Selectivity of Low- and High-Silica Clinoptilolites with Respect to Alkali and Alkaline–Earth Metal Cations

The ion-exchange equilibria involving K⁺ and Ca²⁺ cations were studied using the Na-forms of nine different clinoptilolite samples. The high-silica (in the native state, sodium–potassium form) clinoptilolites were shown to have the increased selectivity with respect to K⁺ ions, whereas the low-silica (in the native state, calcium form) clinoptilolites to Ca²⁺ ions. The phenomenon found is interpreted as a structural memory of clinoptilolites with respect to alkali and alkaline-earth metal ions which had been present during zeolite crystallization under natural conditions.     

Kinetics of metal ion sorption on clinoptilolite

From an investigation into the sorption kinetics of Na⁺, K⁺, and Sr²⁺ ions from standard solutions on finely dispersed clinoptilolite incorporated in a highly permeable inert polyacrylamide gel we have determined the characteristic kinetic size of clinoptilolite and the diffusion coefficients for Na⁺, K⁺, and Sr²⁺ in the clinoptilolite microcrystallites and transport pores. Diagrams have been constructed to enable a valid selection of kinetic models for sorption of the ions from any solutions on clinoptilolite.Institute of Chemistry, Far Eastern Branch of the Russian Academy of Sciences, 690022 Vladivostok. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 273–277, February, 1992.     

Experimental and Modeling Study of Ion Exchange Between Aqueous Solutions and the Zeolite Mineral Clinoptilolite

Ion-exchange experiments were conducted at 25°C between the zeolite mineral clinoptilolite and aqueous solutions of Na⁺/Sr²⁺ (0.005, 0.05, and 0.5 N), K⁺/Sr²⁺ (0.05N), and K⁺/Ca²⁺ (0.05 N). The isotherm data were used to derive equilibrium constants and Gibbs energies for the ion-exchange reactions and Margules parameters for the zeolite solid solution. The Margules model, in combination with the Pitzer equations for activity coefficients of aqueous ions, was used to predict isotherms for ion exchange involving clinoptilolite and aqueous solutions of Na⁺/Sr²⁺, K⁺/Sr²⁺, and K⁺/Ca²⁺ over wide ranges of solution composition and concentration. The ion-exchange isotherms are strongly dependent on the total solution concentration. For Na⁺/Sr²⁺ ion exchange, isotherm values at 0.005 and 0.5 N predicted using thermodynamic parameters derived from the 0.05 N data showed excellent agreement with measured values. The model was also applied to calculations of aqueous composition based on the chemistry of coexisting zeolite phases. The results show that the aqueous composition can be predicted well from the composition of the zeolite, at least for systems that involved binary (two-cation) exchange. Because the thermodynamic model can be easily extended to ternary and more complicated mixtures, it may be useful for modeling ion-exchange equilibria in multicomponent systems.     

Removal of toxic hexavalent chromium by polyaniline modified clinoptilolite nanoparticles

In this work clinoptilolite nanoparticles were modified with conducting polyaniline by the polymerization of anilinium cations in and out side of the clinoptilolite channels and a nanocomposite of polyaniline/clinoptilolite was obtained. Cations (Na⁺, K⁺, Mg²⁺, Ca²⁺...) in the natural clinoptilolite structure were exchanged with anilinium cations by the treatment of clinoptilolite nanoparticles in an acidic solution of aniline monomer. The cation exchange process was confirmed by elemental analysis of nitrogen and carbon atoms of anilinium cations in clinoptilolite dry powder after treatment. The polyaniline/clinoptilolite nanocomposite was obtained by the oxidative polymerization of anilinium cations within the clinoptilolite structure. The polyaniline/clinoptilolite nanocomposite was characterized utilizing FT-IR and X-ray diffraction measurements and was used for the removal of Cr(VI) from aqueous solutions in chromate anion form as an important water pollutant. The effect of a number of parameters such as initial concentration of Cr(VI), amount of nanocomposite and contact time on the removal efficiency of Cr(VI) by polyaniline/clinoptilolite nanocomposite were determined and optimized. It was found that after 5 min of exposure of nanocomposite powder with Cr(VI) solutions in the concentration range of 25 to 100 ppm, more than 98% of chromate anions can be removed and the Cr(VI) removal capacity per one gram of nanocomposite is about 0.3 mmol of Cr(VI).     

New ON-OFF type Ca-selective fluoroionophore having boron-dipyrromethene fluorophores

A new fluorogenic ionophore has been prepared by conjugating calix[4]-crown-5 ether with boron-dipyrromethene fluorophore. The ionophore exhibited a pronounced selective ON-OFF type response toward Ca²⁺ ions over other physiologically important metal ions of Na⁺, K⁺, and Mg²⁺. The interaction with Ca²⁺ ions resulted in very efficient quenching of fluorescence at 507 nm excited by relatively long wavelength irradiation at 480 nm. The selectivity ratios toward Ca²⁺ ions over other tested physiologically important metal ions were larger than 180 in aqueous 95% MeOH solution.     

