Mol Dm Research Articles

Fluoride-Based Deep Eutectic Solvents with Amide Dual-Hydrogen-Bond Donors.

Developing F--containing electrolytes is crucial for electrochemical and chemical fluorination. However, balancing the F- concentration and electrochemical stability of the electrolytes remains a challenge. In this study, fluoride-based deep eutectic solvents (F-DESs) were obtained by using amide hydrogen-bond donors (HBDs) containing dual N-H bonds. The obtained F-DES, [TMA]F·3.5[1,3-DMU], was prepared by facilely mixing solid compounds of tetramethylammonium fluoride ([TMA]F) and 1,3-dimethylurea (1,3-DMU), resulting in a high F- concentration (2.6 mol dm-3) and a wide electrochemical window (3.1 V) at room temperature. The electrochemical window was much wider than that of [TMA]F·3.5[EG] (EG, ethylene glycol) as another F-DES with an alcohol HBD (1.9 V). Moreover, [TMA]F·3.5[1,3-DMU] exhibited an ionic conductivity that was 2 orders of magnitude higher than that of [TMA]F·3.5[1,3-DMTU] (1,3-DMTU, 1,3-dimethylthiourea) around room temperature because of the bifurcated hydrogen bonds between the dual N-H bonds of 1,3-DMU and one F-. Thus, [TMA]F·3.5[1,3-DMU] was demonstrated to be applicable to electrochemical fluorination.

Redox Kinetics and Mechanism of the Reactions of µ –Oxobis [aquobis (2,2’ – Bipyridine)] diruthenium (III) Ion and some Aliphatic Alcohols in Acidic Medium

The redox kinetics and mechanisms of the reactions of μ – oxobis[aquobis(2,2’ - bipyridine)]diruthenium (III) ion, [(bipy)2(H2O)RuORu(H2O)(bipy)2]4+ (hereafter denoted as Ru2O4+ or [(H2O)2(bipy)4Ru2O]4+) and some primary aliphatic alcohols was studied in perchloric acid medium, [H+] = 5.0 x 10-3 mol dm-3, ionic strength (I), = 0.5 mol dm–3 (NaClO4), temperature (T) = 31 ± 1°C and wavelength ,λmax = 660 nm. The reactions, which led to the formation of corresponding aldehydes had a stoichiometry of 1:1, were all first order with respect to each reactant, and second order overall. The reactions proceeded in the absence of acid but when acid was added, the reactions ceased. Varying the ionic strength and dielectric constants of the reaction medium had no effect on the reaction. Added ions catalysed the reaction and free radicals were identified in the reaction mixtures in the course of the reactions. There was no evidence for the formation if intermediate complex in the course of the reaction. The order of reactivity is of the order CH3OH > C2H5OH > C3H7OH Based on the results, it is suggested that all the reactions proceeded through the outer – sphere electron transfer mechanism and a plausible mechanism that represented all the reactions is proposed.

SPECTROPHOTOMETRIC INVESTIGATION OF REDOX REACTION BETWEEN NAPHTHOL GREEN B AND THIOSULPHATE ION IN AQUEOUS ACID: KINETICS AND MECHANISTIC APPROACH METHOD

The kinetics of the redox reaction of naphthol green B (here and thereafter referred to as (NGB3-) with thiosulphate ion has been studied using spectrophotometer at constant ionic strength, I = 0.50 C2mol dm-3 (NaCl), ?H+? = 1.0 ? 10-4 mol dm-3 (HCl) and T = 21 ?1?C. The redox reaction showed a stoichiometry of 2:1 and rate equation for the reaction is: -d[NGB3-]/dt = (a + b[H+])[NGB3-][S2O32-]. The rate of reaction slightly increased with increase in [H+] in the range of (0.5 – 9.0) × 10?4 mol dm?3 investigated. Changes in the ionic strength of the reaction did not affect the rate of the reaction. This showed zero BrØnsted - Debye salt effect. The reaction shows a first order dependence on [oxidant] and [reductant]. Added anion on the reaction rate does not have effect on the rate of the reaction. Michaelis – Menten’s plot of 1/k1 versus 1/ S2O32- and spectrophotometric test suggest presence of an intermediate in the rate determining step. There was evidence of gel formation by the addition of acrylamide to reaction mixture followed by excess methanol. The results obtained suggest the presence of the formation of intermediate complex. Therefore, innersphere mechanism is proposed for this reaction.

