Sulfonated Polysulfone Membranes Research Articles

Utilization of cellulose-based carbon nanodots in sulfonated polysulfone based membrane for direct methanol fuel cell

Sulfonated polysulfone (SPS) composite membranes consisting of cellulose-based carbon nanodots (CNDs) were successfully prepared as a proton exchange membrane (PEM) for direct methanol fuel cell (DMFC) applications. The CNDs were prepared using the top-down hydrothermal method. The structure transformation from cellulose to CNDs was confirmed by the FTIR and XRD analysis. The particle size of CNDs was between 1 and 3 nm. The particles exhibited good optical properties. The incorporation of CND into matrix polymer increased the thermal stability of the membranes. Morphology analysis of the SPS/CND composite membranes revealed that CNDs had been successfully dispersed within the SPS polymer matrix. The cross-linking between SPS and CNDs enhanced the proton conductivity of the composite membranes compared to the pristine SPS membrane. The SPS/CND-1 (1 wt%) exhibited the highest selectivity with a proton conductivity of 35.5 mS.cm−1 and a methanol permeability of 3.50 × 10−6 cm2.s−1. The experimental results indicate that the incorporation of CNDs into the SPS membrane also decreased the amount of methanol that can pass through the membrane when used in DMFCs.

High-Reversibility Sulfur Anode for Advanced Aqueous Battery.

Despite being extensively explored as cathodes in batteries, sulfur (S) can function as a low-potential anode by changing charge carriers in electrolytes. Here, a highly reversible S anode that fully converts from S8 0 to S2- in static aqueous S-I2 batteries by using Na+ as the charge carrier is reported. This S anode exhibits a low potential of -0.5V (vs standard hydrogen electrode) and a near-to-theoretical capacity of 1404mA h g-1 . Importantly, it shows significant advantages over the widely used Zn anode in aqueous media by obviating dendrite formation and H2 evolution. To suppress "shuttle effects" faced by both S and I2 electrodes, a scalable sulfonated polysulfone (SPSF) membrane is proposed, which is superior to commercial Nafion in cost (US$1.82 m-2 vs $3500 m-2 ) and environmental benignity. Because of its ultra-high selectivity in blocking polysulfides/iodides, the battery with SPSF displays excellent cycling stability. Even under 100% depth of discharge, the battery demonstrates high capacity retention of 87.6% over 500 cycles, outperforming Zn-I2 batteries with 3.1% capacity under the same conditions. These findings broaden anode options beyond metals for high-energy, low-cost, and fast-chargeable batteries.

Durability improvement of proton exchange membrane fuel cells by doping silica‒ferrocyanide antioxidant

Proton exchange membranes (PEMs) with remarkable chemical stability are desirable to realize long lifetimes of proton exchange membrane fuel cells (PEMFCs). In our recent work, PEMs containing radical scavenger ferrocyanide (Fc (II))/ferricyanide (Fc (III)) species were demonstrated to possess outstanding chemical stability. However, a challenge in balancing general applicability and retention remains, due to their water solubility. Here, Fc (II) is tethered to a SiO2 support to produce low water soluble SiO2-Fc (II), which could be used as a universal additive in various matrices to mitigate leaching. The composite PEMs, sulfonated polysulfone (SPSf) doped with SiO2-Fc, show much higher oxidative stability, confirmed by Fenton's test, ion exchange capacity retention and proton conductivity retention. The composite PEM also displays obviously improved durability during PEMFC operation, where the antioxidative efficacy of SiO2-Fc is evidently stronger than comparative stand-alone water-soluble species. Moreover, a PEMFC based on SPSf composite PEM shows much higher power output than that based on unfilled SPSf membrane under low humidity conditions, owing to the hydrophilicity and proton conductivity of SiO2-Fc. The present work outlines a prospective route to better utilize Fc (II)/Fc (III) antioxidant with clear benefits in general applicability and good stability, leading to progress in utilization.

Fabrication and Study of Dextran/Sulfonated Polysulfone Blend Membranes for Low-Density Lipoprotein Adsorption.

