Ion-selective Electrode Research Articles

Achieving preeminent stability and reproducibility in an ion-selective electrode for copper ion via introducing a hydrophobic NiCo2S4/PFOA solid-contact

In this work, an ion-selective electrode (ISE) for copper ion with excellent stability and reproducibility is prepared by introducing a solid-contact (SC) layer between the screen-printed electrode (SPE) and ion-selective membrane (ISM). The SC layer is fabricated by the electrodeposition of nano-arrayed NiCo2S4 on SPE, and thereafter is surface-modified by perfluorooctanoic acid (PFOA) to realize superior double layer capacitance (CDL) and hydrophobicity. The results show the water contact angle of the SC is 134°. The CDL of the modified ISE, named as Cu2+-SC(25)ISE, is 48.53 μF·cm−2, about 6.5 times of the ISE without SC. The detection limit of the Cu2+-SC(25)ISE is 4.62 μM. The SC with nano-structured NiCo2S4 frameworks and hydrophobic PFOA chains provides outstanding capacitance and high potential stability simultaneously, and further endows Cu2+-SC(25)ISE with excellent detection accuracy. For the detection of Cu2+ in soil leachate, the average detection errors of the Cu2+-SC(25)ISE and ICP-OES are 4.14 % and 3.02 % respectively, revealing the potential application prospect of this technic. This work puts forward a novel concept to achieve the accurate measurement and flexibility of ISE.

Comparison between the ion-specific electrode and SPADNS methods for analysis of fluoride concentration in the water supply

The maintenance of adequate fluoride (F) concentration in the public water supply is fundamental for ensuring that the community use of F can reach the maximum benefit for caries control and minimum risk for dental fluorosis. Thus, surveillance systems must use accurate and valid analytical methods to determine F concentration and, according to the literature, give preference to the ion-specific electrode (F- ISE) analysis. Aim: The objective of this study was to compare the accuracy of the ISE and SPADNS methods in the determination of the F concentration in the same water sample. Methods: Duplicate water samples were taken from 30 sampling sites in the municipality of Maringá, state of Paraná, monthly for 12 months, totaling 276 samples. An aliquot was analyzed by the FOP-UNICAMP Oral Biochemistry laboratory, using the F- ISE method, and the other one, by the SANEPAR laboratory in Maringá/PR, using the SPADNS method. Descriptive analysis and Pearson’s correlation test were applied, with a significant level of p<0.05. Results: Results were expressed as ppm F (mg F/L), and a very strong positive correlation (r= 0.91; p<0.001) was detected between the two methods of analysis. Conclusion: Our findings suggest that the determination of f luoride concentration in water can be made with accuracy by the SPADNS method, a standardized analysis protocol.

A half-cell reaction approach for pH calculation using a solid-state chloride ion-selective electrode with a hydrogen ion-selective ion-sensitive field effect transistor

Here, we explicitly define a half-cell reaction approach for pH calculation using the electrode couple comprised of the solid-state chloride ion-selective electrode (Cl-ISE) as the reference electrode and the hydrogen ion-selective ion-sensitive field effect transistor (ISFET) of the Honeywell Durafet as the hydrogen ion H+-sensitive measuring or working electrode. This new approach splits and isolates the independent responses of the Cl-ISE to the chloride ion Cl− (and salinity) and the ISFET to H+ (and pH), and calculates pH directly on the total scale pHtotalEXT in molinity (mol (kg-soln)−1) concentration units. We further apply and compare pHtotalEXT calculated using the half-cell and the existing complete cell reaction (defined by Martz et al. (2010)) approaches using measurements from two SeapHOx sensors deployed in a test tank. Salinity (on the Practical Salinity Scale) and pH oscillated between 1 and 31 and 6.9 and 8.1, respectively, over a six-day period.In contrast to established Sensor Best Practices, we employ a new calibration method where the calibration of raw pH sensor timeseries are split out as needed according to salinity. When doing this, pHtotalEXT had root-mean squared errors ranging between ±0.0026 and ±0.0168 pH calculated using both reaction approaches relative to pHtotal of the discrete bottle samples pHtotaldisc. Our results further demonstrate the rapid response of the Cl-ISE reference to variable salinity with changes up to ±12 (30 min)−1. Final calculated pHtotalEXT were ≤±0.012 pH when compared to pHtotaldisc following salinity dilution or concentration. These results are notably in contrast to those of the few in situ field deployments over similar environmental conditions that demonstrated pHtotalEXT calculated using the Cl-ISE as the reference electrode had larger uncertainty in nearshore waters. Therefore, additional work beyond the correction of variable temperature and salinity conditions in pH calculation using the Cl-ISE is needed to examine the effects of other external stimuli on in situ electrode response. Furthermore, whereas past work has focused on in situ reference electrode response, greater scrutiny of the ISFET as the H+-sensitive measuring electrode for pH measurement in natural waters is also needed.