Solution structure, crystal structure, Hirshfeld surface analysis of copper(II) diamide species as an optical chemical sensor

Optical chemical sensors are promising tools for the detection of metal ions in various samples. Copper(II) has received significant attention among metal ions due to its toxic nature and widespread applications in various industrial processes. In recent years, several optical chemical sensors have been developed to detect copper(II) with high sensitivity and selectivity. This paper describes the spectrophotometric determination of trace amounts of copper(II) using N1-(2-aminoethyl)-N2-((pyridin-2-yl)methyl)oxalamide (H2(555)NH2) as an optical chemical sensor. The protonation and formation constants of the Cu(II)/(H2(555)NH2) system were determined at 25 °C and the ionic strength of 0.15 mol dm−3 using glass electrode potentiometry. The structures of the different species, present in solution at different pH values, were determined using UV–vis, 1H NMR, and EPR spectroscopic techniques. At pH 5, the [Cu(H2(555)NH2)]2+ species was formed with the Cu(II) coordinated to the pyridole nitrogen and the terminal amine. Above pH 8, [Cu(H2(555)NH2)H-2] is the most predominant species in solution. Here the Cu(II) coordinates to all four nitrogen atoms. In the solid state, a dinuclear complex, [Cu(H(55)NH3)Cl]2[Cu(H2O)2(NO3)2Cl2]H2O, was formed. Single crystal X-ray structure showed the Cu(II) to be coordinated to the pyridine and the amide N-atoms in addition to an O-atom from one of the two carbonyl groups. The coordination environment was completed by two bridged chloride ions to give a slightly distorted trigonal bipyramidal coordination geometry around the copper centre. The amine was not coordinated. The proposed sensor was successfully applied to determine copper(II) in real samples, with recoveries ranging from 10−5 to 10−3 mol/dm−3. Using H2(555)NH2 as an optical chemical sensor emerged as a powerful tool for detecting copper(II) ions in different aqueous samples.

Cyclodextrin-Assisted Surface-Enhanced Photochromic Phenomena of Tungsten(VI) Oxide Nanoparticles for Label-Free Colorimetric Detection of Phenylalanine.

Herein are presented the results of experiments designed to evaluate the effectiveness of host-guest interactions in improving the sensitivity of colorimetric detection based on surface-enhanced photochromic phenomena of tungsten(VI) oxide (WO3) nanocolloid particles. The UV-induced photochromic coloration of WO3 nanocolloid particles in the presence of aromatic α-amino acid (AA), l-phenylalanine (Phe) or l-2-phenylglycine (Phg), and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TMβCDx) in an aqueous system was investigated using UV-vis absorption spectrometry. The characteristics of the adsorption modes and configurations of AAs on the WO3 surface have also been identified by using a combination of adsorption isotherm analysis and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). A distinct linear relationship was observed between the concentration of AAs adsorbed on the WO3 nanocolloid particles and the initial photochromic coloration rate in the corresponding UV-irradiated colloidal WO3 in aqueous media, indicating that a simple and sensitive quantification of AAs can be achieved from UV-induced WO3 photochromic coloration without any complicated preprocessing. The proposed colorimetric assay in the Phe/TMβCDx/WO3 ternary aqueous system had a linear range of 1 × 10-8 to 1 × 10-4 mol dm-3 for Phe detection, with a limit of detection of 8.3 × 10-9 mol dm-3. The combined results from UV-vis absorption, ATR-FTIR, and adsorption isotherm experiments conclusively indicated that the TMβCDx-complexed Phe molecules in the Phe/TMβCDx/WO3 ternary aqueous system are preferentially and strongly inner-sphere adsorbed on the WO3 surface, resulting in a more significant surface-enhanced photochromic phenomenon. The findings in this study provided intriguing insights into the design and development of the "label-free" colorimetric assay system based on the surface-enhanced photochromic phenomenon of the WO3 nanocolloid probe.

