Metal Cation Exchange Research Articles

Melanin in the Retinal Epithelium and Magnetic Sensing: A Review of Current Studies.

Coming in a variety of forms, melanin is one of the most abundant, stable, diverse, and evolutionarily ancient pigments found in living things in nature. These pigments often serve protective functions, typically well-adapted to their specific roles. One such protective function is metal chelation and cation exchange, which help regulate and buffer metal concentrations within cells. By binding to certain metals, melanin can acquire magnetic properties. Because of this, it may play a role in magnetic effects and possibly in the response of organisms to external magnetic fields and magnetic sensing. While there is melanin in plants, microbes, fungi, and invertebrates, certain types of melanin are specifically associated with the retina in vertebrates, including migrating bird and fish species. In this review, we examine studies focusing on the properties of melanin in these parts of the body and their possible association with magnetic sensing, and generally, magnetic sensing in the retina.

Metal cation exchange with zeolitic acid sites modulates hydrocarbon pool propagation during CO2 hydrogenation

Metal cation exchange with zeolitic acid sites modulates hydrocarbon pool propagation during CO2 hydrogenation

Separator modification with a high-entropy hydroxyphosphate, Co0.29Ni0.15Fe0.33Cu0.16Ca3.9(PO4)3(OH), for high-performance Li-S batteries

The shuttle effect of lithium polysulfides (LiPSs) significantly hinders the practical application of lithium-sulfur batteries (LSBs). Herein, a high-entropy hydroxyphosphate (Co0.29Ni0.15Fe0.33Cu0.16Ca3.9(PO4)3(OH), denoted as HE-CHP), was synthesized by metal cation exchange with calcium hydroxyphosphate (CHP) and then coated on polypropylene (PP) separators to suppress the shuttling of LiPSs. Density functional theory calculations indicated that the various introduced metal cations could effectively modulate the binding strength of soluble polysulfides and enhance the reaction kinetics of LiPSs conversion. As a result, LSBs using the HE-CHP@PP separator exhibited an excellent discharge capacity (1297 mAh g−1 under 0.2 C) and a slow capacity decay during long-term cycling (0.046 % per cycle at 2 C). At a sulfur loading of up to 6.5 mg cm−2, the LSB with HE-CHP@PP separator displayed a discharge capacity of 5.8 mAh cm−2. Notably, the CNT@S||Li Li-S pouch cell with HE-CHP modified separator delivered an initial energy density of 432 Wh kg−1.

Effects of active silicon amendment on Pb(II)/Cd(II) adsorption: Performance evaluation and mechanism

In this study, a high-Si (Si) adsorbent (APR@Sam) was prepared by acid leaching slag (APR) from lead-zinc (Pb-Zn) tailings based on high-temperature alkali melting technology. The synthesized Si-based materials were applied to aqueous solutions contaminated with Pb and cadmium (Cd) to investigate the crucial role of active Si in sequestering heavy metals. The adsorption capacities of APR@Sam and the Si-depleted material (APR@Sam-NSi) were studied under different pH and temperature conditions. The results showed that as the pH increased from 3 to 7, the adsorption capacity increased, the active Si content in the solution increased by 63 %, and the maximum pH of the solution after adsorption was 7.12. After the removal of active Si, the Pb (II) and Cd (II) adsorption capacities of APR@Sam decreased by 45 % and 11.96 %, respectively. OH- promoted the release of Si into the solution, enhancing the material's adsorption efficiency. The reaction mechanism is mainly attributed to surface complexation guided by Si-O and Si-O-Si bonds, metal cation exchange, and bidentate coordination. The results indicated that the Si component is critical for the removal of Pb (II) and Cd (II) by APR@Sam and provide valuable insights into resource recovery strategies from leaching residues.

Synthesis of Sulfur Vacancy-Bearing In2S3/CuInS2 Microflower Heterojunctions via a Template-Assisted Strategy and Cation-Exchange Reaction for Photocatalytic CO2 Reduction.