A Novel Highly Sensitive Zeolite-Based Conductometric Microsensor for Ammonium Determination

Natural zeolite clinoptilolite was successfully applied in the sensing technology for electrochemical detection of ammonium. A novel ammonium-selective sensor was developed based on clinoptilolite, possessing intrinsic ammonium-sieving and ion exchange capacity. The sensor design allowed measurements in both differential mode and requiring no classical reference electrode. The sensor selectivity towards Na⁺, K⁺, Ca²⁺, Mg²⁺, and Al³⁺ was studied. The limit of detection and the dynamic range of the ammonium-selective conductometric microsensor, determined in the phosphate buffer solution, were 1.0 × 10^?8 M and 0–8 mM, respectively. The ammonium sensor presented high operational and storage stability.     

Crystallization of single phase (K,Na)-clinoptilolite

A single phase (K, Na)-clinoptilolite was hydrothermally crystallized without seed crystals from a reactant mixture of (K, Na)-aluminosilicate gel slurry through homogeneous mixing at 150 °C for 144 h. Compositions of the reactant mixtures and reaction temperatures to obtain the clinoptilolite were restricted within narrow limits in the case of syntheses without seed crystals, while the compositions and temperatures were expanded into wide ranges in the case of syntheses with 1 wt.-% of seed crystals. Coexistence of Na⁺- and K⁺-ions with appropriate ratios in the reactant mixture, and homogeneous mixing of this mixture, were indispensable for the crystallization of clinoptilolite. The crystals obtained were characterized by X-ray diffraction, chemical analysis, thermal analysis (DTA/TG), electron microscopy, and electron diffraction. The crystals were assigned as clinoptilolite, not heulandite, based on their chemical compositions and thermal stability.     

The standard thermodynamic characteristics of resolvation of the K<Superscript>+</Superscript>, Ca<Superscript>2+</Superscript>, Cd<Superscript>2+</Superscript>, and Br<Superscript>−</Superscript> ions in water-acetone mixtures

The standard real and chemical thermodynamic characteristics of transfer of the K⁺, Ca²⁺, Cd²⁺, and Br^? ions from water into water-acetone solvents of various compositions were analyzed to study the rules governing the solvation of these ions in mixed solvents and its special features. All calculations were performed within the framework of the vertical jet method at 298.15 K. The energy of resolvation as a function of ion charges and crystallographic radii was found to increase in the series K⁺ < Ca²⁺ < Cd²⁺ < Al³⁺     

Microwave absorption and structure of zeolite water in heulandite and clinoptilolite by <Superscript>1</Superscript>H NMR

The structure of zeolite water in single crystals of natural zeolites represented by clinoptilolite Na₂K₂Ca[Al₆Si₃₀O₇₂]·22H₂O and heulandite Ca₃Mg[Al₈Si₂₈O₇₂]·24H₂O is studied with ¹H NMR. Below 170 K the distribution of H₂O over the structural positions is shown to be fixed but different for the two minerals. Above 290 K translational and orientational diffusion of zeolite water molecules is observed and the structure of water is almost identical in both heulandite and clinoptilolite. Diffusion mechanism may be associated with the interaction between librational modes of H₂O and high-frequency oscillations of aluminosilicate framework. The microwave absorption is shown to be caused in certain conditions by this type of interaction.     

Investigation of clinoptilolite rich natural zeolites from Turkey: a combined XRF,TG/DTG,DTA and DSC study

Turkey clinoptilolite-rich tuffs from Gördes and Bigadiç regions of western of Anatolia and their exchanged forms (K⁺, Na⁺, Mg²⁺ and Ca²⁺) were characterized by TG/DTG-DTA, DSC and XRF methods and the surface areas were also determined for both tuffs. TG-DTG and DTA curves of all clinoptilolite samples were measured in the temperature range 30–1000 °C. All clinoptilolite samples had major, rapid mass losses between 30 and 200 °C, with slower and less significant mass losses at higher temperatures. The mass loss of the Natural-G is 9.54% while that of the Natural-B sample is 10.50%. Water content increases in the order of K < Na < Ca < Mg for Bigadiç clinoptilolite samples and in the following sequence K < Na < Mg < Ca for Gördes clinoptilolite samples. One mass loss step for all clinoptilolite samples was observed using differential scanning calorimeter (DSC) in the range of 30–550 °C.     