Ion-Selective Potentiometry with Plasma-Initiated Covalent Attachment of Sensing Membranes onto Inert Polymeric Substrates and Carbon Solid Contacts.

The physical delamination of the sensing membrane from underlying electrode bodies and electron conductors limits sensor lifetimes and long-term monitoring with ion-selective electrodes (ISEs). To address this problem, we developed two plasma-initiated graft polymerization methods that attach ionophore-doped polymethacrylate sensing membranes covalently to high-surface-area carbons that serve as the conducting solid contact as well as to polypropylene, poly(ethylene-co-tetrafluoroethylene), and polyurethane as the inert polymeric electrode body materials. The first strategy consists of depositing the precursor solution for the preparation of the sensing membranes onto the platform substrates with the solid contact carbon, followed by exposure to an argon plasma, which results in surface-grafting of the in situ polymerized sensing membrane. Using the second strategy, the polymeric platform substrate is pretreated with argon plasma and subsequently exposed to ambient oxygen, forming hydroperoxide groups on the surface. Those functionalities are then used for the initiation of photoinitiated graft polymerization of the sensing membrane. Attenuated total reflection-Fourier transform infrared spectroscopy, water contact angle measurements, and delamination tests confirm the covalent attachment of the in situ polymerized sensing membranes onto the polymeric substrates. Using membrane precursor solutions comprising, in addition to decyl methacrylate and a cross-linker, also 2-(diisopropylamino)ethyl methacrylate as a covalently attachable H+ ionophore and tetrakis(pentafluorophenyl)borate as ionic sites, both plasma-based fabrication methods produced electrodes that responded to pH in a Nernstian fashion, with the high selectivity expected for ionophore-based ISEs.

A rational study of transduction mechanisms of different materials for all solid contact-ISEs

The new era of solid contact ion selective electrodes (SC-ISEs) miniaturized design has received an extensive amount of concern. Because it eliminated the requirement for ongoing internal solution composition optimization and created a two-phase system with stronger detection limitations. Herein, the determination of venlafaxine HCl is based on a comparison study between different ion- to electron transduction materials (such as; multiwalled carbon nanotubes (MWCNTs), polyaniline (PANi), and ferrocene) and illustrating their mechanisms in their applied sensors. Their different electrochemical features (such as bulk resistance (Rb**), double-layer capacitance (Cdl), geometric capacitance (Cg), and specific capacitance (Cp)) were evaluated and discussed by using the Electrochemical Impedance Spectroscopy (EIS), Chronopotentiometry (CP), and Cyclic Voltammetry (CV) experiments. The results indicated that each transducer's influence on the proposed sensor's electrochemical characteristics is determined by their unique chemical and physical properties. The electrochemical features vary for different solid contact materials used in transduction mechanisms. The results confirm that the MWCNT sensor revealed the best electrochemical behavior with the potentiometric response of a near-Nernestian slope of 56.1 ± 0.8 mV/decade with detection limits of 3.8 × 10−6 mol/L (r2 = 0.999) and a low potential drift (∆E/∆t) of 34.6 µV/s. Also, the selectivity study was performed in the presence of different interfering species either in single or complex matrices. This demonstrates excellent selectivity, stability, conductivity, and reliability as a VEN-TPB ion pair sensor for accurately measuring VEN in its various formulations. The proposed method was compared to HPLC reported technique and confirmed no significant difference between them. So, the proposed sensors fulfill their solutions' demand features for VEN appraisal.