The synthesis of the accurate composition and morphological/structural design of multielement semiconductor materials is considered an effective strategy for obtaining high-performance hybrid photocatalysts. Herein, sulfur vacancy (Vs)-bearing In2S3/CuInS2 microflower heterojunctions (denoted Vs-In2S3/CuInS2) were formed in situ using In2S3 microsphere template-directed synthesis and a metal ion exchange-mediated growth strategy. Photocatalysts with flower-like microspheres can be obtained using hydrothermally synthesized In2S3 microspheres as a template, followed by Ostwald ripening growth during the metal cation exchange of Cu+ and In3+. The optimal heterostructured Vs-In2S3/CuInS2 microflowers exhibited CO and CH4 evolution rates of 80.3 and 11.8 μmol g-1 h-1, respectively, under visible-light irradiation; these values are approximately 4 and 6.8 times higher than those reported for pristine In2S3, respectively. The enhanced photocatalytic performance of the Vs-In2S3/CuInS2 catalysts could be attributed to the synergistic effects of the following factors: (i) the constructed heterojunctions accelerate charge-carrier separation; (ii) the flower-like microspheres exhibit highly uniform morphologies and compositions, which enhance electron transport and light harvesting; and (iii) the vs. may trap excited electrons and, thus, inhibit charge-carrier recombination. This study not only confirms the feasibility of the design of heterostructures on demand, but also presents a simple and efficient strategy to engineer metal sulfide photocatalysts with enhanced photocatalytic performance.

The influence of cation exchange on the possible mechanism of erionite toxicity: A synchrotron-based micro-X-ray fluorescence study on THP-1-derived macrophages exposed to erionite-Na

Fibrous erionite is the only zeolite classified as Group 1 carcinogen by the International Agency for Research on Cancer (IARC). Carcinogenesis induced by erionite is thought to involve several factors as biopersistence, the iron role and cation exchange processes. To better understand these mechanisms, a detailed investigation at the micro scale was performed, collecting elemental information on iron and cation release and their distribution in biological systems by synchrotron micro-X-ray fluorescence mapping (SR-micro-XRF) and synchrotron micro-X-ray absorption spectroscopy (SR-micro-XANES) at the TwinMic beamline (Elettra synchrotron) and at the ID21 beamline of the European Synchrotron Radiation Facility (ESRF). By microscopy and chemical mapping, highly detailed maps of the chemical and morphological interaction of biological systems with fibres could be produced. In detail, THP-1 cell line derived macrophages, used as in vitro model, were analysed during erionite-Na phagocytosis at different time intervals, after single dose exposure. For comparison, cellular fluorescent probes were also used to evaluate the intracellular free sodium and calcium concentrations. Synchrotron analyses visualised the spatial distribution of both fibre and mineral particle associated metals during the phagocytosis, describing the mechanism of internalisation of erionite-Na and its accessory mineral phases. The intracellular distribution of metals and other cations was mapped to evaluate metal release, speciation changes and/or cation exchange during phagocytosis. The fluorescent probes complemented microchemical data clarifying, and confirming, the cation distribution observed in the SR-micro-XRF maps. The significant cytoplasmic calcium decrease, and the concomitant sodium increase, after the fibre phagocytosis seemed due to activation of plasma membrane cations exchangers triggered by the internalisation while, surprisingly, the ion-exchange capacity of erionite-Na could play a minor role in the disruption of the two cations intracellular homeostasis. These results help to elucidate the role of cations in the toxicity of erionite-treated THP-1 macrophages and add knowledge to its carcinogenicity process.

Metal-free β zeolite used as an efficient NH3-SCR catalyst can achieve complete immunity to SO2: Unique design strategy of sulfur-resistant catalyst

