Surface Interactions of Actinide Ions with Geologic Materials Studied by XAFS

1999 ◽  
Vol 590 ◽  
Author(s):  
E. R. Sylwester ◽  
E. A. Hudson ◽  
P. G. Allen
Keyword(s):  
Complex Structure ◽  
Outer Sphere ◽  
Equatorial Region ◽  
Uranyl Ion ◽  
Ambient Atmosphere ◽  
Solution Ph ◽  
Aquo Complex ◽  
Inner Sphere ◽  
Silica Alumina ◽  
Sphere Mechanism

ABSTRACTWe have investigated the interaction of the actinyl ion, , with silica, alumina, and montmorillonite surfaces under ambient atmosphere and aqueous conditions using x-ray Absorption Fine Structure (XAFS) Spectroscopy. In acid solution (pH ∼ 3.5), the uranyl ion shows a strong interaction with the silica and alumina surfaces, and a relatively weak association with the montmorillonite surface. The extent of direct surface interaction is determined by comparing structural distortions in the equatorial bonding environment of the uranyl ion relative to the structure of a “free” uranyl aquo complex. Based on this formalism, surface complexation on silica and alumina occurs through an inner-sphere mechanism with surface oxygen atoms binding directly to the equatorial region of the uranyl ion. In contrast, sorption on montmorillonite occurs by an outer sphere mechanism in which the uranyl ion retains the simple aquo complex structure and binds to the surface via ion-exchange. In near-neutral solutions (pH ∼ 6), sorption on all of the materials is dominated by an inner-sphere mechanism. The formation of surface oligomeric species is also observed on silica and alumina.

scholarly journals RuIII(edta) complexes as molecular redox catalysts in chemical and electrochemical reduction of dioxygen and hydrogen peroxide: inner-sphere versus outer-sphere mechanism

RSC Advances ◽  
2021 ◽  
Vol 11 (35) ◽  
pp. 21359-21366
Author(s):  
Debabrata Chatterjee ◽  
Marta Chrzanowska ◽  
Anna Katafias ◽  
Maria Oszajca ◽  
Rudi van Eldik
Keyword(s):  
Hydrogen Peroxide ◽  
Electron Transfer ◽  
Electrochemical Reduction ◽  
Molecular Oxygen ◽  
Outer Sphere ◽  
Transfer Processes ◽  
Edta Complexes ◽  
Inner Sphere ◽  
Electron Transfer Processes ◽  
Sphere Mechanism

[RuII(edta)(L)]2–, where edta4– =ethylenediaminetetraacetate; L = pyrazine (pz) and H2O, can reduce molecular oxygen sequentially to hydrogen peroxide and further to water by involving both outer-sphere and inner-sphere electron transfer processes.

scholarly journals Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate

2015 ◽  
Vol 11 ◽  
pp. 2254-2260 ◽  
Author(s):  
Manuel R Fructos ◽  
Juan Urbano ◽  
M Mar Díaz-Requejo ◽  
Pedro J Pérez
Keyword(s):  
Coordination Sphere ◽  
Outer Sphere ◽  
Transfer Reactions ◽  
Ethyl Diazoacetate ◽  
Inner Sphere ◽  
Carbene Transfer ◽  
Catalyzed Reactions ◽  
Sphere Mechanism ◽  
Nitrogen Evolution

Kinetic experiments based on the measurement of nitrogen evolution in the reaction of ethyl diazoacetate (N2CHCO2Et, EDA) and styrene or methanol catalyzed by the [IPrAu]+ core (IPr = 1,3-bis(diisopropylphenyl)imidazole-2-ylidene) have provided evidence that the transfer of the carbene group CHCO2Et to the substrate (styrene or methanol) takes place in the coordination sphere of Au(I) by means of an inner-sphere mechanism, in contrast to the generally accepted proposal of outer-sphere mechanisms for Au(I)-catalyzed reactions.

