Anion Exchange Properties Research Articles

Influence of surface modification with ceria on transport properties of heterogeneous anion exchange MА-41 membranes

Influence of surface modification with ceria on transport properties of heterogeneous anion exchange MА-41 membranes

Validation of a global method for the simultaneous analysis of polar and non-polar pesticides by online extraction and LC-MS/MS

BackgroundMulti-residue methods for pesticide analysis in food are available for many compounds, but polar pesticides are not generally included due to their specific properties, which include high polarity and low molecular weight. Single residue methods are therefore needed for sample preparation, while chromatographic separation often requires derivatization, ion paring, or dedicated methods suitable for polar compounds, mostly ion chromatography and hydrophilic interaction liquid chromatography (HILIC). These challenges affect the important pesticide glyphosate and the related compounds aminomethylphosphonic acid (AMPA) and glufosinate. There are only a few methods including these compounds in large-scale analysis, mostly complex methods based on multidimensional chromatography. ResultsA new method, for the global online extraction and analysis of pesticides in beer was developed and validated. The method exploited an online trapping device, with reversed-phase (RP) and anion exchange properties, that can trap small molecules from liquid samples. The ion exchange mechanism was used to retain the very polar pesticides glyphosate, AMPA, and glufosinate. The hydrophobic properties of the trapping column were also exploited to trap pesticides suitable for multi-residue investigations. The chromatographic separation was optimized by comparison of HILIC and RP C30, which could separate pesticides, including the polar ones, with modulation by the trapping column after proper selection of the mobile phase composition and basic modifier. The validation for beer provided recoveries in the range 71–112 %, with <15 % RSD, and LOD and LOQ values of 0.02–1 and 0.3–3 μg L−1, respectively. The result was competitive with previous methods on polar pesticide analysis in beer. SignificanceThe method was validated for 15 pesticides, over the log Kow range from −4.4 to 4.5, using a methodology with single and fast chromatographic separation under conditions compatible with multi-residue analysis by RP-LC-MS/MS. In the case of beer, for which the method was validated, the sample preparation was also performed online, after simple degassing, and sample dilution.

In situ mildly synthesized CuZnAl LDHs nanofilm with long-lasting corrosion resistance and self-healing properties induced by corrosive Cl– ions

A smart means to achieve the harmless treatment of corrosive Cl– have been proposed for protecting brass. In this method, intelligent self-healing nanofilms based on the interlayer anion exchange properties of LDHs in situ grow on brass surfaces. The Cl– ions replace the BTA– loaded between LDHs interlayers to induce self-healing, as the binding energy of Cl– is lower than that of BTA–, obtained from theoretical calculations. The simultaneous application of electrochemistry and digital holography technologies confirmed that the constructed film has high instantaneous corrosion inhibition efficiency (99.9 %), long-lasting corrosion resistance, and self-healing ability (50 days).

Architecting layered double hydroxides: Exploring their structural mastery and transformative influence on wood staining

Traditional wood staining processes involve the extensive use of inorganic salts and fixing agents. The exploration of a low-concentration yet highly efficient wood staining method is crucial for the low-carbon, environmentally friendly, and high-quality development of wooden products. In this study, we employed metal-organic framework (MOF) as precursors for layered double hydroxides (LDHs), achieving control over the coloration of poplar wood towards a blue-green hue through the hydrolysis-induced exchange between MOF and hydroxide ions, using an ultra-low concentration (0.016 mol/L) Cu2+ solution. Exploiting the unique micro-nano structure of LDHs and their anion exchange properties, we successfully engineered a superhydrophobic surface (WCA=151.8°) for wood by introducing hydrophobic long chains. The resulting stained wood exhibited superior water resistance, self-cleaning ability, wear resistance, resistance to UV aging, and mold prevention. A key highlight of our preparation process lies in the utilization of extremely low concentrations of metal ion solutions, emphasizing its environmentally friendly, efficient, and multifunctional characteristics. This research provides a novel and efficient green staining approach for wood, opening up new avenues for the high-quality and sustainable development of wood materials.

