Layered hydrous manganese dioxide saturated with alkaline-earth cations: Synthesis and sorption properties

Layered compounds based on hydrous manganese dioxides (hereafter, Mn-phases) saturated with alkaline-earth cations were synthesized at 3–6°C. These phases are analogues of manganese minerals from oceanic iron-manganese sediments (vernadite, birnessite, buserite-I, an asbolan-like phase, and a hybrid phase). All the Mn-phases, as a rule, had poorly ordered structures. The sorption properties of these phases were studied with respect to alkali-metal cations (Na⁺, K⁺), an s-metal cation (Ba²⁺), a p-metal cation (Pb²⁺), and d-metal cations (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺). The exchange capacities of the Mn-phases were 0.45–1.06 mg-equiv/g for the alkali cations and 0.94–5.78 mg-equiv/g for the other cations. The phase composition of the Mn-phase did not affect the alkali cation sorption but affected the divalent cation sorption. The divalent cation exchange capacity increased from well-ordered birnessite to poorly ordered vernadite.     

Solution Chemistry of Arsenic Anions in the Presence of Metal Cations

The interaction of arsenic(V) and arsenic(III) oxyanions with metal cations was investigated by potentiometry under temperature and ionic strength conditions approaching those prevailing in natural waters. The selection includes the major metal cations and some other ions of high environmental relevance. Ionic pairs [M(As^VO₄)]^?, [M(HAs^VO₄)] and [M(H₂As^IIIO₃)]⁺ formation is suggested for all +2 metal cations, based on the potentiometric results. These ion-pairs between arsenic anions and other metal cations are hardly ever mentioned or taken into account when arsenic speciation in natural waters is considered. These results provide the basis for studying arsenic speciation in natural aquatic systems, on which environmental fate, bioavailability and toxicity of the element depend. Some extrapolations to the conditions of the natural waters are presented as well as some insights into the adsorption process onto hydrous oxides.     

A model for cation adsorption to clays and membranes

A cation adsorption model is presented and its recent applications are discussed. The model combines electrostatic equations with specific binding, and considers neutral and positively charged complexes between the negative surface sites and organic cations in a closed system. Extensions in the model account for dye aggregation in solution, and for the formation of solution complexes of inorganic cations, such as [M⁺⁺ Cl^–]⁺. The amounts of 45Ca²⁺ adsorbed to vesicles extracted from the plasma membranes of melon root cells could be adequately simulated and predicted. The binding coefficients determined for Ca²⁺, Na⁺, and Mg²⁺ are in the range of values previously deduced for binding to phospholipid components. Model calculations were applied to the test of hypotheses on the effect of salt stress on the growth of roots. The adsorption of monovalent organic cations to montmorillonite is characterized by binding coefficients that are at least six orders of magnitude larger than those of Na⁺, Mg²⁺, Ca²⁺, and Cd²⁺, or those of CdCl⁺ or CaCl⁺. Monovalent organic cations were found to adsorb 140–200% of the cation exchange capacity of the clay and to cause charge reversal. Deductions from adsorption results of acriflavin are consistent with those drawn from the application of other experimental methods. Preliminary results on the adsorption of divalent organic cations are presented. Agro-environmental applications of organo-clays are discussed.     

Synthesis and sorption properties of layered hydrous manganese dioxide saturated with <Emphasis Type="Italic">s</Emphasis>-, <Emphasis Type="Italic">p</Emphasis>-, and <Emphasis Type="Italic">d</Emphasis>-metal cations

Layered compounds based on hydrous manganese dioxide (hereafter, Mn-phases) saturated with s-metal (Ba²⁺), p-metal (Pb²⁺), and d-metal (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) cations, analogues of manganese minerals of oceanic ferromanganese formations (vernadite, birnessite, buserite-I, and asbolan), were prepared at 4–6°C. All Mn-phases have poorly ordered structures. The sorption properties of phase compounds were studied in relation to alkali-metal (Na⁺ and K⁺) and other s-, p-, and d-metal cations. The exchange capacities of Mn-phases for alkali cations are very low, within 0.02–0.10 mg-equiv/g; for the other cations, the exchange capacities are 0.13–4.20 mg-equiv/g. The sorption of divalent metal cations depends on the phase and chemical composition of the Mn-phase.     