Sulfur oxides present in flue gas can deactivate metal oxide catalysts or metal cation exchange zeolite catalysts used in NH3-SCR, as the deposition of (NH4)2SO4/NH4HSO4 and metal sulfate can obstruct and damage active sites, respectively. The physical poisoning of the (NH4)2SO4/NH4HSO4 deposition can be prevented by selecting an appropriate reaction temperature range (reversible), while chemical poisoning caused by the sulfation of active sites is challenging to avoid and can permanently deactivate the catalyst (irreversible). This research addresses the issue of irreversible catalyst deactivation resulting from sulfur poisoning by employing metal-free β zeolite without redox sites, which effectively prevents redox site sulfation at its source and shields the catalyst from physical poisoning by operating at moderate to high temperatures. This metal-free β zeolite with an appropriate pore structure exhibited exceptional deNOx activity, N2 selectivity, stability, and sulfur resistance at 300 °C. The NO oxidation experiment and DFT analysis demonstrated that the specific pore structure of β zeolite functioned as a sub-nano reactor, facilitating the oxidation of NO to NO2, thereby triggering the subsequent series catalytic reaction of “fast” SCR. Even in an atmosphere with a high concentration of 300 ppm SO2, the β zeolite catalyst maintained over 80 % NOx conversion after 130 h. The slight reduction in activity was attributable to the inhibitory influence of SO2 on the collision reaction between NO and O2; however, SO2 did not have any poisonous impact on the catalyst. The unique design strategy found in present work provides valuable insights for the sulfur resistance of metal-free zeolites used in NH3-SCR process, and provides a new idea for the design of completely sulfur-resistant catalysts.

Impact of Low-Temperature Water Exposure and Removal on Zeolite HY.

Aqueous-phase postsynthetic modifications of the industrially important Y-type zeolite are commonly used to change overall acid site concentrations, introduce stabilizing rare-earth cations, impart bifunctional character through metal cation exchange, and tailor the distribution of Brønsted and Lewis acid sites. Zeolite Y is known to undergo framework degradation in the presence of both vapor- and liquid-phase water at temperatures exceeding 100 °C, and rare-earth exchanged and stabilized HY catalysts are commonly used for fluidized catalytic cracking due to their increased hydrothermal resilience. Here, using detailed spectroscopy, crystallography, and flow-reactor experiments, we reveal unexpected decreases in Brønsted acid site (BAS) density for zeolite HY following exposure even to room-temperature liquid water. These data indicate that aqueous-phase ion-exchange procedures commonly used to modify zeolite Y are impacted by the liquid water and its removal, even when fractional heating rates and inert conditions much less severe than standard practice are used for catalyst dehydration. X-ray diffraction, thermogravimetric, and spectroscopic analyses reveal that the majority of framework degradation occurs during the removal of a strongly bound water fraction in HY, which does not form when NH4Y is immersed in liquid water and which leads to reduced acidity in HY even when dehydration conditions much milder than those typically practiced are employed. Na+-exchanged HY prepared via room-temperature aqueous dissolution demonstrates that Brønsted acid sites are lost in excess of the theoretical maximum that is possible from sodium titration. The structural impact of low-temperature aqueous-phase ion-exchange methods complicates the interpretation of subsequent data and likely explains the wide variation in reported acid site concentrations and catalytic activity of HY zeolites with high-Al content.

Health management of Cd-contaminated soil using Ca-Al layered double hydroxide: Response of different vegetables

The green development of stabilizers is an important part of soil health management. Studying the impact of stabilizers on soil cadmium (Cd) adsorption is critical for sustainable agriculture. Calcium-aluminum layered double hydroxides (Ca-Al-LDH) are widely used to detoxify contaminated water and soil. Nevertheless, little is known about the efficacy of Ca-Al-LDH at modulating the heavy metal bioavailability of various crops. Incubation experiments, greenhouse and 3-year field trials were conducted to investigate the effects of Ca-Al-LDH on Cd, lead (Pb), and zinc (Zn) bioavailability in different soil-crop systems. The main soil type was hydragric anthrosols. The results showed that Ca-Al-LDH remediate heavy metal pollution through surface complexation, surface precipitation, and metal cation exchange with alkali. In incubation experiments, the application of 3 % Ca-Al-LDH for 7–42 d significantly decreased soil CaCl2-extractable Cd, Zn, and Pb by 94.38–96.37 %, 77.90–94.22 %, and 7.23–56.79 %, respectively, relative to the control (p < 0.05). It significantly lowered the exchangeable Cd fraction while increasing the carbonate-bound and the iron-manganese oxide-bound Cd fractions in the incubation and pot experiments. It significantly reduced the Cd content in bioaccumulator crops such as spinach, celery, amaranth, Shanghai bok choy, and lettuce-an. The Cd content in low-Cd-accumulation vegetables, such as bok choy, swamp cabbage, and lettuce-ra, increased following Ca-Al-LDH treatment to soil. Ca-Al-LDH activity remained stable for 3 years. The present study demonstrated that Ca-Al-LDH is a highly effective, sustainable, and versatile amendment for planting high-Cd vegetable cultivars. However, it should be avoided in areas with low Cd contamination or cautiously used when growing vegetables with low Cd-accumulation. It provides a theoretical and practical foundation for evaluating stabilizers and soil health management to remediate Cd-contaminated agricultural soils.