The abnormal increase in low-density lipoprotein (LDL) in human blood is a main independent risk factor for the pathogenesis of atherosclerosis, whereas a reduced LDL level effectively lowers morbidity. It is important to develop LDL adsorption materials with high efficiency and selectivity, as well as to simplify their fabrication processes. In this paper, polysulfone (PSF), sulfonated polysulfone (SPSF), and sulfonated polysulfone/dextran (SPSF/GLU) membranes were successfully fabricated for LDL adsorption using a solution casting technique. Attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements confirmed the success of the preparation. The water contact angle decreased from 89.7 ± 3.4° (PSF) to 76.4 ± 3.2° (SPSF) and to 71.2 ± 1.9° (SPSF/GLU), respectively. BSA adsorption testing showed that the SPSF/GLU with surface enrichment of sulfonate groups and glycosyl groups possessed higher resistance to protein solution. The adsorption and desorption behaviors of the studied samples in single-protein or binary-protein solutions were systematically investigated by enzyme-linked immunosorbent assay (ELISA), The results showed that SPSF/GLU, which had excellent resistance to protein adsorption, possessed a similar adsorption capacity to that of PSF. SPSF membrane exhibited excellent selective affinity for LDL in single and binary protein solutions, suggesting potential applications in LDL removal.

Preparation and characterization of new types of sulfonated poly(ether sulfide sulfone) for application in fuel cell

ABSTRACT Sulfonated polysulfone membranes are among the best candidate for fuel cells. The main challenges are obtaining high conductivity and mechanical properties. Accordingly, disulfonated poly(ether sulfide sulfone) copolymer flexible films were prepared via reaction of bis(4-hydroxyphenyl) sulfide with sulfonated and non-sulfonated bis(4-fluorophenyl) sulfone, and subsequent solution casting. Thermal and mechanical properties, water uptake, oxidative stability, and ion exchange capacity were investigated. Proton conductivity of copolymers at 80°C was 0.131–0.198 S cm−1. Polymer with 45% degree of sulfonation showed optimized favorable properties. Copolymers indicated acceptable properties compared with Nafion that was partially related to the presence of flexible hydroxyphenyl sulfide moiety.

Hydrophilicity and flux properties improvement of high performance polysulfone membranes via sulfonation and blending with Poly(lactic acid)

To achieve increased flow and reduce fouling, polymeric membranes can be functionalized with hydrophilic groups such as sulfone, amines, and others. This research has aimed at the sulfonation of Polysulfone (PSU) with various agents and at varying substitution degrees to change its hydrophobic character. PSU was also blended with Poly(lactic acid) (PLA), which is a more hydrophilic polymer. The phase inversion method was used to make PSU, PLA, sulfonated PSU, and PSU/PLA blend-based membranes. Sulfonation degrees of sulfonated PSU membranes were assessed using FT-IR, mechanical characteristics of membranes were determined, and thermal properties of membranes were clarified using DSC and TGA techniques. Hydrophilic natures and membrane alterations were investigated, as well as contact angle and water uptake measures. Among three distinct sulfonation agents (trimethylsilyl chlorosulfonate (TMSCS), sulfuric acid, and chlorosulfonic acid) employed to produce a 20% sulfonation degree of polysulfone, TMSCS was chosen as having the highest sulfonation efficiency (91.5%). With increasing sulfonation degree, a drop in molecular weight was seen in all sulfonated polysulfone samples. The mechanical strength values of polysulfone after sulfonation with TMSCS rose from 35.23 MPa to 63.35 MPa, while the contact angle value decreased from 85.58° to 71°. The contact angle value reduced from 85.58° to 64.68° while the mechanical strength of the PSU and PSU/PLA (50:50) blend increased from 35.23 MPa to 39.3 MPa. Membranes were also tested for pure water flux, hydrostability, and biostability. In terms of application requirements, it was determined that sulfonated PSU-based membranes manufactured with TMSCS with a 20% sulfonation degree and PSU/PLA blend-based membranes with a 50:50 (w:w) ratio have the optimum compositions with high flux quantities.

Anhydrous proton conductivity of sulfonated polysulfone/deep eutectic solvents (DESs) composite membranes: Effect of sulfonation degree and DES composition

The potential use of deep eutectic solvents (DESs) for anhydrous conductivity of sulfonated polysulfone membrane is presented. To this end, different molar ratios of sodium bromide as hydrogen bond acceptor (HBA) and ethylene glycol as hydrogen bond donor (HBD) are used for the synthesis of DESs. Two sulfonation degrees (DS) of 30 and 40% are also adjusted for the synthesis of sulfonated polysulfones. The synthesized DESs have suitable thermal stability as well as low viscosity to provide interconnected ionic pathways within the membranes. The proton conductivity of membranes is mainly influenced by the HBD/HBA molar ratio of DES as well as the DS of sulfonated polymer. The maximum proton conductivity of 301 mS/cm at 100 °C is obtained for the polymer with 40% DS containing a DES with a higher HBD/HBA molar ratio. The prepared composite membranes have great potential for fuel cell performance, especially in anhydrous conditions.

