ABSTRACT
The pores in an aluminum oxide matrix can be completely filled with 1-alkyl-3-methylimidazolium tetrafluoroborates, hexafluorophosphates, triflates, and bis(trifluoromethylsulfonyl)imides. This possibility can be utilized to produce solid electrolytes for batteries and fuel cells.
ABSTRACT
Theelectrokinetic curves of silica obtained at given total concentrations of heavy metal cations depend on the solid-to-liquid ratio; namely, at low solid-to-liquid ratios the sign of the zeta potential of silica is reversed to positive at relatively low concentrations of heavy metal cations, while at higher solid-to-liquid ratios the electrokinetic curves are not substantially influenced at much higher concentrations. The surface complexation model fails to properly reflect the Ni effect on the course of electrokinetic curves of silica. The course of electrokinetic curves [positions of the isoelectric point(s) and of the maxima in mobility] is correlated with a linear combination of the surface charge density in the absence of heavy metal cations at given ionic strength and the adsorption density of Ni. Copyright 1999 Academic Press.
ABSTRACT
The temperature effect on the magnitude of adsorption was used to explain the mechanism of adsorption of gadolinium on silica at very low concentrations. Standard enthalpy of adsorption of gadolinium equals 36 kJ mol-1 for a total Gd concentration of 2 x 10(-8) mol dm-3 and 67 kJ mol-1 for 2 x 10(-5) mol dm-3. This result confirms the hypothesis that the Gd adsorption at low initial concentration is governed by formation of strong ternary surface complexes involving anionic impurities. Copyright 1999 Academic Press.
ABSTRACT
The viscosity at an arbitrarily selected shear rate of 1.16 s-1 and the yield stress of anatase dispersions are linearly correlated, and both show a maximum at the isoelectric point (IEP) at pristine conditions. The rheological properties of anatase dispersions respond to the shift in the IEP to higher pH values, which is observed in concentrated solutions of 1-1 electrolytes and in the presence of the organic cosolvents, but the shift in the pH corresponding to a maximum viscosity does not exactly match the shift in the IEP. In contrast with the electrokinetic curves, the rheological curves at high ionic strengths are rather insensitive to the nature of the supporting electrolyte. The acidic branch of the viscosity(pH) curves is relatively insensitive to the ionic strength while the slope of the basic branch decreases when the ionic strength increases. Copyright 1999 Academic Press.
ABSTRACT
The sign and magnitude of the ζ potential of mineral oxides in allegedly pure organic solvents (high-quality chemical reagents) depends on the concentration of acidic and basic impurities, chiefly organic acids and amines. "Zetametric titration" with HClO(4) makes it possible to estimate the concentration of basic impurities and offers an attractive alternative to other analytical methods. Titanium(IV) oxide has been chosen as the probe powder in view of its very low solubility and nearly neutral point of zero charge in aqueous systems. Some systems have a high buffer capacity and addition of acid and base has a minor effect on the ζ potential of titania. Specific adsorption of alkali metal cations on anatase can be also a significant problem.
ABSTRACT
The presence of chlorides promotes a positive electrokinetic charge of silica. Silica shows an isoelectric point (iep) at pH 2 in the presence of HCl but at pH < 1.5, if any, in the presence of HClO4 and HNO3. The iep of silica in the presence of different 1:1 salts depends on the nature and concentration of the salt. The highest value of pH, 5.5, was observed for 0.1 mol dm-3 cesium chloride and nitrate. A larger increase in cesium salt concentration shifts the iep back to low pH values and at >0.5 mol dm-3 there is no iep (only negative zeta potentials). Copyright 1998 Academic Press.
ABSTRACT
Standard enthalpies of Ni(II), Gd(III), and Y(III) adsorption on alumina can be estimated from the temperature effect on apparent equilibrium constants of surface reactions. The results are relatively insensitive to the choice of the adsorption model, although the calculated apparent equilibrium constants of surface reactions at a given temperature are model dependent and they often differ by several orders of magnitude from one model to another. The conditions of the experiment-solid-to-liquid ratio, initial concentration of multivalent cations in solution, presence of various 1:1 and 2:1 electrolytes at various concentrations-do not significantly affect the calculated values of standard enthalpies of adsorption. Assuming that the total number of surface sites and the number of protons released per one adsorbed heavy metal cation do not depend on temperature, the standard enthalpies of adsorption on alumina at constant pH are 65 kJ/mol for Ni, 90 kJ/mol for Gd, and 90 kJ/mol for Y. The presence of alkaline earth metal cations (up to 0.05 mol dm-3) does not significantly influence the adsorption of nickel and gadolinium on alumina. Thus, barium and magnesium do not compete with heavy metal cations for the surface sites.
ABSTRACT
Isotherms of adsorption of Ni(II) on silica from 0.01 M NaClO4 are almost linear with a log-log slope of 0.95, and the percentage of uptake at a given pH is insensitive to the initial Ni concentration. At higher ionic strengths (>/=0.1 mol dm-3 ) two kinds of behavior are observed. For low Ni concentrations the adsorption is approximately equal to that observed at lower ionic strengths. For higher Ni concentrations (but still much lower than the concentration of surface sites) the Ni adsorption from 0.1 and 0.3 mol dm-3 NaClO4 is lower than the adsorption from 0.01 M NaClO4 by a factor of 2 (pH 9) to 3 (pH 8). When water is replaced by a mixed solvent (e.g., 2% aqueous DMSO, THF, methanol, glycerol) the Ni adsorption isotherms obtained in the presence of 0.1 mol dm-3 NaClO4 are linear with a log-log slope of 0.95. These adsorption isotherms are rather insensitive to the nature and concentration of the organic cosolvent. It is impossible to explain the Ni adsorption curves over the entire studied range of initial concentrations and ionic strengths in terms of surface complexation model, unless the Boltzmann factor is properly corrected.
ABSTRACT
Gadolinium and yttrium show very similar adsorption behaviors on silica. For the both trivalent cations, the adsorption isotherms are insensitive to the ionic strength. The slope of the log-log adsorption isotherms at a constant pH is considerably lower than 1, except for the range of very low equilibrium concentrations. This behavior can be explained without invoking surface heterogeneity considering the presence of a small concentration of anions, An2-, as an impurity. A hypothetical ternary complex SiOGdAn is very strong and this leads to enhanced uptake at low initial concentrations. When [Gd3+] >> [An2-], only a small fraction of Gd can be adsorbed as SiOGdAn and the percentage of uptake is low. Copyright 1997 Academic Press. Copyright 1997Academic Press
