High Ionic Strength Solutions Research Articles

Long-Term Experimental Determination of Solubilities of Micro-Crystalline Nd(III) Hydroxide in High Ionic Strength Solutions: Applications to Nuclear Waste Management

In this study, the experimental results from long-term solubility experiments up to 1146 days on micro-crystalline neodymium hydroxide, Nd(OH)3(micro-cr), in high ionic strength solutions at 298.15 K under well-constrained conditions, are presented. Hydrogen ion concentrations in our experiments are controlled by the dissolution of Nd(OH)3(micro-cr) without artificial adjustment with addition of either an acid or a base, preventing the possibility of phase change that could be induced especially by addition of a base. Such an experimental design also provides the information about the hydrogen ion concentrations buffered by the dissolution of Nd(OH)3, which is currently lacking. The solubility data produced in this work, applicable to geological repositories in high ionic strength environments, are compared with the solubilities of Am(OH)3(s) predicted by using the Waste Isolation Pilot Plant (WIPP) thermodynamic model. The predicted values for Am(OH)3(s) are in good agreement with the experimental values for Nd(OH)3(micro-cr) obtained in this work. Our experimental data indicate that the pHm (negative logarithm of hydrogen ion concentration on a molal scale) buffered by dissolution of Nd(OH)3(micro-cr) ranges from ~ 9.5 to ~ 9.9. As the equilibrium constant for amorphous neodymium hydroxide, Nd(OH)3(am), is useful for several fields, the equilibrium constant regarding the dissolution of Nd(OH)3(am) for the following reaction, $$ {\text{Nd}}\left( {\text{OH}} \right)_{3} \left( {\text{am}} \right) + 3{\text{H}}^{ + } = {\text{Nd}}^{3 + } + 3{\text{H}}_{2} {\text{O}}\left( {\text{l}} \right) $$ is also obtained by evaluating the experimental data in a wide range of ionic strengths from the literature by using the WIPP thermodynamic model. The $$ \log_{10} K_{{{\text{s}}0}}^{0} $$ at 298.15 K for the above reaction obtained in this work is 16.85 ± 0.20 (2σ), which is similar to, but slightly lower than, the values in the literature evaluated in the low ionic strength range. This value can be applied to amorphous americium hydroxide, Am(OH)3(am), using Nd(III) as an analog to Am(III).

Solubility Model for Ferrous Iron Hydroxide, Hibbingite, Siderite, and Chukanovite in High Saline Solutions of Sodium Chloride, Sodium Sulfate, and Sodium Carbonate

A solubility model is presented for ferrous iron hydroxide (Fe(OH)2(s)), hibbingite (Fe2Cl(OH)3(s)), siderite (FeCO3(s)), and chukanovite (Fe2CO3(OH)2(s)). The Pitzer activity coefficient equation was utilized in developing the model to account for the excess free energies of aqueous species in the background solutions of high ionic strength. Solubility limiting minerals were analyzed before and after experiments using X-ray diffraction. Formation of Fe(OH)2(s) was observed in the experiments that were initiated with Fe2Cl(OH)3(s) in Na2SO4 solution. Coexistence of siderite and chukanovite was observed in the experiments in Na2CO3 + NaCl solutions. Two equilibrium constants that had been reported by us for the dissolution of Fe(OH)2(s) and Fe2Cl(OH)3(s) (Nemer et al.) were rederived in this paper, using newer thermodynamic data selected from the literature to maintain internal consistency of the series of our data analyses in preparation, including this paper. Three additional equilibrium constants for th...

Surface-Engineered Cationic Nanocrystals Stable in Biological Buffers and High Ionic Strength Solutions.

