Spectral and electrochemical behavior of manganese dioxide nanodispersions prepared in reverse micelle

Nanodispersed aggregates of MnO₂ were prepared in the aqueous core of the H₂O/Aerosol OT (AOT)/heptane reverse micelle using the comproportionation reaction between and Mn²⁺ ions. The formed nanoparticles were characterized by transmission electron microscopy (TEM), UV–visible spectroscopy and cyclic voltammetry. The electro-oxidation of dextrose and fructose on platinum modified by reverse micellar MnO₂ deposits was studied. The oxidation of fructose was found to be much more facile than dextrose oxidation. There was a linear correlation between the steady state oxidation currents and the carbohydrate concentrations, which was shown to be useful for analytical application. The sensitivity for fructose detection was found to be about seven times higher than that of dextrose. The scope of developing an electroanalytical method for estimation of dextrose and fructose individually in their mixture was explored.     

Lithium manganese oxide with excellent electrochemical performance prepared from chemical manganese dioxide for lithium ion batteries

Chemical manganese dioxide (CMD) is synthesized by the SEDEMA process and adopted as a precursor for lithium manganese oxide with a spinel structure (LMO). LMO is also prepared from electrolytic manganese dioxide (EMD) as a reference for comparison. X-ray diffraction (XRD) shows that CMD is composed of γ-MnO₂, and scanning electron microscopy (SEM) with transmission electron microscopy (TEM) shows that the nanorods cover a spherical core with a diameter < 1 μm. The LMO prepared from CMD shows a much better rate capability and cycle life performance than that from EMD at high temperatures and high current densities. The excellent electrochemical performance is attributed to the structural stability during charge and discharge and the morphology of the LMO, a loose aggregation of the octahedral particles with a uniform size (<1 μm) and shape, which originated from that of CMD.     

Determination of manganese in uranium by ion exchange and square-wave polarography

Traces of manganese in uranium and its compounds can be determined by ion-exchange separation and square-wave polarography. When a 9 M hydrochloric acid solution of the sample is introduced into a column of strongly basic anion-exchange resin, manganese can be quantitatively separated from uranium by cluting with 9 M hydrochloric acid. The determination of the separated manganese by square-wave polarography is performed in 1 M potassium hydroxide-0.4 M triethanolamine solution with an excellent sensitivity. The lower limit of the method is 0.5 p.p.m. of manganese.     

Phase transitions of cassava starch dispersions prepared with glycerol solutions

The aim of this work was to study the glass transition, the glass transition of the maximally freeze-concentrated fractions, the ice melting and the gelatinization phenomenon in dispersions of starch prepared using glycerol-water solutions. The starch concentration was maintained constant at 50 g cassava starch/100 g starch dispersions, but the concentration of the glycerol solutions was variable (C _g= 20, 40, 60, 80 and 100 mass/mass%). The phase transitions of these dispersions were studied by calorimetric methods, using a conventional differential scanning calorimeter (DSC) and a more sensitive equipment (micro-DSC). Apparently, in the glycerol diluted solutions (20 and 40%), the glycerol molecules interacted strongly with the glucose molecules of starch. While in the more concentrated glycerol domains (C _g>40%), the behaviour was controlled by migration of water molecules from the starch granules, due to a hypertonic character of glycerol, which affected all phase transitions.     

Synthesis of cerium dioxide sols by an ion exchange method

Finely dispersed CeO₂ hydrosol is synthesized through ion exchange in aqueous solutions of cerium chloride in the presence of anionite AV-17-8.     

Preparation and characterization of nano-ZnO flakes prepared by reactive ion exchange method

Nano-ZnO flakes were synthesized by calcination of the precursor of Zn(OH)₂ obtained via the reactive ion exchange method between an ion exchange resin and ZnSO₄ solution at room temperature. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscope, UV-Vis diffuse reflection spectrum and Na₂EDTA titration were used to characterize the structure features and chemical compositions of the as-prepared ZnO. The results show that the as-prepared ZnO flakes have uniform structure and high purity. Heat capacities in the temperature range of 83 to 396 K were measured. The measured heat capacities values were compared with those of coarse crystal powders and the difference between this two heat capacity curves was analyzed.     

Adsorption of carbon dioxide on montmorillonites of different ion exchange forms

The adsorption isotherms of carbon dioxide are measured at 303, 343, 373, and 400 K and pressure P ranged from 0.1 to 6 MPa for three montmorillonites, i.e., the initial sample in the sodium form and two ion exchanged samples in pyridinium and polyhydroxyaluminum forms. It is shown that the linear character of the isosteres of CO₂ adsorption is retained for polyhydroxyaluminum and sodium montmorillonites, a deviation of the adsorption isosteres from linearity is observed for pyridinium montmorillonite at high temperatures (373–400 K) and high surface fillings. The differential excess entropies of CO₂ adsorbate are calculated for different fillings of montmorillonites. Using various approaches, the adsorption volumes for the systems studied are calculated.     

