Formation of tricuprotetraborate 3CuO · 2B2O3 · 6H2O in aqueous solutions

The reaction of copper sulfate, boric acid, and sodium hydroxide in an aqueous solution was studied in relation to the molar ratio and concentration of components, solution pH, temperature, and reaction duration. The conditions under which tricuprotetraborate hexahydrate 3CuO · 2B₂O₃ · 6H₂O is formed were determined.     

New baths for the deposition of manganese and cobalt oxides

New methods have been adopted for the anodic deposition of the different manganese and cobalt oxides. The deposition of the diferent oxides is usually carried out from their metal salt solutions in presence of a reducing agent. The oxides deposited are as follows: Mn₂O₃ from manganous sulphate in presence of boric, acid and formaldehyde at pH=5.5, Mn₃O₄ from manganous sulphate in presence of formic acid at pH=5.0 MnO from manganous sulphate-ammonium chloride solution in presence of telluric acid, Co₂O₃ from cobalt chloride in presence of telluric acid and sodium fluoride, Co₃O₄ from cobaltite in presence of formaldehyde and potassium chloride and finally CoO from cobalt chloride in presence of alcohol. The results of chemical analysis revealed that the purity of the oxides is 99.99% and their molecular formulae are MnO_1.5, MnO_1.33, MnO, CoO_1.5, CoO_1.33 and CoO respectively.     

Carbon paste electrode modified by cobalt ions dispersed into poly (N-methylaniline) preparing in the presence of SDS: application in electrocatalytic oxidation of hydrogen peroxide

Conducting and stable poly (N-methylaniline) film was prepared by using the repeated potential cycling technique in aqueous solution containing N-methylaniline, sulfuric acid, and sodium dodecyl sulfate (SDS) at the surface of carbon paste electrode (CPE). The transition metal ions of Co(ІІ) were incorporated to the polymer by immersion of the modified electrode in 0.1 M cobalt chloride solution for 10 min. The electrochemical characterization of this modified electrode exhibits stable redox behavior of Co(ІІ)→Co(ІІІ) and formation of insoluble oxide/hydroxide cobalt species on the CPE surface. The modified electrode showed well-defined and stable redox couples in alkaline aqueous solution. The modified electrode showed excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response of modified electrode toward the H₂O₂ oxidation was examined using cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, and chronoamperometry. This modified electrode has many advantages such as simple preparation procedure, good reproducibility, and high catalytic activity toward the hydrogen peroxide oxidation. Such characteristics were explored for the specific determination of hydrogen peroxide in cosmetics product sample, giving results in excellent agreement with those obtained by standard method.     

A study on effect of hydrogen reduction reaction on the initial stage of Ni electrodeposition using EQCM

Electrodeposition of Ni from acidic sulfate solution with/without the addition of boric acid was studied by electrochemical quartz crystal microbalance (EQCM) to further investigate the initial stage of Ni deposition. EQCM analysis showed that nickel hydroxide was formed due to the pH increase near the electrode caused by hydrogen evolution in the absence of boric acid. In the presence of boric acid, nickel hydride was formed. EQCM was found to be a useful in-situ tool for investigating the effects of the evolution and absorption of hydrogen on metal deposition and separating the charge used for Ni deposition and for hydrogen reduction.     

Electrodeposition of cobalt oxide films from carbonate solutions containing Co(II)–tartrate complexes

An electrochemical procedure of anodic deposition of cobalt oxyhydroxide film on a glassy carbon substrate in an alkaline medium (i.e. pH 11.6) is described. The electrodeposited film was obtained either by voltage cycling or by potentiostatic conditions using non-deaerated 0.1 M Na₂CO₃ solutions containing 40 mM tartrate ions and 4 mM CoCl₂. The effects on the film formation and growth, such as tartrate–cobalt ratio, pH, applied potential, etc. were widely evaluated. The electrodeposition process, under anodic conditions and moderately alkaline solutions, most likely involves a redox transition Co(II)→Co(III)/Co(IV) with destruction of the tartrate complex and formation of insoluble oxide/hydroxide cobalt species on the glassy carbon surface. The resulting cobalt oxyhydroxide films were characterised by cyclic voltammetry (CV) in 0.1 M NaOH solutions and by scanning electron microscopy (SEM) analysis after different strategies of preparation and various electrochemical treatments. The electrochemical activity of the deposited films was checked using various organic molecules as model compounds.     