Progress in colloidal synthesis in the last two decades has enabled high-quality semiconductor, plasmonic, and magnetic nanocrystals (NCs). As synthesized, these NCs are usually capped with long-chain apolar ligands. Postsynthetic surface functionalization is required for rendering such NCs colloidally stable in polar media such as water. However, unlike small anionic molecules and polymeric coatings, producing positively charged stable NCs, especially at high ionic strengths, has remained challenging. Here, we present a general approach to achieve aqueously stable cationic NCs using a set of small (<2.5 nm long) positively charged ligands. The applicability of this method is demonstrated for a variety of materials including semiconductor CdSe/CdS core/shell NCs, magnetic Fe@Fe3O4, Fe3O4, and FePt NCs, and three different classes of plasmonic Au NCs including large nanorods. The obtained cationic NCs typically have zeta potential values ranging from +30 to +60 mV and retain colloidal stability for days to months, depending on NC/ligand pair, in several biological buffers at elevated pH and in concentrated salt solutions. This allowed us to demonstrate site-specific staining of cellular structures using fluorescent cationic NCs with several different surface chemistries. Furthermore, colloidal stability of the obtained NCs in the presence of other charged species allowed the assembly of cationic and anionic counterparts driven primarily by electrostatic attraction. With this approach, we prepare highly uniform 3D and 2D binary mixtures of NCs through induced homogeneous aggregation and alternating-charge layer-by-layer deposition, respectively. Such binary mixtures may provide a new route in the engineering of nanocrystalline solids for electronics, thermoelectrics, and photovoltaics.

Effect of l-histidine on the heat-induced aggregation of bighead carp (Aristichthys nobilis) myosin in low/high ionic strength solution

In this study, the effects of l-histidine (L-His) on the aggregation of bighead carp (Aristichthys nobilis) myosin induced by heating in low (0.1) or high (0.5) ionic strength solutions were studied. The solubility of natural myosin was significantly enhanced by L-His both in low and high ionic strength solutions. More small particles are suspended in the heated solution containing L-His, inducing a higher solubility than that solution without L-His. The surface hydrophobicity of myosin in a low ionic strength solution containing L-His is higher than that of myosin without L-His. The results of morphology show that L-His induced myosin to form finer aggregates and a honeycomb-like network in a low/high ionic strength solution during heat treatment. These results demonstrate that L-His might disrupt the electrostatic property of unfolded myosin heat-induced through electrostatic binding with the exposed negatively charged amino acid residues, which might disarrange hydrophobic surfaces, resulting in weakening hydrophobic interactions, which ultimately suppresses the fierce aggregation of carp myosin.

Difficulties and flaws in performing accurate determinations of zeta potentials of metal nanoparticles in complex solutions-Four case studies.

The zeta potential (ZP) is a parameter commonly used to characterize metal nanoparticles (NPs) in solution. Such determinations are for example performed in nanotoxicology since the ZP influences e.g. the interaction between cells and different biomolecules. Four case studies on different metal NPs (Cu and Zn NPs, and citrate capped Ag NPs) are presented in this study in order to provide guidance on how to accurately interpret and report ZP data. Solutions of high ionic strength (150 mM NaCl) induce a higher extent of particle agglomeration (elucidated with Ag NPs) when compared with conditions in 10 mM NaCl, which further complicates the prediction of the ZP due to e.g. sedimentation and broadening of the zeta potential distribution. The particle size is seldom included specifically in the standard ways of determining ZP (Hückel and Smoluchowski approximations). However corrections are possible when considering approximations of the Henry function. This was seen to improve the analysis of NPs, since there are cases when both the Hückel and the Smulochowski approximations are invalid. In biomolecule-containing cell media (BEGM), the signal from e.g. proteins may interfere with the measured ZP of the NPs. The intensity distribution of the ZP of both the blank solution and the solution containing NPs should hence be presented in addition to the mean value. Due to an increased ionic strength for dissolving of metal NPs (exemplified by Zn NPs), the released metal ions must be considered when interpreting the zeta potential measurements. In this work the effect was however negligible, as the particle size was several hundred nm, conditions that made the Smoluchowski approximation valid despite an increased ionic strength. However, at low ionic strengths (mM range) and small-sized NPs (tens of nm), the effect of released metal ions can influence the choice of model for determining the zeta potential.Sonication of particle dispersions influences not only the extent of metal release but also the outermost surface oxide composition, which often results in an increased ZP. Surface compositional changes were illustrated for sonicated and non-sonicated Cu NPs. In all, it can be concluded that accurate measurements and interpretations are possible in most cases by collecting and reporting complementary data on characteristics such as particle size, ZP distributions, blank sample information, and particle oxide composition.

Excited State Dynamics of a Photobiologically Active Ru(II) Dyad Are Altered in Biologically Relevant Environments.