Phase behavior of diisobutyl adipate–carbon dioxide mixtures

Phase equilibrium data are reported for diisobutyl adipate (DiBA) in CO₂ at temperatures from 25 to 150 °C. This system exhibits a continuous mixture-critical curve with a maximum near 200 °C and 260 bar. The phase behavior of the DiBA–CO₂ system is well characterized and modeled with the Peng–Robinson equation of state using a single, fixed binary interaction parameter, k_ij. The DiBA–CO₂ data are compared to other solute–CO₂ systems with structures similar to DiBA to demonstrate the impact of the diester end groups in DiBA, which enhance DiBA solubility in CO₂ at low temperatures, relative to a single (ethyl laurate) or no ester end groups (tetradecane), and a single acid end group (tetradecanoic acid). DiBA–CO₂ data are also compared to data for two compounds each with diester groups but one containing an interior aromatic group (dibutyl phthalate) and the other containing the same number of interior carbon groups but with two less carbon groups at either end of the chain (divinyl adipate).     

Thermal behavior of typical weak basic ion exchange resin

Thermal behaviors of typical weak basic ion exchange resins (301 and 315) were studied with thermogravimetry, elemental analysis, and Fourier transform infrared spectrometer in this study. Results indicated that there were three stages for 301 resin mass loss, the first stage and the second stage were mainly related to the decomposition of functional group, and the third stage was the decomposition of main chain. Whereas there were two stages for 315 resin mass loss, the first stage was elimination of moisture, and the second stage was the decompositions of functional group and main chain. Moreover, the decomposition of tertiary amine had three stages, the polyamine was a continuous mass loss process, and the thermostability of tertiary amine was weaker than that of polyamine.     

Phase transitions and microstructure of emulsion systems prepared with acylglycerols/zinc stearate emulsifier

The emulsification processes, during which acylglycerols/zinc stearate emulsifier, water, and oil phase formed ternary systems, such as water-in-oil (W/O) emulsions, oil-in-water (O/W) dispersions, and unstable oil-water mixtures, were investigated in order to characterize the progressive transformations of the dispersed systems. The type, structure, and phase transitions of the systems were found to be determined by temperature and water phase content. Crystallization of the emulsifier caused the destabilization and subsequent phase inversion of the emulsions studied, at a temperature of 60-61 degrees C. The observed destabilization was temporary and led, at lower temperature, to W/O emulsions, "O/W + O" systems, or O/W dispersions, depending on the water content. Simultaneous emulsification and cooling of 20-50 wt % water systems resulted in the formation of stable W/O emulsions that contained a number of large water droplets with dispersed oil globules inside them ("W/O + O/W/O"). In water-rich systems (60-80 wt % of water), crystallization of the emulsifier was found to influence the formation of crystalline vesicle structures that coexisted, in the external water phase, with globules of crystallized oil phase. Results of calorimetric, rheological, and light scattering experiments, for the O/W dispersions obtained, indicate the possible transition of a monostearoylglycerol-based alpha-crystalline gel phase to a coagel state, in these multicomponent systems.     

Magnesium isotope separation by ion exchange using hydrous manganese(IV) oxide

The magnesium isotope effects were investigated by chemical ion exchange with a hydrous manganese(IV) oxide. The capacity of manganese(IV) oxide was 0.5 meq g(-1). The distribution coefficient of magnesium ions on the MnO(2) was determined by a batch method. The heavier isotopes of magnesium were enriched in the solution phase, while the lighter isotopes were enriched in the hydrous MnO(2) phase. The separation factor was determined according to the method of Glueckauf from the elution curve and isotopic assays. The separation factors of (24)Mg(2+)-(25)Mg(2+), (24)Mg(2+)-(26)Mg(2+), and (25)Mg(2+)-(26)Mg(2+) isotope pair fractionations were 1.011, 1.021, and 1.011, respectively.     

A radiochemical study of the kinetics of ion exchange on hydrous titanium dioxide

This paper reports a radiochemical study of the kinetics of ion exchange of Na⁺ and Cs⁺ with H⁺ on hydrous titanium dioxide. The experimental conditions are set to favor the particle diffusion mechanism only, and this is confirmed by the Bt versus t plots. On the basis of these studies the various physical parameters such as the effective diffusion coefficients, activation energies and entropies of activation have been evaluated. Tentative explanations are given for these results, from which some conclusions are drawn.     

Dispersion of rhodium on rutile: Comparison of samples prepared by ion exchange and impregnation

Rh/TiO₂ (rutile) samples have been prepared by impregnation (series I) and ion exchange (series C). Upon reduction at low temperature (473 K) the metal dispersity is larger for samples C than for samples I. Removal of surface OH groups in series C cancels the strong Metal-Support Interaction, thus increasing the metal dispersity measured upon reduction at 773 K.

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Rh/TiO₂ () ( Ї) ( ). (473 K) , . - SMSI- 773 K.