Prediction of the phenol removal capacity from water by adsorption on activated carbon.

High-performance sulfonated polysulfone (SPSf) mixed-matrix membranes (MMMs) were fabricated via a nonsolvent-induced phase separation (NIPS) method using zeolitic imidazolate frameworks-67 (ZIF-67) as a crosslinker. Acid-base crosslinking occurred between the sulfonic acid groups of SPSf and the tertiary amine groups of the embedded ZIF-67, which improved the dispersion of ZIF-67 and simultaneously improved the membrane strzcture and permselectivity. The dispersion of ZIF-67 in the MMMs and the acid-base crosslinking reaction were verified by energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The pore structure analysis of MMMs indicated that filling ZIF-67 into SPSf enhanced the average surface pore sizes, surface porosities and more micropore in cross-sections. The crossflow filtrations showed the MMMs have higher pure water fluxes (57 to 111 L m-2 h-1) than the SPSf membrane (55 L m-2 h-1) but also higher bovine serum albumin (BSA) rejection rate of 93.9-95.8%, a model protein foulant. The MMMs showed a higher water contact angle than the SPSf membrane due to the addition of hydrophobic ZIF-67 and acid-base crosslinking, and also maintained high thermal stability evidenced by the thermogravimetric analysis (TGA) results. At the optimal ZIF-67 concentration of 0.3 wt%, the water flux of the SPSf-Z67-0.3 membrane was 82 L m-2 h-1 with a high BSA rejection rate of 95.3% at 0.1 MPa and better antifouling performance (FRR = 70%).

Enhanced mechanical strength and performance of sulfonated polysulfone/Tröger's base polymer blend ultrafiltration membrane

To improve the mechanical strength and separation performance of sulfonated polysulfone (SPSf) ultrafiltration membranes, Tröger's base (TB) polymer was blended into the casting solution. An acid-base crosslinking structure between the sulfonic acid groups of SPSf and tertiary amine groups in TB would contribute to their good compatibility and influence the membrane formation process, morphology and properties. The formation of acid-base pairs was confirmed by the existence of quaternary amine groups in the X-ray photoelectron spectra of SPSf/TB blend membranes. According to the pore structure analysis of ultrafiltration membranes, the blending of TB polymer into SPSf enhanced the surface and total porosities, and reduced the top layer thickness. In addition, the finger-like pores became more regular and vertically interconnected. The SPSf/TB blend membrane showed a higher water contact angle than SPSf membrane due to the addition of hydrophobic TB polymer and formation of acid-base crosslinking structure. The SPSf/TB blend membranes showed higher pure water fluxes (127.4–342.7 L m−2 h−1) than the SPSf membrane (51.6 L m−2 h−1). All membranes showed similar retention factor for bovine serum albumin (BSA), a model protein foulant. In static experiments, the amount of BSA adsorbed by the SPSf/TB blend membranes was much lower than that of the pristine SPSf membrane because the enhanced charge of the blend membranes (ζ = −72.46 ~ −79.17 mV) strengthened the electrostatic repulsion between membrane surface and BSA. The flux recovery ratio after three ultrafiltration cycles using SPSf/TB blend membranes was lower than that of SPSf membrane because pore blockage and irreversible pollution occurred more easily under a high flux, larger average pore size, and lower hydrophilicity. The introduction of TB polymer enhanced the mechanical strength of the ultrafiltration membrane due to the formation of acid-base crosslinking structure between TB polymer and SPSf.

Tuning the Electrochemical Properties of Novel Asymmetric Integral Sulfonated Polysulfone Cation Exchange Membranes.

In this study, novel asymmetric integral cation exchange membranes were prepared by the wet phase inversion of sulfonated polysulfone (SPSf) solutions. SPSf with different degrees of sulfonation (DS) was synthesized by variation in the amount of chlorosulfonic acid utilized as a sulfonating agent. The characterization of SPSf samples was performed using FTIR and 1H-NMR techniques. SPSf with a DS of 0.31 (0.67 meq/g corresponding ion exchange capacity) was chosen to prepare the membranes, as polymers with a higher DS resulted in poor mechanical properties and excessive swelling in water. By a systematic study, the opportunity to tune the properties of SPSf membranes by acting on the composition of the polymeric solution was demonstrated. The effect of two different phase inversion parameters, solvent type and co-solvent ratio, were investigated by morphological and electrochemical characterization. The best properties (permselectivity of 0.86 and electrical resistance of 6.3 Ω∙cm2) were obtained for the membrane prepared with 2-propanol (IPA):1-Methyl-2-pyrrolidinone (NMP) in a 20:80 ratio. This membrane was further characterized in different solution concentrations to estimate its performance in a Reverse Electrodialysis (RED) operation. Although the estimated generated power was less than that of the commercial CMX (Neosepta) membrane, used as a benchmark, the tailor-made membrane can be considered as a cost-effective alternative, as one of the main limitations to the commercialization of RED is the high membrane price.

