Presence Of Alkaline Earth Cations Research Articles

Application of Alcohols to Inhibit the Formation of Ca(II) Dodecyl Sulfate Precipitate in Aqueous Solutions.

The presence of alkaline earth cations, in particular, Ca2+ and Mg2+ ions in brine, causes undesired effects in solutions containing anionic surfactants because of precipitate formation. In the present study, an anionic surfactant, sodium dodecyl sulfate (SDS), was investigated, focusing on the determination of various properties (surface tension, critical micelle concentration, micelle size, turbidity) in the presence of alcohols and, in particular, the inhibition of the precipitation of SDS with calcium ions. The calcium ions were added to the surfactant in increasing concentrations (3.0-10.0 g/L), and short-carbon-chain alcohols (methanol, ethanol, n-propanol and n-butanol) were used to shift the onset of precipitate formation. The critical micelle concentration (CMC) of SDS in the presence of alcohols was also determined. It was established that among these alcohols, methanol and ethanol did not exert significant effects on the solubility of the Ca(DS)2 precipitate, while n-propanol and n-butanol were found to be much more efficient inhibitors. In addition, all the alcohols in the applied concentration range (up to 20 V/V%) were found to decrease the critical micelle concentration of SDS.

Acceleration of the photocatalytic degradation of organics by in-situ removal of the products of degradation

Photocatalytic degradation of sulphur containing organics in water was substantially accelerated by the in-situ removal of sulphur oxide species formed by the dye degradation as metal sulfate precipitates. The significant enhancement of the degradation of methylene blue (C16H18ClN3S) and acid yellow 42 (C32H24N8Na2O8S2), as examples of sulphur containing organics, was achieved when the reactions were conducted in the presence of alkaline earth cations (such as Ca2+, Sr2+, and Ba2+).

Phase Formation in Copper and Calcium Titanate Dielectric Ceramic Obtained by Polymeric Precursor Method

The polycrystalline ceramic named calcium and copper titanate is a dielectric ceramic with very high dielectric constant applicable in several electronic devices. The powder form for that advanced ceramic can be synthesized through chemical route, like the Polymeric Precursor Method at relative lower temperatures the presence of alkaline earth cations harms the structural homogenization during the crystallization process. In this work, the calcium and copper titanate powder was obtained by Polymeric Precursors Method by imposing a slow thermal decomposition of polymeric precursor and several crushing steps before the calcination at 800 °C for 4 hours. The entire process was observed by thermogravimetric analysis and FTIR spectrometry, including the nitrogen adsorption-desorption isotherms and X-ray diffractometry techniques for calcined power samples. It was observed the crystallization of the cubic Im-3 Ca1/4Cu3/4TiO3phase only starts after organics removal and full calcium carbonate elimination above 700 oC, which is followed by pore elimination and particle sintering. The chemical synthetic route used in this work shows the ability to prepare CCT powders sample with very structural homogeneity, which characteristics are required to manufacturing many electronic devices.

Photo- and ionochromic properties of aza crown derivatives of enamino 1-benzothiophen-2-ones

2-(N-Acyl-N-arylaminomethylidene)-1-benzothiophen-3(2H)-ones exhibit photochromic properties due to photoinitiated Z/E isomerization with respect to the exocyclic C=C bond and subsequent fast thermal N→O migration of the acyl group and syn→anti isomerization of the N-acyl isomer. Introduction of a 15-azacrown-5 substituent into the para position of the aryl group reduces the quantum yield of the N→O rearrangement down to zero. By contrast, under irradiation with a mercury lamp, crown ether complexes with alkaline earth cations are converted almost completely into the O-acyl isomers which, unlike their N-acyl analogs, show no fluorescence. The highest quantum yields for the N→O acyl group migration are observed for the calcium complexes. The obtained compounds constitute a new class of acylotropic molecular switches operating under photoinitiation exclusively in the presence of alkaline earth cations.

Structure of Alginate Gels: Interaction of Diuronate Units with Divalent Cations from Density Functional Calculations

The complexation of (1→4) linked α-L-guluronate (G) and β-D-mannuronate (M) disaccharides with Mg(2+), Ca(2+), Sr(2+), Mn(2+), Co(2+), Cu(2+), and Zn(2+) cations have been studied with quantum chemical density functional theory (DFT)-based method. A large number of possible cation-diuronate complexes, with one and two GG or MM disaccharide units and with or without water molecules in the inner coordination shells have been considered. The computed bond distances, cation interaction energies, and molecular orbital composition analysis revealed that the complexation of the transition metal (TM) ions to the disaccharides occurs via the formation of strong coordination-covalent bonds. On the contrary, the alkaline earth cations form ionic bonds with the uronates. The unidentate binding is found to be the most favored one in the TM hydrated and water-free complexes. By removing water molecules, the bidentate chelating binding also occurs, although it is found to be energetically less favored by 1 to 1.5 eV than the unidentate one. A good correlation is obtained between the alginate affinity trend toward TM cations and the interaction energies of the TM cations in all studied complexes, which suggests that the alginate affinities are strongly related to the chemical interaction strength of TM cations-uronate complexes. The trend of the interaction energies of the alkaline earth cations in the ionic complexes is opposite to the alginate affinity order. The binding strength is thus not a limiting factor in the alginate gelation in the presence of alkaline earth cations at variance with the TM cations.