Application of emulsion liquid membranes to recover cobalt ions from a dual-component sulphate solution containing nickel ions

Emulsion liquid membranes (ELMs) containing 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) have been applied to recover cobalt II ions from a dilute sulphate solution containing equal amounts of nickel II ions (0.16 g/l). We focused on the study to develop an effective technique to recover cobalt as a target metal. It is found that polyamine (PX 100) membranes allow better permeation rates of cobalt ions than sorbitan monooleate (Span 80) membranes. The separation factor (β_Co/Ni) in polyamine membranes averaged 70 at a carrier concentration of 12 mol/m³ and feed solution pH 5.5. The permeation rate of Co II was found to increase proportionately with feed pH while for Ni II it decreased substantially at pH above 5.5 indicative of slower interfacial reaction rate. We found that short contact time (4–6 min) of feed solution and emulsion improved separation factor (β_Co/Ni) at feed pH above 5.5 and also minimized chances of emulsion break up. We have also observed that Span 80 membranes are hydrolyzed readily in a moderate acidic sulphate solution (pH 4.0–5.5) to form viscous gels. Results have shown that excess carrier [(HR)₂] affects the stability of emulsion and thus the separation factor. The critical ratio of carrier to emulsifier [(HR)₂]/[C_sf] was found to be approximately 0.5. This paper concludes with a discussion on the prospects of ELM system in practical use.     

Properties of Zinc alloy electrodeposits produced from acid and alkaline electrolytes

Zinc–cobalt (Zn–Co) and zinc–nickel (Zn–Ni) alloy electrodeposits each prepared from acid and alkaline formulations were compared for their properties. Compared to alkaline baths, acid baths offer higher metal percent of the alloying element and higher current efficiency. In alkaline baths, the variation of metal percent in deposit with current density is less significant, but that of current efficiency with current density is more. Electrolyte pH does not change significantly in alkaline solutions compared to acid solutions. X-ray diffraction evaluation of Zn–Co deposits from both electrolytes indicated their presence in the η-phase, while Zn–Ni shows pure γ-phase for deposits obtained from alkaline solutions and the existence of γ-phase with traces of η-phase of zinc for deposits obtained from the acid electrolytes. Scanning electron microscope examination shows finer grain structure for deposits obtained from alkaline solutions, and atomic force microscope studies confirm their nanostructure with reduced surface roughness. Deposits obtained from the alkaline baths exhibited higher corrosion resistance probably due to their nanostructure.     

Influence of operating conditions on the rejection of cobalt and lead ions in aqueous solutions by a nanofiltration polyamide membrane

The potential use of nanofiltration polyamide membrane for removing cobalt and lead ions from wastewater was investigated. Rejection experiments were conducted with Pb(NO₃)₂ and Co(NO₃)₂ in both single-salt solutions and mixtures. Experimental rejection rates were corrected for concentration polarization phenomenon by means of film theory. The structural features of the membrane (pore radius and thickness-to-porosity ratio) were first estimated from the fitting of glucose rejection rates. Its surface charge properties were then investigated in single-salt solutions at pH values between 3 and 7. Rejection of both heavy metal ions was found to be influenced by operating conditions such as permeate flux, solution pH and feed salt concentration. In single-salt solutions, rejection of lead was higher than that of cobalt at pH ≥ 5. This behavior may be explained by (i) higher normalized volume charge density in the Pb(NO₃)₂ than in the Co(NO₃)₂ solution and (ii) lower ionic strength of the Pb(NO₃)₂ solution as compared with the Co(NO₃)₂ solution. At pH < 5, the dielectric exclusion would be more important for Co(NO₃)₂ than for Pb(NO₃). Lead rejection was almost the same in both single-salt solutions and ternary mixtures, whereas cobalt rejection was strongly affected by the presence of lead. Cobalt was found to be rejected much more than lead in mixtures at equal mass concentrations, the difference between rejections of the two cations being greater as pH increased.     