Development of disposal SPCE pH sensor based on polypyrrole and cloth as conductive polymer

In fish farming, monitoring water quality is crucial for the health and growth of the fish. This field area needs a robust device to monitor the pH meter. In this research, a disposal pH sensor was developed from alternative materials that can offer a wider application area than the conventional glass sensor. Polypyrrole (PPy) membrane was applied to the carbon electrode and acted as a pH-sensitive material when combined with the counter electrode. The carbon electrode was made by printing the carbon paste into cotton-rayon cloth and electrodeposition processing to create a PPy layer on the electrode surface. Afterward, the working electrode was evaluated using cyclic voltammetry and ion-selective electrode potentiometry to optimize the performance. The experimental measurements show that the electrodeposition process at 4.5 A and 30 s creates PPy deposits with optimum sensor performance. pH response and stability tests have also been performed, as the results show that the pH sensor has met the requirement for Nernst effect and IUPAC standard. Finally, the sensor was validated using a reference pH meter to test the water sample acquired from local lake, river, and fishpond, where the result shows that the pH sensor gives accurate measurements.

Potentiometric detection of apomorphine in human plasma using a 3D printed sensor

Apomorphine is a dopamine agonist that is used for the management of Parkinson's disease and has been proven to effectively decrease the off-time duration, where the symptoms recur, in Parkinson's disease patients. This paper describes the design and fabrication of the first potentiometric sensor for the determination of apomorphine in bulk and human plasma samples. The fabrication protocol involves stereolithographic 3D printing, which is a unique tool for the rapid fabrication of low-cost sensors. The solid-contact apomorphine ion-selective electrode combines a carbon-mesh/thermoplastic composite as the ion-to-electron transducer and a 3D printed ion-selective membrane, doped with the ionophore calix[6]arene. The sensor selectively measures apomorphine in the presence of other biologically present cations – sodium, potassium, magnesium, and calcium – as well as the commonly prescribed Parkinson's pharmaceutical, levodopa (L-Dopa). The sensor demonstrated a linear, Nernstian response, with a slope of 58.8 mV/decade over the range of 5.0 mM–9.8 μM, which covers the biologically (and pharmaceutically) relevant ranges, with a limit of detection of 2.51 μM. Moreover, the apomorphine sensor exhibited good stability (minimal drift of just 188 μV/hour over 10 h) and a shelf-life of almost 4 weeks. Experiments performed in the presence of albumin, the main plasma protein to which apomorphine binds, demonstrate that the sensor responds selectively to free-apomorphine (i.e., not bound or complexed forms). The utility of the sensor was confirmed through the successful determination of apomorphine in spiked human plasma samples.

Evidence of transient potentials in ion-selective electrodes based on thin-layer ion-exchange membranes

Polymeric membranes with ion-exchange properties have found numerous applications in water treatment, dialysis, energy storage, chemical sensors, and bio-interfaces, among others. Notably, it is common to operate under non-equilibrium conditions while pursuing specific features (e.g., current generation) through an electron-to-ion mechanism. To maximize the final performance, it is crucial to understand the role of each interface within the system, which becomes complex when the device is tailored with several materials and films. This is the case for ion sensors based on thin membranes in backside contact with a redox active conducting polymer. Herein, we investigate such a system operating under a charge transfer mechanism, which features electroneutrality maintenance as the main driving force upon application of a linear sweep potential. This potential is modeled as being unequally distributed among the various system interfaces. Our results demonstrate and quantify the existence of a transient membrane potential at the membrane-electrolyte interface, owing to the implementation of a strategical measurement point on the buried membrane side and connected to a built-in electrometer for the exclusive acquisition of the potential difference at such an interface. The transient membrane potential was found to be <1 % of the total applied potential, meaning that the ion-transfer process at the electrolyte-membrane interface is less energetically costly that the electron transfer and doping processes occurring at the conducting polymer side. This small contribution can be potentiated by increasing the ion-exchange capacity of the membrane, which indirectly enlarges the system current and serves as a strategy for increasing the efficiency of the device.