Esterification of oleic acid employing sulfonated polystyrene and polysulfone membranes as catalysts

Esterification of oleic acid employing sulfonated polystyrene and polysulfone membranes as catalysts

Hydration, Ion Distribution, and Ionic Network Formation in Sulfonated Poly(arylene ether sulfones)

We use molecular dynamics simulations to probe hydration, ion spacing, and cation-anion interaction in two sulfonated polysulfones with different ion distributions along the polymer backbone. At room temperature, these polymers remain in a glassy state even with water contents more than 10%. At the equilibrium water uptake, the ions exhibit a similar level of hydration as they would in their saturated aqueous solution. The framework of Manning's limiting law for counterion condensation is used to examine ionic interactions in the simulated polysulfones. The dielectric constant that the ions experience can be well approximated by a volume-weighted average of the dielectric constants of the polymer backbone and water. Our results show that a reasonable estimate of the average inter-ion distance, b, is obtained by using the distance where the sulfonate-sulfonate coordination number reaches 1. The spacing of the sulfonate ions along the polysulfone backbone plays a role in determining their spatial distribution inside the hydrated polymer. As a result, the value of b is slightly larger for polymers where the sulfonate ions are more evenly spaced along the backbone, which is consistent with experimental evidence. The simulations reveal that the sulfonate ions and sodium counterions form fibrillar aggregates at water contents below the equilibrium water uptake. Such extensive ionic aggregates are expected to facilitate ion transport in sulfonated polysulfone membranes, without the need for long-range chain motion as in the case of traditional rubbery ionic polymers. Our estimates for the dielectric constant and b are used in conjunction with Manning's theory to estimate the fraction of counterions condensed to the fixed ions. The prediction of Manning's theory agrees well with the simulation result.

Synthesis and applicability study of novel poly(dopamine)-modified carbon nanotubes based polymer electrolyte membranes for direct methanol fuel cell

Abstract Novel sulfonated polysulfone (SPS) based composite polymer electrolyte membranes (PEMs) filled with polydopamine modified carbon nanotubes (PD-CNTs) have been prepared using the phase inversion technique. The present study reports the development of novel and cost- efficient nanocomposite materials with excellent properties for polymer electrolyte membranes preparation. The progress is noteworthy towards the synthesis of economical organic-inorganic nanocomposites through which fuel cell related properties can be tailored. The applicability of prepared PEMs for direct methanol fuel cell (DMFC) has been investigated in terms of water uptake, methanol permeability, and proton conductivity by changing the filler content (0.5–1.0 wt. %). The carbon nanotubes were surface functionalized using polydopamine (PD) as the modifying agent. The resultant functionalized carbon nanotubes (PD-CNTs) have been incorporated into SPS polymer matrix to prepare the composite PEMs. The functional groups, structural properties, elemental analysis, morphological and topographical aspects of the resulting composite membranes were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Energy dispersive X-ray spectrometer (EDS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM), respectively. It was found that PD served as an outstanding glue because of its adhesive qualities, facilitated the homogeneous dispersion of CNTs into the polymer matrix, and created new proton-conducting pathways in the subsequent membranes. A detailed analysis showed that water uptake and proton-conducting properties of the engineered PEMs have been improved significantly. Composite membarne (0.5 wt. % PD-CNTs) showed 43 % increase in proton conductivity compared to the pristine SPS membrane, increasing from 0.085 S/cm for pristin to 0.1216 S/cm for the composite membrane at 80 °C. The prepared PEMs also showed an impressive 75 % decrease in methanol permeability (5.68 × 10−7 cm2/s) compared to recast Nafion®117 membarne (23.00 × 10−7 cm2/s). These results demonstrated the immense potential of polydopamine functionalized CNTs based PEMs for DMFC application. The ability of the newly synthesized membrane to retain water, and its capability to give a structural framework for maximum proton conductivity with reduced fuel crossover towards the catalyst are the significant advances from the present study.

