisms. Furthermore, the addition of benzyltributylammonium chloride, a cationic surfactant, to the PIP solution effectively improved the water permeance of the membrane without impairing its magnesium ion (Mg2+) rejection by loosening its PA network while enhancing its positive surface charge. Consequently, our tailor-made PA membranes with the proper pore structures and strong positive surface charges exhibited ultrahigh Li+/Mg2+ selectivity of up to 150 (under single-salt conditions) and 887 (under mixed-salt conditions), significantly outperforming commercial and other reported laboratory-made NF membranes. Our strategy provides a facile and effective means to manufacture Li-selective membranes with high commercial viability.

Effect of solution ions on the charge and performance of nanofiltration membranes

Considering growing efforts to understand and improve the solute-specific selectivity of nanofiltration (NF) membranes, we explored the ion-specific effects that govern the charge and performance of a loose polyamide NF membrane that is commonly used for solute-solute separations. Specifically, we systematically evaluated the zeta potential of the membrane under different conditions of pH, salinity, and ionic composition, and correlated the obtained data with membrane performance tested under similar conditions. Our results identify the pKa of both carboxylic and amine groups bonded to the membrane surface and suggest that the highly polarizable chloride anions in the solution adsorb to the polyamide, increasing its negative charge. We also show that monovalent cations of different “stickiness” can neutralize the negative membrane charge to different extents due to their varying tendency to sorb to the polymer matrix or screen the fixed carboxyl groups on the membrane surface. Notably, our correlation between zeta potential measurements and permeability experiments indicates the substantial contribution of solution ions to Donnan exclusion in NF membranes.

Partial fluorinated silica incorporated with tuneable alkyl cross-linker based multi-cationic alkaline membrane for vanadium redox flow battery

Herein, we report partial fluorinated polymer (poly(vinylidene fluoride-co-hexafluoropropylene); PVDF-co-HFP)-based multi-cationic (quaternary ammonium, and imidazolium groups) cross-linked (tuneable carbon chain cross-linker) anion exchange membrane (AEM) incorporated with functionalized silica to avoid any structural deformations under harassed environment. Prepared membranes are cross-linked using different cross-linking agents, to study the effect of cross-linker chain length on the membrane performance. Incorporation of functionalized silica by acid-catalyzed sol-gel process improves membrane properties and stabilities. Reported PVIm-C10-APS AEM shows high conductivity (7.20 × 10−2 S/cm), and ion exchange capacity (1.48 meq/g). Well optimized positively charged PVIm-C10-APS AEM exhibits extremely low permeability of vanadium cations because of “Donnan exclusion” (9.80 × 10−7 cm2/s). During VRFB operation, PVIm-C10-APS AEM exhibits 98.10% coulombic efficiency (CE) and 77.60% voltage efficiency at 100 mA/cm2 without any significant deterioration up to 300 charge-discharge cycles. Further, PVIm-C10-APS membrane also shows >1.50 V OCV and 345 mW/cm2 peak power density at 400 mA/cm2. Reported AEM has been bench-marked with other membranes reported in the literature, and assessed as a promising material for VRFB or membrane separator for energy devices.

Development of an efficient, low-operating-pressure graphene oxide/polyethersulfone nanofiltration membrane for removing various water contaminants

Conventional wastewater treatment technologies tend to be high-capex, energy-intensive solutions that lack specificity for different pollution classes, and do not lend themselves to wide-scale deployment, particularly in areas of the world where industrial wastewater discharge is a significant environmental problem. In tandem, solid waste pollution arising, particularly plastic containing waste, is a persistent and serious pollution issue. This work focuses on the concept of "waste treating waste" and a multidisciplinary effort ranging from materials science and environmental management to sustainable water treatment, in addition to production of graphene oxide from mineral water waste bottles using a simple synthetic procedure that can be economically scaled up for use as a cost-effective adsorbent. Prepared graphene oxide was supported on a polyethersulfone (PES) membrane, and batch filtration studies were performed to examine its performance in the removal of methylene blue (MB) dye, Gentimicin sulphate (GMS) antibiotic, and Na2SO4 and MgSO4 salts from an aqueous solution. Operating parameters such as initial pollutant concentration, time, and solution pH were investigated and optimized using a response surface methodology (RSM) model. The results confirm the significant efficiency of the filtration process, with a maximum rejection of about 91% for MB, 93% for GMS, 67% for Na2SO4, and 64% for MgSO4, with maximum water flux of 1322, 1367, 1225, and 1059 LMH, respectively. Density functional theory calculations were considered for the GO, PES membrane, and GO/PES membrane with a GGA/PBE optimization level. Adsorption annealing locator analysis was performed for the GO/PES membrane, and the process was recalculated for MB as adsorbate. In conclusion, the adsorption effect employing produced GO/PES membrane is the most important removal, followed by Donnan exclusion and steric hindrance effect. Therefore, it is possible to build new eco-friendly membranes for nanofiltration that are affordable, stable, and effective in removing various pollutants from water systems.

