Anion-exchange Materials Research Articles

Magnetic and reusable Fe3O4/PPE-2 functional material for efficient photodegradation of organic dye.

Composite photocatalysts based on metal nanoparticles and functional polymers attract much attention compared to inorganic photocatalysts. In this study, a reusable magnetite/anion exchanger (Fe3O4/PPE-2) functional material is synthesized by a hydrothermal method, and its photocatalytic activity is evaluated for the photocatalytic degradation of Rhodamine B (RhB). The results from materials characterization confirm a well-defined morphology of magnetic Fe3O4/PPE-2 functional material and the formation of Fe3O4 nanocrystals with different shapes and sizes on the surface of anion exchange material (PPE-2). The optimized Fe3O4/PPE-2 in 180°C (FM180) photocatalyst exhibited a band gap energy of 1.90eV, demonstrating significant photocatalytic potential. Using RhB as a model pollutant, magnetic Fe3O4/PPE-2 (FM180) functional material achieved 98.2% degradation efficiency after 160min of visible light irradiation (rate constant k=0.03496 min-1). Efficiency of the photocatalytic materials, of photocatalytic degradation of RhB is 28.4% for pure anion exchanger (PPE-2), 56.5%, 64.7% and 98.2% for magnetic functional Fe3O4/PPE-2 materials, synthesized under conditions of 140°C (FM140), 160°C (FM160) and 180°C (FM180), respectively. Compared to individual PPE-2 anion exchange material and Fe3O4, the magnetic functional FM180 material exhibits a remarkable photocatalytic reaction rate as high as four times that of PPE-2, with superior reusability over 10 cycles. The computational study and Mott-Schottky plots verify the formation of the internal electric field. Possible reaction pathways for the photocatalytic degradation of RhB are presented. In addition, the results demonstrate that the Fe3O4/PPE-2 functional material very efficiently removed Rhodamine B from textile wastewater. This work offers a simple route for the preparation of magnetic and reusable Fe3O4/PPE-2 magnetic functional material that can be used in the water purification process.

Silver 4,4'-Vinylenedipyridine Coordination Polymers: Linker Effects on Formation Thermodynamics and Anion Exchange.

Four new and one previously reported silver 4,4'-vinylenedipyridine (Vpe) coordination polymers were tested as anion exchange materials to assess their potential for pollutant sequestration and compared to analogous silver 4,4'-bipyridine (bipy) coordination polymers. The materials were synthesized using nitrate, tetrafluoroborate, perchlorate, perrhenate, or chromate as the anion to produce cationic coordination polymers with solubilities ranging from 0.0137(7) to 0.21(5) mM. These values are much lower than silver bipy coordination polymers [0.045(3) to 5.5(5) mM] and agree with thermochemical calculations. [Ag(Vpe)+][BF4-], [Ag2(Vpe)2.52+][CrO42-]·5H2O, and [Ag(Vpe)+][ReO4-]·2H2O structures are reported. Perrhenate and chromate ions in an equimolar solution were fully adsorbed by [Ag(Vpe)+][NO3-]·3H2O [620(2) and 137.1(6) mg/g, respectively] as well as by [Ag(Vpe)+][BF4-] [661.8(3) and 190(3) mg/g, respectively] via anion exchange. DFT calculations show that torsional energetics play a significant role in the formation thermodynamics by reducing the energy cost by as much as 4.8 kJ/mol when bipy is replaced with Vpe in silver-based coordination polymers. The results obtained with the flat Vpe ligand highlight the potential role of coordination polymers in practical anion exchange.

Evaluating the Impact of Cell Assembly and Operating Conditions on the Performance of Anion Exchange Membrane Electrolyzers