Enhancement in proton conductivity by blending poly(polyoxometalate)-b-poly(hexanoic acid) block copolymers with sulfonated polysulfone

Designing polymer chains which contain building blocks with well-defined dimension is an efficient method to induce microphase separation and regulate the ionic channels of polymer electrolyte membranes (PEMs). In this study, a Wells-Dawson-type polyoxometalate (POM) is synthesized and chemically bonded to a norbornene derivative to prepare poly (POM) blocks. Then the block copolymer poly (POM)10-b-poly (COOH)300 is fabricated using poly (POM) and poly (COOH) blocks. Finally, the block copolymer is blended with sulfonated polysulfone (SPS). The electrostatic interactions between the block copolymer and SPS confer the blend membrane with enhanced mechanical and dimensional stabilities. Due to the homogenous distribution of POM clusters and the hydrophilic-hydrophobic interactions between POMs and polymer backbones, the adjacent hydrophilic domains are connected and continuous proton-transfer channels are induced. As a result, the blend membrane displays proton conductivity of 0.053 S cm−1 (25 °C, 100% RH) and 1.5 × 10−2 S cm−1 (80 °C, 40% RH), which are 2.52 and 6.25 times higher than those of the plain SPS membrane. Furthermore, SPS/POM-BC-30 shows a maximum power density of 164.9 mW cm−2, which is 54.7% higher than SPS.

Layer‐by‐layer self‐assembly of multifunctional enzymatic UF membranes

ABSTRACTIn order to eliminate membrane fouling and to ensure enzymatic hydrolysis of urea, multifunctional biocatalytic membranes were prepared by using urease (URE) and trypsin (TRY) enzymes on the sulfonated polysulfone (SPSf) ultrafiltration membrane via layer‐by‐layer (LbL) self‐assembly method. The membrane architecture consisted of multilayer assembly with TRY and URE enzymes as the outer layer and inner sandwiched layer, respectively. Polyethyleneimine (PEI) and alginate (ALG) were used as cationic and anionic polyelectrolytes. Sulfonation and PEI deposition were successfully accomplished as confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy analysis, contact angle measurements, staining with toluidine blue and Congo red dyes and dead‐end filtration experiments. A characteristic value of SPSf membrane with a high water permeability (1000 L/m2.h.bar) and 95% bovine serum albumin (BSA) rejection was observed. In static conditions, URE activities of SPSf2‐PEI‐URE membrane were not affected by BSA fouling, while TRY immobilizations with increased concentrations (SPSf2‐PEI‐URE‐PEI‐ALG‐TRY) significantly lowered the activity of URE. In dynamic conditions, each deposited layer exhibited individual resistance to flow that can be considered as irreversible fouling and caused 90% of flux decline for the SPSf2‐PEI‐URE‐PEI‐ALG‐TRY membrane assembly. The recovery of the initial flux for the multilayered membrane at the end of six fouling and washing cycles was observed 85%. Moreover, at the end of 5 cycles, 78% of the URE initial activity of the multilayered membrane was preserved. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48750.

High performance acid-base composite membranes from sulfonated polysulfone containing graphitic carbon nitride nanosheets for vanadium redox flow battery

In this paper, a series of proton exchange membranes are fabricated with graphitic carbon nitride (g-C3N4) nanosheets as nanofillers and sulfonated polysulfone (SPSF) as membrane matrix via a simple solution-casting method. The structure, physicochemical properties and single-cell energy efficiency of SPSF/g-C3N4 composite membranes are detailed investigated. The introduced g-C3N4 nanosheets greatly optimize the ion selectivity of SPSF membrane, and SPSF/g-C3N4-1 shows the higher ion selectivity (21.8 × 103 S min cm−3) than Nafion 117 (4.0 × 103 S min cm−3) and pristine SPSF (4.6 × 103 S min cm−3). For the vanadium redox flow battery (VRFB) single-cell performance, SPSF/g-C3N4-1 further demonstrates its higher coulombic efficiency (CE, 95.5% and 98%) and energy efficiency (EE, 90.4% and 87.3%) than that of Nafion 117 membrane (CE, 91.3% and 96.5%; EE, 81.7% and 75.7%) at 50 and 100 mA cm−2, respectively. Besides, a good structure stability and durability of SPSF/g-C3N4-1 is proved after 100 charge-discharge cycles, and its chemical stability shows an obvious enhancement under strong acidic and oxidizing condition. Such a contribution from the acid-base interfacial interaction from g-C3N4 and SPSF indicates an effective method to improve the performance of proton exchange membrane. Therefore, SPSF/g-C3N4 composite membranes are applicable as proton exchange membrane for VRFB system.

