Pulse radiolysis study of monovalent cadmium, cobalt, nickel and zinc in aqueous solution. Part 1.—Formation and decay of the monovalent ions

Buxton, George V.; Sellers, Robin M.

doi:10.1039/f19757100558

Cited by 52 publications

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“…13 However, the formation of carbon dioxide upon y-irradiation of a 10 -2 M aqueous solution of the cobalt00 salt and formate ions allowed the authors of Ref. 13 to assert that the COx'-radical ion can reduce the Co 2+ ion. According to the estimation performed, the rate constant of this reaction can range within 102--105 mol -I L s -l. The results of our studies agree with the lower limit of this value.…”

Section: Radiation-chemical Redaction Of Co 2+ In Aqueousmentioning

confidence: 96%

“…The contribution of this reaction to the reduction of the Co 2 § ions can be pronounced in sufficiently concentrated solutions of Co(C104) 2 only, as this has been observed previously. 13 The aforementioned autocatalytic character of the reduction of the cobalt ions indicates unambiguously the participation of the metal sols. In our opinion, the CO2"-radical ions cannot reduce efficiently the Co 2+ ions, especially in dilute solutions.…”

Section: Radiation-chemical Redaction Of Co 2+ In Aqueousmentioning

confidence: 97%

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Radiation-chemical reduction of CO2+ ions in aqueous solution. Metal sols and their properties

Ершов

1998

Russ Chem Bull

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The radiation-chemical reduction of Co 2+ ions in an aqueous solution of Co(CIO4)2 containing sodium formate was studied. Stable metal sols containing spherical particles with a diameter of 2--4 nm are formed under v-irradiation in the presence of polyacrylate as the stabilizing additive. An aqueous solution of colloidal cobalt has an optical absorption that increases smoothly in the UV region without a maximum to 200 nm (c200 = 1.3" 104 mol -I L cm-I). It is estabfished that the radiation--chemical reduction of the Co 2+ ions occurs via an autocatalytic mechanism. The metal sols catalyze the reduction of the Co 2+ ions by CO2"-radical ions formed under irradiation. The properties of the sols were studied, and it is shown that they are readily oxidized by hydrogen peroxide and other oxidants. The mechanism of chemical reactions involving the sols is discussed.Key words: y-irradiation, aqueous solution, reduction, cobalt, colloids, sols, optical absorption, autocatalysis.It is known (see, e.g., Refs. 1--4) that ionizing irradiation of deaerated aqueous solutions of salts of noble and some other metals (cadmium, lead, nickel, etc.) with addition of organic compounds (alcohols, salt of organic acids) results in the reduction of the metal ions. In the presence of stabilizers (polyelectrolytes are commonly used), stable metal hydrosols, including those of cadmium, 5 thaUium, 6 lead, 7 and others, can be obtained. The sols have intense optical absorption bands in the UV or visible spectral region, and their characteristics are determined to a considerable extent by their size and shape 8-t~ and the state of the particle surface. H Therefore, optical spectroscopy is widely used as an efficient method for the study of the nature and properties of metallic nanoaggregates in aqueous solutions.This work is aimed at obtaining stable aqueous solutions of colloidal cobalt and studying its properties. The theoretically calculated absorption spectrum 9 of the sol of spherical cobalt particles with a diameter of 10 nm is a band with kmax < 200 nm, which increases smoothly from the visible to UV region. It is known lz that y-irradiation of deaerated aqueous solutions of Co 2+ ions containing HCOO-ions as scavengers of hydroxyl radicals (the reaction of OH" with HCOO-affords the CO2"-radical ion) results in the formation of carbon dioxide. This suggested that CO2"-can reduce Co 2+ ions. The formation of a metal precipitate was not reported. It has been shown 13 by pulse radiolysis technique that hydrated electrons reduce the Co 2+ ion (the rate constant of the reaction is controlled by diffusion and is equal to 1.2" I0 t~ tool -I L s -I) to form a shortlived Co + ion (absorption with Lma x at 310 and 370 nm). Reaction of the CO2"-radical ion with the Co 2+ ion under pulse irradiation conditions was not observed. The authors of the known work 13 believe that this indicates that the rate constant of this reaction is very low and ranges within 102--105 mol -I L s -t. These data suggest a possibility to obtain stable aqueous solutio...

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Section: Radiation-chemical Redaction Of Co 2+ In Aqueousmentioning

confidence: 96%

Section: Radiation-chemical Redaction Of Co 2+ In Aqueousmentioning

confidence: 97%

Radiation-chemical reduction of CO2+ ions in aqueous solution. Metal sols and their properties

Ершов

1998

Russ Chem Bull

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“…Co and Ni are adjacent on the periodic table and have similar electronegativity, specific heat, melting points, and densities. The divalent forms (Co(II) and Ni(II)) also have the same rate constant limits for reactivity with CO 2 − (Buxton & Sellers, ). These properties can result in similar geological partitioning behavior.…”

Section: Factors Influencing Biological Co Utilizationmentioning

confidence: 99%

Geological and Chemical Factors that Impacted the Biological Utilization of Cobalt in the Archean Eon

et al. 2018

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The geosphere and biosphere coevolved and influenced Earth's biological and mineralogical diversity. Changing redox conditions influenced the availability of different transition metals, which are essential components in the active sites of oxidoreductases, proteins that catalyze electron transfer reactions across the tree of life. Despite its relatively low abundance in the environment, cobalt (Co) is a unique metal in biology due to its importance to a wide range of organisms as the metal center of vitamin B12 (aka cobalamin, Cbl). Cbl is vital to multiple methyltransferase enzymes involved in energetically favorable metabolic pathways. It is unclear how Co availability is linked to mineral evolution and weathering processes. Here we examine important biological functions of Co, as well as chemical and geological factors that may have influenced the utilization of Co early in the evolution of life. Only 66 natural minerals are known to contain Co as an essential element. However, Co is incorporated as a minor element in abundant rock‐forming minerals, potentially representing a reliable source of Co as a trace element in marine systems due to weathering processes. We developed a mineral weathering model that indicates that dissolved Co was potentially more bioavailable in the Archean ocean under low S conditions than it is today. Mineral weathering, redox chemistry, Co complexation with nitrogen‐containing organics, and hydrothermal environments were crucial in the incorporation of Co in primitive metabolic pathways. These chemical and geological characteristics of Co can inform the biological utilization of other trace metals in early forms of life.