     

Reduction of colloidal manganese dioxide by manganese(II)

The reduction of colloidal MnO(2) by Mn(2+) in aqueous HClO(4) has been studied by a spectrophotometric method. The reaction product is Mn(III). The reaction is of first order in both colloidal MnO(2) and H(+), whereas it presents a fractional order (0.58+/-0.02) in Mn(2+). The reaction is retarded by addition of NaClO(4), but is not affected by addition of tert-butanol. The corresponding activation energy is 29.5+/-1.3 kJ mol(-1). The reaction is catalyzed by Na(4)P(2)O(7), and the pyrophosphate-catalyzed reaction is of first order in both colloidal MnO(2) and pyrophosphate and of fractional order (0.64+/-0.01) in Mn(2+), whereas its rate presents a complex dependence on the concentration of H(+). The pyrophosphate-catalyzed reaction is accelerated by addition of both NaClO(4) and tert-butanol. The corresponding activation energy is 49.7+/-3.0 kJ mol(-1). Mechanisms in agreement with the experimental data are proposed for both the parent and the pyrophosphate-catalyzed reactions.     

Phase behavior of β-d galactose pentaacetate–carbon dioxide binary system

Phase behavior of β-d galactose pentaacetate–carbon dioxide binary system is investigated by dew-point and bubble-point measurements conducted in a high pressure variable volume sapphire cell. The phase envelope for solutions of β-d galactose pentaacetate in supercritical CO₂ is obtained for β-d galactose pentaacetate concentrations between 2 and 26 wt%, and for the temperature range of 308–323 K. The system exhibits lower critical solution temperature (LCST) behavior and high solubility of β-d galactose pentaacetate is observed. The densities of the system are also measured, and liquid-like densities (near 1 g/cm³) are observed for single-phase solutions of β-d galactose pentaacetate in supercritical CO₂ at concentrations of 18 wt% and higher. Viscosity is measured for solutions of 18 and 25 wt% β-d galactose pentaacetate in the single-phase region at 313 K and 17 MPa and the viscosity values, 0.095 and 0.103 cp, respectively, are similar in magnitude to the viscosity of pure carbon dioxide.     

Effects of urea induced protein conformational changes on ion exchange chromatographic behavior

Urea is widely employed to facilitate protein separations in ion exchange chromatography at various scales. In this work, five model proteins were used to examine the chromatographic effects of protein conformational changes induced by urea in ion exchange chromatography. Linear gradient experiments were carried out at various urea concentrations and the protein secondary and tertiary structures were evaluated by far UV CD and fluorescence measurements, respectively. The results indicated that chromatographic retention times were well correlated with structural changes and that they were more sensitive to tertiary structural change. Steric Mass Action (SMA) isotherm parameters were also examined and the results indicated that urea induced protein conformational changes could affect both the characteristic charge and equilibrium constants in these systems. Dynamic light scattering analysis of changes in protein size due to urea-induced unfolding indicated that the size of the protein was not correlated with SMA parameter changes. These results indicate that while urea-induced structural changes can have a marked effect on protein chromatographic behavior in IEX, this behavior can be quite complicated and protein specific. These differences in protein behavior may provide insight into how these partially unfolded proteins are interacting with the resin material.     

Phase behavior and photocrosslinking kinetics of semi-interpenetrating polymer networks prepared from miscible polymer blends

Mixtures of polystyrene derivatives (PSCS) and poly(vinyl methyl ether) (PVME) were made photocrosslinkable by chemically labeling PSCS chains with photoreactive anthracene. Miscibility of these anthracene-labeled PSCS/PVME blends was examined by light scattering under several crosslinking conditions in the one-phase region via photodimerization of anthracenes. As the reaction proceeds, the coexistence curve of PSCS/PVME blends shifts toward the low temperature side. By following the changes in concentration of anthracenes with irradiation time, it was found that the crosslinking reaction of PSCS chains in the blends does not follow the mean-field kinetics. However, it can be well expressed by the Kohlrausch–Williams–Watts (KWW) relaxation mechanism, indicating that the crosslinking reaction proceeds inhomogeneously in the blends. By scaling the reaction time with the average reaction rate obtained from the KWW equation modified for the reaction kinetics, all the crosslinking data obtained in the miscible region of the reacted blends fall on a single master curve. These experimental results suggest the universal behavior of the photocrosslinking kinetics obtained under the “shallow quench” conditions in the region far away from the coexistence curve of the reacting blends. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 455–462, 1998     

Isotopic exchange between manganese hydroxide and manganese ions in aqueous solution

Heterogeneous isotopic exchange between manganese hydroxide and manganese ions in aqueous solutions tagged with radioactive⁵⁴Mn has been studied at different values of α, the ratio of the quantity of exchangeable ions in the solid phase to that in the liquid phase. The aging of the precipitate in its mother liquor prior to the exchange has a significant effect on both the extent and rate of the exchange reaction. A marked feature of great interest is the appearance of two aging-times, one at about 10² and the other at about 10⁴ min. The overall reaction appears to be of the consecutive type. In the case of a fresh precipitate, “complex-surface-exchange” and “self-diffusion” mechanisms are the most probable rate-determining steps in the initial and final stages of the reaction, respectively. “Complex-surface-exchange” is a new suggested mechanism. In the case of a well-aged precipitate, “surface-exchange” and ‘self-diffusion” mechanisms are the most probable-determining steps in the initial and final stages of the reaction, respectively.