Cobalt(II) Oxide Solubility and Phase Stability in Alkaline Media at Elevated Temperatures

A platinum-lined, flowing autoclave facility was used to investigate the solubility behavior of cobalt(II) oxide (CoO) in deoxygenated ammonium and sodium hydroxide solutions between 22 and 288°C. Co(II) ion activity in aqueous solution was controlled by a hydrous Co(II) oxide when nitrogen was used for deoxygenation and by metallic cobalt when hydrogen was used. Measured cobalt solubilities are interpreted using a Co(II) ion hydroxo- and amminocomplexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A common set of thermodynamic properties for the species Co(OH)⁺, Co(OH)₂(aq) and Co(OH)(NH₃)⁺ is provided to permit accurate cobalt oxide solubility calculations over broad ranges of temperature and alkalinity.     

Electrodeposition of zinc + cobalt alloys.: Relation between the electrochemical response and the composition and morphology of the deposits

The electrodeposition of cobalt and zinc + cobalt alloy in aqueous chloride solution has been studied on vitreous carbon electrodes under different concentration conditions (total concentration of metallic ion 0.1 mol dm ⁻³, chloride ion 1 mol dm ⁻³, pH = 3), particularly during the initial stages of the deposition process. For the alloy a relation has been found between the shape of the current-time transients, the morphology of the deposits, the stripping analysis and the results of X-ray microanalysis. The different alloy phases present in the deposits were identified using X-ray microanalysis data, stripping voltammetry results and literature data.The results indicate that the electrocrystallization of cobalt is inhibited even at very low concentrations of zinc in solution: voltammetric and galvanostatic results indicate that the deposition potentials always correspond to more negative values than those for cobalt deposition. This inhibition depends strongly on both the metallic ion ratio in solution and the applied overpotential (or current density). For Zn(II)/Co(II) ratios greater than 1/9, low overpotentials (or low current densities) favoured homogeneous and compact deposits that were rich in zinc and were mainly composed of γ-phases of zinc + cobalt alloy. However, when high overpotentials or current densities were used and/or when the Zn(II)/Co(II) ratio was very low (< 1/9), dendritic and non-homogeneous cobalt-rich deposits were obtained.     

Liquid–liquid extraction of Cu(II), Co(II) and Ni(II) with salicylidèneaniline from sulphate media

For a fundamental study on the development of novel extraction divalent metal, the extraction behaviour of copper(II), cobalt(II) and nickel(II) is studied with salicylidèneaniline (SAN). The phenol group in the Schiff base moiety leads to a large increase in the percentage of transition metal ions. SAN has both good reactivity towards metal ions and solubility in organic solvents. The solvent extraction of copper(II), cobalt(II) and nickel(II) with salicylidèneaniline from sulphate media is studied with the following parameters: pH, concentration of the extractant and the nature of diluent. The stoichiometry coefficients of the extracted species are determined by the slope analysis method. The extraction reaction proceeds by cation exchange mechanism and the extracted species are: CuL₂HL, CoL₂HL and NiL₂. The extaction constants are evaluated for the different diluents. Under suitable conditions of pH, the solvent extraction of cobalt(II) and nickel(II) in different diluents leads to third phase formation. This tendency is confirmed from numerical extraction constants for both metal cations (log?K _ex?=??15.10?±?0.03 for nickel(II) in CHCl₃) and (log?K _ex?=??12.56?±?0.04 for cobalt(II) in CHCl₃). The extraction efficiency is found to follow the order Cu(II)?>?Co(II)?>?Ni(II).     

Solvent extraction of copper(II), nickel(II), cobalt(II), zinc(II), and iron(Ill) by high molecular weight hydroxyoximes

The effects of pH have been examined on the extraction of the title ions by complexing with LIX-64N in kerosene. The extent of metal extraction as a function of pH is: Cu(II) < Fe(III) < Ni(II) < Zn(II) < Co(II). Stripping of all metal ions but cobalt with sulphuric acid from loaded kerosene complexing solutions is easily accomplished. Oxidation of Co(II) to Co(III) in the organic phase prevents stripping of this metal ion.     

