COBALT–NICKEL SEPARATION: THE EXTRACTION OF COBALT(II) AND NICKEL(II) WITH BIS(2-ETHYLHEXYL) PHOSPHINIC ACID (PIA-8) IN TOLUENE

The extraction behaviour of cobalt(II) and nickel(II) from sulfate solutions with bis(2-ethylhexyl) phosphinic acid (PIA-8) in toluene has been studied. Quantitative extraction of Co(II) was observed at pH 5.0–5.9 while that of Ni(II) at pH 6.8–7.0 with 0.03 M PIA-8 in toluene. The difference in pH_0.5 for Co(II) and Ni(II) was 1.9. The stoichiometry of the extracted species were determined by slope analysis method. The extraction reaction proceeds by cation exchange mechanism and the extracted species were Co · R₂(HR)₂ and Ni · R₂ · 2(HR)₂. Temperature dependance of the extraction equilibrium constants were determined to estimate the apparent thermodynamic functions (ΔG, ΔS and ΔH). The method was used for separation of cobalt(II) and nickel(II). Cobalt(II) was separated from nickel even at 1:20 (Co:Ni) ratio. The separation of cobalt(II) from nickel(II) was favoured with the increase in temperature.     

UV/VIS diffuse reflectance spectroscopic (DRS) study of cobalt-containing Y zeolites dehydrated at elevated temperatures

The coordination changes of Co²in Y-zeolite prepared by ion-exchange and dehydrated at various temperatures, have been investigated by UV/VIS diffuse reflectance spectroscopy. Fully hydrated zeolites show an octahedral coordination of [Co(H₂O)₆]2 in the supercage with some interaction with the framework. During dehydration at high temperatures, Co² in Y-zeolite changes its coordination, first from a symmetric to distorted tetrahedral and, successively, to an octahedral coordination. Fully hydrated sample of impregnated cobalt nitrate in Y-zeolite shows an octahedral coordination of Co(H₂O)₆(NO₃)₂. During dehydration at high temperature, the cobaltous nitrate decomposes to the cobalt oxide. However, the small amount of coblat ions in cobalt nitrate are ion-exchanged simultaneously.     

ADSORPTION BEHAVIOR OF COBALT( II) IONS ON LAYERED DIHYDROGEN TETRATITANATE HYDRATE FIBERS IN AQUEOUS SOLUTIONS IN THE RANGE FROM 298 to 523 K

The adsorption properties of cobalt(II) ions have been studied on layered dihydrogen tetratitanate hydrate fibers, H₂Ti₄O₉,?nH₂O, in the temperature range from 298 to 523?K. The distribution coefficients of the adsorption of cobalt (II) ions were increased with increasing temperatures up to 367?K, but were decreased in the temperature range between 367 and 523?K. The X-ray powder diffraction patterns of the fibers indicate that the fibers hold layer structure up to 367?K, but change to low crystalline anatase or its precursor above that temperature. It is notable that the material has the capability of cobalt (II) adsorption even at 523?K, although the maximum is present at 367?K.     

乙酰丙酮钴(Ⅱ)对甲苯液相空气氧化反应的催化性能

以乙酰丙酮钴(Co(acac)₂)为催化剂,在1 L高压搅拌反应釜中研究了其对甲苯液相空气氧化反应的催化性能和反应产物分布,考察了催化剂用量对甲苯转化率和苯甲酸收率的影响,并考察了不同温度下不同催化剂用量时的催化剂寿命。结果表明,Co(acac)₂催化甲苯液相氧化是平行连串的复杂反应,Co(acac)₂的催化活性存在"催化-抑制转换"现象,适宜的催化剂用量为0.0044%(质量分数);催化剂的寿命随反应温度变化存在一个最大值,165℃时催化剂寿命最长,反应温度较低(<165℃)时催化剂更容易失活;在165℃、Co(acac)₂用量为0.0044%时,反应4 h,甲苯转化率为19%,苯甲酸收率为80%;与醋酸钴、环烷酸钴等钴盐催化剂相比,Co(acac)₂催化剂具有用量少、催化活性时间长的优点,可有效地减缓钴盐结垢现象,Co(acac)₂催化剂对甲苯液相空气氧化反应具有良好的催化性能。     