Chromium uptake from tricomponent solution in zeolite fixed bed

Removal of Cr³⁺,Ca²⁺,Mg²⁺ and K⁺ in equilibrium isotherms and in tricomponent solutions (Cr/Ca/K, Cr/Ca/Mg and Cr/Mg/K) were investigated in NaX and NaY packed beds at 30^∘C. The equilibrium selectivity was obtained as Cr⁺³ > Mg²⁺ > Ca²⁺≈K⁺ for zeolite NaY and Ca^{2 +}≫Cr^{3 +} > Mg^{2 +}≈K⁺ for zeolite NaX. The breakthrough curves showed sequential ion exchange where chromium ions are able to replace the competing cations. Some mass transfer parameters, such as length of unused bed and overall mass transfer coefficient, were investigated. Chromium retention was also investigated through a mass balance. Based on the breakthrough results, it was concluded that chromium-uptake mechanism was hardly influenced by the competition and interaction between the entering ions. NaY showed a higher affinity towards Cr³⁺ for both equilibrium and dynamic systems and its sites were more efficiently used in the ion exchange process. Chromium was less retained in NaX due to the high selectivity towards calcium ions.     

Thermal Study of Surfactant and Anion Adsorption on Clinoptilolite

The mechanism of surfactant adsorption on various forms of clinoptilolite was studied by DTA, TG and DTG analyses. The examined series of surfactant modified clinoptilolite (SMC) was previously prepared by the adsorption of the surface-active oleylamine on Ca²⁺, Na⁺, H⁺ and mechanochemically treated forms of clinoptilolite. The oleylamine was most strongly adsorbed on H⁺-forms of clinoptilolite due to the largest number and strength of adsorption sites. The surfactant adsorption mechanism on H⁺-form of clinoptilolite was studied by recording the series of variously surfactant-loaded samples. The products of sulphate, dihydrogenphosphate and hydrogenchromate adsorption on SMC were analyzed by DTA, TG and DTG in order to investigate the mechanism of anion adsorption.This revised version was published online in November 2005 with corrections to the Cover Date.     

Novel Ca-selective merocyanine-type chromoionophore derived from calix[4]arene-diamide

The synthesis and calcium-selective chromogenic ion binding properties of benzothiazolium derivative of calix[4]arene are described. The merocyanine-type ionophore derived from calix[4]arene-diamide showed selective chromogenic properties toward Ca²⁺ ions in aqueous methanol. The compound showed significant Ca²⁺ ion dependent changes in UV-vis spectral properties in the presence of other physiologically important metal ions (Na⁺, K⁺, and Mg²⁺). The pH sensitive chromogenic behavior also suggests that the compound can be used as a sensitive pH indicator around pH 6.5.     

Enhanced Separation of Potassium Ions by Spontaneous K+‐Induced Self‐Assembly of a Novel Metal–Organic Framework and Excess Specific Cation–π Interactions

A novel metal–organic framework (MOF) was fabricated by spontaneous K⁺‐induced supramolecular self‐assembly with the embedded tripodal ligand units. When the 3D ligand was loaded onto Fe₃O₄@mSiO₂ core‐shell nanoparticles, it could effectively separate K⁺ ions from a mixture of Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions through nanoparticle‐assisted MOF crystallization into a Fe₃O₄@mSiO₂@MOF hybrid material. Excess potassium ions could be extracted because of the specific cation–π interaction between K⁺ and the aromatic cavity of the MOF, leading to enhanced separation efficiency and suggesting a new application for MOFs.     

New tetrapyrazolic macrocycle. Synthesis and preliminary use in metal ion extraction

A new macrocycle containing two bipyrazolic units, with a side-arm bearing an attached donor-group is reported. The complexing properties of this compound towards heavy metal ions (Hg²⁺, Cd²⁺, Pb²⁺) and alkaline metal ions (Ca²⁺, Cs⁺, K⁺, Na⁺, Li⁺) was studied by a liquid-liquid extraction process and the extracted cation percentage was determined by atomic absorption measurements and UV spectroscopy.     

Influence of the exchangeable cations on SO<Subscript>2</Subscript> adsorption capacities of clinoptilolite-rich natural zeolite

The sulfur dioxide adsorption on clinoptilolite-rich tuff from Bigadiç region of Western of Turkey and its modified forms (Na⁺, K⁺, Ca²⁺ and Mg²⁺) have been studied at 273 K and 293 K up to 100 kPa. The structural properties of clinoptilolites were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). The quantitative XRD analysis demonstrated that the Natural-B sample is mainly constituted by clinoptilolite (80–85%) with minor contents of quartz (7–8%), feldspar (5–6%) and mica-illit (4–5%). It was found out that the adsorption capacity and the affinity of SO₂ with clinoptilolite samples depended mainly on the type of exchanged cations and decreased as Na-B > K-B > Mg-B > Natural-B > Ca-B for both temperature. These results show that clinoptilolite-rich zeolites are considered potentially good adsorbents for SO₂ removal.     

