Sorption properties of freshly precipitated alumogels

The influence of the pH of precipitation and the ionic medium nature on the composition, surface charge, and kinetic sorption characteristics of aluminum oxyhydroxides formed by alkaline hydrolysis of an aqueous solution of aluminum nitrate was studied. The methods of drop titration with alkali, argentometric titration, point of zero charge, and indicator reactions of heterogeneous hydrolysis were used. The composition of the freshly precipitated hydrogels of aluminum(iii) oxyhydroxide, rate constants of heterogeneous hydrolysis of the IrCl₆ ^2– ions as indicator reactions, and the pH of the point of zero charge were determined. The rate of indicator reactions (as for other oxyhydroxide hydrogels) depends strongly on the pH of precipitation. However, it is lower than the rates characteristics of iron(iii) and chromium(iii) oxyhydroxides obtained under similar conditions. The pH of the point of zero charge for the alumogels in a chloride medium is 8.3 and that in a sulfate medium is 9.5.     

Effect of ligands on the thermolysis of the double complexes [Co(NH3)6]2C2O4[Cu(C2O4)2]2 and [Co(NH3)6]Cl[Cu(C7H4O3)2]

The thermolysis of the complexes [Co(NH₃)₆]₂C₂O₄[Cu(C₂O₄)₂]₂ (I) and [Co(NH₃)₆]Cl[Cu(C₇H₄O₃)₂] (II) in air and hydrogen at 200, 350, and 500°C and the composition and properties of the thermolysis products are considered. The oxidative thermolysis of the complexes yields mixtures of cobalt and copper oxides, including mixed ones. The reductive thermolysis of the complexes yields a Co + Cu bimetallic powder in the case of compound I and a Co + Cu + C powder in the case of compound II. The thermal behavior of the complexes is governed by the nature of the ligand coordinated to the copper atom. The observed data are explicable in terms of the properties of this ligand. The chemistry of the oxidative and reductive thermolysis is discussed. Original Russian Text ? D.P. Domonov, S.I. Pechenyuk, N.L. Mikhailova, A.T. Belyaevskii, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1104–1110.     

The thermal behavior of double complex compounds with the cation [Cr(ur)6]3+ in a reducing atmosphere

Journal of Thermal Analysis and Calorimetry - The thermal behavior of double complex compounds (DCC) [Cr(ur)6][Co(CN)6]·4H2O (I), [Cr(ur)6][Co(C2O4)3]·3.5H2O (II),...     

The use of the pH at the point of zero charge for characterizing the properties of oxide hydroxides

The modern theoretical views on the point of zero charge of the oxide hydroxide surface are considered. Methods for determination of the pH of the point of zero charge and the use of this value to characterize the properties of oxide hydroxides are described. Examples of using the pH of the point of zero charge in studies of oxide anodes and amorphous oxide hydroxide sorbents are presented. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1029–1035, June, 1999.     

Synthesis, properties, and thermal decomposition of compounds [Co(En)3][Fe(CN)6] · 2H2O and [Co(En)3]4[Fe(CN)6]3 · 15H2O

Binary complex salts, [Co(En)₃][Fe(CN)6] · 2H₂O and [Co(En)₃]₄[Fe(CN)₆]₃ · 15H₂O, are synthesized. The properties of the salts and their thermolysis in air, dihydrogen, and argon are studied. Oxides of the central ions of the binary complex salts are found to be the thermolysis products in an oxidative atmosphere. Solid solutions (intermetallic compounds) CoFe are the thermolysis products in the reductive atmosphere, whereas intermetallides containing considerable amounts of C and N and an impurity of Co and Fe oxides are the thermolysis products in an inert atmosphere. Gaseous thermolysis products in dihydrogen and argon are NH₃, hydrocarbons, and ethylenediamine.     

Estimation of oxyhydroxide specific surface area using the amounts of OH groups adsorbed

A procedure for pH-metric determination of the limiting adsorption of OH groups (A _OH) by Fe^III, Zr^IV, Cr^III, and In^III oxyhydroxide hydrogels from 0.1 and 1.0 M solutions of NaCl is described. Data on the molecular area occupied by a single OH group on the hydrogel surface (S _OH) and the S _spec values, which were calculated from A _OH and S _OH, are presented. The S _spec value does not depend on the pH of hydrogel precipitation; the true S _spec value can be determined only from sorption of the OH groups at the actual point of zero charge of the hydrogel. The A _OH values for hydrogels were found to change only slightly during aging of hydrogels in electrolyte solutions.     