Effects of the electrodeposition potential and temperature on the electrochemical capacitance behavior of ordered mesoporous cobalt hydroxide films

Novel ordered mesoporous cobalt hydroxide film (designated H_I-e Co(OH)₂) has been successfully electrodeposited from cobalt nitrate dissolved in the aqueous domains of the hexagonal lyotropic liquid crystalline phase of Brij 56. Experimental electrodeposition parameters such as deposition potentials and deposition temperatures are varied to analyze their influences on the electrochemical capacitor behavior. The films are physically characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine the effects of deposition potentials and temperatures on the surface morphology and nanostructure. Electrochemical techniques such as cyclic voltammetry (CV) and chronopotentiometry are applied to systematically investigate the effects of deposition potentials and temperatures on the capacitance of the films. The results demonstrated that the capacitive performance of the H_I-e Co(OH)₂ film achieved the highest value when it is electrodeposited at −0.75 V under the deposition temperature of 50 °C.     

Structure and catalytic properties of Co/ porcelain in the synthesis of 2,3‐dihydrofuran

The cyclodehydration of 1,4‐butanediol over cobalt catalysts in the liquid phase is used for the production of 2,3‐dihydrofuran. The catalyst preparation parameters considered were the metal loading, precipitation pH and reduction temperature of cobalt salt. It was found that the use of Co(NO₃)₂ together with Na₂CO₃ in a 1:1 ratio yielded better catalysts. Under the conditions used in this study the optimum cobalt loading for the selective production of 2,3‐dihydrofuran is in the range 15–50 wt%. The optimum reduction temperature of Co/porcelain catalyst depends on cobalt loading. The optimum reduction temperatures for 15 and 50 wt% cobalt loading are 773 and 723 K (reduction time 20 min), respectively. © 2001 Society of Chemical Industry     

Cinetique electrochimique du couple cobalt(III)—cobalt(II) en milieu acide phosphorique concentre

The electrochemical behaviour of the cobalt(III)—cobalt(II) couple in 96.5% and 85 wt% H₃PO₄ have been studied at a stationary gold electrode by using chronopotentiometry and triangular voltamperometry. The results have shown that the Co(III)—Co(II) system is reversible and the electrode reaction involves a single electron. The Co(II) ions' diffusion coefficient in the two phosphoric acid solutions was determined as 4.3 × 10⁻⁸ cm².s⁻ in 96.5% wt % H₃PO₄ and 1.2 × 10⁻⁷ cm².s⁻¹ in 85 wt % H₃PO₄. The stabillity of the Co(III) ion in 96.5 wt % H₃PO₄ media was also investigated.     

Structure and magnetic properties of multi-walled carbon nanotubes modified with cobalt

The magnetic properties of multi-walled carbon nanotubes (MWCNTs) modified with cobalt nanoparticles were studied in the temperatures and magnetic field range of (4.2–290) K and (0.03–5) T, respectively. Nanoparticles of cobalt encapsulated inside MWCNTs were obtained by using the chemical vapor deposition technique. The low temperature SQUID magnetization measurements were supplemented with structural investigations by means of high-resolution transmission electron microscopy, scanning electron microscopy as well as thermogravimetric and X-ray diffraction analysis. X-ray diffraction revealed the presence of MWCNTs, f.c.c. Co and h.c.p. Co phases. The magnetic characterization provided the remanent magnetization value (M_R) of about 0.07 emu/g (∼40% of the saturation moment), while the coercive field (H_C) value amounts to 600 Oe. Both parameters M_R and H_C slightly decrease with the rise of temperature. The substantial magnetization increase observed at low temperatures suggests the existence of nano Co clusters (in the atomic scale size).     