In this study femtosecond and nanosecond time-resolved transient absorption spectroscopy was used to investigate the influence of ionic strength and complexity on the excited state dynamics of a Ru(II)-based metal-organic dyad. The bis-heteroleptic complex [Ru(bpy)2(ippy)]2+ (1), where bpy = 2,2'-bipyridine and ippy = 2-(1-pyrenyl-1H-imidazo[4,5-f][1,10]phenanthroline, is a potent photosensitizer for in vitro photodynamic therapy (PDT) and photodynamic inactivation (PDI) of microorganisms owing to a long-lived triplet excited state derived from a metal-to-ligand charge-transfer (3MLCT) state that is equilibrium with an intraligand (3IL) state. The prolonged lifetime provides ample opportunity for bimolecular quenching of this state by oxygen; thus singlet oxygen (1O2) sensitization is very efficient. In simple aqueous solution, fast cooling within the 3MLCT manifold is followed by energy transfer to an 3IL state, which is facilitated by rotation of a pyrenyl unit about the imidazo-pyrenyl (ip) coannular bond. For solutions of 1 in high ionic strength simulated biological fluid (SBF), a more physiologically relevant solvent that contains a complex mixture of ions at pH 7.4, femtosecond studies revealed an additional excited state, possibly based on an ion-ligand interaction. This new state appearing in high ionic strength SBF was not observable in water, simple buffers, or low ionic strength SBF. These photoinduced dynamics were also affected by the presence of biomolecules such as DNA in simple buffer, whereby relaxation on the picosecond time scale was accelerated from 39 to 18 ps with DNA intercalation by 1. The increased rate of coplanarization of the pyrene and the imidazole units was attributed to DNA-induced conformational restriction of the pyrenyl unit relative to the ip bond. Quantitative changes to excited state decay rates of 1 in solutions of high ionic strength were also observed when probed on the microsecond time scale. Notably, the thermalized excited state decay pathways were altered substantially with DNA intercalation, with access to some states being completely blocked. Experimentally, this manifested in the absence of the slowest microsecond decay channel, which is normally observed for 1 in solution. The quantitative and qualitative observations from this study highlight the importance of employing biologically relevant solvents and potential biomolecule targets when the excited state dynamics and photophysical properties (under cell-free conditions) responsible for the potent photobiological effects are assessed in the context of photodynamic therapy and photodynamic inactivation.

Beyond the Debye length in high ionic strength solution: direct protein detection with field-effect transistors (FETs) in human serum

In this study, a new type of field-effect transistor (FET)-based biosensor is demonstrated to be able to overcome the problem of severe charge-screening effect caused by high ionic strength in solution and detect proteins in physiological environment. Antibody or aptamer-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) are used to directly detect proteins, including HIV-1 RT, CEA, NT-proBNP and CRP, in 1X PBS (with 1%BSA) or human sera. The samples do not need any dilution or washing process to reduce the ionic strength. The sensor shows high sensitivity and the detection takes only 5 minutes. The designs of the sensor, the methodology of the measurement, and the working mechanism of the sensor are discussed and investigated. A theoretical model is proposed based on the finding of the experiments. This sensor is promising for point-of-care, home healthcare, and mobile diagnostic device.

Block Polymer Membranes Functionalized with Nanoconfined Polyelectrolyte Brushes Achieve Sub-Nanometer Selectivity.

The well-defined nanostructure of membranes manufactured from self-assembled block polymers enables highly selective separations; however, recent efforts to push the pore size of block polymer-based membranes to the lower end of the size spectrum have only been moderately successful for a variety of reasons. For instance, the conformational changes of the stimuli-responsive functional groups lining the pore walls of some block polymer membranes result in varied pore sizes that limit their operational range. Here, we overcome this challenge through the directed design of the third moiety of an A-B-C triblock polymer. The use of this macromolecular design paradigm allows for the preparation of a 500 nm thick polyisoprene-b-polystyrene-b-poly(2-acrylamido-ethane-1,1-disfulonic acid) (PI-PS-PADSA) coating atop a hollow fiber membrane support. This nanoporous test bed, which exhibits an average pore radius of 1 nm, demonstrates an extremely high solute selectivity by fully gating solutes that have only an 8 Å size difference, a separation that is based solely on a sieving mechanism. Furthermore, the nanoscale structural characteristics of the solvated PADSA pore walls are elucidated by quantifying the rejection of neutral solutes and calculating the hydraulic permeability values in solutions of high ionic strength (1 mM ≤ I ≤ 3 M) and over a broad range of solution pH (1 ≤ pH ≤ 13). These key results provide a solid foundation for defining structure-property-performance relationships in the emerging area of nanoporous triblock polymer thin films. Moreover, the successful demonstration of the test bed separation device offers a tangible means by which to manufacture next-generation nanofiltration membranes that require a robust performance profile over a dynamic range of conditions.