Valproate intercalated in layered double hydroxides: Synthesis, characterization, release kinetics and biocompatibility studies

Layered double hydroxides (LDHs) are biocompatible materials with excellent anion exchange properties, making them suitable for use as drug carriers by incorporating the drug in its anionic form within their layered structure. In this study, an LDH was synthetized through ion exchange with valproate (VAL), an anticonvulsant drug, using an LDH with nitrate as the parent material. The resulting LDH-VAL sample underwent a comprehensive multi-technique characterization using XRD, TG-DSC, TEM, SEM, EDS, FTIR, XPS and zeta potential measurements. Dissolution kinetics and VAL release kinetics in an ample range of pH (3–9), along with biological assays to test biocompatibility, were also performed. All techniques confirmed the successful intercalation of the drug into the LDH structure, displacing all the nitrate ions of the parent material and increasing the basal spacing d003 from 8.8 Å to 18.3 Å. VAL release in NaCl and physiological buffer solutions was incongruent with LDH dissolution, clearly indicating that VAL release was controlled by an ion exchange process. In 0.9 % NaCl solutions, 90–100 % of VAL was released with only 15–20 % of LDH dissolution, and in buffer solutions 100 % of VAL was released with, at the most, 30 % of LDH dissolution. Biological assays, including lactate dehydrogenase activity, serum calcium concentration and histological analysis of blood samples, confirmed that the prepared LDH-VAL is a biocompatible material with a potential use as a nanodrug carrier.

Granular composite of polyvinyl chloride anion exchange resin encapsulated with nano TiO2 for arsenic removal from water

Persistently high arsenic levels in drinking water threaten underprivileged areas worldwide. Although nanomaterials exhibit exceptional arsenic removal properties, their implementation presents challenges. We converted N-methylimidazole-modified polyvinyl chloride into a granular anion exchange resin (PNAXRs) using an environmentally friendly and gentle synthesis method. Additionally, a unified approach for embedding nanomaterials within these resins was proposed, yielding a TiO2 composite resin (TiO2@PNAXRs). Structural characterization confirmed the successful grafting of imidazolium cations with anion-exchange properties onto polyvinyl chloride side chains. BET analysis indicates a high specific surface area of 70.31 m2/g for the PNAXRs. TGA curves demonstrate the successful encapsulation of approximately 24.9% TiO2 within the composite resin. The SEM-EDS results show a uniform distribution of TiO2 in the PNAXRs, which facilitates the effective utilization of TiO2. Adsorption experiments in conjunction with XPS analysis provided insights into the dual role of inner-sphere complexation and ion exchange in the adsorption mechanism of As(V) by TiO2@PNAXRs. In dynamic adsorption tests utilizing high-As(V) groundwater from the Datong Basin as the influent, TiO2@PNAXRs demonstrated the ability to produce effluents that meet the World Health Organization's recommended limit for arsenic in drinking water, with a capacity of 1780 bed volumes. These findings support the use of PNAXRs as ideal matrices for TiO2 and their practical application in As(V) removal processes.

Sebacate intercalated Ca[sbnd]Al layered double hydroxide pigments for corrosion protection of low carbon steel: Anion exchange and electrochemical properties

Sebacate (SB) molecules were incorporated into CaAl layered double hydroxides (CaAL-LDH) using a hydrothermal method. The resulting products underwent characterization through X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. To investigate the release kinetics and thermodynamics of the corrosion inhibitor, total organic carbon analysis (TOC) was employed. A comparison was made with CaAl-LDH prepared without corrosion inhibitors, in which nitrates were the primary anions within the layered clay structure. An assessment of anion exchange between nitrates and chlorides was conducted using total nitrogen analysis (TN). The SB anion comprised approximately 49.2% of the total dried powder synthesized, with a maximum release efficiency of around 86.7% fitting a Langmuir model. For the evaluation of the corrosion inhibition effect on steel surfaces, electrochemical impedance spectroscopy, potentiodynamic polarization, and scanning vibrating electrode technique were employed. The corrosion inhibition impact was ascribed to the liberation of SB anions from the CaAl-LDH pigments, accompanied by alkalinization stemming from partial particle dissolution. Additionally, the incorporation of organic molecules notably enhanced the stability of pigments in aqueous solutions compared to similar ones hosting nitrates. These findings suggested that CaAl-LDH pigments have potential as nanocontainers for organic inhibitors, showing promising prospects in the field of corrosion research.

