Order Cs Research Articles

N‐alkylation of chitosan by β‐halopropionic acids in the presence of various acceptors

AbstractN‐carboxyethylation of chitosan by β‐halopropionic acids in the presence of various proton and halogen ion acceptors was investigated. It has been observed that carboxyethylation of chitosan in aqueous medium is accompanied by the by‐processes of hydrolysis and dehydrohalogenation of the β‐halopropionic acids yielding β‐hydroxypropionic acid, bis(2‐carboxyethyl) ether, and acrylic acid. Degree of carboxyethyl substitution (DS) of chitosan and the relative rates of the by‐processes varied significantly depending on the conditions used and nature of the proton or halogen ion acceptor. At carboxyethylation of chitosan with the alkaline β‐bromopropionates, the DS increased in the order Cs+ < Rb+ < K+ ∼ Na+ < Li+. For alkaline earth salts BrCH2CH2COOM0.5 (M = Be2+, Mg2+, Ca2+, Sr2+, Ba2+), the highest DS was obtained with strontium and barium salts, which could be subsequently removed from the reaction mixture by precipitation as sulfates. Among the organic bases applied (tetrabutylammonium hydroxide, triethylamine, trimethylamine, pyridine, 4‐N,N‐dimethylaminopyridine, 2,6‐lutidine, and 1,5‐diazabicyclo[4.3.0] non‐5‐ene), the highest DS was obtained using a moderately strong base triethylamine. For the halogen acceptors (Pb2+, Ag+, Tl+), the stoichiometrically highest DS was achieved in a system comprising iodopropionic acid plus Tl+ and a comparable conversion rate was obtained using also a combination of chloropropionic acid and Ag+. A novel alternative preparative approach—gel‐state synthesis—was suggested that provides for the highest DS at the optimum reaction conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Ethylene oxide-bridged bipyridine oligomers that function as selective host molecules for the encapsulation of small alkali cation guests

Two novel ethylene oxide-bridged bipyridine oligomers were synthesized that contain host pockets with four (1) or six (2) oxygen donor atoms and a pyridyl nitrogen donor. The alkali picrate extracting ability and selectivity of these free ligands was investigated using a liquid–liquid dichloromethane–water extraction study. Both open-chain oligomer frameworks display unexpectedly high extraction efficiency (EE) values for specific guest ions (EE = 57% Na+ extracted by 1, and EE = 39% Cs+ extracted by 2). These extraction values are comparable to macrocyclic analogues and their ion selectivities follow the ‘same-fit’ concept that has been extensively reported for fixed pocket systems. The shorter chain oligomer (1) binds ions in the series (Na+ > K+ > Cs+), while the larger oligomer (2) binds ions in the reverse order (Cs+ > K+ > Na+). Formation of the host–guest ligand–ion complexes were verified by 1H NMR spectroscopy and MALDI-TOF mass spectrometry experiments. A Job’s plot analysis based on UV spectral data also supported the 1:1 (oligomer to ion) complexation observed in the MALDI mass spectra.

Stability of complexes of alkali metal cations with p-tert-butylcalix[4]arene-tetrakis (N, N-dimethylthioacetamide) in nitrobenzene saturated with water

From extraction experiments and -activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq)+NaL+(nb) ML+(nb)+Na+(aq) taking place in the two-phase water–nitrobenzene system [M+ = Li+, K+, Rb+, Cs+; L = p-tertbutylcalix[4]arene-tetrakis (N, N-dimethylthioacetamide); aq = aqueous phase, nb = nitrobenzene phase] were evaluated. Furthermore, the stability constants of the ML+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the cation order Cs+<Rb+<K+<Li+<Na+.

Stability of Complexes of Alkali Metal Cations with Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate in the Water–Nitrobenzene Extraction System

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq) + NaL+(nb) ⇔ ML+(nb) + Na+(aq) taking place in the two-phase water–nitrobenzene system (L = tetraethyl p-tert-butylcalix[4]arene tetraacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the ML+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the cation order Cs+ &lt; Rb+ &lt; K+ &lt; Li+ &lt; Na+.