Sorption behaviour of Np(IV) on illite, shale and MX-80 in high ionic strength solutions

Sorption behaviour of Np(IV) on illite, shale and MX-80 in high ionic strength solutions

The influence of solvent formulations on thermosensitive hydroxybutyl chitosan hydrogel as a potential delivery matrix for cell therapy

Many cell delivery matrices have been developed due to the low transplantation efficiency of cell therapy. In the present study, thermosensitive hydroxybutyl chitosan (HBC) hydrogels were prepared with different formulations’ solvent (Dulbecco’s modified eagle’s medium/phosphate buffered saline [DMEM/PBS], 0:100, 30:70, 50:50, 70:30, 100:0 [v/v]). Their gelation temperature was raised with DMEM ratio increase (from 9.5°C to 20.9°C). Pore sizes of HBC hydrogels treated with high ionic strength solutions became smaller. HUVECs cultured with HBC hydrogels exhibited proliferation in high DMEM ratio groups, and the optimal solvent formulation was DMEM/PBS 70:30 (v/v). Upon exposure to PBS, HUVECs encapsulated in HBC hydrogels could survive better than that when seeded on the surface of HBC hydrogels. These results demonstrated that HBC hydrogel could be a potential cell delivery matrix for cell therapy applications, especially when DMEM proportion in solvent formulations was higher than 50% (DMEM/PBS>50:50 [v/v]).

Investigation of DNA Detection Mechanism with AlGaN/GaN High Electron Mobility Transistor (HEMT) Biosensor in High Ionic Strength Solution

In this research, the electrical double layer HEMT device is used to serve as the cardiovascular disease (CVD) RNA biomarkers biosensor. In this experiment, we try to use the DNA equivalent to miRNA-126 to test the ability of the novel DNA sensors. Short Debye length has been a haunted problem among all the field effect transistor (FET) biosensor for years. As the Debye length is extremely short in high ionic strength solutions, the traditional FET may not be directly detecting the biomolecule. The novel HEMT sensors using AlGaN/GaN can perform high sensitivity and great specificity in DNA sequences testing. The detection limit can be down to the 1fM and the specificity measurement can identify the signals between two DNA sequences with six-base mismatch. Furthermore, the mechanism of the sensor structure has also been studied. Since the structure of the device has the separation between source drain channel and gate electrode, the comparison with different electrode area and gap distance has been done as well. With repeating electrical measurement confirming, the reusability can also be seen after the 95℃ dehybridization process. With the Gibbs free energy ∆G of the specific sequences, we can also predict the equilibrium reaction constant and the binding ratio of probe DNA with the target DNA. The comparison between the thermal dynamics with the experiment consequence has been demonstrated too.

Investigation of DNA Detection Mechanism with AlGaN/GaN High Electron Mobility Transistor (HEMT) Biosensor in High Ionic Strength Solution

In this research, the electrical double layer HEMT device is used to serve as the DNA biosensor. In this experiment, we try to use the DNA sequence of miRNA-126, which serve as a novel biomarkers of cardiovascular disease (CVD), to test the ability of the novel DNA sensors. Debye length has been a haunted problem among all the field effect transistor (FET) biosensor for years. As the Debye length is extremely low in high ionic strength solutions, the traditional FET may not be direct detect the biomolecular. The novel HEMT sensors using AlGaN/GaN can performs high sensitivity and great specificity in DNA sequences testing. The sensitivity can be down to the 1fM and the specificity measurement can separate the signals between two DNA sequences with two mismatch differences. Furthermore, the mechanism of the sensor structure has also been studied. Since the structure of the device has the separation between source drain channel and gate electrode, the comparison with different electrode area and gap distance has been done as well. With repeating electrical measurement confirming, the reusability can also be seen after the 95℃ dehybridization process. With the Gibbs free energy of the specific sequences, we can also predict the equilibrium reaction constant and the binding ratio of probe DNA with the target DNA. The comparison between the thermal dynamics with the experiment consequence has been demonstrated too. Figure 1