Fabrication of polyethyleneimine grafted maleopimaric acid glycidyl methacrylate ester stationary phase for mixed-mode liquid chromatography

Due to their advantages of low green toxicity, diverse sources, renewable nature, and excellent biocompatibility, natural products have been extensively utilized in the exploration and development of novel stationary phase materials for liquid chromatography. In this study, we fabricated a rosin-based stationary phase material for mixed-mode chromatography by utilizing maleopimaric acid glycidyl methacrylate ester (MPAG) and polyethyleneimine (PEI) as ligands. Initially, silica was functionalized with MPAG through thiol-ene click reaction, followed by the grafting of PEI via an imidization reaction to produce Sil-MPAG-PEI material. This material exhibited both anion exchange and hydrophilic interaction properties due to the presence of PEI, allowing for the switching of its retention mode from reversed-phase mode to a mixed-mode incorporating reversed-phase, hydrophilic interaction and ion-exchange chromatography (RPLC/HILIC/IEC) under different mobile phase conditions. Consequently, Sil-MPAG-PEI demonstrated the ability to provide various interactions, including hydrophobic, π-π, hydrogen bond, hydrophilic, ion exchange, and electrostatic interactions. These interactions enabled selective separation among compounds with different polarities, such as nucleosides/bases, benzoic acids, flavonoids, alkylbenzenes, phenols, anilines, and polycyclic aromatic hydrocarbons (PAHs). Furthermore, Sil-MPAG-PEI demonstrated excellent chromatographic stability, as evidenced by the low relative standard deviations (RSDs) of the retention time for interday precision and interday precision were 0.042 %-0.275 % (n = 10) and 0.159 %-0.932 % (n = 7). The column was also successfully employed for the quantitative determination of evodiamine and rutaecarpine in an extract solution of Evodiae fructus, achieving concentrations of 9.102 and 3.256 mg/g, respectively. These results demonstrate the potential of Sil-MPAG-PEI in the analysis of complexsamples. Briefly, this study investigated and confirmed the potential application of rosin derivatives in mixed-mode liquid chromatography separations has been investigated and verified. The exceptional separation ability of Sil-MPAG-PEI indicates that it is a promising separation material for chromatographic separation.

Structural features and dynamic behaviour of the interlayer space of layered double hydroxide coatings

Layered double hydroxide (LDH) offer great potentialities to design functional coatings with customizable properties by exploiting their anion exchange properties. We investigated the anion exchange properties and expansion capacity of the interlayer space relating to the starting film morphology. ZnAl LDH coatings of different thicknesses and morphologies were first obtained by an in situ method using Al-based substrates. When the anion to intercalate is relatively bigger than the starting nitrates, the intercalation may be constrained by the initial LDH particle size and density composing the film. After optimising the morphology, the intercalation of three functional anions with potential antimicrobial properties was successfully achieved with an expansion of the interlayer space up to 150 % while holding the coating integrity. The release of the guest anion was studied by immersion in physiological saline solution. Finally, the possibility to regenerate the coating was demonstrated supporting the potential of these hybrid coatings for applications.

Layered Double Hydroxides as the Unique Product of Target Ionic Construction for Energy, Chemical, Foods, Cosmetics, Medicine and Ecology Applications.

Layered Double Hydroxide (LDH) is an α-modification of the M-host (M2+ ) hydroxide, in which some part of the M-host cations is replaced by M-guest cations (M3+ or M4+ ). The emerging excess positive charge is compensated by the intercalation of anions into the interlayer space, which also contains water molecules. LDHs exhibit anion exchange properties. Targeted ionic design of LDHs via combining three components (M-host, M-guest cations, intercalated anions) allows the creation of a very wide range of highly efficient electrochemical, electrocatalytic, electrochromic substances, catalysts, ion exchangers, sorbents, color pigments, pharmacological drugs, food, and cosmetic additives. In this review, the structure and areas of application of LDHs are considered from the perspective of the targeted ionic design of a substance for a specific application.

Layered Double Hydroxide Materials: A Review on Their Preparation, Characterization, and Applications

Layered double hydroxides (LDHs), a type of synthetic clay with assorted potential applications, are deliberated upon in view of their specific properties, such as adsorbent-specific behavior, biocompatibility, fire-retardant capacity, and catalytic and anion exchange properties, among others. LDHs are materials with two-dimensional morphology, high porosity, and exceptionally tunable and exchangeable anionic particles with sensible interlayer spaces. The remarkable feature of LDHs is their flexibility in maintaining the interlayer spaces endowing them with the capacity to accommodate a variety of ionic species, suitable for many applications. Herein, some synthetic methodologies, general characterizations, and applications of LDHs are summarized, encompassing their broader appliances as a remarkable material to serve society and address several problems viz. removal of pollutants and fabrication of sensors and materials with multifaceted useful applications in the medical, electrochemical, catalytic, and agricultural fields, among others.