Effects of combination of tramadol and sildenafil citrate (Viagra) on hepatic and renal function parameters in Male Albino Rats

Erectile dysfunction, premature ejaculation and pleasure seeking have increased the use of sildenafil citrate, tramadol and their combination by youths who believe these drugs could positively impact their sexual life. Sildenafil citrate and tramadol are metabolized in the liver, and their by-products excreted through the kidneys, making these organs possible targets for toxicity. Aim: This study evaluates the effects of combination of tramadol and sildenafil citrate on hepatic and renal function parameters in male albino rats. Methodology: A total of forty-nine (49) male albino rats weighing between 150 to 180g were used for the study. Sildenafil citrate and tramadol were administered to the rats by means of oral gavage for 28 days. The liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were determined using the Reitman-Frankel method. Alkaline phosphatase (ALP) was determined using the Colorimetric endpoint method. Total protein (TP) was determined using the biuret method. Albumin (ALB) was determined using the bromocresol green method. Sodium (Na+), potassium (K+) and chloride (CL-) were determined using ion selective electrode (ISE) method. Bicarbonate (HCO3-) was determined using titrimetric method. Urea was determined using Urease bertholet method. Creatinine was determined using Jaffe-Slot method. Results: There were no significant differences (P&gt;.05) in the liver enzymes ALT, AST and ALP in all the treatment groups compared to the negative control. Total protein (TP) and albumin (ALB) also showed no significant differences (P&gt;.05) in the groups, compared to the negative control. there were no significant differences (P&gt;.05) in the electrolyte levels in the treatment groups, compared to the negative control. Urea and creatinine levels were also not significantly different (P&gt;.05) in the treatment groups, compared to the negative control. Conclusion: Administration of sildenafil citrate singularly and in combination with tramadol, at recommended and double doses for 28 days, did not impact the liver and was also non-toxic to the kidneys.

Ion transfer mediated by TEMPO in ionophore-doped thin films for multi-ion sensing by cyclic voltammetry

We report here on the development of thin-layer ion-selective membranes containing lipophilic TEMPO as a phase-transfer redox mediator for the simultaneous detection of non-redoxactive ions. This redox probe was recently introduced by our group and provides ideal ion-transfer waves when the membrane is interrogated by cyclic voltammetry. To perform multianalyte detection in the same sensing film, plasticized PVC-based membranes were doped with lithium and potassium ionophores in addition to a lipophilic cation-exchanger. The ionophores allow for ion discrimination owing to the different ionophore-cation complexation constants and the oxidation of TEMPO to the oxoammonium form results in the selective transfer of lithium and potassium at different potentials. The resulting voltammograms have half-peak widths of 100 and 102 mV, and the peak separation between anodic and cathodic scans is 8 and 9 mV for lithium and potassium, respectively, close to theoretical expectations. High peak resolution was observed, and the ion-transfer waves are still distinguishable when the ion activities differ by three orders of magnitude. These parameters are remarkably better than those obtained with other redox probes, which is important for multianalyte detection in the same voltammetric scan. Optimized membranes showed independent Nernstian shifts (slopes of 59.23 mV and 54.8 mV for K+ and Li+, respectively) of the peak position for increasing ion concentrations. An idealized model for two ionophore-based membranes combining redox and phase-boundary potentials was applied to the proposed system with excellent correlation. Potassium and lithium ions were simultaneously detected in undiluted human serum samples with good accuracy and precision.

Application of ionic liquids in ion-selective electrodes and reference electrodes: A review.

Ionic liquids (ILs) are organic chemical compounds that are composed only of ions, a large organic cation and a smaller inorganic or organic anion. These are salts whose melting point is lower than the boiling point of water. ILs have many interesting properties, thanks to which they find great practical applications in analytics, electrochemistry, separation techniques, catalysis and others. One of the many areas of application of ionic liquids is sensors especially electrochemical sensors including ion-selective electrodes. In this case, the properties of ILs that are particularly useful include very good electrical conductivity, high electrochemical stability, good extraction properties, hydrophobic character and compatibility with other materials, e. g. polyvinyl chloride plasticizers or carbon nanomaterials. ILs were used as components of ion-selective membranes, both polymeric ones based on PVC and membranes in carbon paste electrodes. ILs performed various functions in these membranes, including lipophilic ionic additive, ionophore/ion exchanger, plasticizer, transducer media and matrix. They were also used as a component of the intermediate layer in solid contact ISEs. The last chapter presents examples of the use of ILs in reference electrodes. This review discusses the use of ionic liquids in ion-selective electrodes (ISEs) and reference electrodes over the last ten years.