Blood Based Biomarker Detection Using FET Biosensor: Towards Self-Health Management

Diseases that are the leading causes of mortality worldwide such as cardiovascular diseases (CVD), cancer and infectious diseases can be better managed and cured with early and prompt diagnosis and prognosis. Molecular biomarkers in whole blood (blood serum proteins) have predictive, diagnostic and prognostic capacity and semiconductor based electronic biosensors can be used to deliver reliable and affordable point-of-care disease monitoring. GaN High Electron Mobility Transistor (HEMT) based sensors have previously been used in a variety of applications such as ion, gas and biomolecule sensing. However, the limitations of FET biosensors set by the charge screening effect in high ionic strength solutions required additional sample processing steps, making them practically unusable in terms of point-of-care testing. With a novel biosensing technique enabling direct detection of target proteins in high salt concentration medium using GaN HEMT and innovative biosensor packaging methodology, a portable biosensor system has been designed and fabricated which can provide quantitative blood biomarker analysis in 5 minutes with less than 5 µl sample. Antibody or aptamer functionalized reference gate electrode and transistor channel form an electrical double layer (EDL) FET structure that can detect binding of target proteins with very high sensitivity. The sensing and packaging techniques have been specifically optimized to meet the requirements and convenience of a mobile diagnostic system that can be used by anyone, at all times. HEMT chip is fabricated in a 4-5 mask process: mesa isolation, ohmic metal deposition and annealing, interconnect metal deposition and device passivation. A simple and robust two step epoxy based planar HEMT chip packaging allows for easy integration with commercially available reader sockets, much like the micro-SD card. A single step surface functionalization strategy is followed for immobilizing receptors which allows for high sensitivity with a wide dynamic range of detection. Pulsed gate voltage modulates the channel conductivity which behaves as a function of the charge distribution within the EDL structure. Thus, without complex sample pre-treatments and extremely low sampling requirements, quantitative detection of protein biomarkers can be achieved. The structural design of EDL FET brings the potential to investigate the binding events that were previously undetectable in traditional FET based biosensors. Results from testing purified proteins and clinical serum samples elucidate the potential of the sensing technique to overcome the charge screening effect and offer sensing beyond Debye length in physiological salt environment, with high sensitivity and ultra-low detection limit. This diagnostic technique can be applied to all types of FET based sensors that uses immunological reactions to detect the target. Owing to standard semiconductor fabrication processes and minimal or no sampling requirements, the portable sensing system can be affordable and accessible to all. Enabled with cloud management, this diagnostic system houses the potential to be a pioneering IoT biosensor. Figure 1

Biopolymeric nano/microspheres for selective and reversible adsorption of coronaviruses

A novel biopolymeric material in the form of nano/microspheres was developed which was capable of adsorbing coronaviruses. The biopolymer was obtained by crosslinking of chitosan (CHIT) with genipin, a nontoxic compound of plant origin, in inverted emulsion and reacting the chitosan nano/microspheres obtained (CHIT-NS/MS) with glycidyltrimethyl-ammonium chloride (GTMAC). As a result the nano/microspheres of N-(2-hydroxypropyl)-3-trimethyl chitosan (HTCC-NS/MS) were obtained. HTCC-NS/MS were studied as the adsorbents of human coronavirus NL63 (HCoV-NL63), mouse hepatitis virus (MHV), and human coronavirus HCoV-OC43 particles in aqueous virus suspensions. By studying cytopathic effect (CPE) caused by these viruses and performing PCR analyses it was found HTCC-NS/MS strongly adsorb the particles of HCoV-NL63 virus, moderately adsorb mouse hepatitis virus (MHV) particles, but do not adsorb HCoV-OC43 coronavirus. The adsorption capacity of HTCC-NS/MS well correlated with the antiviral activity of soluble HTCC against a given virus. Importantly, it was shown that HCoV-NL63 particles could be desorbed from the HTCC-NS/MS surface with a salt solution of high ionic strength with retention of virus virulence. The obtained material may be applied for the removal of coronaviruses, purification and concentration of virus samples obtained from biological matrices and for purification of water from pathogenic coronaviruses.