High-Performance Integrated rGO-[Polymeric Ionic Liquid] [Heteropolyanions] for Catalytic Degradation of Azo Dyes

Polymeric ionic liquid (such as poly[ViEtIm]Br)-modified reduced graphene oxide (rGO), rGO-poly[ViEtIm]Br, was nominated as an open carrier to construct a degradation platform. The large specific surface of rGO together with the anion-exchange property of poly[ViEtIm]Br terminals led to the wide growth of heteropolyanions (like [PW12O40]3-, [PMo12O40]3-, and [SiW12O40]4-), thus assembling the integrated catalyst rGO-poly[ViEtIm][heteropolyanions]. The grafted poly[ViEtIm]Br provided an anchor point to interlink the polar heteropolyanions and the nonpolar rGO substrate, endowing this graphene-based catalyst with excellent dispersibility. The adequate exposure of heteropolyanions further promoted the decolorization capability during the degradation procedure. Morphology, structure, and properties of materials were confirmed and monitored via transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) spectroscopy, etc. rGO-poly[ViEtIm][PW12O40] was selected as the optimal catalyst with degradation efficiency toward methyl orange reaching 98.7% in 3 h. In addition, the excellent structural stability of the catalyst improved the decolorization efficiency, which reached 95% after recycling five times.

Adsorption of Arsenic, Lead, Cadmium, and Chromium Ions from Aqueous Solution Using a Protonated Chabazite: Preparation, Characterization, and Removal Mechanism

The adsorption of As(V), Pb(II), Cd(II), and Cr(III) ions from aqueous solutions on natural and modified chabazite was studied. The functionalization of chabazite was performed via a protonation and calcination with the aim of generating Lewis acid sites to improve its anion exchange properties. The surface and physicochemical properties of both adsorbents were studied and compared. The adsorption isotherms of tested heavy metal ions were quantified and modeled to identify the best isotherm equation. Steric parameters for the adsorption of these ions were also calculated with a monolayer statistical physics model. Natural chabazite showed the maximum adsorption capacity for Pb(II), while the modified zeolite improved its As(V) properties in 79%. These results showed that the modified zeolite was able to remove both cations and anions from aqueous solution. The application of this functionalized chabazite can be extended for the removal of other anionic pollutants from water, thus opening the possibility of preparing new adsorbents with tailored properties for water treatment.

Hydrophilic fillers for anione exchange membranes of alkaline water electrolyzers

Alkaline water electrolysers are widespread in many industries, including systems with hydrogen cycle of energy storage. One of the problems of modern alkaline water electrolysers is insufficient purity of generated electrolysis gases relative to electrolysis systems with solid-polymer electrolyte. In this regard, work on modification of existing porous diaphragms is actively carried out. One new area of research is the impregnation of new hydrophilic fillers into the composition of existing diaphragms and the transition to ion-solvate membranes. In this work the synthesis of zirconium hydroxide hydrogel inside a porous diaphragm with the hydrophilic filler TiO2 was carried out. This synthesis makes it possible to obtain a membrane with anion-exchange properties. A possible mechanism of OH- hydroxyl ion transfer by immobilized K+ ion was also proposed. The obtained results demonstrated the resistance of the membrane to concentrated alkaline solutions.

A New Method for the Synthesis of Layered Europium Hydroxide Using Propylene Oxide as the Precipitating Agent

A new method for the synthesis of layered europium basic chloride in up to 90% yield was developed. The method is based on hydrolysis of europium chloride in the presence of propylene oxide. The effect of reaction temperature on the yield and composition of the products of europium chloride hydrolysis in the presence of propylene oxide was analyzed. The obtained layered europium basic chloride had pronounced anion exchange properties. The possibility of intercalation of the isonicotinate anion into a layered rare earth hydroxide was demonstrated for the first time. The intercalation of the benzoate or isonicotinate anions into layered europium hydroxide led to luminescence sensitization and decrease in the Eu3+ local symmetry.

Regulation of Structure and Anion-Exchange Performance of Layered Double Hydroxide: Function of the Metal Cation Composition of a Brucite-like Layer.