Effect of Group II Metal Cations on Catecholate Oxidation

The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation.

Improving the efficiency of rapid sandfilters by adding small amounts of ferric salts (βFe ≤ 0.1 mg·L-1)

Improved removal of suspended matter during the treatment of water from Lake Constance has been achieved by pre-ozonation (βO3 = 1 mg·L-1 corresponding to 0.8 mg O3/mg DOC) and the addition of small quantities of iron salts (βFe≤0.1 mg·L-1; “Fe(III)-assisted filtration”) followed by rapid sand filtration. As shown by investigations on a large-scale installation (bypass mode) over several years, this procedure reliably reduces particulate matter in the water by about 3 orders of magnitude in long-term use. However, the high efficacy of Fe(III)-assisted filtration cannot be explained on the basis of known coagulation mechanisms (adsorption-charge neutralization, co-precipitation). Instead, the essential step was found to be the conditioning of the filter medium by coating it with colloids containing Fe(OH)3, and this “Fe coating” process only occurs in the presence of alkaline earth cations (especially Ca2+). According to further experiments, the enhanced solid-liquid separation was ultimately traced to chemical interactions such as the formation of calcium-NOM bridges between the iron hydroxides and other solids.

Ion specificity and viscosity of rutile dispersions

The isoelectric point (IEP) of rutile is shifted to higher pH values in the presence of greater than 10−4 mol dm−3 Ba2+, Ca2+ and Mg2+, and when a critical concentration (5 × 10−4 mol dm−3 for Ba2+ and 1 × 10−3 mol dm−3 for Ca2+) is exceeded there is no IEP at all and the ζ potential is always positive. A common intersection point for the ζ-potential curves of the different concentrations of salt is found, but for the various salts the point is shifted from ζ = 0 mV for Mg2+ up to ζ = 20 mV for Ba2+. Between the IEP and the charge-reversal point a rheologically unstable region is discovered. The shear stress of rutile dispersions (2.5 g rutile + 4 g electrolyte solution) at shear rates of 116 s−1 shows the same pH dependence irrespective of the concentration of alkaline-earth metal cations up to 10−2 mol dm−3. The shear stress is less than 1 Pa below pH 3.8 and in the pH range 5–12 it assumes a value between 50 and 80 Pa at 116 s−1 with some scatter; however, no systematic trend with concentration of alkaline-earth metal cations and a rather insignificant decrease with pH at pristine conditions are observed. The acidic branch of the yield stress (pH) and low shear rate viscosity (pH) curves is insensitive to the presence of alkaline-earth metal cations, and the same behaviour is found for the ζ potential. The alkaline-earth metal cations induce an increase in viscosity in the basic region and a shift in the pH of maximum viscosity to high pH values. It was also discovered that the effect different alkaline-earth metal cations have on the rheological properties at the same concentration is different from the effect induced by indifferent electrolytes. When the ζ potential increases the viscosity at high pH is increased in a series which follows the increase in size of the cation.

Surface properties of catalytic aluminas modified by alkaline-earth metal cations: A microcalorimetric and IR-spectroscopic study

Lewis acidic properties of transition aluminas whose surfaces have been doped with alkaline-earth metal cations (Ca2+ and Ba2+) were studied by means of the room temperature adsorption of carbon monoxide. The vibrational features of CO adsorbed at the surface of doped aluminas were investigated by IR spectroscopy in comparison with pure parent aluminas, while the quantitative and energetic features were studied by adsorption microcalorimetry. Various CO adspecies were found to form at the surface of both pure and doped-alumina, owing to the structural heterogeneity of the Al2O3 surface and to the presence of alkaline-earth metal cations. The surface heterogeneity was revealed by different vco stretching frequencies, namely vco≈2230, 2218 and 2205 cm−1 for coordinatively unsaturated tetrahedral Al3+ cations in different crystallographic configurations, and vco≈2186 and 2172 cm−1 for coordinatively unsaturated Ca2+ and Ba2+ cations, respectively. Heats of adsorption of ≈80, 70 and 55 kJ/mol were assigned to the formation of Al3+/CO complexes, ≈45 kJ/mol for Ca2+/CO and ≈30 kJ/mol for Ba2+/CO complexes. The latter value was estimated through a correlation curve existing between vco stretching frequencies and adsorption enthalpies. This correlation, already proposed in the past for CO adsorbed on non-d/d0/d10 metal cations, has been revisited and confirmed here, by including Al2O3 data for which an apparent lack of correlation between the two parameters was first observed. With respect to pure alumina, the population of Lewis acidic sites was found to be significantly depressed by the presence of alkaline-earth cus metal cations. These acidic sites are intrinsically weaker than tetrahedral cus Al3+ cations, as witnessed by smaller upward shifts of the vco stretching frequencies with respect to CO gas and lower heats of adsorption, in accordance with expectations from the charge/ionic radius ratios. Ca2+ cations were found to compete in adsorbing CO with Al3+ cations more efficiently than the larger Ba2+ cations. In the case of CaO/Al2O3 systems outgassed at 1023 K, a thin surface layer of calcium aluminate, not detected by XRD or HRTEM, was suggested to form.