Proton-conducting amino acid-modified chitosan nanofibers for nanocomposite proton exchange membranes

Proton transfer using amino acids as proton delivery sites is a ubiquitous and important process in organisms. In this study, novel proton-conducting nanofibers were prepared on the basis of a bionic design concept from two perspectives, namely, proton transfer site and proton transfer route, by immobilizing four kinds of amino acids, namely, serine, arginine, lysine, and glycine, onto chitosan (CS) nanofibers. Nanocomposite membranes were then fabricated by filling the pores of the amino acid-functionalized CS nanofiber mats (AA-CSNFs) with sulfonated polysulfone (SPSF). The methanol crossover of the nanocomposite membranes with AA-CSNFs was reduced and their proton conductivity was increased compared with those of pure SPSF membrane. The nanocomposite membrane embedded with the serine-functionalized CS nanofibers exhibited an excellent proton-conducting ability with the highest proton conductivity of 0.192 S/cm at 80 °C. Results indicated that these nanocomposite membranes showed potential for applications in proton exchange membrane fuel cells with superior combined properties.

Enhanced Proton Conductivity of Sulfonated Polysulfone Membranes under Low Humidity via the Incorporation of Multifunctional Graphene Oxide

Development of proton exchange membranes with sufficiently high proton conductivity, especially at low relative humidity (RH), remains a big challenge in the field of fuel cells. In this study, gra...

Sulfonated polysulfone proton exchange membrane influenced by a varied sulfonation degree for vanadium redox flow battery

A series of sulfonated polysulfone (SPSF) proton exchange membranes with varied degree of sulfonation (DS) are prepared through controlling the molar ratio of sulfonated agent and polysulfone (PSF). An optimum DS for SPSF membranes is given by characterizing the physicochemical properties, ion selectivity and vanadium redox flow battery (VRFB) performance. SPSF membrane with DS = 62% (SPSF-62) demonstrates the best membrane performance, where the ion selectivity is 4.6 × 103 S min cm−3 that is higher than that of Nafion 117 (4.0 × 103 S min cm−3). At current density of 50 and 100 mA cm−2, coulombic efficiency (CE, 94.9% and 98.8%) and energy efficiency (EE, 89.2% and 86.2%) of SPSF-62 are much higher than that of Nafion 117 (CE, 91.3% and 96.5%; EE, 81.7% and 75.7%), respectively. In the meantime, the SPSF-62 membrane demonstrates a good durability over 100-time charging-discharging cycles. The present study of SPSF membranes proves a promising VRFB application as proton exchange membrane.

Codeposition Modification of Cation Exchange Membranes with Dopamine and Crown Ether To Achieve High K+ Electrodialysis Selectivity.

Surface modification has been proven to be an effective approach for ion exchange membranes to achieve separation of counterions with different valences by altering interfacial construction of membranes to improve ion transfer performance. In this work, we have fabricated a series of novel cation exchange membranes (CEMs) by modifying sulfonated polysulfone (SPSF) membranes via codeposition of mussel-inspired dopamine (DA) and 4'-aminobenzo-15-crown-5 (ACE), followed by glutaraldehyde cross-linking, aiming at achieving selective separation of specific cations. The as-prepared membranes before and after modification were systematically characterized in terms of their structural, physicochemical, electrochemical, and electrodialytic properties. In the electrodialysis process, the modified membranes exhibit distinct perm selectivity to K+ ions in binary (K+/Li+, K+/Na+, K+/Mg2+) and ternary (K+/Li+/Mg2+) systems. In particular, at a constant current density of 5.0 mA·cm-2, modified membrane M-co-0.50 shows significantly prominent perm selectivity [Formula: see text] in the K+/Mg2+ system and M-co-0.75 exhibits remarkable performance in the K+/Li+ system [Formula: see text], superior to commercial monovalent-selective CEM (CIMS, [Formula: see text], [Formula: see text]). Besides, in the K+/Li+/Mg2+ ternary system, K+ flux reaches 30.8 nmol·cm-2·s-1 for M-co-0.50, while it reaches 25.8 nmol·cm-2·s-1 for CIMS. It possibly arises from the effects of pore-size sieving and the synergistic action of electric field driving and host-guest molecular recognition of ACE and K+ ions. This study can provide new insights into the separation of specific alkali metal ions, especially on reducing influence of coexisting cations K+ and Na+ on Li+ ion recovery from salt lake and seawater.