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“…Indeed, the energy of splitting-off the first electron from a cobalt atom (the ionization potential) is less than one half of that for the second electron ( I 1 = 7.866 eV, I 2 = 17.057 eV) [4]. According to the stage mechanisms, the first ionization stage yields cobalt ions with intermediate oxidation state (1+), which were detected in the studies on the pulse radiolysis of cobalt salt solutions [5,6]. Hydrated electrons formed during the pulse radiolysis of the cobalt (II) salt aqueous solutions are strongly reducing agents [ E 0 (1/2H 2 / ) = -2.9 V (NHE)] and they react with Co 2+ ions [7].…”

mentioning

confidence: 98%

“…The reaction yields Co + ions that were shown by rapidly recording the optical spectra. The corresponding absorption maxima are observed at the wavelengths of 315 ± 5 and 370 ± 5 nm [5,6]. The Co + ions are very active chemical agents with a short lifetime in aqueous solutions.…”

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confidence: 99%

The Mechanism of the Cobalt Anodic Ionization in Chloride Solution

et al. 2005

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The kinetics and mechanism of the cobalt anodic ionization markedly depend on the conditions of the anodic process, namely, the pH, composition and temperature, of the electrolyte and the material and surface state of the electrode. Therefore, numerous mechanisms are discussed in the literature concerning the cobalt anodic ionization, which satisfactorily explain the anodic behavior under particular experimental conditions [1][2][3].Most often stage mechanisms of the cobalt anodic ionization with a subsequent splitting-off of two electrons are encountered. They are more probable than a one-stage mechanism with the transfer of two electrons in one elementary ionization act at the electrode/electrolyte interface. Indeed, the energy of splitting-off the first electron from a cobalt atom (the ionization potential) is less than one half of that for the second electron ( I 1 = 7.866 eV, I 2 = 17.057 eV) [4]. According to the stage mechanisms, the first ionization stage yields cobalt ions with intermediate oxidation state (1+), which were detected in the studies on the pulse radiolysis of cobalt salt solutions [5,6]. Hydrated electrons formed during the pulse radiolysis of the cobalt (II) salt aqueous solutions are strongly reducing agents [ E 0 (1/2H 2 / ) = -2.9 V (NHE)] and they react with Co 2+ ions [7]. The reaction yields Co + ions that were shown by rapidly recording the optical spectra. The corresponding absorption maxima are observed at the wavelengths of 315 ± 5 and 370 ± 5 nm [5,6]. The Co + ions are very active chemical agents with a short lifetime in aqueous solutions.A thermodynamic estimate of the standard redox potential is E 0 (ëÓ 2+ /ëÓ + ) = -3.1 V (NHE) [8]. However, this value contradicts the experimental data [7] showe aq -ing that the Co 2+ ions are reduced by hydrated electrons with a high rate constant. The experimental estimate of the E 0 (ëÓ 2+ /ëÓ + ) potential also yielded more positive value. For example, the electrochemical behavior of the one-valent cobalt ions at mercury electrode was studied [9] using laser photoelectron emission from the metal. Thus determined rate constant for the reduction of twovalent to one-valent cobalt ions was compared to the rate constant for the reverse reaction, which resulted in a redox potential of the Co 2+ /Co + couple equal to − 0.94 ± 0.05 V (NHE).Monograph [10] compares standard redox potentials E 0 (åÂ z + /Me + ) and E 0 (åÂ + /åÂ 0 ) of a set of metals of the Ib, IIb, IIIb, IVb, and Vb subgroups of the Mendeleev Periodic System (Au, Cu, Hg, Mg, In, Zn, Al, Sn, Bi, etc.) to their standard redox potentials E 0 (åÂ z + /åÂ 0 ) . Here M + denotes the ions in an intermediate oxidation state. It is shown the E 0 (åÂ z + /Me + ) potentials are somewhat more negative, while E 0 (åÂ + /åÂ 0 ) ones, somewhat more positive than the E 0 (åÂ z + /åÂ 0 ) potentials, yet the difference between E 0 (åÂ z + /åÂ + ) [or E 0 (åÂ + /åÂ 0 ) ] and E 0 (åÂ z + /åÂ 0 ) does not exceed 0.20 to 0.25 V; that between E 0 (åÂ z + /Me + ) and E 0 (åÂ + /åÂ 0 ) , 0.5 V. However...

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Pulse radiolysis study of monovalent cadmium, cobalt, nickel and zinc in aqueous solution. Part 1.—Formation and decay of the monovalent ions

Cited by 52 publications

References 0 publications

Radiation-chemical reduction of CO2+ ions in aqueous solution. Metal sols and their properties

Radiation-chemical reduction of CO2+ ions in aqueous solution. Metal sols and their properties

Geological and Chemical Factors that Impacted the Biological Utilization of Cobalt in the Archean Eon

The Mechanism of the Cobalt Anodic Ionization in Chloride Solution

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