Influence of Electrolyte Concentration on the Electrochemical Behavior of Copper Hexacyanoferrate as an Active Material for Zinc-Ion Batteries

This study investigates the impact of electrolyte concentration on the electrochemical behavior of copper hexacyanoferrate (CuHCF), a promising active material for aqueous zinc-ion battery electrodes. Cyclic voltammetry, charge-discharge measurements, and X-ray diffraction analysis were employed to assess the electrochemical reactions and structural integrity of the CuHCF electrode under varying electrolyte concentrations. The results revealed a significant influence of electrolyte concentration on the electrochemical performance of the CuHCF electrode. Specifically, the charge-discharge capacity exhibited an initial increase as the electrolyte concentration increased from 1.0 to 2.0 mol dm‒3, followed by a subsequent decrease. This decrease in capacity was attributed to the occurrence of an electrode/electrolyte interfacial reaction in the low-potential region of 0.0–0.3 V, coupled with structural changes in the CuHCF active material. Notably, these findings underscore the strong correlation between the electrochemical performance of the CuHCF electrode and the hydration structure of zinc ions, as well as the pH of the electrolyte solution. Thus, optimizing the electrolyte composition holds significant potential for enhancing the performance of aqueous zinc-ion batteries employing CuHCF electrodes.

Interaction of 3,9-disubstituted acridine with single stranded poly(rA), double stranded poly(rAU) and triple stranded poly(rUAU): molecular docking – A spectroscopic tandem study

RNA plays an important role in many biological processes which are crucial for cell survival, and it has been suggested that it may be possible to inhibit individual processes involved in many diseases by targeting specific sequences of RNA. The aim of this work is to determine the affinity of novel 3,9-disubstited acridine derivative 1 with three different RNA molecules, namely single stranded poly(rA), double stranded homopolymer poly(rAU) and triple stranded poly(rUAU). The results of the absorption titration assays show that the binding constant of the novel derivative to the RNA molecules was in the range of 1.7–6.2 × 104 mol dm−3. The fluorescence and circular dichroism titration assays revealed considerable changes. The most significant results in terms of interpreting the nature of the interactions were the melting temperatures of the RNA samples in complexes with the 1. In the case of poly(rA), denaturation resulted in a self-structure formation; increased stabilization was observed for poly(rAU), while the melting points of the ligand-poly(rUAU) complex showed significant destabilization as a result of the interaction. The principles of molecular mechanics were applied to propose the non-bonded interactions within the binding complex, pentariboadenylic acid and acridine ligand as the study model. Initial molecular docking provided the input structure for advanced simulation techniques. Molecular dynamics simulation and cluster analysis reveal π – π stacking and the hydrogen bonds formation as the main forces that can stabilize the binding complex. Subsequent MM-GBSA calculations showed negative binding enthalpy accompanied the complex formation and proposed the most preferred conformation of the interaction complex.

Elucidating the Complex Oxidation Behavior of Aqueous H3PO3 on Pt Electrodes via In Situ Tender X-ray Absorption Near-Edge Structure Spectroscopy at the P K-Edge.