Performance and deactivation mechanism of a carbon-based solid acid catalyst in the esterification of soybean saponin acid oil

In this study, a bamboo charcoal-based solid acid catalyst (BC) was generated by one-step carbonization and sulfonation at 150 °C for 4 h in the presence of sulfuric acid. The BC was characterized by Fourier transform infrared spectrometry, elemental analysis, X-ray powder diffraction, and Brunauer-Emmet-Teller specific surface area analysis. The BC had a specific surface area of 4.54 m2/g, pore volume of 0.0142 cm3/g, and acid density of 1.476 mmol/g. Subsequently, the catalytic activity and deactivation mechanism of the BC in the esterification of soybean saponin acid oil (SAO) and methanol were investigated. The results showed that the conversion yield of esterification reached 98.28% under optimal reaction conditions (i.e., catalyst addition of 10 wt%, methanol/oil molar ratio of 10:1, temperature of 65 °C, and time of 8 h). The conversion yield decreased as reuse batches increased, and was below 80% after three batches. The loss of sulfonic acid groups from the BC occurred mainly in the first esterification batch, caused by residual sulfuric acid leaching and chemical derivatization of sulfonic acid groups. In the second to fourth esterification batches, chemical derivatization was the main reason for deactivation, where the generation of sulfonate esters and exchange of metal cations with hydrogen ions accounted for more than 75% of the chemical derivatization loss. Therefore, without impurity purification of SAO, reducing the amount of sulfonate ester generated on the catalyst was found to be essential for increasing the reuse performance of the BC and reducing the cost of biodiesel production.

Dibasic Magnesium Hypochlorite as an Oxidant to Tune Pasting Properties of Potato Starch in One Step

Modified starches are used widely in the food industry but often have a low nutritional value, lacking minerals vital for the human body, such as magnesium. Magnesium addition to native starches has been shown to result in changes in pasting properties. However, little work has been done on the addition of magnesium and other divalent cations to highly oxidised starches. In this work, we used dibasic magnesium hypochlorite (DMH) to oxidise potato starch to an industrially relevant degree of oxidation while at the same time introducing magnesium into the starch structure. We found that magnesium incorporation changes the pasting properties of starch and increases the gelatinisation temperature significantly, possibly due to an ionic cross-linking effect. These properties resemble the properties found for heat-moisture-treated potato starches. This change in properties was found to be reversible by performing a straightforward exchange of metal cations, either from sodium to magnesium or from magnesium to sodium. We show in this work the potential of the addition of divalent cations to highly oxidised starches in modifying the rheological and pasting properties of these starches and at the same time adding possible health benefits to modified starches by introducing magnesium.

Screening of Alkali Metal-Exchanged Zeolites for Nitrogen/Methane Separation.

Methane (CH4) is the primary component of natural gas and must be purified to a certain level before it can be used as pipeline gas or liquified natural gas (LNG). In particular, nitrogen (N2), a common contaminant in natural gas needs to be rejected to increase the heating value of the gas and meet the LNG product specifications. The development of energy-efficient N2 removal technologies is hampered by N2's inertness and its resemblance to CH4 in terms of kinetic size and polarizability. N2-selective materials are so rare. Here, for the first time, we screened 1425 alkali metal cation exchange zeolites to identify the candidates with the best potential for the separation of N2 from CH4. We discovered a few extraordinary zeolite frameworks capable of achieving equilibrium selectivity toward N2. Particularly, Li+-RRO-3 zeolite with a specific two-dimensional structure demonstrated a selective N2 adsorption capacity of 2.94 mmol/g at 283 K and 1 bar, outperforming the capacity of all known zeolites. Through an ab initio density functional theory study, we found that the five-membered ring of the RRO framework is the most stable cationic site for Li+, and this Li+ can interact with multiple N2 molecules but only one CH4, revealing the mechanism for the high capacity and selectivity of N2. This work suggests promising adsorbents to enable N2 rejection from CH4 in the gas industry without going for energy-intensive cryogenic distillations.

