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"Ion exchange"
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Heavy metal decontamination by ion exchange polymers for water purification: counterintuitive cation removal by an anion exchange polymer
Ion exchange polymers were used for mercury and lead ions removal in water. The heavy metal ion concentration was analyzed by two independent methods: inductively coupled plasma–optical emission spectroscopy (ICP-OES) and gravimetry. The studied cation exchange polymer (CEP) was sulfonated poly(ether ether ketone) (SPEEK), and the anion exchange polymer (AEP) was poly(sulfone trimethylammonium) chloride (PSU-TMA). The removal capacity was connected with the ion exchange capacity (IEC) equal to 1.6 meq/g for both polymers. The concentration ranges were 0.15–0.006 mM for Hg
2+
and 10.8–1.0 mM for Pb
2+
. SPEEK achieved 100% removal efficiency for mercury and lead if the concentration was below the maximum sorption capacity (
Q
max
), which was about 210 mg/g for Pb
2+
with SPEEK. For PSU-TMA, the surprising removal efficiency of 100% for Hg
2+
, which seemed incompatible with ion exchange, was related to the formation of very stable complex anions that can be sorbed by an AEP. Langmuir adsorption theory was applied for the thermodynamic description of lead removal by SPEEK. A second-order law was effective to describe the kinetics of the process.
Journal Article
Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement
Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.
Journal Article
Estimating and leveraging protein diffusion on ion-exchange resin surfaces
Protein mobility at solid–liquid interfaces can affect the performance of applications such as bioseparations and biosensors by facilitating reorganization of adsorbed protein, accelerating molecular recognition, and informing the fundamentals of adsorption. In the case of ion-exchange chromatographic beads with small, tortuous pores, where the existence of surface diffusion is often not recognized, slow mass transfer can result in lower resin capacity utilization. We demonstrate that accounting for and exploiting protein surface diffusion can alleviate the mass-transfer limitations on multiple significant length scales. Although the surface diffusivity has previously been shown to correlate with ionic strength (IS) and binding affinity, we show that the dependence is solely on the binding affinity, irrespective of pH, IS, and resin ligand density. Different surface diffusivities give rise to different protein distributions within the resin, as characterized using confocal microscopy and small-angle neutron scattering (length scales of micrometer and nanometer, respectively). The binding dependence of surface diffusion inspired a protein-loading approach in which the binding affinity, and hence the surface diffusivity, is modulated by varying IS. Such gradient loading increased the protein uptake efficiency by up to 43%, corroborating the importance of protein surface diffusion in protein transport in ion-exchange chromatography.
Journal Article
Biochemical Characterization of Thermostable Carboxymethyl Cellulase and β-Glucosidase from Aspergillus fumigatus JCM 10253
Abstract Second-generation biofuel production has emerged as a prominent sustainable and alternative energy. The biochemical properties of cellulolytic enzymes are imperative for cellulosic biomass conversion into fermentable sugars. In the present study, thermostable CMCase and β-glucosidase were purified and characterized from Aspergillus fumigatus JCM 10253. The enzymes were purified through 80% ammonium sulfate precipitation, followed by dialysis and DEAE-cellulose ion-exchange chromatography. The molecular masses of the purified CMCase and β-glucosidase were estimated to be 125 kDa and 90 kDa, respectively. The CMCase and β-glucosidase demonstrated optimum activities at pH 6.0 and 5.0, respectively. Their respective maximum temperatures were 50 and 60 °C. The cellulase activities were stimulated by 10 mM concentration of Ca2+, Ni2+, Fe2+, Mg2+, Cu2+, Mn2+, Zn2+, and Pb2+ ions. The CMCase activity was enhanced by surfactant Triton X-100 but marginally influenced by most inhibitors. The β-glucosidase retained its activity in the presence of organic solvents (30%) isoamyl alcohol, heptane, toluene, and ethyl acetate, while CMCase was retained with acetone during a prolonged incubation of 168 h. The Km and Vmax values of the two cellulases were studied. The properties of high thermostability and good tolerance against organic solvents could signify its potential use in biofuel production and other value-added products.
Journal Article
Effect of the type of ion exchange membrane on performance, ion transport, and pH in biocatalyzed electrolysis of wastewater
Previous studies have shown that the application of cation exchange membranes (CEMs) in bioelectrochemical systems running on wastewater can cause operational problems. In this paper the effect of alternative types of ion exchange membrane is studied in biocatalyzed electrolysis cells. Four types of ion exchange membranes are used: (i) a CEM, (ii) an anion exchange membrane (AEM), (iii) a bipolar membrane (BPM), and (iv) a charge mosaic membrane (CMM). With respect to the electrochemical performance of the four biocatalyzed electrolysis configurations, the ion exchange membranes are rated in the order AEM > CEM > CMM > BPM. However, with respect to the transport numbers for protons and/or hydroxyl ions (tH/OH) and the ability to prevent pH increase in the cathode chamber, the ion exchange membranes are rated in the order BPM > AEM > CMM > CEM.