Influence of the composition on the electronegativity and on the oxygen charge distribution in a binary hydrotalcite-like by modified Sanderson method

An intuitive and computationally non-intensive model for the classification of Hydrotalcite-like compounds (HTLCs) based simply on the chemical composition using the Sanderson Method led to good prediction of basicity and different basic sites (oxygen atoms with different charge). That model was evaluated at different M³⁺ /(M²⁺+M³⁺) ratio and with different divalent and trivalent metallic cations.AMS subject classification: 92E10     

Thermopower composition dependence in ferrospinels

The composition dependence of thermoelectric power (Seebeck coefficient) in ferrospinels with fixed valence foreign cations has been calculated via combined small polaron and cation distribution models. Satisfactory agreement with experimental data is achieved assuming cation distribution thermodynamic constants to be independent of foreign cation concentration. Data are analyzed for a trivalent foreign cation (Al³⁺) at elevated temperature and for divalent foreign cations (Ni²⁺, Mg²⁺, Zn²⁺) at lower temperatures.     

Studies on the ion-exchange behaviour of chromium ferrocyanide

The sorption of univalent, bivalent and trivalent ions has been studied on chromium ferrocyanide gel. The studies reveal a high sorption capacity for Cs⁺, Tl⁺, Ag⁺, Cu²⁺, Zn²⁺, Cd²⁺, Fe³⁺ and Th⁴⁺. The sorption of monovalent cations show purely ion-exchange mechanism while the uptake of bivalent and trivalent cations is non-equivalent in nature. Single elution of Rb⁺, Cs⁺ and Tl⁺ has been performed from the columns of this exchanger and the recovery is almost complete in all the cases. Cu²⁺ and Ag⁺ get completely adsorbed on the gel column and their elution is not possible probably due to the formation of some new solid phases. Depending on the K_d values of the metal ions, a large number of separations of radiochemical as well as analytical importance can be performed on the columns of this exchanger material.     

Inorganic particulates in removal of toxic heavy metal ions

The removal behavior of amorphous aluminum hydroxide for Hg(II) ions from aqueous solutions was investigated by employing a radiotracer technique at micro down to trace level concentrations. The batch type experiments were performed to obtain various physico-chemical parameters, viz., effect of sorptive concentration, temperature and pH. It was observed that the increase in sorptive concentration (from 1·10⁻⁸ to 1·10⁻² mol·dm⁻³), temperature (from 303 to 333K) and pH (from 3.4 to 10.3) apparently favored the uptake of Hg(II) by this solid. Similarly, the presence of anions (six fold) viz., oxalate, phosphate, glycine and EDTA also enhanced the uptake behavior of aluminum hydroxide for Hg(II). Whereas, the added cations viz., Na⁺, K⁺, Ba²⁺, Sr²⁺, Mg²⁺, Cd²⁺ and Fe³⁺ more or less suppressed the removal behavior of the adsorbent. Further, the adsorption process followed the classical Freundlich adsorption isotherm and deductions of various thermodynamic data revealed that the uptake of Hg(II) on aluminum hydroxide followed the ion-exchange type mechanism and thermodynamically it was found to be endothermic in nature. Part IX: Rapid and efficient removal of Hg(II) by hydrous manganese and tin oxides, J. Coll. Interf. Sci., 279 (2004) 61.     

Simultaneous separation of common mono- and divalent cations on silica gels modified with aluminium and zirconium

The modification of silica gel with aluminium and zirconium can be used for the preparation of advanced silica-based cation-exchange stationary phases for use in ion chromatography with conductimetric detection (IC-CD) for cations. Silica gels modified with aluminium (Al-silica) and zirconium (Zr-silica) act as cation-exchangers under strongly acidic conditions. Highly sensitive indirect conductimetric detection and excellently simultaneous separation for common mono- and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) can be achieved on the Al-silica and Zr-silica columns in IC-CD by using acidic eluents containing 15-crown-5 (1,3,7,10,13-pentaoxacyclopentadecane). The Al-silica and Zr-silica can also be applied successfully as cation-exchange stationary phases in ion-exclusion chromatography for the separation of various aliphatic and benzenecarboxylic acids.     