In situ tender X-ray absorption near-edge structure (XANES) spectroscopy at the P K-edge was utilized to investigate the oxidation mechanism of aqueous H3PO3 on Pt electrodes under various conditions relevant to high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) applications. XANES and electrochemical analysis were conducted under different tender X-ray irradiation doses, revealing that intense radiation induces the oxidation of aqueous H3PO3 via H2O yielding H3PO4 and H2. A broadly applicable experimental procedure was successfully developed to suppress these undesirable radiation-induced effects, enabling a more accurate determination of the aqueous H3PO3 oxidation mechanism. In situ XANES studies of aqueous 5 mol dm-3 H3PO3 on electrodes with varying Pt availability and surface roughness reveal that Pt catalyzes the oxidation of aqueous H3PO3 to H3PO4. This oxidation is enhanced upon applying a positive potential to the Pt electrode or raising the electrolyte temperature, the latter being corroborated by complementary ion-exchange chromatography measurements. Notably, all of these oxidation processes involve reactions with H2O, as further supported by XANES measurements of aqueous H3PO3 of different concentrations, showing a more pronounced oxidation in electrolytes with a higher H2O content. The significant role of water in the oxidation of H3PO3 to H3PO4 supports the reaction mechanisms proposed for various chemical processes observed in this work and provides valuable insights into potential strategies to mitigate Pt catalyst poisoning by H3PO3 during HT-PEMFC operation.

Pyrene-Appended Boronic Acids on Graphene Foam Electrodes Provide Quantum Capacitance-Based Molecular Sensors for Lactate.

Molecular recognition and sensing can be coupled to interfacial capacitance changes on graphene foam surfaces linked to double layer effects and coupled to enhanced quantum capacitance. 3D graphene foam film electrodes (Gii-Sens; thickness approximately 40 μm; roughness factor approximately 100) immersed in aqueous buffer media exhibit an order of magnitude jump in electrochemical capacitance upon adsorption of a charged molecular receptor based on pyrene-appended boronic acids (here, 4-borono-1-(pyren-2-ylmethyl)pyridin-1-ium bromide, or abbreviated T1). This pyrene-appended pyridinium boronic acid receptor is employed here as a molecular receptor for lactate. In the presence of lactate and at pH 4.0 (after pH optimization), the electrochemical capacitance (determined by impedance spectroscopy) doubles again. Lactic acid binding is expressed with a Hillian binding constant (Klactate = 75 mol-1 dm3 and α = 0.8 in aqueous buffer, Klactate = 460 mol-1 dm3 and α = 0.8 in artificial sweat, and Klactate = 340 mol-1 dm3 and α = 0.65 in human serum). The result is a selective molecular probe response for lactic acid with LoD = 1.3, 1.4, and 1.8 mM in aqueous buffer media (pH 4.0), in artificial sweat (adjusted to pH 4.7), and in human serum (pH adjusted to 4.0), respectively. The role of the pyrene-appended boronic acid is discussed based on the double layer structure and quantum capacitance changes. In the future, this new type of molecular capacitance sensor could provide selective enzyme-free analysis without analyte consumption for a wider range of analytes and complex environments.

Reaction of mono- and dichlorophenols with •OH and hydrated electrons: A pulse radiolysis study

The reactivity of monochlorophenols and dichlorophenols towards •OH and hydrated electrons was investigated applying pulse radiolysis coupled with time resolved spectroscopy. Rate constants, transient spectra and stability of transient species were studied for mono and dichlorophenols. Reactivity of 3,4-dichlorophenol (3,4-DCP) towards •OH and hydrated electrons, its transient spectra and respective rate constants have been explained in detail as a model for the current pulse radiolysis experiments. The trends and behaviors in the reactivity of mono and dichlorophenols towards •OH and hydrated electrons were analyzed. All the corresponding OH-adducts demonstrated λmax values range between 295 and 435 nm and their rate constants exhibited a range of (3.4–21) x 109 dm3 mol−1 s−1. Likewise, e-adducts illustrated λmax values ranged between 295 and 355 nm and their rate constants displayed a range of (0.025–6.2) x 109 dm3 mol−1 s−1. Full geometry optimizations and electron charge density calculations based on DFT (density functional theory) presented the existence of a strong correlation of electron charge density and polarizability with the reactivity of chlorophenols towards hydrated electrons and •OH radical. This research represents the first thorough exploration of its kind, aiming to comprehend the reactivity of all dichlorophenols and their corresponding transient spectra through pulse radiolysis.