The alkaline water electrolyzer (AWE) and proton exchange membrane water electrolyzer (PEMWE) are the two dominant commercial platforms to produce hydrogen through electrolysis. Recent efforts have focused on combining the benefits of the two technologies, leading to the creation of the anion exchange membrane water electrolyzer (AEMWE). AEMWEs operate under high pH conditions, like AWEs, enabling the use of cost-effective materials as cell components and non-noble electrocatalysts. AEMWEs also utilize the same high-performance zero-gap design PEMWEs and also have the ability to operate at high differential pressures. Therefore, AEMWEs offer the opportunity to optimize both cost and performance, out-pacing both incumbent technologies after further development.As the “active” materials in AEMWEs, the anion exchange membranes and ionomers and the catalysts have been widely studied and a number of materials have been proposed and reported on in the literature and throughout the last several ECS meetings. However, such materials are only one piece of the overall puzzle when it comes to the operation of AEMWEs. There are several aspects of cell assembly and operation that go a long way to dictating the performance of an operating cell.Therefore, the overarching goal of this study was to investigate several operational variables for AEMWEs with a known high-quality set of anion-exchange materials, known commercially as Aemion+™ paired with commercially available catalysts – PtNi/C at the cathode and either IrOx or NiFeOx at the anode. For cell assembly, representative variables that were changed were the type of membrane and electrode pre-treatment, gasket thickness, cell torque and membrane thickness. Operationally, temperature, current density and break-in procedure were adjusted. This talk will link each of these variables to the polarization performance and galvanostatic durability

Efficient capture of ReO4−/TcO4− on anion exchange resin from wastewater

It is still a challenge to capture TcO4− from wastewater due to its nature of non-complexing and radioactive. Herein, two types of anion exchange resins (D201 and IRA-410 resin) were selected and explored the adsorption properties for perrhenate (ReO4−, as a surrogate for TcO4−). It is found that both D201 and IRA-410 resin exhibited fast adsorption kinetic (within 120 min), and superior adsorption capacities, which could reach 671.1 mg g−1 and 561.8 mg g−1 for D201 and IRA-410 resin, respectively. In addition, D201 and IRA-410 resin showed excellent adsorption selectivity for ReO4− in the presence of a variety of 1000-fold competing anions (NO2−, Cl−, SO42−, and PO43−). Importantly, the two resins still demonstrated outstanding performance after acid/alkaline soaking, calcination procedures as well as high doses of ionizing radiation, they also could remove ReO4− from simulated Hanford and SRS wastewater by automatic separation system. Finally, the anion-exchange mechanism was revealed by characterization and DFT. This work demonstrates that D201 and IRA-410 resin are efficient adsorbents for 99Tc removal from nuclear wastewater and provides a basis for designing other novel anion exchange materials for capturing ReO4− and TcO4−.

From Batch to Continuous Small-Scale Production of Particles: Mixer Design Methodology for Robust Operation

Layered double hydroxides (LDHs) are a vital tool in many different areas, such as drug delivery, catalysis, anion exchange (materials), polymer processing, etc. Conventionally, LDHs are synthesized in a batch process that consists of particle generation and ripening, where product properties are manipulated for stability and the optimal uptake of genetic material. Continuous processing and intensive mixing holds high promise for improved particle generation and characteristic control. In this contribution, an iterative method, using the mentioned particle generation as a use case, was applied to quickly generate a continuous process optimization platform for continuous, plugging-free particle generation with the required characteristics. Assisted by rapid prototyping and additive manufacturing, a vortex mixer was produced that delivers satisfactory long-term results.

A four-fold interpenetrated MOF for efficient perrhenate/pertechnetate removal from alkaline nuclear effluents

The sequestration of 99Tc represents one of the most challenging tasks in nuclear waste decontamination. In the event of a radioactive waste leak, 99TcO4– (a main form of 99Tc) would spread into the groundwater, a scenario difficult to address with conventional anion exchange materials like resin and inorganic cationic sorbents. Herein, we present a nickel(II) metal-organic framework (MOF), TNU-143, featuring 3D four-fold interpenetrated networks. TNU-143 exhibits efficient ReO4– (a nonradioactive analogue of 99TcO4–) removal with fast anion exchange kinetics (<1 min), high sorption capacity (844 mg/g for ReO4–), and outstanding selectivity over common anions. More importantly, TNU-143 shows superior stability in alkaline solution and can remove 91.6% ReO4– from simulated alkaline high-level waste (HLW) streams with solid-liquid ratio of 40 g/L. The uptake mechanism is elucidated by the single-crystal structure of TNU-143(Re), showing that ReO4– anions are firmly coordinated to nickel cation to result in a 2D layered structures. Density functional theory (DFT) calculations confirm the transformation from TNU-143 to TNU-143(Re) is a thermodynamically favorable process. This work presents a new approach to the removal of ReO4–/99TcO4– from alkaline nulcear fuel using MOF sorbents.