Participation of electrolyte cations in albumin adsorption onto negatively charged polymer latices

The participation of electrolyte cations in the adsorption of bovine serum albumin (BSA) onto polymer latices was investigated. The latices used were hydrophobic polystyrene (PS), and hydrophilic copolymers, i.e., styrene (St)/2-hydroxyethyl methacrylate(HEMA) copolymer [P(St/HEMA)] and styrene/acrylamide (AAm) copolymer [P(St/AAm)]. Three kinds of electrolyte cations (Na⁺, Ca²⁺, Mg²⁺) were used as the chloride. The amount of BSA adsorbed in every cation medium showed a maximum near the isoelectric point (iep, pH about 5) of the protein. The amounts of BSA adsorbed onto copolymer latices (except in the acidic pH region lower than the iep) were considerably smaller than that onto PS latex because of the steric repulsion and the decrease in the hydrophobic interaction between BSA and copolymer latices. In the acidic pH region, there was little difference in the amount of BSA adsorbed in every cation medium. However, in the pH region higher than the iep, the amounts of BSA adsorbed (particularly onto PS latex) in divalent cations (Ca²⁺ and Mg²⁺) media were relatively greater compared with that in a monovalent (Na⁺) one. This result was interpreted on the basis of the differences in such effects of electrolyte cations as dehydration power, suppression of the electrostatic repulsion, and binding affinity to BSA molecule. Ion Chromatographic estimation of the amounts of electrolyte cations captured upon BSA adsorption (in pH > 5) revealed that divalent cations were incorporated into the contact interface between the latex and BSA molecule so as to prevent the accumulation of anion charge and facilitate the protein adsorption.     

Heat of adsorption of carbon dioxyde and ethene on zeolites a exchanged with Li+, Ni2+ and Cu2+

Various contents of Li⁺, Ni²⁺ or Cu²⁺ were introduced in zeolite NaA by conventional cation exchange. Crystal damages are observed on samples having suffered the lowerpH. The heat of adsorption of CO₂ and C₂H₄ was determined by isothermal calorimetry. Very high initial heats (100–120 kJ mol^?1) are found in NaA as well as in Li⁺ exchanged samples, perhaps due to chemisorption on alkaline cations; they vanish when Ni²⁺ or Cu²⁺ replaces more than 20% of Na⁺, in like manner with Co²⁺ or ZnI²⁺. For the adsorption of C₂H₄, high initial heats are absent in the case of NaA, but gradually appear when divalent cations are introduced. Apart from these strong initial values, the heats of adsorption present a plateauvs. the adsorbed amount. Abnormal low values at the plateau are indicative of crystal damages.     

Synthesis and adsorption properties of the cation exchange forms of OFF-type zeolite

The possibility of the ion-exchange of Na⁺ and K⁺ cations contained in OFF-type zeolite for H⁺, Ni²⁺, Cu²⁺, Co²⁺, and La³⁺ cations is investigated. Chemical and phase compositions, the morphology of crystals, and the adsorption properties of synthesized samples are studied via X-ray fluorescence and X-ray diffraction analysis, IR spectroscopy, scanning electron microscopy, and adsorption measurements.     

Application of pure silica gel as cation-exchange stationary phase in lon chromatography with indirect photometric detection for common mono-and divalent cations using aromatic monoamines as eluents

Summary A pure silica gel (Pia Seed 5S-60-SIL), synthesized by the hydrolysis of pure tetraethoxysilane [Si(OCH₂CH₃)₄], was applied as a cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono-and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) using various protonated aromatic monoamines (tyramine [4-(2-aminethyl) phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine) as eluet ions. When using 0.75 mM tyramine-0.25 mM oxalic acid-1.5 mM 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) at pH 5.0 as the eluent, excellent simultaneous separation and highly sensitive detection at 275 nm for these mono-and divalent cations were achieved on the Pia Seed 5S-60-SIL column (150×4.6 mm I.D.) in 20 min.     

