Electrochemical assessment of water|ionic liquid biphasic systems towards cesium extraction from nuclear waste

A room temperature ionic liquid (IL) composed of a quaternary alkylphosphonium (trihexyltetradecylphosphonium, P66614(+)) and tetrakis(pentafluorophenyl) borate anion (TB) was employed within a water| P66614TB (w|P66614TB or w|IL) biphasic system to evaluate cesium ion extraction in comparison to that with a traditional water|organic solvent (w|o) combination. Cs-137 is a major contributor to the radioactivity of spent nuclear fuel as it leaves the reactor, and its extraction efficiency is therefore of considerable importance. The extraction was facilitated by the ligand octyl(phenyl)-N, N'-diisobutylcarbamoylphosphine oxide (CMPO) used in TRans- Uranium EXtraction processes and investigated through well established liquid| liquid electrochemistry. This study gave access to the metal ion to ligand (1: n) stoichiometry and overall complexation constant, beta, of the interfacial complexation reaction which were determined to be 1: 3 and 1.6 x 10(11) at the w| P66614TB interface while the study at w|o elicited an n equal to 1 with beta equal to 86.5. Through a straightforward relationship, these complexation constant values were converted to distribution coefficients, da, with the ligand concentrations studied for comparison to other studies present in the literature; the w|o and w|IL systems gave delta(alpha) of 2 and 8.2 x 10(7), respectively, indicating a higher overall extraction efficiency for the latter. For the w|o system, the metal ion-ligand stoichiometries were confirmed through isotopic distribution analysis of mass spectra obtained by the direct injection of an emulsified water-organic solvent mixture into an electron spray ionization mass spectrometer. (c) 2014 Elsevier B.V. All rights reserved

Electrochemical oxygen reduction at soft interfaces catalyzed by the transfer of hydrated lithium cations

The oxygen reduction reaction by decamethylferrocene (DMFc), triggered by hydrophilic metallic cations behaving as Lewis acids towards water molecules in a homogeneous organic phase reaction, was investigated using cyclic voltammetry at the water|1,2-dichloroethane (w|DCE) interface. Simulated CVs, prepared through a facile 1-dimensional geometry in COMSOL Multi-physics software and incorporating interfacial and homogeneous reactions, were compared to experimental ones in order to elucidate the kinetics, thermodynamics, and viability of the proposed mechanism. The predominant O2 reduction reactions were proposed to occur in bulk organic phase, or in the vicinity of the w|DCE interface; six organic phase reactions were put forward. The first step was hydrolysis made possible through polarization of the O−H bond of water molecules available in the cations hydration shell. The metal ion behaves as a Lewis acid coordinating to the oxygen and weakening the O−H bond, making the proton more acidic, thereby facilitating attack by decamethylferrocene (DMFc) to form DMFc-H+. DMFc-H+ then participates in dioxygen reduction, generating the O2H• radical species and DMFc+. Afterwards, the radical oxidizes another equivalent of DMFc to produce O2H−, that can then abstract a proton from the metal ions hydration sphere to generate hydrogen peroxide. The disproportionation of O2H− and the ion-pair formation of Li+ and OH− make up the other two reactions. The CV analysis was based on two curve features; the DMFc+ transfer wave and the positive limit of the polarizable potential window – the edge of scan potential profile – including the metal ion return peak. The goal of this article is to determine the kinetic/thermodynamic aspects of this mechanism from the experimental electrochemical data

Mechanism of oxygen reduction by metallocenes near liquid|liquid interfaces

The mechanism of the oxygen reduction reaction (ORR) at a liquid|liquid interface, employing ferrocene (Fc) derivatives – such as decamethylferrocene (DMFc) – as a lipophilic electron donor along with sulfuric acid as an aqueous proton source, was elucidated through comparison of experimentally obtained cyclic voltammograms (CVs) to simulated CVs generated through COMSOL Multiphysics software which employs the finite element method (FEM). The simulations incorporated a potential dependent proton transfer (i.e . ion transfer, IT) step from the water (w) to organic (o) phases along with two homogeneous reactions (C1C2) occurring in the organic phase – an IT-C1C2 mechanism. The reaction of DMFc with H+(o) to form DMFc-hydride (DMFc-H+) was considered the first step (reaction 1), while reaction of DMFc-H+ with oxygen to form a peroxyl radical species, View the MathML sourceHO2, and DMFc+ was deemed the second step (reaction 2). Subsequent reactions, between View the MathML sourceHO2 and either DMFc or H+, were considered to be fast and irreversible so that 2 was a ‘proton-sink’, such that further reactions were not included; in this way, the simulation was greatly simplified. The rate of 1, kcf, and 2, kchem, were determined to be 5 × 102 and 1 × 104 L mol−1 s−1, respectively, for DMFc as the electron donor. Similarly, the rates of biphasic ORR for 1,1′-dimethylferrocene (DFc) and Fc were considered equivalent in terms of this reaction mechanism; therefore, their rates were determined to be 1 × 102 and 5 × 102 L mol−1 s−1 for 1 and 2, respectively. The reactive and diffusive layer thicknesses are also discussed

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Electrochemical behaviour of ferrocenes in tributylmethylphosphonium methyl sulfate mixtures with water and 1,2-dichloroethane