Halogen bonding and hydrophobic interactions: A new strategy for synergistically enhancing ReO4−/99TcO4− binding

Efficient removal of 99TcO4− from strongly acidic and alkaline nuclear wastewater is essential due to environmental protection and nuclear fuel cycle issues associated with the nuclear industry. However, the combined features of anion exchange materials with decent acid/base stability, high capacity, and high selectivity toward ReO4−/99TcO4− have not yet been achieved. Here, we explore a new strategy to overcome the aforementioned challenges by pre-organizing pyridinium-based cationic polymer network (TFTA-BPD) with sigma-holes and strongly hydrophobic fluorine atoms, which can effectively form strong halogen bonding and enhance hydrophobic interactions for selective ReO4−/99TcO4− binding. This emerging strategy not only significantly enhances the stability of the adsorbent, but also remarkably strengthens the specific affinity toward ReO4−/99TcO4− due to the synergistic effect of halogen bonding and hydrophobic interactions, compared to reported cationic polymer networks. More importantly, our TFTA-BPD exhibit fast removal kinetics, high capacity, excellent removal selectivity, and encouraging reusability, enabling efficient removal of ReO4− from simulated low activity waste (LAW) at Hanford and high-level waste (HLW) at the Savannah River Site in both dynamic column separation and batch experiments. Experimental and computational results indicate that the halogen-functionalized TFTA-BPD can regulate the electron distribution of adjacent N atoms and enhance charge separation through the halogen electron traction effect. This work demonstrates the enormous potential of halogen bonding and hydrophobic interactions in synergistically enhancing ReO4−/99TcO4− binding and paves the way for constructing high-performance adsorbents for HLW and LAW treatment.

Fiber chromatographic enabled process intensification increases monoclonal antibody product yield.

The most straightforward method to increase monoclonal antibody (mAb) product yield is to complete the purification process in less steps. Here, three different fiber chromatographic devices were implemented using a holistic approach to intensify the mAb purification process and increase yield. Fiber protein A (proA) chromatography was first investigated, but traditional depth filtration was not sufficient in reducing the contaminant load as the fiber proA device prematurely fouled. Further experimentation revealed that chromatin aggregates were the most likely reason for the fiber fouling. To reduce levels of chromatin aggregates, a chromatographic clarification device (CCD) was incorporated into the process, resulting in single-stage clarification of harvested cell culture fluid and reduction of DNA levels. The CCD clarified pool was then successfully processed through the fiber proA device, fully realizing the productivity gains that the fiber technology offers. After the proA and viral inactivation neutralization (VIN) hold step, the purification process was further intensified using a novel single-use fiber-based polishing anion exchange (AEX) material that is capable of binding both soluble and insoluble contaminants. The three-stage fiber chromatographic purification process was compared to a legacy five-step process of dual-stage depth filtration, bead-based proA chromatography, post-VIN depth filtration, and bead-based AEX chromatography. The overall yield from the five-step process was 60%, while the fiber chromatographic-enabled intensified process had an overall yield of 70%. The impurity clearance of DNA and host cell protein (HCP) for both processes were within the regulatory specification (<100 ppm HCP, <1 ppb DNA). For the harvest of a 2000 L cell culture, the intensified process is expected to increase productivity by 2.5-fold at clarification, 50-fold at the proA step, and 1.6-fold in polishing. Relative to the legacy process, the intensified process would reduce buffer use by 1088 L and decrease overall process product mass intensity by 12.6%.

Tyrosine Amino Acid as a Foulant for the Heterogeneous Anion Exchange Membrane.