Electrosynthesis of cobalt (III) ions in concentrated H3PO4 medium

The electrosynthesis of cobalt(III) ions from cobalt(II) ions has been studied in 29, 57 and 85 wt % H₃PO₄ solutions. It has been shown that the conversion of Co(II) to Co(III) is limited by the chemical reaction between Co(III) ions and water. A kinetic study demonstrated that this reaction becomes more rapid as the Co(III) ion concentration increases. In order to find the best conditions for the electrolysis, the effect of some experimental parameters on the current yield and the chemical efficiency has been examined. A comparison between gold and platinum anodes has also been made. The following conditions were found to be the best: anode material, gold; initial Co(II) ion concentration, 5×10^–3 M; solvent, 85 wt % H₃PO₄ solution; current density, 1 mA cm^–2; temperature, 20–30° C. Under these conditions the maximum value of current yield, and chemical efficiency are 66% and 48% respectively.

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Résumé L'electrosynthèse des ions cobalt(III) à partir des ions cobalt(II) a été étudiée dans les solutions H₃PO₄ 29, 57, et 85% en masse. II a été montré que la conversion de Co(II) en Co(III) est limitée par la réaction chimique entre les ions Co(III) et l'eau. Une étude cinétique a montré que cette réaction devient plus rapide au fur et à mesure que la concentration de l'ion Co(III) augmente. Dans le but de trouver les conditions favorables pour l'electrolyse, l'effet de certains paramètres expérimentaux, sur les rendements électrique et chimique, a été examiné. Les résultats obtenus avec une anode en or et une anode en platine ont été comparés. Les conditions d'électrolyse suivantes ont été retenues: le matériau de l'anode, Au; concentration initiale de l'ion Co(II), 5×10^–3 M; solvant, solution H₃PO₄ 85% en masse; densité de courant, 1 mA cm^–2; température, 20–30° C Dans ces conditions, les valeurs des rendements faradique et chimique maximum sont respectivement de 66% et 48%.

     

In situ FT-IR Spectroscopic Studies on the Mechanism of the Catalytic Oxidation of Carbon Monoxide over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (5% as metal Co loading on SiO₂, Al₂O₃ and TiO₂) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. Then, all catalysts were calcined in air at 400 °C (assigned as 5Co/Si C400, 5Co/Al C400 and 5Co/Ti C400). Their catalytic activities towards the CO oxidation were studied in a continuous flow micro-reactor. Adsorption of carbon monoxide (CO) and the co-adsorption of CO/O₂ over cobalt oxide were further tested under in situ FT-IR. The results showed that both 5Co/Si C400 and 5Co/Al C400 had higher activity than 5Co/Ti C400. The T₅₀ (50% conversion) for both 5Co/Si C400 and 5Co/Al C400 was reached at temperatures as low as ambient temperature. According to the in situ FT-IR analysis, the variation in oxidation of CO was interpreted with different mechanisms, i.e., the reaction between adsorbed CO and lattice oxygen of cobalt oxide, and part of CO₂ formation via carbonates on 5Co/Si C400; both types of carbonates are formed on 5Co/Al C400 to promote the CO oxidation; while both strong adsorption of CO on TiO₂ and CO₂ on cobalt oxide for 5Co/Ti C400 leads to affect the activity.     

EXTRACTION CHEMISTRY OF COBALT AND NICKEL BY DI(1-METHYLHEPTYL)PHOSPHINIC ACID

The fundamental characteristics and mechanism of extraction of cobalt (II) and nickel(II) by di-(1-methylheptyl) phosphinic acid (DMHPA) were studied. The extraction ability of cobalt(II), nickel (II) and various metals by DMHPA decreases in the order Fe(III) > Zn ? Pb(II) > Mn(II) > Cu(II) > Co(II) > Mg > Ca > Ni(II). The difference of the pH_½ values for nickel and cobalt reaches 2.06 pH units, which is apparently greater than those from extraction by di(2-ethylhexyl)phosphoric acid (DEHPA)and 2-ethyl-hexyl ester 2-ethylhexylphosphonic acid(DHEHPA).The slope analysis and IR spectroscopy reveal that the stoichiometrics of cobalt and nickel extracted species are Co(HA₂)₂ and Ni(HA₂)₂(H₂O)₂ respectively. As demonstrated by the study of the electronic spectroscopy the structure of the extracted complexes were shown as tetrahedral and octahedral configuration respectively. Furthermore, the coordination field parameters of the complexes were calculated.     