Surface complexation modelling of uranyl adsorption onto kaolinite based clay minerals using FITEQL 3.2

2006 ◽  
Vol 94 (12) ◽  
Author(s):  
Deniz Arda ◽  
Julide Hizal ◽  
Resat Apak
Keyword(s):  
Clay Minerals ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Uranyl Ion ◽  
Sphere Surface ◽  
Hexavalent Uranium ◽  
Inner Sphere

The aim of this study is to explain how the kaolinite-based clay minerals adsorb hexavalent uranium (uranyl ion), and to model uranyl adsorption based on inner-sphere surface complexation with the kaolinite edge hydroxyl sites and outer-sphere complexation with the permanent charge sites. The adsorption of UO

Kinetics and mechanism of redox reactions of U(III) ions with monochloroacetic and dichloroacetic acids

1979 ◽  
Vol 44 (2) ◽  
pp. 401-405 ◽  
Author(s):  
Ľubica Adamčíková ◽  
Ľudovít Treindl
Keyword(s):  
Redox Reactions ◽  
Reaction Rate ◽  
Activation Parameters ◽  
Outer Sphere ◽  
Alcohol Concentration ◽  
Kinetics And Mechanism ◽  
Solvent Structure ◽  
Influence Of Ph ◽  
Sphere Mechanism

The kinetics and mechanism of the redox reactions of U3+ ions with mono- and dichloroacetic acids were studied. The influence of pH was observed mainly in the second case and led to the determination of the rate constants and activation parameters corresponding to two parallel steps, namely oxidation of U3+ with CHCl2COO- ions and oxidation of U3+ with CHCl2.COOH molecules. The influence of binary mixtures of water with methanol, ethanol, isopropanol, or tert-butenol on the reaction rate was followed. Increasing alcohol concentration influences the rate constant not only through changing dielectric constant and solvation of the reactants but also through a change of the solvent structure which plays a role in reactions with an outer sphere mechanism of the electron transfer.

Protonation effects on dynamic flux properties of aqueous metal complexes

2009 ◽  
Vol 74 (10) ◽  
pp. 1543-1557 ◽  
Author(s):  
Herman P. Van Leeuwen ◽  
Raewyn M. Town
Keyword(s):  
Complex Formation ◽  
Metal Ion ◽  
Good Description ◽  
Minor Component ◽  
Outer Sphere ◽  
Metal Species ◽  
Central Metal ◽  
Inner Sphere ◽  
A Minor ◽  
Protonated Ligand

The degree of (de)protonation of aqueous metal species has significant consequences for the kinetics of complex formation/dissociation. All protonated forms of both the ligand and the hydrated central metal ion contribute to the rate of complex formation to an extent weighted by the pertaining outer-sphere stabilities. Likewise, the lifetime of the uncomplexed metal is determined by all the various protonated ligand species. Therefore, the interfacial reaction layer thickness, μ, and the ensuing kinetic flux, Jkin, are more involved than in the conventional case. All inner-sphere complexes contribute to the overall rate of dissociation, as weighted by their respective rate constants for dissociation, kd. The presence of inner-sphere deprotonated H2O, or of outer-sphere protonated ligand, generally has a great impact on kd of the inner-sphere complex. Consequently, the overall flux can be dominated by a species that is a minor component of the bulk speciation. The concepts are shown to provide a good description of experimental stripping chronopotentiometric data for several protonated metal–ligand systems.

Features of the formation of zinc(II) and cadmium(II) complexes with the inner-sphere and outer-sphere position of the decahydro-closo-decaborate anion in the presence of azaheterocyclic ligands

2021 ◽  
Vol 520 ◽  
pp. 120315
Author(s):  
Svetlana E. Korolenko ◽  
Aleksey S. Kubasov ◽  
Lyudmila V. Goeva ◽  
Varvara V. Avdeeva ◽  
Elena A. Malinina ◽  
...  
Keyword(s):  
Outer Sphere ◽  
Inner Sphere ◽  
Closo Decaborate Anion

scholarly journals Dy-DOTA integrated mesoporous silica nanoparticles as promising ultrahigh field magnetic resonance imaging contrast agents

Nanoscale ◽  
2018 ◽  
Vol 10 (45) ◽  
pp. 21041-21045 ◽  
Author(s):  
Xiao-Yu Zheng ◽  
Juan Pellico ◽  
Alexandr A. Khrapitchev ◽  
Nicola R. Sibson ◽  
Jason J. Davis
Keyword(s):  
Magnetic Resonance Imaging ◽  
Mesoporous Silica ◽  
Mesoporous Silica Nanoparticles ◽  
Silica Nanoparticle ◽  
Outer Sphere ◽  
Resonance Imaging ◽  
Mesoporous Silica Nanoparticle ◽  
Ultrahigh Field ◽  
Magnetic Resonance Imaging Contrast ◽  
Sphere Mechanism

Integrating Dy-DOTA motifs into mesoporous silica nanoparticle scaffolds significantly amplifies the ultrahigh field T2 relaxivity via a Curie outer-sphere mechanism.

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