Influences of A- or B-site substitution on the activity of LaMnO3 perovskite-type catalyst in oxidation of diesel particle

LaMnO3 was partially substituted at A- or B-site by Sol-Gel method and characterized by XRD, SEM and BET. Perovskite oxides were formed in all substitutions. The catalytic activities of substituted catalysts on carbon black oxidation were measured by Temperature Programming Oxidation (TPO). Experimental results showed that all substitutions increased the catalytic activity of LaMnO3, and La0.8Cs0.2MnO3 showed the highest catalytic activity. Under tight contact, the activity enhancement of different substitutions decreased in the order Cs>K>V>Ce>Co>Cu>Fe. Dynamic analysis showed that partial substitutions increased the pre-exponential factor and the catalytic activity by increasing the oxygen vacancy on the catalyst surface. The active components on the surfaces of La0.8Ce0.2MnO3 and LaMn0.8V0.2O3 included CeO2 and LaVO4, which changed the apparent activities and dynamic parameters of these two catalysts.

A contribution to the physicochemical characterization of nonstoichiometric salts of tungstosilicic acid

Nonstoichiometric cesium and rubidium salts of tungstosilicic acid (TSA) were synthesized by precipitation. These solids are insoluble in water, due to the low solvation energy of large cations, have high specific surface area, and a mainly microporous structure. In turn, nonstoichiometric potassium salts prepared by solution evaporation have a low specific surface area and porosity, high solubility in water, and a negligible porosity. All the synthesized tungstosilicates presented a cubic structure, with a lattice parameter that slightly decreases in the order Cs + > Rb + ≅ K + salts. The salts displayed the characteristic FT-IR bands of TSA, though the band assigned to the stretching of the W O terminal bond presented a slight widening and a shoulder, and the band attributed to a bridged W O W bond was shifted to a lower wavenumber and showed a shoulder. Such effects are indicative of the interaction between the [SiW 12O 40] 4− anion and the alkaline cations. Assuming that an increase in 1H MAS-NMR chemical shift is due to a higher acid strength, the cesium salts would have acid sites with higher acid strength than the others. The potassium salts, however, presented protons in different acid environments, with a low proportion of very strong acid sites. The acidity measurement by potentiometric titration with n-butylamine also showed that the cesium salts have acid sites with higher strength than those of rubidium. The same behavior was observed for the potassium salts, which exhibited an acid strength higher than expected. The number of protons determined by titration decreased in the order Cs + > Rb + ≅ K + salts and also decreased for the more substituted salts.

Separation of cobalt-60, strontium-90, and cesium-137 radioisotopes by competitive transport across polymer inclusion membranes with organophosphorous acids

The removal and separation of Co-60, Sr-90, and Cs-137 radioisotopes from nitrate aqueous solutions were studied by competitive transport across cellulose triacetate plasticized membranes using organophosphorous acids compounds (D2EHPA, Cyanex 272, Cyanex 301 and Cyanex 302). Competitive transport of trace radionuclides ions from 0.10 M NaNO 3 aqueous solutions across polymer inclusion membranes containing cellulose triacetate as the support, D2EHPA as the ion carrier and o-nitrophenyl pentyl ether as the plasticizer provide the selectivity order: Co(II) > Cs(I) > Sr(II). The affinities of the radioisotopes investigated for Cyanex 272 and Cyanex 302 follow the order Cs(I) > Sr(II) > Co(II). The influence of ion carrier acidity on cation transport selectivity and effectiveness was explored. The results show a linear decrease of permeability coefficient values for Co(II) with an increase of pK a values of ion carriers. A long-term transport experiment was carried out to demonstrate the durability of polymer inclusion membranes.

Contribution to the Thermodynamics of Complexes of Alkali Metal Cations with Benzo-18-Crown-6 in the Water–Nitrobenzene Extraction System

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq) + NaL+(nb) ⇔ ML+(nb) + Na+(aq) taking place in the two–phase water–nitrobenzene system (M+ = Li+, K+, Rb+, Cs+; L = benzo-18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the ML+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the cation order Cs+ &lt; Rb+ &lt; Li+ &lt; Na+ &lt; K+.