The features of organic fouling have been revealed for highly basic anion exchange membranes during prolonged electrodialysis in solutions containing the aromatic amino acid tyrosine. With increased operation time when using MA-41 heterogeneous membranes in tyrosine solution, an increase in hydrophobicity and roughness characteristics of the material surface is detected. A reduction in tyrosine flux through the membrane occurs which is caused by its pores plugging and deposition of the amino acid at the membrane surface induced by tyrosine adsorption and local supersaturation of the solution in the membrane phase. The long-term contact of the anion exchange membrane with a solution of tyrosine leads to some structural changes in the anion exchange material. An accumulation of the studied amino acid with phenolic fragment and tyrosine oxidation products (DOPA, DOPA-quinone) is found and confirmed by IR- and UV-spectroscopy techniques. The organic fouling is accompanied by an increase in density and a decrease in moisture content of the studied membrane. A comparative analysis of the chemical and electrochemical cleaning results for fouled samples of the MA-41 membrane demonstrates a partial restoration of the material transport characteristics using electrochemical cleaning in the intensive current mode of electrodialysis. The best efficiency of regeneration is reached when carrying out chemical cleaning with a solution of hydrochloric acid, providing almost complete restoration of the membrane characteristics.

Structural, Morphological, and Textural Properties of Coprecipitated CaTiO3 for Anion Exchange in the Electrolyzer

The limitation in fossil fuel and the emission of greenhouse gases (GHG) resulting in global warming is one of the global challenging issues. Similarly, efficient and cost-effective renewable energy resources are always in demand for the overcome of the limitation. One of the best alternatives to fossil fuels based on renewable energy sources is hydrogen fuel. The main component of the hydrogen fuel generator is the Electrolyzer. Among different types of electrolyzers, the incorporation of an anion exchange membrane is one approach. In this work, we are focusing on the preparation, characterization, and analysis of anion exchange material CaTiO3 used for the electrolyzer. A co-precipitation method was used for the preparation of CaTiO3 XRD shows the orthorhombic structure of the CaTiO3. FT-IR shows the vibrational spectra of CaTiO3. The particles were spherical and crystalline with an average size of 200 nm when viewed through the Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), and High-Resolution Transmission Electron Microscopy (HRTEM). The SAED pattern verifies the single crystalline nature of the sample. In this way, the CaTiO3, the anion exchange agent was synthesized and characterized successfully.

Anion exchange material based on polyvinylchloride and urea for the removal of chromium(vi) ions from aqueous solutions

AbstractIn this study, an anion exchange material obtained by chemically modifying granulated polyvinyl chloride with urea was examined. To study the structural morphology of the anion exchanger, polymer PVC‐based anion exchange resin second type (PPE‐2), we applied different characterization techniques including X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR), scanning electron microscopy (SEM), and water vapor adsorption analysis. Moreover, PPE‐2 was used to remove hexavalent chromium ions from aqueous media. A pseudo‐second order model was used to describe sorption kinetics as well as the adsorption mechanism. The Langmuir isotherm and the pseudo‐second order kinetic model led to the most consistent results in describing ion removal from solution. In the case of hexavalent chromium ions, the maximum adsorption capacity was 148.4 mg g−1. The Dubinin‐Radushkevich (D‐R) free energy of adsorption (ED) was &gt;16 kJ mol−1, which indicates chemical interaction between the ion exchange material and Cr(VI) ions. The Gibbs energy ΔG, enthalpy ΔH, and entropy ΔS changes during binding showed that the sorption process is spontaneous and involves chemical sorption through endothermic ion exchange reactions. In addition, the results demonstrate that the anion exchanger (PPE‐2) very efficiently removed hexavalent chromium ions from industrial wastewater.

Insights into the Path-Dependent Charge of Iridium Dissolution Products and Stability of Electrocatalytic Water Splitting

The electrocatalytic stability of the oxygen evolution reaction (OER) is challenging for the storage of fluctuating renewable energies using polymer electrolyte membrane water electrolyzers (PEMWEs). Investigations are commonly conducted in so-called half-cell setups and different OER-related dissolution pathways have been proposed. However, the orders of magnitude difference in dissolution rate between half-cells and PEMWE using membrane electrode assemblies (MEA) is not well understood. In this work, the charge-related absorption affinity of Iridium (Ir) dissolution products, from both half-cell and MEA setups, is investigated, using cation and anion exchange materials. In the half-cell, a roughly constant ratio of cationic to anionic dissolution species is indicative of a single, dominant OER-related Ir dissolution pathway. While Ir dissolved in half-cells is mainly cationic, the Ir species from the MEA appear mainly in anionic form. This can be explained by the transport conditions of different Ir ions inside the catalyst layer, influenced by their ionomer absorption affinity and the migration driving force. Based on this understanding, key influences of electrocatalytic stability of MEAs, the effect of confinement of dissolved Ir species and the stability discrepancy to half-cells are discussed.