Insights into Activation of Cobalt Pre-Catalysts for C(sp2)−H Functionalization

The activation of readily prepared, air-stable cobalt(II) bis(carboxylate) pre-catalysts for the functionalization of C(sp²)−H bonds has been systematically studied. With the pyridine bis(phosphine) chelate, ^iPrPNP, treatment of 1 - (O₂C^tBu)₂ with either B₂Pin₂ or HBPin generated cobalt boryl products. With the former, reduction to (^iPrPNP)Co^IBPin was observed while with the latter, oxidation to the cobalt(III) dihydride boryl, trans-(^iPrPNP)Co(H)₂BPin occurred. The catalytically inactive cobalt complex, Co[PinB(O₂C^tBu)₂]₂, accompanied formation of the cobalt-boryl products in both cases. These results demonstrate that the pre-catalyst activation from cobalt(II) bis(carboxylates), although effective and utilizes an air-stable precursor, is less efficient than activation of cobalt(I) alkyl or cobalt(III) dihydride boryl complexes, which are quantitatively converted to the catalytically relevant cobalt(I) boryl. Related cobalt(III) dihydride silyl and cobalt(I) silyl complexes were also synthesized from treatment of trans-(^iPrPNP)Co(H)₂BPin and (^iPrPNP)CoPh with HSi(OEt)₃, respectively. No catalytic silylation of arenes was observed with either complex likely due to the kinetic preference for reversible C−H reductive elimination rather than product- forming C−Si bond formation from cobalt(III). Syntheses of the cobalt(II) bis(carboxylate) and cobalt(I) alkyl of ^iPrPONOP, a pincer where the methylene spacers have been replaced by oxygen atoms, were unsuccessful due to deleterious P−O bond cleavage of the pincer. Despite their structural similarity, the rich catalytic chemistry of ^iPrPNP was not translated to ^iPrPONOP due to the inability to access stable cobalt precursors as a result of ligand decomposition via P−O bond cleavage.     

Synthesis,structures and properties of a meso-substituted pyrazolyl porphyrin and its Co(II) porphyrin complex

In this work, one new porphyrin, 5, 10, 15, 20-tetrakis(4-N-pyrazolyl)phenyl porphyrin (H₂Pp) was synthesized and characterized. The single crystal structures of H₂Pp and its cobalt(II) porphyrin (Co(II)Pp) were obtained with a space group of P₁⁻ and I2/c, respectively. The porphyrin macrocycle is close to a perfect plane in H₂Pp, while Co(II)Pp exhibits a saddle-type distortion due to the formation of shorter Co–N coordination bonds. In H₂Pp, the molecules are interconnected through π⋯π and C–H⋯π interactions to form 3D architecture, while in Co(II)Pp the porphyrin molecules are interlinked only by C–H⋯π interactions to yield 3D structure. We examined the UV–vis spectra and fluorescent spectra of H₂Pp and Co(II)Pp in CH₂Cl₂ and solid state at room temperature. In addition, the catalytic activities of Co(II)Pp to the ethylbenzene oxidation was examined, the results indicate that Co(II)Pp exhibits a high selectivity to acetophenone (> 99%) with the conversion of 83%.     