Enhanced Oxygen Reduction Activity of Platinum Micropore

AbstractThe high overpotential of oxygen reduction reaction (ORR) prevents the wide commercialization of fuel cells and metal‐air batteries. To accelerate the reaction rate, porous electrocatalysts draw attention to obtain a higher specific surface area. However, the effect of micropores on ORR kinetics has not been understood because of the non‐uniform pore sizes, length, and tortuosity of practical electrocatalysts. In this study, we evaluate ORR activity in a micropore using platinum model electrodes with arrays of cylindrical pores with a uniform pore diameter of 1.8 nm. The model electrodes having pore lengths of 45, 100, and 380 nm are fabricated, and their ORR performances are examined by electrochemical measurements and numerical simulations in 0.1 mol dm−3 KOH aqueous solution. The intrinsic ORR activity of the micropore is successfully obtained with the electrode having a pore length of 45 nm, where oxygen transport resistance in the micropore has little effect on ORR. It is found that the intrinsic ORR activity of the micropore is higher than that of a planar Pt surface. X‐ray photoelectron spectroscopy and CO stripping voltammetry indicate a downshift of the d‐band center, which can be the origin of the high intrinsic ORR activity.

Bimetallic bis-Aroyldihydrazone-Isatin Complexes of High O=V(IV) and Low Cu(II) Valent Ions as Effective Biological Reagents for Antimicrobial and Anticancer Assays.

Due to the versatile bioreactivity of aroyldihydrazone complexes as cost-effective alternatives with different transition metals, two novel bimetallic homo-complexes (VOLph and CuLph) were prepared via the coordination of a terephthalic dihydrazone diisatin ligand (H2Lph) with VO2+ and Cu2+ ions, respectively. The structure elucidation was confirmed by alternative spectral methods. Biologically, the H2Lph ligand and its MLph complexes (M2+ = VO2+ or Cu2+) were investigated as antimicrobial and anticancer agents. Their biochemical activities towards ctDNA (calf thymus DNA) were estimated using measurable titration viscometrically and spectrophotometrically, as well as the gel electrophoresis technique. The growth inhibition of both VOLph and CuLph complexes against microbial and cancer cells was measured, and the inhibition action, MIC, and IC50 were compared to the inhibition action of the free H2Lph ligand. Both VOLph and CuLph showed remarkable interactive binding with ctDNA compared to the free ligand H2Lph, based on Kb = 16.31, 16.04 and 12.41 × 107 mol-1 dm3 and ΔGb≠ = 47.11, -46.89, and -44.05 kJ mol-1 for VOLph, CuLph, and H2Lph, respectively, due to the central metal ion (VIVO and CuII ions). VOLph (with a higher oxidation state of the V4+ ion and oxo-ligand) exhibited enhanced interaction with the ctDNA molecule compared to CuLph, demonstrating the role and type of the central metal ion within the performed electronegative and electrophilic characters.

The physicochemical and DNA binding studies of ceftazidime pentahydrate and cefotaxime sodium in aqueous medium