Journal Article
The Use of Weakly Basic Ion Exchange Resin Amberlite IRA-68 for the Chromatographic Separation of Rare Earth Elements
The possibility of applying the system: weakly basic Amberlite IRA-68 resin-nitrilotriacetic acid (NTA) solutions for the separation of rare earth elements (REE) by ion exchange chromatography was investigated. Preliminary research results revealed that the affinity of REE towards the ion exchanger is closely correlated with the stability of their negative complexes that they form with NTA. Three separate groups of lanthanides could be distinguished, i.e. light (La, Ce, Pr, Nd), medium (Y, Sm, Eu, Gd, Tb, Dy, Ho, Er) and heavy (Tm, Yb, Lu, Sc). Moreover, it seemed that within the first and third groups it was possible to individually separate elements from each other. Based on the experimentally obtained relationships, the theoretically assumed course of the ion exchange reaction of anionic REE complexes with NTA on the Amberlite IRA-68 resin was confirmed. The influence of the ion exchanger particle size, column size and composition of the mobile phase, i.e. pH, NTA and neutral salt (NaNO 3 ) concentration, on the chromatographic separation of REE was investigated. It has been shown that the proper selection of these parameters makes it possible not only to divide REE into the three groups mentioned above, but also to individually separate some elements, i.e. La, Ce, Pr, Nd, Tm, Yb, Lu and Sc.
Journal Article
Alkali and ion exchange co-modulation strategies to design magnetic–dielectric synergistic nano-absorbers for tailoring microwave absorption
Alkali and Co
2+
co-modulation has seldom been investigated as a prospective strategy to achieve high-efficient microwave absorbing (MA) materials. In this work, a new alkali and Co ion exchange co-modulation strategy was first reported, leading to broadband MA capacity through simultaneous manipulating multiple factors, such as composition, micromorphology, and heterogeneous interface. And enhancements in impedance matching and magnetic–dielectric loss were synergistically realized. Consequently, the optimized FeCo alloy@porous carbon (FPC) nanocomposite with the alkali regulation delivered an effective absorption bandwidth (EAB) of 6.72 GHz, making it the merely single FeCo-based metal-organic framework derived FPC absorber with a low filler content of 15 wt.%. Interestingly, the nanocomposites by ion exchange strategy realized the switchable “on/off” states on electromagnetic response. Furthermore, the radar cross-section (RCS) reduction value of the products reached 25.6 dB·m
2
under the incident angle of 0°. In brief, this work not only offers the special role of alkali and Co
2+
co-modulation in composition regulation, structure design, and MA capacity, but also provides a reliable strategy to develop smart nano-absorbers to cope with electromagnetic pollution issues.
Journal Article
Removal of cesium ions from aqueous solutions using various separation technologies
Cesium is the major fission product of uranium, which widely exists in radioactive wastewater. Radiocesium has potential adverse effects on human health and ecological environment. Different methods such as chemical precipitation, coagulation/co-precipitation, solvent extraction, membrane process, chemical reduction, and adsorption have been used to remove radioactive cesium from aqueous solution. However, the development of innovative technologies capable of selectively removing radioactive cesium is still imperative yet challenging. This review focused on cesium removal using various separation technologies, including chemical precipitation, solvent extraction, membrane separation, and adsorption. The key restraints for cesium removal, as well as the recent progress of these methods have also been discussed. Particular attention has been paid to the adsorption methods, which has been highlighted by introducing the latest advances in inorganic adsorbents (such as metal hexacyanoferrates, clay minerals, carbon-based-adsorbents, and ammonium molybdophosphate), organic adsorbents (such as ion exchange resin, metal–organic frameworks and supramolecular/indicator grafting adsorbents), and biosorbents (such as agroforestry wastes and microbial biomass). Adsorption-based methods are high efficient in separation of cesium ions from aqueous streams, and adsorption of cesium ions has been investigated intensively and even used in practical applications, there is still considerable scope for improvement in terms of adsorption capacity and selectivity.
Journal Article
Ion-exchange resins improve the analysis of metal nanoparticles in wastewater using single-particle inductively coupled plasma–mass spectrometry
Improved measurement and analysis technologies are needed for investigating nanoparticle generation characteristics in sewage treatment plants. Single-particle inductively coupled plasma–mass spectrometry (spICP-MS) can be used to analyze metal nanoparticle characteristics. However, during spICP-MS analysis of environmental samples, high concentrations of ionic materials obscure the signals of particulate materials by increasing background signals. This can increase the threshold value for separating background and particle signals and increase the background-equivalent diameter (BED). In this study, particle size distributions in influent and effluent collected from sewage treatment plants were investigated using an improved spICP-MS method combining spICP-MS with ion-exchange resin (IER) column pretreatment. The ion removal effect of the IER column was first examined using a synthetic mixture of Ag nanoparticles (AgNPs) and ions. The method was then applied to wastewater from six different sewage treatment plants using an optimal IER packing of 5 g. The ion removal efficiency for samples containing a proper mixture of AgNPs and Ag ions was 99.98%, and the BED significantly decreased from 73.0 ± 1.0 to 6.1 ± 0.3 nm. Particle size distributions measured in the treatment plant influent and effluent ranged from 28.5 nm (Co) to 220.3 nm (Mg) and from 26.8 nm (Co) to 291.8 nm (Mg), respectively. spICP-MS/IER enabled the detection of smaller particles by removing ions from the sample and significantly decreasing the size detection limit. The results of this study offer a reference for developing predictive models for removing metal nanoparticles during sewage/wastewater treatment.
Journal Article