Asymmetrically charged polyamide nanofilm of intrinsic microporosity containing quaternary ammonium groups for heavy metal removal

High-performance nanofiltration (NF) is a highly hopeful approach for removing heavy metals from water, which can effectively solve the hazards of heavy metals to the public health and environment security. In this study, a polyamide (PA) nanofilm of intrinsic microporosity was fabricated through interfacial polymerization of the novel spirocyclic diamine monomer (SBI) with trimesoyl chloride (TMC). The PA nanofilm demonstrated high microporosity due to the porous structure formed by the covalent cross-linking of SBI with TMC and the stacking of the SBI monomers due to its rigidly-contorted structure. Consequently, its free volume was high with the water permeance of 19.3 L m−2 h−1·bar−1. Meanwhile, the PA nanofilm exhibited asymmetrical charges on both sides with a positively charged bottom and a negatively charged top. The quaternary ammonium moieties in SBI produced positively charged nanochannels in the PA nanofilm, reinforcing the Donnan exclusion against multivalent cations. The proposed SBI-TMC membrane was able to effectively remove heavy metals from water, with rejections of Cu2+, Ni2+, Zn2+, and Pb2+ at 93.3%, 93.0%, 91.8%, and 88.3%, respectively. This study confirmed that the fit-for-purpose design of monomer with rigidly-contorted structure is a feasible approach to fabricate NF membrane with enhanced separation performance.

Asymmetric polyelectrolyte multilayer membranes: Influence of bottom section polycation on layer growth and retention mechanisms

It has been previously demonstrated that asymmetric polyelectrolyte multilayer (PEM) membranes are highly promising for use in water treatment due to their ability to combine a high selectivity with a high permeability. This is achieved by first coating a more open (highly permeable) bottom PEM to fill the pores of the support membrane, and subsequently a more dense (highly selective) top PEM. However, fundamental understanding on the interaction between top and bottom PEM section and the effect of the bottom section on the resulting membrane properties is still lacking. In this study, symmetric membranes with different polycations are prepared and compared with asymmetric membranes which contain an additional poly (allylamine hydrochloride)/poly (acryl amide) (PAH/PAA) top section. PEM layer growth was first studied with optical reflectometry, demonstrating that the growth of the top PEM section is dependent on the previously deposited bottom PEM section. Membrane performance was assessed with cross-flow measurements, where permeability and molecular weight cutoff (MWCO) measurements showed distinct differences for the symmetric membranes. Although these properties converge upon coating of the top section, differences remain. This can be explained by a contribution of the bottom section to hydraulic resistance and by intermixing of the top and bottom section. The degree of intermixing is attributed to differences in mobility of the used polycations. Single salt retention measurements even show that changing the bottom section polycation allows for tuning of the salt retention mechanism of the resulting asymmetric membranes. Whereas membranes with PAH in the bottom section are dominated by dielectric exclusion, membranes with Poly (vinylbenzyltrimethylammonium chloride) (PVBTMAC) in the bottom section show a dominant Donnan exclusion. These observations were confirmed by varying both the salt concentration and the operational flux. Overall, our work demonstrates that asymmetric coating on different bottom PEM chemistries can be used as a promising tuning parameter in layer-by-layer coating. This allows for a more rational design of asymmetric PEM membranes, opening opportunities for tuning membranes towards specific applications.

Nanofiltration Ceramic Membranes as a Feasible Two-Pronged Approach toward Desalination and Lithium Recovery.

Ceramic membranes are taking center stage for separation technologies in water treatment. Among them, ceramic nanofiltration membranes are at the forefront of membrane technologies. The desalination of seawater using ceramic nanofiltration membranes is a potential application toward increasing the global water supply and tackling water scarcity. However, while the high fabrication cost poses a challenge to their large-scale applications, high-value separation applications can help to offset the overall cost. In this regard, ceramic nanofiltration membranes can also be explored as a viable option for high-value lithium extraction from the waste seawater brine. In order to determine the potential of nanofiltration ceramic membranes for desalination and lithium recovery from seawater, the current efficiency of salt rejection across various operation parameters must be thoroughly evaluated. Specifically, the interactions between the Donnan exclusion, steric exclusion, zeta potential, and salt concentration play an important role in determining the salt rejection efficiency. Several strategies are then proposed to guide ceramic nanofiltration membranes toward potentially practical applications regarding desalination and lithium recovery.