Extraction of NH4+, K+, Rb+ and Tl+ into nitrobenzene using cesium dicarbollylcobaltate in the presence of dibenzo-21-crown-7

From extraction experiments and g-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq) + CsL+(nb) U ML+(nb) + Cs+(aq) taking place in the two-phase water-nitrobenzene system (M+ = NH, K+, Rb+, Tl+; L = dibenzo-21-crown-7; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the ML+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Cs+<K+ = Rb+»NH<Tl+.

CO 2 adsorption in Y and X zeolites modified by alkali metal cation exchange

Ion exchange was performed on NaY and NaX zeolites with alkali metal cations Li +, K +, Rb +, and Cs + and studied by adsorption of CO 2. This is the first study to examine adsorption equilibrium isotherms and capacities of CO 2 on the alkali metal series for both Y and X zeolites under mild conditions. CO 2 capacity increased as Cs < Rb ≈ K < Li ≈ Na for Y zeolites. For X zeolites, the capacity for CO 2 increased in the order Cs < Rb < K < Na < Li (the order of decreasing ionic radii). For both zeolites the larger cation forms (Cs, Rb, K) exhibited strongly nonlinear concave downward isotherms, which is indicative of strong interactions between CO 2 and the zeolite. This is consistent with an increased basicity of the framework compared to the smaller cation forms, given that CO 2 is a weakly acidic gas. This is also reflected by the Henry’s law slopes obtained from the Toth isotherm equation. Our measurements show that, in general, CO 2 capacities are greatest for the Li forms, in which the ion–quadrupole interaction is dominant. Adsorption equilibrium measurements of CO 2 on each ion-exchanged material reveal behaviors and trends based on cation size and acid–base surface properties that can have an important impact on tuning adsorptive properties of zeolites by ion exchange.

Preparation and Alkali Metal Ion Exchange Properties of Protonated Rb8Nb22O59 Compound.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation and Alkali Metal Ion Exchange Properties of Protonated Rb8Nb22O59 Compound

An ion-exchanger H8Nb22O59·8H2O was prepared by extracting Rb+ from Rb8Nb22O59, and its ion-sieve properties for alkali metal ions were investigated. The Rb+ can be effectively extracted using a concentrated HNO3 solution at room temperature, leading to a protonated compound with composition of Rb0.14H7.9Nb22O59·8.2H2O. The protonated (hydronium ion form) crystal has the lattice parameters (a = 7.5104(2) and c = 43.0780(8) A of hexagonal symmetry, R3m), very close to the Rb+-form precursor. The exchange capacity increased in the order Cs+ ≪ Rb+ < K+, Na+ < Li+, which agrees with the decreasing order of ionic radius. The capacities for Li+, Na+, and K+ were close to the theoretical value of 2.55 mmol/g calculated from the composition of protonated compound. The distribution coefficients (Kd) of alkali metal ions were determined in the condition of microamount of ion loading. The selectivity sequence was Cs+, Li+ ≪ Na+ < Rb+ ≪ K+ at pH around 3; the protonated samples showed markedly high selectivity for t...

Catalytic removal of carbon particulates over MgF&lt;Subscript&gt;2&lt;/Subscript&gt;O&lt;Subscript&gt;4&lt;/Subscript&gt; catalysts

We have studied the catalytic combustion of carbon particulates over Mg ferrite catalysts prepared by the malic acid method. The catalyst was modified to enhance the catalytic activity by the substitution of alkali metal ions into Mg sites. In the MgFe 2 O 4 catalyst, the partial substitution of alkali metal ions into Mg sites enhanced the catalytic activity for the combustion of carbon particulates.It decreased in the following order Cs>K>Na. In Mg 1-x Cs x Fe 2 O 4 catalysts, the catalytic activity increased with the increase of x and was almost similar at x>0.2. The partial substitution of Mn into Fe site enhanced the oxidation rate of carbon particulates.