As anion-exchange materials, layered double hydroxides (LDHs) have attracted increasing attention in the fields of selective adsorption and separation, controlled drug release, and environmental remediation. The metal cation composition of the laminate is the essential factor that determines the anion-exchange performance of LDHs. Herein, we review the regulating effects of the metal cation composition on the anion-exchange properties and LDH structure. Specifically, the internal factors affecting the anion-exchange performance of LDHs were analyzed and summarized. These include the intercalation driving force, interlayer domain environment, and LDH morphology, which significantly affect the anion selectivity, anion-exchange capacity, and anion arrangement. By changing the species, valence state, size, and mole ratio of the metal cations, the structural characteristics, charge density, and interlayer spacing of LDHs can be adjusted, which affect the anion-exchange performance of LDHs. The present challenges and future prospects of LDHs are also discussed. To the best of our knowledge, this is the first review to summarize the essential relationship between the metal ion composition and anion-exchange performance of laminates, providing important insights for regulating the anion-exchange performance of LDHs.

Synthesis of Anion Exchange Membranes Containing PVDF/PES and Either PEI or Fumion®.

In this work, the preparation of dense blended membranes, from blends of poly(vinylidene fluoride) (PVDF), poly(ether sulfone) (PES) and polyethyleneimine (PEI) or Fumion®, with possible applications in alkaline fuel cell (AEMFC) is reported. The blended PEI/Fumion® membranes were prepared under a controlled air atmosphere by a solvent evaporation method, and were characterized regarding water uptake, swelling ratio, thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), ion exchange capacity (IEC), OH− conductivity and novel hydroxide ion exchange rate (HIER), which is related to the mass transport capacity of the OH− ions through the membrane. The effect of the chemical composition on its morphological and anion exchange properties was evaluated. It was expected that the usage of a commercial ionomer Fumion®, in the blended membranes would result in better features in the electrical/ionic conductivity behaviour. However, two of the membranes containing PEI exhibited a higher HIER and OH− conductivity than Fumion® membranes, and were excellent option for potential applications in AEMFC, considering their performance and the cost of Fumion®-based membranes.

Synthesis and properties of new strongly basic fibrous anion exchangers

A synthesis method of new fibrous anion exchangers with strong base groups has been developed. The synthesis was carried out by alkylation of weakly basic anion exchangers based on polyacrylonitrile fiber using two alkylating agents: epichlorohydrin and ethylene chlorohydrin. The influence of the reaction conditions on the physicochemical properties of new anion exchangers was investigated. The synthesis parameters were determined: the molar ratio of “amino groups: alkylating agent”, the concentration of the alkylating agent, the reaction time and temperature – to obtain anion exchangers with maximum exchange capacity for strong base groups. New strongly basic fibers possess satisfactory mechanical properties allowing their processing into various textile forms.

Self-supported trimetallic NiZnLa nanosheets on hierarchical porous graphene oxide-polymer composite fibers for enhanced phosphate removal from water

Phosphate-induced water eutrophication has attracted global attention. Fabricating adsorbents with both high phosphate adsorption affinity and accessible separation property is challenging. Herein, PG@NZL, a hierarchical nanocomposite fibrous membrane, was fabricated via in-situ growth of La-doped NiZn-LDH (NiZnLa0.1) over electrospun graphene oxide-polymer composite fibers (PG). The porous surface of the PG fibers provided abundant anchor sites for the vertical self-supported growth of NiZnLa0.1 nanosheets, contributing to a high surface area. The La-doped NiZnLa0.1 trimetallic LDH achieved a much higher adsorption capacity than NiZn-LDH. The negative adsorption energy (-1.45 eV), calculated with DFT, confirmed its spontaneous adsorption potential for phosphate. Interestingly, the PG fibers contributed to oxygen vacancies and the metal center electronic structure evolution of NiZnLa0.1, thus strengthening the coordination with phosphate. Mechanistic analysis revealed that the high adsorption capacity of PG@NZL is attributed to its superior anion exchange property, oxygen vacancies, and inner-sphere complexation. Therefore, the flexible and easily separated PG@NZL nanocomposite fibrous membrane is a promising adsorbent for effectively treating phosphate-bearing wastewater.

Physico-Сhemical Properties of Aqueous Solutions of Diethanolamine Borate

The concentration functions of the electrical conductivity and pH for aqueous solutions of an ionic liquid (IL) based on diethanolamine and boric acid (DEAB) have been determined. Correlations have been established between the physicochemical properties of an aqueous solution of DEAB and the processes of dissociation of the components of the system. It was shown that anions are charge carriers in DEAB solutions. It was found that an aqueous solution of DEAB possesses unipolar electrical conductivity and anion-exchange properties with an anion transfer number of 0.79