Construction of ZnS/Sb2S3 Heterojunction as an Ion‐Transport Booster toward High‐Performance Sodium Storage

AbstractMetal sulfides have shown great promise for sodium‐ion batteries due to their excellent redox reversibility and relatively high capacity. However, metal sulfides generally suffer from sluggish charge transport and serious volume change during the charge–discharge process. Herein, potato chip‐like nitrogen‐doped carbon‐coated ZnS/Sb2S3 heterojunction (ZnS/Sb2S3@NC) is precisely synthesized through a sulfurization reaction, and a subsequent metal cation exchange process between Zn2+ and Sb3+. The theoretical calculations and experimental studies reveal the boosted charge transfer in ZnS/Sb2S3@NC composites. Therefore, the ZnS/Sb2S3@NC electrode exhibits excellent cycling stability (a high reversible capacity of 511.4 mAh g‐1 after 450 cycles) and superior rate performance (400.4 mAh g‐1 at 10 A g‐1). In addition, ZnS/Sb2S3@NC is based on a conversion‐alloy reaction mechanism to store Na+, which is disclosed by the X‐ray diffraction and high resolution transmission electron microscopy analysis. This effective synthesis method can provide a reference for the design of other high‐performance electrode materials for sodium‐ion batteries.

Inside Back Cover: Directing the Morphology, Packing, and Properties of Chiral Metal–Organic Frameworks by Cation Exchange (Angew. Chem. Int. Ed. 34/2022)

Predicting crystal morphologies is challenging because of the many factors influencing their growth. Dan Oron, Michal Lahav, Milko E. van der Boom, and co-workers demonstrate in their Research Article (e202205238) how metal cation exchange in metal–organic frameworks (MOFs) results in a series of chiral crystals having a similar morphology, packing, and a rare space group (P622). The fact that the crystals maintain their morphology facilitates a quantitative comparison of their optical and magnetic properties. The metal cation exchange is likely to be mediated by differently sized nanochannels.

Structural Alteration, Hydration Stability, Heavy Metal Removal Efficiency, and Montmorillonite Porosity Fate by Coupling the Soil Solution pH and a Thermal Gradient

Clay minerals are considered as a promising material in the context of geological barrier for the confinement of radioactive and industrial waste. Understanding the usefulness of the smectite mineral, in this approach, remains insufficient. The deep investigation about structural response/changes, hydrate stability, cation exchange process, permeability, and heavy metal/radionuclide adsorption/removal efficiency under external constraints is needed. To explore the structural alteration, the hydration stability, and the evolution of montmorillonite porosity under a first order of external applied constraints coupling, a reference Na-rich montmorillonite specimen is used as a starting material, and three exchangeable heavy metal cations (Ba2+, Cu2+, and Co2+) have been selected. The applied constraint coupling is realized at laboratory scale and assured by simultaneously varying of the soil solution pH and the thermal gradient. The evaluation of the mineral fraction response is established by correlation of quantitative XRD analysis results, thermal analysis, and porosity measurements. The quantitative XRD analysis allows rebuilding of the theoretical model describing the interlamellar space (IS) configurations/damages, structural heterogeneity degrees, and hydrous stability. Obtained results show a dominant interstratified hydration character, for all studied complexes, attributed to a new IS organization versus the applied constraint strength. Furthermore, all samples exhibit a heterogeneous hydration behavior traduced by the coexistence of different layers of type population within the crystallite. Additionally, the theoretical XRD profile decomposition allowed us to prove link between the domination of the segregated stacking layers mode against the constraint strength. Thermal analysis allowed us to develop theoretical models describing the decrease of the water molecule amounts as a function of the increase in temperature and soil solution pH. Moreover, a specific hydration footprint response and an interstratification mapping are assigned for each corresponding stress degrees. The evolution of montmorillonite porosity is determined by adsorption measurement, based on Brunauer, Emmett, and Teller (BET) and Barrett-Joyner-Halenda (BJH) pore size distribution analyses which confirms for all samples, the exfoliation process, and the mesopore diameter rise by increasing the constraint intensity.