Spectral and thermal studies on new hydrazinium metal sulfite dihydrates

Some new hydrazinium transition metal sulfite dihydrate complexes of the formula (N₂H₅)₂M(SO₃)₂(H₂O)₂ where M=Fe, Co, Ni, Cu and Zn have been prepared and characterized by hydrazine and metal analyses, magnetic studies, electronic and infrared spectra and thermal analysis. The magnetic studies coupled with electronic spectra of iron, cobalt, nickel and copper complexes indicate their high spin octahedral nature. However the zinc complex is diamagnetic and show only the charge transfer transition. The infrared spectra shows that both the hydrazinium ions are coordinated to the metal ions, the sulfite ions are present as bidentate ligand. The simultaneous TG-DTA of these complexes were investigated in air and nitrogen atmospheres. In air, cobalt, nickel and zinc complexes give respective metal sulfate as the final residue while iron and copper complexes give the mixture of respective metal oxide and sulfate as the decomposition product. In nitrogen atmosphere respective metal sulfites are formed as the end residue.     

Sorption behavior of Co(II) on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the presence of humic acid

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including cosorbing or complexing. In this work, the effects of pH, humic acid HA/Co(II) addition orders, ionic strength, concentration of HA, and foreign cations on the Co(II) sorption on γ-Al₂O₃ in the presence of HA were investigated. The sorption isotherms of Co(II) on γ-Al₂O₃ in the absence and presence HA were also studied and described by using S-type sorption model. The experimental results showed that the Co(II) sorption is strongly dependent on the pH values, concentration of HA, but independent of HA/Co(II) addition orders, ionic strength, and foreign cations in the presence of HA under our experimental conditions. The results also indicated that HA enhanced the Co(II) sorption at low pH, but reduced the Co(II) sorption at high pH. It was hypothesized that the significantly positive influence of HA at low pH on the Co(II) sorption on γ-Al₂O₃ was attributed to strong surface binding of HA on γ-Al₂O₃ and subsequently the formation of ternary surface complexes such as ≡S-OOC-R-(COO⁻) _x Co^2−x . Chemi-complexation may be the main mechanism of the Co(II) sorption on γ-Al₂O₃ in the presence of HA.     

Complexation and sorption studies of Co(II) with γ-alumina-bound fulvic acid: effect of pH,ionic strength,fulvic acid and alumina concentration

The removal of heavy metal ion Co(II) from aqueous solution is studied using γ-Al₂O₃ by batch technique. The experiments are performed at T = 20 ± 2 °C, in 0.01 M NaNO₃ solutions and under aerobic conditions. The effect of pH, ionic strength, fulvic acid (FA) and alumina concentration on the sorption of Co(II) on alumina are also respectively investigated. The pH affects the sorption of Co(II) significantly as compared with the effect of FA and ionic strength. The results indicate that strong chemical bonds are formed between Co(II) and the bare or FA coated alumina surface, and a transition from the adsorption to surface-induced precipitation of Co(II) on alumina surface takes place. The addition sequences of Co/FA on Co(II) sorption is also studied and the results indicate that the sorption of Co(II) in ternary system is independent of addition sequences. The results also suggest that the sorption of metal ions on mineral surface depends on the nature of mineral, nature of organic ligand and nature of metal ion.     

Effect of gamma radiation on folic acid and its cobalt complex solutions

Gamma-radiolysis of folic acid and its cobalt complex were studied in aqueous solutions at doses ranged from 2 to 10 krad and from 2 to 10 Mrad using⁶⁰Co source. The variations in their spectra of IR, UV, and visible due to their radiolysis were shown. Also the change in pH after radiolysis was determined. The results showed that decomposition of folic acid by gamma-radiation occurred without variation of pH. Fine measurements of pH for irradiated CoCl₂ and cobalt-folic acid complex solutions can be utilized for dose determination in the studied range of 2–10 Mrad. IR spectra showed that addition of cobalt chloride to folic acid decreased its decomposition by gamma-radiation. This result proved the importance of addition of cobalt chloride in keeping foodstuffs, which contain folic acid, by irradiation. The mechanism for the effect of radiation on cobalt chloride and cobalt-folic acid complex was discussed.     