Abstract Ceftazidime pentahydrate (CP) and cefotaxime sodium (CS) are semisynthetic cephalosporin antibiotics and are used to treat a variety of diseases worldwide. In order to explore the efficiency of a medicinal compound, it is important to have a deep understanding of its solution and physiochemical behaviour along with its interaction with biological molecules. In this regard, the solution of two drugs i.e., ceftazidime pentahydrate (CP) and cefotaxime sodium (CS) were investigated in detail. The physicochemical properties of drugs solutions and their interaction with deoxyribonucleic acid (DNA) were studied in water under varying experimental parameters. In the present study the physicochemical properties such as density, viscosity, surface tension, and conductance of aqueous solution, having various molar concentrations, of CP and CS were traced out at different temperatures. Five various concentrations (0.05, 0.1, 0.15, 0.2, and 0.3 mol dm−3) of each drug in an aqueous medium were prepared separately, and the physicochemical properties of each solution, were studied individually at temperatures such as 293, 303, 313, 323, and 333 K respectively. Most of these parameters have shown different behaviour with varying concentration of solution and temperature of the medium. In addition, these drugs showed a spontaneous surface-active and association behaviour in aqueous solutions and drug DNA solution. The flow behaviour, surface properties, volumetric behaviour and solute–solvent interaction of this drug were prominently influenced by experimental variables. UV-Visible spectroscopy was also used to study the interaction of these drugs with DNA in aqueous media in detail. Calculated values of binding constants (K b) for all drug–DNA are positive, indicating constructive binding and interactions between the molecules. In addition the binding efficiency of ceftazidime pentahydrate was found more than that of cefotaxime sodium. The interaction of drug–DNA was not only affected by the nature of the drug but also by the drug-to-DNA ratio and nature of the medium used.

Detailed mass transfer studies of a ternary system associated with intermittent jerking of the liquid − liquid interface

Experiments were carried out to transfer diethylamine (DEA) from water to carbon tetrachloride under static conditions inside a 50 cm3 buret for the fixed initial concentration of 2.5 mol dm−3. Initial concentration was chosen after ruling out lower concentrations to study the long-term instability. The phase volumes (i.e., 5 and 10 cm3) were equal for the separate trials at different extraction times. During extraction, intermittent interfacial jerking occurred up to 1800 s. After this time, the jerking frequency decreased and disappeared by 3600 s. The jerking time interval increased as the extraction progressed. Jerking resulted in profuse streaming into the extract phase, coupled with a throw of liquid from the interfacial region to the bulk of the aqueous phase. The complete concentration profiles of the solute in both phases were developed immediately after the jerking phenomena. In the aqueous phase, the concentration profiles revealed one and two zones of the minimum concentration of DEA in the bulk of the 5- and 10-cm3 phase volumes, respectively. The interfacial mass transfer coefficient during the jerking was high due to the absence of any interfacial barrier. The interfacial mass transfer coefficient in the absence of instability was much less than that in the presence of jerking. Also, it was higher than that for the systems where unidirectional ejections occurred due to the energy instability of the liquid–liquid interface. This work has also estimated the average spreading velocity of the interface, which caused the jerking due to the obstruction from the wall.

Quantitative reaction monitoring using parahydrogen-enhanced benchtop NMR spectroscopy.

The parahydrogen-induced polarisation (PHIP) NMR signal enhancement technique is used to study H2 addition to Vaska's complex (trans-[IrCl(CO)(PPh3)2]) with both standard high-field (9.4 T) NMR and benchtop (1 T) NMR detection. Accurate and repeatable rate constants of (0.84 ± 0.03) dm3 mol-1 s-1 and (0.89 ± 0.03) dm3 mol-1 s-1 were obtained for this model system using standard high-field and benchtop NMR, respectively. The high-field NMR approach is shown to be susceptible to systematic errors associated with interference from non-hyperpolarised signals, which can be overcome through a multiple-quantum filtered acquisition scheme. This challenge is avoided when using benchtop NMR detection because the non-hyperpolarised signals are much weaker due to the lower magnetic field, enabling the use of a simpler and more efficient single RF pulse detection scheme. Method validation against several experimental parameters (NMR relaxation, %pH2 enrichment and temperature) demonstrates the robustness of the benchtop NMR approach but also highlights the need for sample temperature control throughout reaction monitoring. A simple temperature equilibration protocol, coupled with use of an insulated sample holder while manipulating the sample outside the spectrometer, is found to provide sufficient temperature stabilisation to ensure that accurate and repeatable rate constants are obtained. Finally, the benchtop NMR reaction monitoring protocol is applied to the analysis of a complex mixture, where multiple reaction products form simultaneously. H2 addition to a mixture of three Vaska's complex derivatives was monitored, revealing the presence of competitive reaction pathways within the mixture.