Study on solute–solvent and solute–solute interactions for the dibenzo-24-crown-8-alkali metal picrate extraction system

The constants of overall extraction equilibrium ( K ex) and distribution ( K D,MLA) for various diluents and aqueous ion-pair formation ( K MLA) of dibenzo-24-crown-8 (DB24C8)–alkali metal (Na–Cs) picrate (MA) 1:1:1 complexes (M(DB24C8)A) were determined at 25 °C; the partition constants of DB24C8 were also measured at 25 °C. The distribution behavior of DB24C8 and M(DB24C8)A complexes can be explained by regular solution theory; the molar volumes and the solubility parameters of DB24C8 and M(DB24C8)A were determined. The log K D,MLA value for the same diluent decreases from Na to K and increases from K to Cs; however, the reverse is true of the log K MLA values. The extraction selectivity of DB24C8 for the alkali metal picrates decreases in the order Cs>Rb>K>Na or Cs>K≥or >Rb>Na. This is governed largely by the aqueous stability order for the M(DB24C8) + complex ions. For every diluent, the plot of log K ex values against the reciprocal effective ionic radii of the alkali metals gives a straight line, which is related to Born's formula of solvation free energy. The reason for this was elucidated.

Influence of Cation Exchange on M-Pt-ETS-10 Molecular Sieve: Correlation between ab Initio Results, Catalytic Activity, and Physicochemical Investigations

The electronic property of Pt supported on cation-exchanged Pt-M-ETS-10 [where M = Li, Na, K, Rb, Cs, Mg(OH), Ca(OH), Sr(OH), and Ba(OH) ions] depends on the location of Pt and the nature of the exchanged metal ion. Electronic changes on the Pt cluster are highly influenced when it is near TiO6 rather than SiO4 units. The benzene selectivity in the transformation of n-hexane over Pt-M-ETS-10 molecular sieves is found to correlate with the basicity of the exchanged cations and the average electron density of Pt. The relationship between electron density on Pt and the amount of CO2 adsorbed (from TPD) and the frequency of the ν3 band of CO2 adsorbed in FTIR is established. We report here the results of ab initio Hartree−Fock calculations on model clusters representing the Pt (active) site, molecular sieve with cations, Pt-M-molecular sieve, benzene, and H2S adsorbed over Pt-molecular sieve. Generally, the charge density on Pt decreases in the order Cs > Rb > K > Ba(OH) > Na > Sr(OH) > Ca(OH) > Li > Mg(OH) a...

Voltammetric studies of microcrystalline C60 adhered to a carbon electrode surface and placed in contact with aqueous electrolyte containing potassium ions

The reduction of microcrystalline C60 fullerene, adhered at a carbon electrode and immersed in aqueous electrolyte, has been studied under various voltammetric conditions. This work reports mainly the voltammetric studies carried out principally in electrolyte containing potassium ions. Comparison of adherence techniques, such as solvent casting and mechanical transfer methods, are made to assess if the type of adhered techniques has any significant influence on the observed electrochemistry. The solvent casting method is found to produce three peaks in the potential for C600/n- redox couple as compared to a single and large peak produced when a mechanical transfer technique is employed. When the reduction potential of microcrystalline C60 in the presence of K+ is compared with other cations, such as Li, Na, Rb and Cs, it is observed that the shift of reduction potential follows the change in the hydration energy in the order Cs>Rb>K>Na>Li. In a mixed electrolyte study of CsCl/KCl, the reduction potential and peak shape of C600/n- redox couple during cyclic voltammetry is observed to change with concentration of the cations and the observed electrochemistry can be attributed to a cation-exchange mechanism. The reduction of C60 is irreversible in aqueous electrolyte containing alkaline cations as the re-oxidation process does not produce any observed electro-activity. Evidence of the formation of a passive coating of K nC60 fulleride, which does not appear to undergo dissolution is obtained under cyclic voltametric conditions. This coating remains electrochemically active in the presence of tetrabutylammonium ions in acetonitrile. Scan rate, chronocoulometric, and scanning electron microscopic studies provide evidence of the presence of a surface process involving solid–solid transformation.