Experiments and Thermodynamic Modeling of Chukanovite (Fe2(OH)2CO3) to High Ionic Strengths

ABSTRACTWhile conducting siderite (FeCO3) solubility experiments in NaCl-Na2CO3 brines, evidence for a second phase was detected. Experiments, in which synthesized siderite was reacted with high ionic strength (0.18 – 7.5 m) solutions at room temperature and high pH (&gt;10), were conducted in a glovebox. As the aging time of siderite-bearing experiments increased, the pH of the solution decreased, signaling formation of a hydroxyl-bearing phase. Decreasing pH values are interpreted to indicate that a hydroxyl-bearing phase, such as chukanovite, is the reaction controlling solid in the solid assemblage. Chukanovite was tentatively identified by XRD analysis. We set out, therefore, to determine the thermodynamic stability of chukanovite under the experimental conditions. Aqueous thermodynamic model parameters were determined with experimentally analyzed Fe(II) solubility data, and subsequently yielded a proposed formation free energy of chukanovite (-1149.8 kJ/mol).

Direct Detection of Low Concentration DNA in High Ionic Strength Solution with AlGaN/GaN High Electron Mobility Transistors

In this research, the direct detection of DNA sequences in physiological salt concentration by FET based biosensor has been investigated. FET having high transconductance gain, can significantly improve the S/N ratio and sensitivity. As the complementary DNA concentration, ranging from 1fM to 100fM, is introduced, the current gain of the device changes accordingly. The sensor can efficiently detect target DNA down to a low concentration of 1 fM.

Acceptor-type hydroxide graphite intercalation compounds electrochemically formed in high ionic strength solutions.

The intercalation of hydroxide ions (OH-) into graphite formed graphite intercalation compounds (GICs) in high ionic strength solutions. GICs of solvated OH- anions with two water molecules (OH-·2H2O) in alkaline aqueous solutions and GICs of only OH- anions in a molten NaOH-KOH salt solution were electrochemically synthesized.

Editors' Choice—Field-Effect Transistor-Based Biosensors and a Portable Device for Personal Healthcare

In this study, miniaturized AlGaN/GaN high electron mobility transistors (HEMTs) were embedded in a plastics substrate and connected with metal electrodes. The plastic substrates were then engraved as the shape of a micro SD card, followed by capping capillary channel for guiding fluids. C-reactive protein (CRP) aptamer were then immobilized on the HEMT for CRP detection. The sensor chip can be inserted into a micro SD card socket, which is connected to a circuit designed for reading out the electrical signals of the sensor. The circuit is controlled by an application software in a laptop. A new methodology was developed to directly detect proteins in high ionic strength solution, such as in 1XPBS or serum, avoiding complicated washing process, leading to less automatics for sample pre-treatment and simpler system and operation. It turns out that the system can be small, cheap, and user-friendly for lay-persons. CRP is demonstrated to be directly detected in human serum with the new methodology. CRP prepared in 1XPBS is successfully detected with this disposable sensor chip and the portable readout device. The result shows that this portable system is promising in personal healthcare in the future.

Highly stretchable hydrogels from complex coacervation of natural polyelectrolytes.

The controlled complex coacervation of oppositely charged hyaluronic acid (Mw ≈ 800-1000 kg mol-1) and chitosan (Mw ≈ 160 kg mol-1, degree of acetylation = 15%) led to hydrogels with controllable properties in terms of elasticity and strength. In this work, we performed desalting by dialysis of high ionic strength solutions of mixed polyelectrolytes and showed that the control of the pH during the polyelectrolyte assembly greatly impacts the mechanical properties of the hydrogel. First, for pHs from 5.5 to 7.5, a slight coacervation was observed due to low chitosan protonation and poor polyelectrolyte associations. Then, for pHs from 3.0 to 5.5, coacervation and syneresis led to free-standing and easy to handle hydrogels. Finally, for pHs from 2.0 to 3.0 (close to the pKa of the hyaluronic acid), we observed the unusual stretchability of these hydrogels that could arise from the pre-folding of hyaluronic acid chains while physical crosslinking was achieved by hyaluronic acid/chitosan polyelectrolyte complexation.

Covalent Cross-Linking of Porous Poly(ionic liquid) Membrane via a Triazine Network.

Porous poly(ionic liquid) membranes that were prepared via electrostatic cross-linking were subsequently covalently cross-linked via formation of a 1,3,5-triazine network. The additional covalent cross-links do not affect pore size and pore size distribution of the membranes and stabilize them toward salt solutions of high ionic strength, enabling the membranes to work in a broader environmental window.