Wavelength-dependent rearrangements of an α-dione chromophore: a chemical pearl in a bis(hypersilyl) oyster.

The symmetric bissilyl-dione 3 reveals two well-separated n → π* absorption bands at λmax = 637 nm (ε = 140 mol-1 dm3 cm-1) and 317 nm (ε = 2460 mol-1 dm3 cm-1). Whereas excitation of 3 at λ = 360/365 nm affords an isolable siloxyketene 4 in excellent yields, irradiation at λ = 590/630 nm leads to the stereo-selective and quantitative formation of the siloxyrane 5. These remarkable wavelength-dependent rearrangements are based on the electronic and steric properties provided by the hypersilyl groups. While the siloxyketene 4 is formed via a hitherto unknown 1,3-hypersilyl migration via the population of a second excited singlet state (S2, λmax = 317 nm, a rare case of anti-Kasha reactivity), the siloxyrane 5 emerges from the first excited triplet state (T1via S1λmax = 637 nm). These distinct reaction pathways can be traced back to specific energy differences between the S2, S1 and T1, an electronic consequence of the bissilyl substited α-dione (the "pearl"). The hypersilyl groups act as protective ''oyster shell", which are responsible for the clean formation of 4 and 5 basically omitting side products. We describe novel synthetic pathways to achieve hypersilyl substitution (3) and report an in-depth investigation of the photorearrangements of 3 using UV/vis, in situ IR, NMR spectroscopy and theoretical calculations.

Simple and convenient preconcentration procedure for the isotopic analysis of uranium in seawater.

The demand for monitoring anthropogenic U isotopes, 236U and 233U, in seawater will continue to increase due to radioecological issues and the need for tools for environmental dynamics research. In response to this growing demand, herein, a novel and simple method was developed for the collection of U isotopes in seawater, both in the laboratory and field, using a fabric-like amidoxime adsorbent. The results from the adsorption studies showed that the optimum conditions for processing seawater in a glass beaker were as follows: seawater pH 4, amidoxime adsorbent 0.20 mmol per 500 g seawater and an adsorption time of 9 hours. Alternatively, when using a closed polyethylene container in experiments on-board a ship and using the same ratio of adsorbent to seawater as in the beaker experiment in the laboratory, the optimum conditions were as follows: seawater pH 8 and an adsorption time of 24 hours. Under the above-mentioned conditions, more than 95% of the U underwent adsorption in both the beaker and the polyethylene container experiments. In the case of analyte desorption, more than 80% of U in seawater was recovered using 2-3 mol dm-3 HCl or HNO3 as the eluent. Thus, it was concluded that the amidoxime adsorbent can serve as a simple and effective pre-concentration method for the ultra-trace monitoring of U isotopes in seawater.

Kinetics and oxidation of thiocarbohydrazide by hexacyanoferrate(III) in aqueous perchloric acid medium

Hexacyanoferrate(III) [HCF(III)] was used to oxidize thiocarbohydrazide (TCH) in an aqueous perchloric acid (HClO4) medium, and the reaction kinetics were studied spectrophotometrically at 420 nm while keeping a constant ionic strength of 1.0 mol dm−3 and modulating the temperature between 298K–318K. The stoichiometry of the reaction among TCH and HCF in the HClO4 medium is 1:2. The reaction has a lower than unit order in both TCH and HClO4 and is of the first order in HCF. The impact of varying the ionic strength and dielectric constant of the medium on the rate has been investigated. The effect of temperature on the reaction rate was studied, and different activation parameters of reaction Ea, ΔH#, ΔS#, ΔG#, and log10 A were calculated. The products of oxidation were analyzed by simple qualitative analysis. On the basis of the collected data, the rate law has been derived, and a probable mechanism has been proposed.