Preparation and Alkali-Metal Ion Extraction/Insertion Reactions with Nanofibrous Manganese Oxide Having 2 × 4 Tunnel Structure

Sodium manganese oxide with a 2 × 4 tunnel structure (Na-2 × 4) was hydrothermally synthesized from Na−birnessite material in NaOH solutions at relatively low temperatures. The Na+ extraction and alkali-metal ion insertion reactions were investigated by chemical and X-ray analyses, SEM observation, FT-IR spectroscopy, TG-DTA analyses, pH titration, and Kd measurements. A considerable amount (81%) of Na+ ions in the 2 × 4 tunnel sites were topotatically extracted by acid treatment, accompanied by a slight change of the lattice parameters. Alkali-metal ions could be inserted into the 2 × 4 tunnel sites of the acid-treated sample (Na-2 × 4 (H)), mainly by an ion-exchange mechanism. The pH titration study showed that Na-2 × 4 (H) had simple monobasic acid behavior toward alkali-metal ions with a relatively low exchange capacity below pH 10; the exchange capacity increased in the order Cs+ < Li+ < Na+ < K+ ≅ Rb+ at pH 6. The distribution coefficient (Kd) study on Na-2 × 4 (H) showed the selectivity sequence of Cs+ < Li+ < K+ < Rb+ around pH 4. These results suggest that manganese oxide with a 2 × 4 tunnel structure has a weak ion-sieve property for the adsorption of ions with an effective ionic radius around 1.7 Å.

Diffusion mechanism of Cs+, Zn2+ and Eu3+ ions in the particles of zirconium titanate ion exchanger using radioactive tracers

Abstract Diffusion behaviour of Cs+, Zn2+ and Eu3+ ion exchange on zirconium titanate (ZrTi) were studied under particle diffusion conditions and the limited batch technique. The values of the diffusion coefficients, activation energy and the entropy of activation were calculated and compared with those obtained for other inorganic and organic resins. The values of the obtained effective diffusion coefficient were found to increase in the order Cs+>Zn2+>Eu3+. The activation energy was found to decrease with decreases in the entropy of the activation of the system. From all the data obtained it is anticipated that the above mentioned cations are exchanged with H− of ZrTi in the unhydrated form.

Desorption of 90 Sr and 137 Cs from Flood Plain Deposits of the Sozh River and Rocks of the Adjacent Catchment Areas

Desorption of 90Sr and 137Cs from flood plain warps, meadow sod, humus-containing sandy loam, peat, clays, limonite, meadow marl, and friable rocks of the adjacent catchment areas (moraine clay, loam, sandy loam) was studied. 137Cs is sorbed the most strongly on clays by the mechanism of isomorphic ion-exchange incorporation into the crystal lattice of montmorillonite-type minerals. 137Cs is also tightly fixed on buried and peaty soils due to association with the poorly mobile species of humic acids and humin. The strong fixation of 90Sr on amorphous iron hydroxides is caused by its association with poorly soluble ferrite-type minerals. Sorption of 90Sr on peaty soils can be attributed to their association with aluminum and iron-containing organomineral complexes. 137Cs sorbed on flood plain warps, sandy loams, and loams exhibits increased mobility and is leached with all the tested desorbing solutions. These deposits apparently contribute maximally to the redistribution of radiocesium over flood plain and the adjacent catchment areas. The desorption efficiency of cations of the desorbing solutions decreases in the order Cs+ > K+ > Fe3 + > NH4 + > Ca2 + > H+ for radiocesium and Fe3 + > Sr2 + > K+ > H+ > Ca2 + > NH4 + for radiostrontium.

PET fabric supported fixed site carrier membrane for selective metal ion transport

Development of a novel fixed site carrier membrane (FCM), supported by PET fabric for metal ion separation is reported. The membranes were prepared by dipping PET fabric into the methylene chloride solution of Poly(5-vinyl-m-phenylene-m′-phenylene-32-crown-10)_ (P(VCE)), a polymeric metal ion carrier. It was found that the flux of mono-valent metal ion transported across the membrane is significantly differed from each other and the flux decreases in the order Cs+>Rb+>K+>Na+>Li+ irrespective to the anion except perchlorate anion. It was explained in terms of the stability of the complex, formed by crown ether unit of the P(VCE) and the various metal ions, meanwhile, the lower rate of transport in the presence of perchlorate anion was ascribed to its low hydrophilicity.