Cost-effective synthesis of MIL-101(Cr) from recyclable wastes and composite with polyaniline as an ion-to-electron transducer for potentiometric Pb2+ sensing

Fabricating an ion-to-electron transducer (IET) from waste in the solid contact screen-printed ion-selective electrodes (SC-SP-ISEs) technique is challenging because its properties determine the potential stability and reproducibility of the designed sensors. Herein, we fabricated an IET substrate from recyclable wastes, and we applied it as an IET layer in an ISE-based sensor for fast and on-site detection of lead ions (Pb2+) in an environmental sample. First, MIL-101(Cr) was prepared based on a combination of PET and Cr+6 waste recycling (R-MIL-101(Cr)). Polyaniline (PANI) was polymerized over R-MIL-101(Cr) to prepare a conductive PANI@R-MIL-101(Cr) composite. Then, it was applied as an IET substrate in the construction of pb2+-ISE for the detection of Pb2+ ions in sediment samples collected from Lake Idku, Egypt. Three Pb2+ sensors were fabricated and abbreviated as sensors I, II, and III corresponded to PANI, R-MIL-101(Cr), and PANI@R-MIL-101(Cr) as IET substrates, respectively. The performance of the sensors was studied to be applied for fast and selective detection of Pb2+ at low concentration levels. Among the fabricated sensors, PANI@R-MIL-101(Cr) shows fast response (5 sec), low detection limit (1 × 10−7 mol/L), and long lifetime reaches 70 days with a potential drift of 0.9 mV h−1. The electrochemical characteristics prove the fast ion-to-electron transportation in the case of PANI@R-MIL-101(Cr) owing to its lower impedance and high capacitance. In-situ polymerization of PANI significantly enhanced the conductivity of the PANI@R-MIL-101(Cr) composite. The hydrophobic nature of PANI@R-MIL-101(Cr) ensures high stability by preventing the formation of water layers at the electrode/membrane interface. These results show the great potential of the IET-based PANI@R-MIL-101(Cr) layer for Pb2 + sensing in environmental samples with low detection limits and high stability for the future development of SC-ISEs.

Hydrophilic redox buffers for textile-based potentiometric sensors

One of the barriers to the more widespread use of ion-selective electrodes (ISEs) in resource-limited areas is the need for frequent recalibration of such devices. The incorporation of a redox buffer to minimize the effect of redox-active impurities in the system has previously been shown to significantly improve reproducibility. To date, however, there have been no examples of redox buffers compatible with anion-sensing polymeric sensing membranes that can be incorporated into the inner filling solution of an ISE. Here, we introduce a novel hydrophilic redox buffer, cobalt(II/III) bis(terpyridine), and show the improvement of the standard deviation of E0 of chloride sensors from 2.7 to 0.3 mV upon introduction of the redox buffer into the inner filing solution of conventional, rod-shaped electrodes. The redox buffer is also compatible with a textile-based sensing platform, which was shown by incorporation into a textile-based platform with embedded ion-sensing and reference membranes. As only a surprisingly small number of hydrophilic redox buffers have been reported in the literature, the cobalt(II/III) bis(terpyridine) redox buffer may also find applications outside of the field of ISEs.

Charge-Gradient Sulfonated Poly(ether ether ketone) Membrane with Enhanced Ion Selectivity for Osmotic Energy Conversion.