Synthesis and catalytic behaviors of cobalt nanocrystals with special morphologies

Cobalt nanocrystals with highly ordered snowflake-like, cauliflower-like, ball-like morphologies, and some less ordered shapes were prepared through the reduction of Co(NO₃)₂ by hydrazine hydrate in the solution of methanol, ethanol, ethylene glycol, and 1,2-propanediol. Based on the characterization results of X-ray powder diffraction and scanning electron microscope, crystal and morphologic structures of cobalt particles were correlated with the reaction conditions of temperature, Co(NO₃)₂ concentration, and the alcohols used. By changing temperature and/or Co(NO₃)₂ concentration, pure hexagonal close-packed (hcp) cobalt or a mixture of hcp and face-centered cubic (fcc) cobalt was obtained. The catalytic performance of as-prepared cobalt nanocrystals for the thermal decomposition of ammonium perchlorate (AP) was evaluated by differential scanning calorimetry. The decomposition temperature of AP was significantly decreased, and the apparent decomposition heat was over doubled when 2 wt.% cobalt was added into AP. Among the samples tested, snowflake-like cobalt showed the best performance in the aspect of decreasing the decomposition temperature of AP while the ball-like cobalt exhibited the highest apparent decomposition heat.     

A heterogeneous cobalt(II) sensitive electrode and its applications

The preparation of a heterogeneous cobalt(II) sensitive electrode, based on cation exchange resin using silicone rubber as binding material, has been described. The working pH range is 2.3 to 8.5. The selectivity coefficient for Cu(II), Ni(II), Zn(II) or Al(III) ions is found to be less than unity, and satisfactory determination of Co(II) in presence of these ions is possible. The values of stepwise stability constant of Co(II)—nitroso—R-salt complexes in solution, using the Co(II) sensitive electrode, are; log K₁ 6.87; and log K₂ 5.39 (25°; μ ≈ 0.01), which agree with literature values.     

The Effect of Cobalt on the Degradation of Methyl β-D-Gluco-Pyranoside by Oxygen in Aqueous Sodium Hydroxide Solution

Abstract

The effect of Co(II) (0 to 0.25 mW CoSO₄) on the degradation of methyl β-D-glucopyranoside (MBG) at 120°C in 1.25M NaOH with 0.68 MPa oxygen pressure was studied. When the Co(II) was increased from 0.00 to 0.01 to 0.05 mM the MBG half-life decreased from 12 to 6 to 1.5 hours, reflecting approximately a 0.5 order kinetic dependence on cobalt. An oxidation-reduction cycle between Co(II) and Co(III) involving oxidation of Co(II) by oxygen and oxidation of the glucoside by Co(III), hydroxyl radical, or superoxide is proposed for the degradation. At the 0.25 mM Co(II) addition level highly adsorptive Co(OH)₂ formed prior to reaction initiation with oxygen and removed otherwise soluble cobalt from solution. This resulted in lower rates of MBG degradation than obtained even at 0.01 mM Co(II) addition. However, Co(II) solubility could be enhanced if silicate anions or polyols (including MBG) were added to the alklaine medium prior to the Co(II) addition. In reactions initially containing 0.25 mM soluble Co(II), an adsorptive precipitate, presumably CoO(OH), gradually formed after reaction initiation with oxygen. Precipitation of the Co(III) solid coincided with a rapid decline in the rate of MBG degradation. Cobalt had little effect on the products of MBG degradation.     

Synthesis,Crystal Structure and DNA Interaction of a Novel Three-Nuclear Cobalt(II) Complex with Schiff Base Derived from 4-Chloroanthranilic Acid and 2,4-Dihydroxybenzaldehyde