Studies on the equilibrated thermodesorption of <Emphasis Type="Italic">n</Emphasis>-hexane from ZSM-5 zeolite

Equilibrated thermodesorption (TPED) and quasi-equilibrated temperature programmed desorption and adsorption (QE-TPDA) were employed as methods for studying the influence of different extraframework cations (Na⁺, K⁺, Li⁺, Cu²⁺, Zn²⁺, or Mg²⁺) on adsorption of n-hexane on ZSM-5 zeolite with high Al content (Si/Al = 15). Considerable influence of the cations on both initial adsorption in the micropores and ordering of the adsorbed molecules, occurring at high coverages, has been observed. This influence is reflected by the values of the adsorption enthalpy and entropy, determined by fitting the dual site Langmuir (DSL) adsorption function to the equilibrated thermodesorption profiles. However, no clear correlation between the determined parameters and properties of the extraframework cations could be found.     

Theoretical study of interaction of 2,6-dithiopurine with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cations

The geometries of the complexes of Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ metal cations with different possible 2,6-dithiopurine anions (DTP) were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d, p) basis set. The interactions of the metal cations at different nucleophilic sites of various possible 2,6-dithiopurine anions were considered. It was revealed that metal cations would interact with 2,6-dithiopurine anions in a bicoordinate manner. In the gas phase, the most preferred position for the interaction of Li⁺, Na⁺, and K⁺ cations is between the N₃ and S₂ sites, while all divalent cations Be²⁺, Mg²⁺, and Ca²⁺ prefer binding between the N₇ and S₆ sites of the corresponding 2,6-dithiopurine. The influence of aqueous solvent on the relative stability of different complexes has been examined using the Tomasi’s polarized continuum model. The basis set superposition error (BSSE) corrected interaction energy was also computed for complexes. The AIM theory has been applied to analyze the properties of the bond critical points (electron densities and their Laplacians) involved in the coordination between 2,6-dithiopurine anions and the metal cations. It was revealed that aqueous solution would have significant effect on the relative stability of complexes obtained by the interaction of 2,6-dithiopurine anions with Mg²⁺ and Ca²⁺ cations. The effect of metal cations on different NH and CS stretching vibrational modes of 2,6-dithiopurine has also been discussed.     

Lead‐Free Silver‐Bismuth Halide Double Perovskite Nanocrystals

Lead‐free perovskite nanocrystals (NCs) were obtained mainly by substituting a Pb²⁺ cation with a divalent cation or substituting three Pb²⁺ cations with two trivalent cations. The substitution of two Pb²⁺ cations with one monovalent Ag⁺ and one trivalent Bi³⁺ cations was used to synthesize Cs₂AgBiX₆ (X=Cl, Br, I) double perovskite NCs. Using femtosecond transient absorption spectroscopy, the charge carrier relaxation mechanism was elucidated in the double perovskite NCs. The Cs₂AgBiBr₆ NCs exhibit ultrafast hot‐carrier cooling (<1 ps), which competes with the carrier trapping processes (mainly originate from the surface defects). Notably, the photoluminescence can be increased by 100 times with surfactant (oleic acid) added to passivate the defects in Cs₂AgBiCl₆ NCs. These results suggest that the double perovskite NCs could be potential materials for optoelectronic applications by better controlling the surface defects.     

An insight into aggregation kinetics of polystyrene nanoplastics interaction with metal cations

Once inevitably released into the aquatic environment, polystyrene nanoplastics (PS-NPs) will present complicated environmental behaviors, of which the aggregation is a key process determining their environmental fate and impact. In this study, the aggregation kinetics of different sizes (30 nm and 100 nm) of PS-NPs with metal cations (Na⁺, K⁺, Ca²⁺, Mg²⁺ and Pb²⁺) at different solution pH (3, 6 and 8) were investigated. The results showed that the aggregation of PS-NPs increased with cation concentration. Taking Pb²⁺ as an example, the adsorption behavior of cations onto PS-NPs was determined by transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectroscopy, which demonstrated Pb²⁺ could be adhered onto the surface of PS-NPs with the effect of charge neutralization. The critical coagulation concentrations (CCC) of smaller PS-NPs were higher than that of larger PS-NPs for monovalent cations, whereas a different pattern is observed for divalent cations. It was suggested that there were other factors that DLVO theory does not consider affect the stability of NPs with different particle sizes. In addition, it should be noted that PS-NPs had the capacity of adsorbing large amounts of heavy metal cations and carried them transport to a long distance, and the corresponding ecological risks need to further elucidate.     