Revealing the Dynamics and Roles of Iron Incorporation in Nickel Hydroxide Water Oxidation Catalysts.

The surface of an electrocatalyst undergoes dynamic chemical and structural transformations under electrochemical operating conditions. There is a dynamic exchange of metal cations between the electrocatalyst and electrolyte. Understanding how iron in the electrolyte gets incorporated in the nickel hydroxide electrocatalyst is critical for pinpointing the roles of Fe during water oxidation. Here, we report that iron incorporation and oxygen evolution reaction (OER) are highly coupled, especially at high working potentials. The iron incorporation rate is much higher at OER potentials than that at the OER dormant state (low potentials). At OER potentials, iron incorporation favors electrochemically more reactive edge sites, as visualized by synchrotron X-ray fluorescence microscopy. Using X-ray absorption spectroscopy and density functional theory calculations, we show that Fe incorporation can suppress the oxidation of Ni and enhance the Ni reducibility, leading to improved OER catalytic activity. Our findings provide a holistic approach to understanding and tailoring Fe incorporation dynamics across the electrocatalyst-electrolyte interface, thus controlling catalytic processes.

Selective Adsorption of Potassium in Seawater by CoHCF Thin Film Electrode and Its Electrochemical Desorption/Regeneration.

Cobalt Hexacyanoferrate (CoHCF) was tested for the selective uptake of K from seawater and the electrochemical method was adopted for the desorption and regeneration of the material. Powder form CoHCF could adsorb about 6.5 mmol/g of K from the seawater. For the ease of the electrochemical desorption and regeneration, CoHCF thin film was coated onto the Indium Tin Oxide (ITO) glass to obtain a CoHCF electrode. K adsorption kinetics on CoHCF thin film was found to be well fitted with the intraparticle diffusion model, which was a two-step process. Five consecutive adsorption-desorption-regeneration cycles were carried out to know the gradual decrease in the adsorption capacity owing to changes in the redox states of two metals, Co and Fe, in the material. Fourier Transform Infrared Spectroscopy (FT-IR) and Ultraviolet-Visible (UV-Vis) measurement results corresponded to the color change of CoHCF thin film, indicating the valence change of transition metals and the exchange of alkali metal cations happened on the CoHCF at different operation stages. In order to elucidate the reaction mechanism, composition of the material was analysis in the following steps: adsorption, desorption, and regeneration. It was proved that the system based on CoHCF thin film modified electrode had the potential of recovering potassium from seawater.

Pyrolysis characteristics of metal ion-exchanged Shendong coal and its char gasification performance

The effects of ion-exchanged metal cations (Na+, K+, Ca2+, Mg2+, Co2+ and Ni2+) on the pyrolysis reactivity of Shendong demineralized coal (SD-coal) and the gasification performance of pyrolysis chars were investigated by Py-GC/MS, TG-FTIR, FBR (the fixed-bed reactor), FTIR, SEM, XRD and CO2 reactivity. The results show that the order of pyrolysis weight loss rates is SD-coal-Ni > SD-coal-Co > SD-coal-Mg > SD-coal-Na > SD-coal-Ca > SD-coal-K. The char yields decrease and the pyrolysis gas yields increase during the pyrolysis of metal ion-exchanged coals compared with those of SD-coal. Ion exchange of Co2+ and Ni2+ increases the coal tar yields, especially the yield of coal tar obtained from SD-coal-Co pyrolysis increases to 9.45 %. Ion exchange of alkali and alkaline earth metal cations is generally conducive to the formation of naphthalene and its derivatives in coal tar. The catalytic effect of these metal cations on coal pyrolysis is Na+ > K+ > Ni2+ > Ca2+ > Mg2+ > Co2+. The values of Lc and Nave in chars derived from metal ion-exchanged coal pyrolysis are reduced compared with SD-coal char. The effect of ion-exchanged metal cations on the gasification reactivity of chars is K+ > Na+ > Mg2+ > Co2+ > Ni2+. And on this basis, the mechanisms of metal ion-exchanged coal pyrolysis and char gasification are concluded.