Electron transfer (ET) reactions in ionic liquid (IL)vertical bar organic solvent (1,2-dichloroethane, DCE) and IL vertical bar water mixtures were investigated using a Pt disk ultramicroelectrode (UME) along with ferrocene (Fc) and ferrocenemethanol (FcCH(2)OH) redox probes as electroactive species dissolved in the respective mixtures. The IL utilized was tributylmethylphosphonium methyl sulfate (P4441CH3SO4). The diffusion coefficient of each redox species was determined at each incremental increase of DCE or water to the IL using a chronoamperometric technique that is concentration independent. The IL vertical bar DCE mixture exhibited little change in the Fc diffusion coefficient, D-Fc, up to a DCE mole fraction (chi(DCE)) of 0.5; the observed value, 2.0 x 10(-)8 cm(2) s(-1), agrees well with that typically reported for ILs in the literature. After which, the DFc quickly rose to a value commonly found in conventional molecular solvents, 1.3 x 10(-5) cm(2) s(-1) (at chi(DCE) = 0.8). An analogous result was not observed for IL vertical bar water mixtures using FcCH(2)OH, such that D-FcCH2OH varied from 0.2 to 1.2 x 10(-9) cm(2).s(-1) at a chi H2O of 0 to 0.8. It was proposed that a large increase in the D-Fc in the IL vertical bar DCE mixture versus DFcCH(2)OH in the IL vertical bar water series was owing to P4441CH3SO4's more hydrophobic character. Its hydrophobicity was quantified by measuring the formal ion transfer potentials of the IL component ions at a water vertical bar DCE immiscible interface

Trends in Hydrophilicity/Lipophilicity of Phosphonium Ionic Liquids As Determined by Ion-Transfer Electrochemistry

Ionic liquids (ILs) have become valuable new materials for a broad spectrum of applications including additives or components for new hydrophobic/hydrophilic polymer coatings. However, fundamental information surrounding IL molecular properties is still lacking. With this in mind, the microinterface between two immiscible electrolytic solutions (micro-ITIES), for example, water|1,2-dichloroethane, has been used to evaluate the hydrophobicity/lipophilicity of 10 alkylphosphonium ILs. By varying the architecture around the phosphonium core, chemical differences were induced, changing the lipophilicity/hydrophilicity of the cations. Ion transfer (IT) within the polarizable potential window (PPW) was measured to establish a structure–property relationship. The Gibbs free energy of IT and the solubility of their ILs were also calculated. For phosphonium cations bearing either three butyl or three hydroxypropyl groups with a tunable fourth arm, the latter displayed a wide variety of easily characterizable IT potentials. The tributylphosphonium ILs, however, were too hydrophobic to undergo IT within the PPW. Utilizing a micro-ITIES (25 μm diameter) housed at the tip of a capillary in a uniquely designed pipet holder, we were able to probe beyond the traditional potential window and observe ion transfer of these hydrophobic phosphonium ILs for the first time. A similar trend in lipophilicity was determined between the two subsets of ILs by means of derived solubility product constants. The above results serve as evidence of the validation of this technique for the evaluation of hydrophobic cations that appear beyond the conventional PPW and of the lipophilicity of their ILs

Scanning Electrochemical Microscopy of Belousov-Zhabotinsky reaction: how confined oscillations reveal short lived radicals and auto-catalytic species

Oscillating chemical reactions, encapsulated within artificial vesicles have been demonstrated as a powerful analogy of living cells for the investigation of chemical communication and morphogenesis. However, little is understood with regards to the influence of confinement on the reactivity of such systems. Herein, the effect of confinement on the Belousov-Zhabotinsky (BZ) oscillating reaction in bulk solution, (employing ferroin as a catalyst and malonic acid as the organic substrate) is investigated using scanning electrochemical microscopy (SECM) toward different insulating surfaces such as glass, silanized glass, or PTFE. An unexpected increase in the amplitude of the BZ reaction at a tip-substrate distance of ∼12-15 μm is observed. By simulating different reaction mechanisms, from simple EC' catalysis to more sophisticated Oregonator or even an 11-reaction scheme, it is shown that such behavior reveals the intervention of redox catalysis processes and particularly the short-lived highly reactive radical intermediate BrO2 • indirectly detected at micromolar concentrations. The reinspection of the EC' mechanism shows that the homogeneous catalysis route is confirmed and kinetically characterized from SECM toward an insulating substrate, with promising potentiality in many systems. More specifically to the complex chemical case of BZ reactions, the mechanism is understood from the envelope curves of the oscillations, which are assessed in the absence of the oscillation (absence of organic substrate)

Kinetic differentiation of bulk/interfacial oxygen reduction mechanisms at/near liquid/liquid interfaces using scanning electrochemical microscopy

The present work describes the application of scanning electrochemical microscopy (SECM) in the feedback mode to determine the kinetics of oxygen reduction at or near the liquid/liquid interface – between water and 1,2-dichloroethane (w/DCE). The system contained decamethylferrocene (DMFc) in DCE as the electron donor and acids in water as a proton source. In this approach, decamethylferrocenium (DMFc+ ) is reduced at the tip of a microelectrode in DCE and the electrogenerated DMFc reacts with protons and oxygen to be re-oxidized in a following chemical reaction (catalytic EC’ mechanism). When a high Galvani potential difference was applied across the liquid/liquid interface, protons would transfer rapidly to the organic phase. Under this condition, SECM approach curves toward the liquid/liquid interface showed dramatic current increases at distances far from the interface. This indicates that oxygen reduction takes place mainly in the bulk DCE; however, at lower Galvani potential differences, where the proton transfer is slow, oxygen reduction was also observed at the interface. Finally, SECM feedback mode measurements with the tip approaching a conductive substrate were used to determine the kinetics of the homogeneous reaction, with an obtained apparent rate constant of 0.2–0.5 m3 mol1 s1