Phase Transition Behavior of Biphasic Systems Affected By the Charge-Transfer Process

Lithium-ion batteries have attracted attention with the development of electric vehicles and the introduction of renewable energy. For use in these applications, lithium-ion batteries with fast charge and discharge acceptability are particularly important. The charge and discharge reactions of lithium-ion batteries are limited by several factors such as ion and electron transfer in the electrode and electrolyte, charge transfer at the electrode-electrolyte interface, and reaction rates during phase transitions. It has been reported that the rate limiting factor of the biphasic materials is the phase boundary rearrangement, and the activation energy of such phase transition has been investigated in previous studies. However, there are variations in the reported activation energy values even for the same electrode material. Since there are many unexplored factors that affect the phase transition rate, we have examined the effect of these factors on the phase transition rate using LiFePO4as model electrodes. In our previous presentation, we showed that the phase transition behavior of LiFePO4 electrode changes depending on the electrolyte, suggesting the influence of the electrode/electrolyte interface. (1) In this presentation, we report the relationship between the activation energy of the biphasic reaction and that of the solvation/desolvation of the electrolyte measured using a four-probe cell (2), and the effect on the phase transition behavior when the transferred ion species is changed from Li+ to Na+. A non-aqueous-type three-electrode cell was composed of the LiFePO4 as a working electrode, lithium foils as a counter and reference electrodes, and a 1 mol dm–3 solution of LiPF6 in ethylene carbonate and diethyl carbonate (1:1 v/v) as an electrolyte solution and was constructed in an Ar-filled glove box. An aqueous-type three-electrode cell was composed of the LiFePO4 as a working electrode, a Ni wire as a counter electrode, Ag/AgCl/sat’d KCl aq as a reference electrode, and a 0.5 mol dm–3 Li2SO4 aqueous solution as an electrolyte solution. The charging–discharging behavior was firstly measured to confirm the cell characteristics and then the potential step measurement was employed. The Avrami plots based on the potential step results (3) were used to obtain the reaction rate constant k. Further experiments at different temperatures were performed and the Arrhenius plots were drawn to calculate the activation energy of the phase transition. (3) The activation energy for solvation/desolvation of the electrolyte was calculated by making a four-probe cell with the counter electrode and reference electrode symmetrically arranged across the solid electrolyte Li2OAl2O3SiO2P2O5TiO2 (OHARA) and measuring AC impedance spectra at different temperatures. For the Na+ system, the LiFePO4 electrode was electrochemically delithiated to produce FePO4, and then Na+ was inserted into FePO4 to obtain NaFePO4 in the aqueous electrolyte. Electrochemical measurements were performed with the obtained electrode. The potential step measurements were performed with the aqueous and non-aqueous electrolyte cells. Their activation energies were obtained from the Arrhenius plots with the k values and compared. The activation energy measured in the aqueous electrolytes was smaller than that measured in the nonaqueous electrolyte. The activation energy for the solvation/desolvation processes was also smaller for the aqueous electrolytes system, suggesting that the charge transfer process between electrode and electrolyte is involved in the rate-determining process of the phase transition. Next, we performed the same experiment by changing the mobile ion species from Li+ to Na+. The activation energy for Na+extraction was nearly zero, suggesting very fast phase transition. If the volume change corresponding to the phase transition limits the rate, large Na+ extraction would lead to high activation energy than Li+ extraction. The tendency was the opposite, suggesting that the weak interaction of Na+ and water affects the whole phase transition.References(1) C. Yamamoto, A. Ikezawa and H. Arai, The 242nd Electrochemical Society Meeting, A02-0130 (2022).(2) Z. Ogumi., Electrochemistry, 78, 319 (2010).(3) J. Allen, T.R. Jow, and J. Wolfenstine, Chem. Mater., 19, 2108-2011 (2007).(4) Y. Orikasa, T. Maeda, Y. Koyama, T. Minato, H. Murayama, K. Fukuda, H. Tanida, H. Arai, E. Matsubara, Y. Uchimoto, and Z. Ogumi, J. Electrochem. Soc. 160, A3061-A3065 (2013). Figure 1

Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.