Engineered asymmetric heterogeneous ion-selective membranes have become a focal point for their improved efficiency in harnessing osmotic energy from ionic solutions with varying salinity. However, achieving both energy conversion efficiency and excellent chemical stability necessitates effectively mitigating the formation of detrimental interface cracks between two different layers. We develop a charge-gradient sulfonated poly(ether ether ketone) (SPEEK) membrane (CG-SPEEK) on a large-scale using a straightforward coating method. As an osmotic energy generator, CG-SPEEK membrane achieves an impressive output power density of 9.2 W m-2 and exhibits ultrahigh cation selectivity (0.99), with an energy conversion efficiency of 48% at a 50-fold NaCl concentration gradient. The results highlight the ion diode effects of CG-SPEEK, driven by a charge density gradient that accelerates cation transport while suppressing ion concentration polarization. Density functional theory simulations provide further insights, revealing that the energy barrier for Na+ ion transport through CG-SPEEK membrane is lower than that through a homogeneous SPEEK membrane. This work not only enhances our understanding of ion transport dynamics but also establishes the CG-SPEEK membrane as a promising candidate for efficient osmotic energy conversion applications.

Multifunctional Siloxene-Decorated Laser-Inscribed Graphene Patch for Sweat Ion Analysis and Electrocardiogram Monitoring.

Potentiometric detection in complex biological fluids enables continuous electrolyte monitoring for personal healthcare; however, the commercialization of ion-selective electrode-based devices has been limited by the rapid loss of potential stability caused by electrode surface inactivation and biofouling. Here, we describe a simple multifunctional hybrid patch incorporating an Au nanoparticle/siloxene-based solid contact (SC) supported by a substrate made of laser-inscribed graphene on poly(dimethylsiloxane) for the noninvasive detection of sweat Na+ and K+. These SC nanocomposites prevent the formation of a water layer during ion-to-electron transfer, preserving 3 and 5 μV/h potential drift for the Na+ and K+ ion-selective electrodes, respectively, after 13 h of exposure. The lamellar structure of the siloxene sheets increases the SC area. In addition, the electroplated Au nanoparticles, which have a large surface area and excellent conductivity, further increased the electric double-layer capacitance at the interface between the ion-selective membranes and solid-state contacts, thus facilitating ion-to-electron transduction and ultimately improving the detection stability of Na+ and K+. Furthermore, the integrated temperature and electrocardiogram sensors in the flexible patch assist in monitoring body temperature and electrocardiogram signals, respectively. Featuring both electrochemical ion-selective and physical sensors, this patch offers immense potential for the self-monitoring of health.

Nanofiber Ion-Selective Membrane-Coated Carbon Paper All-Solid-State Sensors: One Stone, Two Birds.

Potentiometric sensors with nanostructural ion-selective membranes were prepared and tested. Electrospun nanofiber mats were applied in novel all-solid-state sensors, using carbon paper as an electronically conducting support. For the sake of simplicity, application of a solid contact layer was avoided, and redox-active impurities naturally present in the carbon paper have proven to be effective as ion-to-electron transducers. Application of a nanostructural ion-selective membrane requires an innovative approach to combine the receptor layer with the support. The nanofiber mat portion was fused with carbon paper in a hot-melt process. Applying temperature close to 120 °C for a short time (3 s) allowed binding the nanostructural ion-selective membrane with carbon paper, without significant changes in the nanofiber structure. This process was conveniently performed together with the lamination of the carbon paper support. The thus obtained, potentially disposable sensors were characterized as exhibiting highly reproducible potential readings in time as well as between sensors belonging to the same batch. The benefits of the application of nanostructural ion-selective membranes include shorter equilibration time, lower detection limit, and significantly lower material consumption. However, the nanostructural membrane is characterized by a higher electrical resistance, which is attributed to higher porosity.

Simple Solution Processed Solid‐State Organic Transistor Chip for Multi‐Ion Sensing

AbstractIon concentrations in the human body are closely tied to crucial biological functions and thus serve as important diagnostic health markers. Biological samples are chemically complex, containing a wide range of ions and molecules, necessitating the use of sensors that are highly selective to the target analyte. In this work, a multi‐ion sensing chip, capable of selectively detecting potassium (K+), sodium (Na+), and calcium (Ca2+) ions at physiologically relevant concentrations, is demonstrated. Each sensor consists of a simple, solution‐processed, all solid‐state, and low‐voltage organic thin film transistor, functionalized with polyvinyl chloride (PVC) ion selective membranes sandwiched between the insulator and gate electrode. The sensors are responsive to 4–5 decades of each primary ion. When a response from interfering ions is seen at higher concentrations, the sensors can uniquely discriminate between primary and interfering ions by a difference in the polarity of the current modulation. The sensors function well in mixed‐ion solutions, and can detect K+, Na+, and Ca2+ in simulated human blood serum, demonstrating the feasibility of using these devices for the analysis of complex analytes. This work represents an important step toward the development of simple, inexpensive organic multi‐ion sensors.