A novel transition metal coordination polymer [Co₃(C₁₄H₈NO₄Cl)₄(CH₃OH)₄·4CH₃OH]_n with Schiff base (C₁₄H₈NO₄Cl: 4-chloroanthranilic acid- 2,4-dihydroxybenzaldehyde) was synthesized using 4-chloroanthranilic acid, 2,4-dihydroxybenzaldehyde and cobalt(II) acetate as source, and its structure was characterized by IR spectroscopy, elemental analysis, ¹H NMR and single crystal X-ray diffraction. X-ray crystallography shows that every cobalt atom is six-coordinated. Two cobalt atoms on the two sides are respective coordinated with two nitrogen atoms from –C=N–, two carboxylic oxygen atoms and two hydroxyl oxygen atoms in different ligands, while the cobalt atom in the middle links two ligands on the side through two carboxylic oxygen atoms and coordinates with four oxygen atoms of methanol, forming a three-nuclear Co(II) complex. The complex forms a two-dimensional layer structure through O–H···O intermolecular hydrogen bonds. The interaction of the Co(II) complex with calf-thymus DNA (CT-DNA) was investigated by UV absorption spectroscopy, fluorescence emission spectroscopy, viscosity and cyclic voltammetry. All measurements revealed that the Co(II) complex binds to DNA via a intercalative mode.     

ADSORPTION OF COBALT ONTO GRAPHITE NANOCARBON–IMPREGNATED ALGINATE BEADS: EQUILIBRIUM,KINETICS, AND THERMODYNAMICS STUDIES

A novel adsorbent was developed impregnating graphite nanocarbon (GNC) into alginate beads (AB) for efficient cobalt (Co(II)) removal from an aqueous solution. Physicochemical and spectroscopic properties of graphite nanocarbon–impregnated alginate beads (ABGNC) were characterized and compared with those of AB. Co(II) adsorption on ABGNC was quantitatively evaluated by determining kinetics and thermodynamics parameters. The Co(II) adsorption capacity onto ABGNC was highest at neutral pH condition. Increasing the temperature from 288 to 318 K resulted in a 2.5-fold higher Co(II) adsorption onto AB, while thermal dependence of Co(II) adsorption on ABGNC was not found. Kinetic studies showed an applicability of the pseudo-second-order kinetic model for both AB and ABGNC. Monolayer adsorption was the dominant mechanism of Co(II) adsorption on both AB and ABGNC. Thermodynamic studies revealed that Co(II) adsorption was an endothermic and spontaneous process. Positive values of entropy indicate randomness in solid/aqueous phases, and mean free energy (E _a ) fits in the range of chemisorption.     

Synthesis and crystal structure of the mixed-valence trinuclear cobalt complex {[Co(CN)3(tBuNC)2](μ-CN)[Co(tBuNC)4](μ-CN)[Co(CN)3(tBuNC)2]}

The mixed-valence trinuclear cobalt compound {[Co(CN)₃(^tBuNC)₂](μ-CN)[Co(^tBuNC)₄](μ-CN)[Co(CN)₃(^tBuNC)₂]} is produced from the reaction of CoCl₂ with KCN and tert-butylisocyanide. In the resulting structure two cobalt atoms formally show the oxidation state +III, whereas the central cobalt still exhibits the formal oxidation state +II. All cobalt atoms are octahedrally coordinated by cyanide and isocyanide ligands. The supramolecular structure is determined by C–H⋯O and C–H⋯N hydrogen bonds linking acetone molecules to the trimeric complex as well as connecting the complex units into infinite chains.     

Synthesis,Spectroscopic, Surface and Catalytic Reactivity of Chitosan Supported Co(II) and Its Zerovalentcobalt Nanobiocomposite

Chitosan was used as a stabilizer to synthesize chitosan cobalt(II) [Chit–Co(II)] and its zerovalentcobalt nanobiocomposite via chemical reduction. The complex and Chit–ZVCo were used to polymerize vinylacetate in aqueous Na₂SO₃. The Chit–Co(II) and Chit–ZVCo were characterized by spectroscopic (FT-IR and UV–Visible), XRD and SEM techniques. Application of these biomaterials for the polymerization of VAc afforded polyvinylacetate with improved yield. Comparing the reactivity of Chit–Co(II) and Chit–ZVCo, it was evident that Chit–ZVCo performed as better heterogeneous catalyst based on the synergic effect of interaction of cobalt nanoparticles and chitosan at the nanometric scale.