Pyridinium-functionalized Ionic Porous Organic Polymer for Rapid Scavenging of Oxoanions from Water.

Metal oxoanions adversely affect the food chain through bioaccumulation and biomagnification. Therefore, they are among the major freshwater contaminants that require immediate remediation. Although several adsorbents have been developed over the years for sequestering these micropollutants, the selective removal of oxoanions remains still a formidable challenge. Herein, pyridinium and triazine-based ionic porous organic polymer, iPOP-Cl, developed through a Brønsted acid-catalyzed aminal formation reaction, has been reported as a suitable anion exchange material for the selective removal of metal oxoanions from wastewater. The positively charged nitrogen centers, along with exchangeable chloride counter-ions in the porous polymer, allow facile oxoanion uptake. iPOP-Cl is found to be a selective scavenger of permanganate (MnO4 - ) and dichromate (Cr2 O7 2- ) from water in the presence of a high concentration of competing anions generally found in brackish water. The material exhibits fast sorption kinetics, a high uptake capacity (333mg g-1 for MnO4 - and 358mg g-1 for Cr2 O7 2- ), and excellent recyclability. This article is protected by copyright. All rights reserved.

Polymer-nucleobase composites for chemotherapy drug capture.

Intravenous chemotherapy (e.g., doxorubicin (DOX)) is standard treatment for many cancers but also leads to side effects due to off-target toxicity. To address this challenge, devices for removing off-target chemotherapy agents from the bloodstream have been developed, but the efficacy of such devices relies on the ability of the underlying materials to specifically sequester small-molecule drugs. Anion-exchange materials, genomic DNA, and DNA-functionalized iron oxide particles have all been explored as drug-capture materials, but cost, specificity, batch-to-batch variation, and immunogenicity concerns persist as challenges. Here, we report a new class of fully synthetic drug-capture materials. We copolymerized methacrylic acid and ethylene glycol dimethacrylate in the presence of several nucleobases and derivatives (adenine, cytosine, xanthine, and thymine) to yield a crosslinked resin with nucleobases integrated into the material. These materials demonstrated effective DOX capture: up to 27 mg of DOX per g of material over 20 minutes from a phosphate-buffered saline solution with an initial concentration of 0.05 mg mL-1 of DOX. These materials use only the individual nucleobases for DOX capture and exhibit competitive capture efficacy compared to previous materials that used genomic DNA, making this approach more cost-effective and reducing potential immunological concerns.

Green hydrogen from anion exchange membrane water electrolysis

Current scientific opinion is that in order for H2 to be used for energy storage on a massive scale requires significant reduction or even complete elimination of the use of critical raw materials including rare PGM metals Pt, Ru and Ir. This has given a tremendous boost to interest in water electrolyzers that use anion exchange membranes. This quickly developing field has made significant advances in terms of performance in the last 24 months. This short review summarizes very recent efforts and the remarkable improvements in single-cell electrolysis activity. The combination of improved anion exchange materials, PGM-free catalysts, and MEA preparation methods each provide a piece to assembling the puzzle. This review finishes with recommendations for further research efforts, required to translate the performance of single laboratory cells to large systems for ramp-up to commercialization.

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.

Nitrate adsorption characteristics of synthesized allophanes with various chemical compositions

AbstractAllophane-related aluminium silicates with various chemical compositions were synthesized using a hydrothermal reaction with inorganic reagents as starting solutions. The X-ray diffraction traces of the synthesized allophanes showed broad reflections centred at 0.34 and 0.23 nm, which were attributed to the imogolite-like structure of the allophanes. Energy-dispersive X-ray measurements confirmed that the Al-rich materials were synthesized as targeted. The specific surface area of the synthesized allophanes was 313–500 m2 g–1, which is greater than that of a natural allophane (248 m2 g–1). The amount of nitrate adsorbed on the synthesized allophanes tended to increase as the Al content increased. The maximum amount of nitrate adsorbed was 2.07 mmol g–1 at pH ~2, which was comparable to that of a common anion-exchange material. A possible adsorption mechanism for nitrate at lower pH levels is the weak NO3– interaction of the positively charged surface of Al-OH2+ sites.