Effect of counterion condensation on the acid-base equilibrium of a pH-sensitive merocyanine dye covalently attached to polyelectrolytes

Effects of monovalent and divalent counterions on the acid-base equilibrium of a pH-sensitive merocyanine dye covalently attached to copolymers of acrylic acid and acrylamide with varying charge densities (0.28 < ξ < 2.8) were investigated. Added chloride salts of Li⁺, Na⁺, K⁺, and NH⁺₄ (< 0.2 mM) had essentially no effect on pK observed (pK^obs) for the equilibrium. By contrast, the salts of Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ caused a significant decrease in pK^obs for the copolymers with larger ξ. With smaller ξ, most likely when ξ < 0.5, no decrease in pK^obs was observed upon addition of the salts of divalent cations. A competitive effect of Ca²⁺ and Na²⁺ ions on pK^obs in the presence of an excess of Na⁺ ions implied that Ca²⁺ ions at very low concentrations were preferentially, and therefore exhaustively, condensed on the polyanions with sufficiently large ξ probably until effective charge density was lowered to 0.5. The observed difference in the influence of the monovalent and divalent cations on pK^obs was discussed in terms of the difference in the microscopic behavior of the condensed monovalent and divalent cations. © 1993 John Wiley & Sons, Inc.     

Impact of metal substitutions for cobalt in YBaCo4O7

The “114” YBaCo₄O₇ cobaltite undergoes structural transition just beyond room temperature at T_S∼310 K. Correspondingly, its signature in the physical properties is detected by T-dependent measurements of electrical resistivity, magnetic susceptibility and thermoelectric power. It is found that low-level substitutions of divalent (M=Zn²⁺) or trivalent (M=Ga³⁺, Al³⁺) cations for cobalt according to the YBaCo_4−xM_xO₇ formula with x?0.4 have a strong impact upon this transition. On the one hand, Zn²⁺ substitutions preserve the transition but with T_S decreasing as x increases. On the other hand, for x=0.2 Ga³⁺ or Al³⁺, the transition is suppressed, i.e., for only 5% trivalent foreign cation substituted for cobalt. Though at first, this contrasted behaviour between divalent and trivalent substituting cations appears to be linked to the opposite evolution of hole carriers “Co³⁺” concentration with x, a possible destabilization of 3Co²⁺: 1Co³⁺ charge ordering induced by the M³⁺ cations is considered.     

The effect of metallic cations on the electrophoretic properties of a pretreatedHevea latex

High-ammonia latex concentrate prepared from doubly-centrifuged fieldHevea latex was exhaustively dialysed to remove any residual water-soluble non-rubber constituents. The electrophoretic mobilities of the dialysed latex in the presence of various metallic cations were investigated as a function of electrolyte concentration. The mobility decreased with increasing concentration of the cations Na⁺, Ba²⁺, Mg²⁺ and Ca²⁺ in a manner consistent with the effect of simple electrolyte on compression of the electric double layer. Anomalous behaviour was noted for the divalent ion copper, in that it reversed the charge of the latex particles at a concentration even lower than that of uranyl ions. Multivalent cations (lanthanum, cerium and thorium) had a profound influence on the latex particles where very low charge reversal concentrations were observed. It is believed that strong adsorption of hydrolysed species from the metallic ions was responsible for reversing the charge of the originally negative latex particles. These experiments indicated that the efficiency with which the cations reversed the charge of the latex particle surface was in the order: lanthanum > cerium > copper > thorium > uranyl > calcium > magnesium > barium > sodium. The number of cation binding sites on the latex particle surface and the chemical free energies of cation adsorption were calculated. It was found that the interaction of the latex particle with the hydrolysable metallic cations was much more stronger than that with the simple divalent cations and that this intercation was comparable to that of biological surfaces.