Factors Affecting the Adsorption of Complexed Heavy Metals on Hydrous Al2O3

Factors influencing the adsorption behavior of heavy metals, viz Cu(II), Zn(II), Cd(II), Pb(II) and Ni(II), onto Al2O3 from aqueous solutions containing complexing ligands were investigated using batch adsoption experiments. For the Cu(II)/NTA/ γ-Al2O3, system, increasing the system ionic strength reduced Cu adsorption through activity coefficient and surface electrical double layer effects. The presence of alkaline earth cations (Ca(II) and Mg(II)) also reduced Cu removal from solution by lowering the ability of NTA to prevent Cu(OH)2 precipitation and through specific adsorption to the alumina surface. The adsorption of the heavy metals on Al2O3 from solutions containing NTA followed the sequence: Cu >Zn > Cd > Pb ≈ Ni. Increase in system temperature tended to decrease metal adsorption.

Oxidizing agents produced by radiolysis of alkali-metal halide melts

1. The optical spectra of the oxidizer components of radiolysis of alkali-metal halide melts, the molecular anion-radicals Γ 2 − , are similar to the spectra of the corresponding species in aqueous solutions. 2. Rate constants have been measured for the disappearance of Γ 2 − , which goes forward mainly in the reaction of Γ 2 − with the reduced form of the cation. 3. In the presence of alkaline-earth metal cations, owing to the fast disproportionation of their reduced form, there is a greater contribution from the relatively slow reaction of disproportionation of Γ 2 − , leading to an observed retardation of the rate of Γ 2 − disappearance and an increase in the yield of molecular halogen.

Decomposition of n-butane on alkaline-earth mordenites

The acidity of alkaline-earth mordenites, as observed by the ir spectra of adsorbed pyridine, has been correlated with their activity as catalysts for n-butane decomposition. The results indicate that Brønsted acid sites are the origin of the catalytic activity. However, the presence of Lewis acid sites is necessary for the reaction to take place, suggesting an inductive effect of these sites on the Brønsted sites. The presence of alkaline-earth cations in decationated mordenites decreases the activity of the original sample; this influence increases with decreasing ionic radius. This result is interpreted as a weakening of the inductive effect produced by the structural Lewis sites through a fall in their number by the cation exchange process. The reactant molecules are coordinatively bound to the cations to an extent which is strongly dependent on their electrostatic field, thus influencing the accessibility of the Brønsted sites.

Adsorption of Alkaline Earth, Transition, and Heavy Metal Cations by Hydrous Oxide Gels of Iron and Aluminum

AbstractFreshly precipitated Fe and Al gels (points of zero change at pH 8.1 and 9.4, respectively) strongly specifically adsorb divalent cations from 1M NaNO3 solution. Adsorption from a mixed solution of eight divalent cations (each 0.125 × 10‐3M) in suspensions of freshly precipitated Fe and Al gels (0.093M with respect to Fe or Al) was measured as a function of pH in 1M NaNO3. The selectivity sequence (lower pH = greater selectivity) for the retention of the alkaline earth cations by Fe gel was Ba > Ca > Sr > Mg, but for the Al gel was Mg > Ca > Sr > Ba. The selectivity sequence (Figures in parentheses indicate pH ± 0.2 for 50% retention) for the Fe gel was: Pb (3.1) > Cu(4.4) > Zn(5.4) > Ni(5.6) > Cd(5.8) > Co(6.0) > Sr(7.4) > Mg(7.8), whereas the sequence for the Al gel was: Cu(4.8) > Pb(5.2) > Zn(5.6) > Ni(6.3) > Co(6.5) > Cd(6.6) > Mg(8.1) > Sr(9.2). Significant adsorption occurred even when the extent of cation hydrolysis was much < 1%, and invariably occurred at a pH lower than that for hydroxide precipitation. Although the adsorption‐pH sequences are related to cation hydrolysis and hydroxide precipitation pH values, the relationship is far from perfect, as is evidenced by the different sequences for the two gels. On aging of the Al gel in the presence of alkaline earth cations, the retention of Mg increased, while that of Ca, Sr, and Ba decreased. This result was thought to result from the structural incorporation of some Mg and the exclusion of the other cations.