Biological As(III) Oxidation Coupled with As(V) Interception by Fibrous Anion Exchange Material FFA-1

A combined process, including As(III) oxidation and As removal by the fibrous anion exchange material FFA-1, was established to treat arsenite ([As(III)] = 10 mg L−1)-polluted groundwater. Both fixed-bed reactors (R1 and R2) were separately filled with pozzolana and FFA-1. After 72 h of inoculation and 10 days of operation, As(III) oxidation efficiency reached around 100% and the total As in the effluent was below 10 µg L−1 for over 100 days. Then, the combined system was stopped and a desorption experiment on the FFA-1 collected from R2 was carried out. The results revealed that the As trapped by the FFA-1 was distributed linearly along the axial length of R2, and the maximum capacity for removal of the FFA-1 from R2 was about 28 mg As g−1 FFA-1. Moreover, the anions’ competing test showed that they were preferentially sequestrated by the FFA-1 according to the following order: SO42− &gt; PO43− ≈ AsO43− &gt; NO3− at neutral pH. Furthermore, the microorganisms attached to the FFA-1, including some arsenite-oxidizing microorganisms (AsOBs), could be a beneficial complement to the As(III) oxidation and, thus, the total As removal. At the same time, the regeneration test proved that the As(V) interception capacity of FFA-1 was barely affected by the presence of biofilm. Additionally, the calculated operating cost showed that this combined process has great potential for the remediation of As-polluted groundwater.

Mechanochemical synthesis of bismuth-based anion exchange materials to immobilize arsenic pollution - Prospects for advanced treatment of anion-containing wastewater

Many types of anionic pollutants exit in the aqueous environment including the group containing halogen (F-, I-, IO3-, BrO3-, ClO3−), the group containing heavy metals (VO43−, AsO33−, CrO42−, AsO43−), and eutrophic elements resulting from agricultural, aquacultural, urban and industrial activities (NO3−, PO43−). Except for layered double hydroxide, anionic exchangeable resin, few choices are available to work for the treatment of the anionic pollutants. In this study, a new type of anion exchangeable compound was reported as an alternative. Sulfate-based layered bismuth oxide with the formula of Bi2O(OH)2SO4 as a clear crystalline phase was prepared simply by ball milling Bi oxide and sulfate together. Several analytical methods such as XRD, XPS, FTIR were used to characterize the products after the As (V) adsorption to understand the ions exchange mechanism. The excellent performance to fix arsenate anion reaching over 99.9% of As(V) removal percentage with Bi2O(OH)AsO4 as adsorption product was understood probably due to the synergistic effect of several exchangeable anions inside the prepared sample. This research may open a promising way to effectively remove toxic and harmful anions by the newly prepared anion exchangeable materials.

Isotherm model for moisture-controlled CO2 sorption.

Moisture-controlled sorption of CO2, the basis for moisture-swing CO2 capture from air, is a novel phenomenon observed in strong-base anion exchange materials. Prior research has shown that Langmuir isotherms provide an approximate fit to moisture-controlled CO2 sorption isotherm data. However, this fit still lacks a governing equation derived from an analytic model. In this paper, we derive an analytic form for an isotherm equation from a bottom-up approach, starting with a fundamental theory for an alkali liquid. In the range of interest relevant to CO2 capture from air, an isotherm equation for an alkali liquid reduces to a simple analytic form with a single parameter, Keq. In the limit Keq ≫ 1, a 2nd order approximation simplifies to a Langmuir isotherm that, however, deviates from experimental data. The isotherm theory for an alkali liquid has been generalized to a strong-base anion exchange material. In a strong-base anion exchange material, water concentration inside a sorbent, [H2O], is not large enough to be regarded as constant, which allows us to extend Keq to Keq(AEM)eff = Keq(AEM) × [H2O]-n according to the law of mass action. The final isotherm formula has been validated by experimental data from the literature. For a moisture-controlled CO2 sorbent, Keq(AEM)eff varies significantly with moisture content of the sorbent. Depending on moisture level, the observed Keq(AEM)eff in a specific sorbent ranges from a few times to a few thousand times the value of Keq of a 2 mol L-1 alkali liquid.