Two-dimensional metal–organic framework nanocomposite membranes with shortened ion pathways for enhanced salinity gradient power harvesting

Harnessing energy through the reverse electrodialysis-based salinity gradient power conversion is an exciting and promising technological endeavor. The key to its success lies in developing the advanced ion-selective membrane capable of enhancing ion flux and accelerating ion transport at confined nanospaces. Traditional two-dimensional (2D) membranes typically employ a layer-by-layer arrangement of nanosheets with an extremely narrow layer separation, limiting ion flux and creating elongated 2D ion pathways. In response to this limitation, our study introduces an innovative design of the 2D metal–organic framework (MOF)-based nanocomposite membrane (named as Cu-TCPP@SNF), which is composed of the 2D Cu-TCPP and natural-based silk nanofibers (SNFs). We show that the introduction of the space-charged SNFs can significantly enhance the stability of the 2D MOF nanocomposite membrane in electrolyte solutions, and this unique framework facilitates a multitude of abundant one-dimensional ion pathways across the membrane while maintaining the advantage of minimal layer separation. Our results demonstrate that the Cu-TCPP@SNF exhibits low resistance, thus facilitating ion transport. Furthermore, numerical simulations elucidate the impacts of the SNF content and membrane thickness on power performance. Remarkably, our membrane achieves a notable power density of ∼6.48 W/m2 by mixing artificial seawater and river water. Impressively, an ultrahigh performance of ∼29.5 W/m2 can be achieved under a 5 M/0.01 M NaCl gradient, surpassing the existing advanced membranes. These findings hold significant promise for the future of composite 2D membrane development, paving the way for scalable applications in salinity-based energy harvesting.

Advancing Ion Selective Membranes with Micropore Ion Channels in the Interaction Confinement Regime.

Ion exchange membranes allowing the passage of charge-carrying ions have established their critical role in water, environmental, and energy-relevant applications. The design strategies for high-performance ion exchange membranes have evolved beyond creating microphase-separated membrane morphologies, which include advanced ion exchange membranes to ion-selective membranes. The properties and functions of ion-selective membranes have been repeatedly updated by the emergence of materials with subnanometer-sized pores and the understanding of ion movement under confined micropore ion channels. These research progresses have motivated researchers to consider even greater aims in the field, i.e., replicating the functions of ion channels in living cells with exotic materials or at least targeting fast and ion-specific transmembrane conduction. To help realize such goals, we briefly outline and comment on the fundamentals of rationally designing membrane pore channels for ultrafast and specific ion conduction, pore architecture/chemistry, and membrane materials. Challenges are discussed, and perspectives and outlooks are given.

Uniform Nanoscale Ion-Selective Membrane Prepared by Precision Control of Solution Spreading and Evaporation.

Ion-selective membrane has broad application in various fields, while the present solution-processed techniques can only prepare uniform membrane with microscale thickness. Herein, a high-quality polymer membrane with nanoscale thickness and uniformity is precisely prepared by controlling solution spreading and solvent evaporation stability/rate. With the arrayed capillaries, the stable spreading of polymer solution with volume of microliter induces the formation of solution film with micrometers thickness. Moreover, the fast increase of solution dynamic viscosity during solvent evaporation inhibits nonuniform Marangoni flow and capillary flow in solution film. Consequently, the uniform Nafion-Li membranes with ∼200 nm thickness are prepared, while their Li+ conductivity is 2 orders of magnitude higher than that of commercially Nafion-117 membrane. Taking lithium-sulfur battery as a model device, the cells (capacities of 8-10 mAh cm-2) can stably operate for 150 cycles at a S loading of 12 mg cm-2 and an electrolyte/sulfur ratio of ∼7.