钴基催化剂在费-托反应过程中的失活行为

 考察了 Co/SiO₂, Co/Ru/SiO₂ 和疏水改性 Co/Ru/SiO₂ 催化剂在费-托合成过程中的稳定性.结果发现, 随着反应的进行, 三种催化剂都呈现一定程度的失活,它们稳定性高低顺序为: 疏水改性 Co/Ru/SiO₂ > Co/SiO₂ > Co/Ru/SiO₂. Co/SiO₂ 催化剂的失活是由于催化剂上 Co 晶粒的长大和硅酸钴物种的生成, 而 Co/Ru/SiO₂和疏水改性 Co/Ru/SiO₂的失活则是由于催化剂上 Co 晶粒的长大所致. 由于 Co/Ru/SiO₂ 催化剂的 Co 晶粒比 Co/SiO₂催化剂的小得多, 在反应过程中更容易长大, 所以 Co/Ru/SiO₂催化剂稳定性更差; 而疏水改性 Co/Ru/SiO₂催化剂表面的疏水性既抑制了硅酸钴物种的形成, 又使 Co 晶粒长大较慢, 因此其稳定性最高.     

A Molecular Approach to Self‐Supported Cobalt‐Substituted ZnO Materials as Remarkably Stable Electrocatalysts for Water Oxidation

In regard to earth‐abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt‐substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low‐temperature solvolysis of molecular heterobimetallic Co_4?xZn_xO₄ (x=1–3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self‐supported water‐oxidation electrocatalyst, which was observed by HR‐TEM on FIB lamellas of the EPD layers. The Co‐rich hydroxide‐oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours.     

Size Distribution of Cobalt Particles in Catalysts for the Fischer-Tropsch Synthesis

The effect of the size distribution of metal particles on the process kinetics was studied for the oxidation and reduction of cobalt nanoparticles (6–10 nm) in the Co/SiO₂, Co/Al₂O₃, and Co/ZrO₂ systems in both isothermic and temperature-programmed regimes in the temperature range from 280 to 500 K. The average size of the cobalt particles was estimated by measurements of the coercive force and residual magnetization using a vibration magnetometer. It was found that the average particle size increases upon cobalt oxidation and decreases upon cobalt reduction due to changes in the fraction of nonsuperparamagnetic particles with sizes of at least 6.5 nm.     

Evidence for the Formation of Trioctahedral Clay upon Sorption of Co on Quartz

The sorption mechanism of Co on quartz at room temperature has been investigated by an in-depth analysis of published extended X-ray absorption fine structure (EXAFS) spectroscopy and solution chemistry data. In particular, the 3.5–5 Å mid-range atomic environment of Co has been determined with unprecedented precision by combining ad initio FEFF7.02 calculations and results obtained by polarized EXAFS on the mid-distance structure of sheet silicate minerals. The local atomic environment around sorbed Co atoms is identical to that of Co in trioctahedral clays and substantially different from that in the cobalt hydroxide Co(OH)_2(s). Neoformation of a trioctahedral clay is consistent with calculated thermodynamic solubilities, which indicate that 2:1 and 1:1 Co-rich hydrous silicates, similar to kerolite and chrysotile, are less soluble than Co(OH)_2(s). Consequently, precipitation of Co-rich clay is favored over that of Co(OH)_2(s) at pH values below 9 and for a dissolved Si concentration equal to quartz solubility. New experimental data show that dissolved Si concentrations can approach, and even exceed, that of quartz solubility during the short times of sorption experiments. Based on the available data, it is not possible to conclude unequivocally if the Co layer silicate grew epitaxially on the quartz surface, topotactically in a surface amorphous layer, or independently of the quartz framework structure. The structural and chemical interpretation is supported by recent published studies in which sorption of a hydrolyzable cation leads to the neoformation of a mixed layer phase formed from the sorbate species and the sorbent metal. This surface-induced precipitation mechanism is a general phenomenon that may account for the formation of secondary clays as coatings on silicates.