Controlling factors on nickel uptake by plants growing on Ni-laterites: A case study in biogeochemical exploration from the Mazayejan area, SW Iran

Nickel bearing soils derived from serpentinized ultramafic rocks are widely exposed as two parallel zones in Bavanat region along the Sedimentary Zagros Orogenic (SZO) and Metamorphic Sanandaj-Sirjan (MSS) belts. These laterites in the Mazayejan area of the Northern zone are divided into two groups; the in situ soils found mainly in the east, and the transported soils which are common in the west of the study area. The maximum Ni concentration of the studied soils is 1787 μg g−1. The main vegetation types of the area include open shrub lands and semi-desert steppes. Many soil characteristics in the study area are quite variable, such as Mg/Ca ratio, exchangeable metal fraction, extraction efficiency (EF), pH, organic content (OM), texture, and cation exchange capacity (CEC) as well as seasonal variation of Ni availability and metal transfer to plants. This study indicated that low Mg/Ca ratio (0.1–2.3 μg g−1), high carbonate content (up to 42.8 wt%) and very low exchangeable Ni fraction (0.01–0.34 μg g−1) result in low uptake of nickel by plants. Low EF, but high pH and OM result in Ni fixation in the soils, and consequently low Ni transfer factor to plants. Clay textured soils with high CEC (10.5 wt%) are characterized by the lowest transfer coefficient of Ni from soil to plant, due to the stronger adsorption of Ni in the soils. Ni concentration in living tissues change with the season, the leaves of the same plants investigated in autumn contain more Ni than in spring. As a result, plant sampling in autumn should be preferred for nickel exploration when using biogeochemical and other methods such as Ni phytoextraction, by selected plants.

ELECTRICAL CONDUCTIVITY AND SORPTION PROPERTIES OF THE COMPOSITES BASED ON ION EXCHANGE POLYMERS

The review is devoted to the conditions for the creation and functional properties of organіс-inorganic ion-exchange materials, which in the form of sorbents and membranes can be applied in the processes of ion separation, as well as the purification of water and combined solutions of technological origin. The structure of air dry and hydrated organic ion-exchange polymers, conditions for the creation of organiс-inorganic ion-exchange materials, as well as their components, interaction of components and the corresponding classification are considered. Dry ion-exchange materials contain heterogeneities of different sizes, which are formed during the synthesis of polymer, with the smallest heterogeneities represent clusters, and the larger ones are related to crystallinity. The structure of hydrated ion- exchange materials adequately describes the cluster channel model of Hsu and Girke. The number of charged particles transferred corresponds to the contribution of clusters and channels (volume fractions) to total porosity. The size of the clusters and channels can be determined by the method of small-angle X-ray scattering. The complex porous structure of ion-exchange polymers makes it possible to form inorganic particles in the one’s pores. The introduction of inorganic ion exchangers into the polymer leads to the appearance of additional osmotically active centers (fixed ions and antimony modifiers) that influence the compression pressure of composites. Regarding the functional properties of organiс-inorganic materials, data on the influence of the form and size of the nanoparticles of the inorganic component on the electrical conductivity of composites, examples of the use of organiс-inorganic sorbents in ion-exchange columns, and also effective diffusion coefficients corresponding to the exchange of two-charge metal cations (Zn2+, Pb2+, Cu2+, Ca2+, Ni2+) on H+ organic-inorganic sorbents, for the most part, organic resin- Dowex HCR-S with incorporated particles of zirconium hydrophosphate, are presented. The prospect of application of such materials in ion-exchange and membrane processes of separation and purification of aqueous solutions, as well as in the processes of efficient selective extraction of target ions, is shown.