Anion effect on the thermolysis of double complexes [Co(NH3)6][Fe(CN)6] and [Co(NH3)6]4[Fe(CN)6]3

The thermolysis of complexes [Co(NH₃)₆][Fe(CN)₆] and [Co(NH_{3 6}]₄[Fe(CN)₆]₃ under an air or hydrogen atmosphere at 200, 350, and 500°C is studied. The composition and properties of thermolysis products are determined. The oxidative thermolysis yields mixtures of oxides of the central metals; the reductive thermolysis yields intermetallic compounds CoFe. The density of the complexes and the specific surface area of the intermetallic compounds are measured. Average particle sizes are calculated. The morphology and dispersion of the powders are dictated by the shape and density of the crystals of the precursor double salts and the thermolysis temperature. The thermolysis chemism in the oxidative and reductive atmospheres is discussed in the context of the nature of the complex anion. Original Russian Text ? S.I. Pechenyuk, D.P. Domonov, D.L. Rogachev, A.T. Belyavskii, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1110–1115.     

Changes in the adsorption activity of metal oxyhydroxide hydrogels during their ageing in electrolyte solutions

Adsorption properties of Ti(IV), Zr(IV), In(III), Cr(III) and Fe(III) oxyhydroxides aged in sodium chloride and sulphate solutions have been studied. The main research method was determination the rates of heterogeneous hydrolysis reactions for RhCl₆³⁻ and IrCl₆²⁻ complexes. The rate constants of these reactions were a measure of adsorption activity of the oxyhydroxides on which surface they occur. For comparison the corresponding data for freshly formed oxyhydroxides are presented. It was found that adsorption activity (the values of rate constants K_obs) of ferro- and indiogels decrease slowly with increasing of duration and temperature of ageing. The sulphate electrolyte promotes the decrease of sorption activity more than chloride electrolyte. In contrast, the samples of titano- and chromogels aged during 2 h at 80°C have much greater adsorption activity than freshly formed ones, and this activation holds for a very long time. The zirconogel keeps in these conditions stable adsorption activity for a very long time. Apparently, after precipitation the chromo-, titano- and zirconogels some metastable non-crystalline or micro-crystalline structures stable to further ageing form rapidly. The oxyhydroxides behaviour is obviously connected with the electronic structure of outer electronic shell of their central ions. The chromium(III) oxyhydroxide with a unsymmetrical, partially filled 3d-sublevel is the most effective sorbent and has the most stable sorption properties.     

Products of binary complex compounds thermolysis: Catalysts for hydrogen peroxide decomposition

Samples are obtained via the thermolysis of binary complex compounds in a hydrogen atmosphere. Their catalytic activity in hydrogen peroxide decomposition is studied. The values of the rate constants and activation energies for the catalytic reaction are estimated. The correlation between catalytic activity, composition, specific surface area (S _sp), and particle size of the samples is analyzed.     

Conversions of coordinated ligands by reducing thermolysis of some double complex compounds

Thermal decomposition of binary complexes [M(NH₃) _k ] _x [M′L _n ] _y (M = Ni, Co; M′ = Fe, Cr, Cu; L = CN⁻, SCN⁻, C₂O₄²⁻) in a hydrogen atmosphere showed conversion of coordinated CN⁻ groups into ammonia and hydrocarbons; SCN⁻ into ammonia, hydrogen sulfide, and hydrocarbons; and C₂O₄²⁻ into hydrocarbons and CO₂. In all cases, methane prevails in the resulting hydrocarbons; ethylene is the second in relative yield, which however strongly depends on the temperature and combination of the central ions of double complex salts. The yield of ethylene is especially high from the reduction of Co-Fe complexes at 350°C, Co₄-Fe₃ complexes at 500°C, Ni₃-Fe₂ and Ni₃-Cr₂ complexes at 350°C. The observed conversions of coordinated groups can be interpreted as arising from the catalytic effect caused by the reduced forms of the central atoms in the binary complexes to the interaction of ligands with hydrogen.