Synthesis,crystal structures and competitive complexation property of a family of calix-crown hybrid molecules and their application in extraction of potassium from bittern

A family of calix-crown hybrid molecules containing calix[4]arene and crown-5/6, either at lower rim or at both upper and lower rims, have been synthesised, characterised and their competitive complexation property towards alkali and alkaline earth metal ions in aqueous media have been investigated. The competitive metal ion extraction study, carried out with equimolar mixture of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺ and Sr²⁺ in aqueous media, revealed that the amount of K⁺ extracted is remarkably high compared to other metal ions. Complexation with K⁺ has been investigated by ¹H NMR, association constants and thermodynamic parameters have been determined by isothermal calorimetric study. The molecular structures of one of the receptors and two of the K⁺ complexes have been established by single crystal X-ray study. One of the receptors formed bimetallic complex and it exhibited interesting polymeric network structure with bridged picrate anion. These receptors have been applied for extraction of metal ions from bittern.     

Facilitated Transfer of Alkali and Alkaline‐Earth Metal Ions by a Calix[4]arene Derivative Across Water/1,2‐Dichloroethane Microinterface: Amperometric Detection of Ca2+

The host–guest complexation reactions between 5,11,17,23‐tetra‐tert‐butyl‐25,27‐diethoxycarbonylmethoxy‐26,28‐dimethoxy calix[4]arene (BDDC4) and alkali and alkaline‐earth metal ions were investigated by facilitated ion transfer processes across water/1,2‐dichloroethane microinterface by using steady‐state cyclic voltammetry and differential pulse voltammetry. The obtained facilitated transfers for Li⁺, Na⁺, K⁺, Rb⁺ and Ca²⁺ were evaluated under the different experimental conditions, at the excess concentrations of metal ions with respect to BDDC4 and vice versa. The association constants having 1 : 1 stoichiometry for Li⁺, Na⁺, K⁺ and Rb⁺ in 1,2‐DCE were determined. Also, we demonstrated that BDDC4 can play an important role for the development of highly selective chemical sensor for Ca²⁺ among alkaline‐metal ions in the concentration range of 0.1–1.0 mM in aqueous solution.     

New ICT probes: synthesis and photophysical studies of N-phenylaza-15-crown-5 aryl/heteroaryl oxadiazoles under acidic condition and in the presence of selected metal ions

Molecular probes 6 and 7, incorporating N-phenylaza-15-crown-5 and aryl/heteroaryl oxadiazole have been designed to function as the new intramolecular charge transfer (ICT) probes. Photophysical properties have been studied under acidic condition as well as in the presence of selected metal ions, Ca²⁺, Ba²⁺, Mg²⁺, Na⁺, K⁺, and Li⁺. The changes in the ICT character of the probes, following the addition of trifluoroacetic acid, were interpreted in terms of site and degree of protonations. Based on the cation affinity, the ICT bands in both UV-vis and emission spectra experienced varying degrees of blue shifts due to removal of the aza-crown ether nitrogen from conjugation. The cation-induced spectral shifts and the stability constants revealed binding strength in the order Ca²⁺>Ba²⁺?Li⁺>Na⁺>K⁺>Mg²⁺. Competitive experiments performed in a matrix of ions also indicated superior interaction of 6 and 7 with Ca²⁺. The excited state decay profiles remained largely unperturbed in the presence of metal ions. The studied probes displayed positive solvatochromism and the Stokes shifts and excited state lifetimes increased with increasing solvent polarity. These findings can be rationalized by invoking highly polar nature of the emittive states. The chemoionophores 6 and 7 constitute potentially interesting Ca²⁺ sensitive probes due to their relatively high binding interaction for Ca²⁺ (log K_s=3.55-3.10) vis-a-vis that of biologically interfering Mg²⁺ (log K_s=1.67-1.30).     

A miniaturized solid-contact potentiometric multisensor platform for determination of ionic profiles in human saliva

This paper describes a miniaturized multisensor platform (MP-ISES) consisting of electrodes: a reference one (RE) and ion-selective electrodes (ISEs) for monitoring Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and SCN⁻ ions and pH in human saliva. Gold electrode surface was modified by deposition of two layers: electrosynthesized PEDOT:PSS forming an intermediate layer, and ion-selective membrane. The developed ISEs were characterized by a wide linear range and sensitivity consistent with the Nernst model. The entire MP-ISEs are characterized by satisfactory metrological parameters demonstrating their applicability in biomedical research, in particular in measurements concerning determination of ionic profiles of saliva. Saliva samples of 18 volunteers aged from 20 to 26 participating in a month experiment had been daily collected and investigated using the MP-ISEs assigned individually to each person. Personalized profiles of ions (ionograms) in saliva, such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SCN⁻, and H⁺, were obtained.