Aqueous Perchloric Acid Solutions Research Articles

Electropolymerization of 5-amino-2-naphthalenesulfonic acid and their application as the electrode material for supercapacitors

Electropolymerization is a powerful tool in constructing conducting polymers that can be utilized as the electrode materials for flexible supercapacitors. The 5-amino-2-naphthalenesulfonic acid is electropolymerized at anodic potential on carbon cloth from aqueous perchloric acid solutions. The poly(5-amino-2-naphthalenesulfonic acid) coated carbon cloth electrodes (PANS/CC) are characterized, and are used as the electrode material for supercapacitors. The PANS/CC-40 exhibits the optimum charge storage performance, with the specific capacity of 85.5 mAh g−1 at 1 A g−1 charge-discharge current density in 1 M H2SO4. Specific capacities of 44.8 and 38.5 mAh g−1 are achieved for the PNAS/CC-40 in 1 M ZnSO4 and 1 M (NH4)2SO4, respectively, at 1 A g−1. Kinetic analyses show that the PNAS/CC-40 is a battery-type electrode material, and the surface-controlled processes contribute over 80 % of the stored charge. Evidences of cation (de)intercalation accompanying with the redox of amine/imine groups are given. A symmetric supercapacitor is assembled using two PNAS/CC-40 and the PVA/H2SO4 gel electrolyte, and it can deliver the energy density of 1.1 Wh kg−1 and the power density of 136.9 W kg−1 at 1 A g−1. The capacity retention of the symmetric supercapacitor is 88 % after 10,000 cycles at 5 A g−1.

Towards Quantitative Interpretation of Normal Incidence Differential Reflectance (NIDR) Measurements for Electrochemical Dynamics Experiments

Normal incidence differential reflectance, or NIDR, is an in-situ technique suitable for high time resolution monitoring of the interfacial structure and composition of electrode-solution interfaces. Recent efforts have been focused in our laboratory on formulating quantitative models for interpreting the potential-, and coverage-dependence of NIDR signals for use in monitoring interfacial dynamics at Au electrodes in various electrolytes. A simple model capturing the aforementioned dependences will be presented. Within the framework of this model, different limiting behaviors are anticipated depending on the optical properties of the adsorbate and the nature of its interactions with the Au surface. In addition, some exemplary data sets on Au electrodes will be discussed, namely cyclic voltammetry and potential steps on single crystals and polycrystalline Au surfaces in aqueous perchloric acid solutions. The NIDR responses to these potential perturbations can be rationalized on the basis of the optical properties of perchlorate and its interaction with the surface. All NIDR data are consistent with adsorbed perchlorate exhibiting optical properties that deviate minimally from that of water, as well as perchlorate physisorbing on Au rather than chemisorbing. In essence, the NIDR signal is proportional to the charge stored on the Au surface, with no change in said proportionality with perchlorate adsorption, rendering this adsorbate essentially ‘invisible’ to NIDR. This has obvious implications when using perchlorate salts as a supporting electrolyte in NIDR experiments, as perchlorate will produce no NIDR response and therefore will not convolute with the NIDR response arising from other adsorbates. To demonstrate this in practice, NIDR experiments for Se covered Au electrodes in aqueous perchloric acid electrolytes will be discussed and the clear dependence of the NIDR response on Se coverage will be demonstrated.

Kinetics of catalytic activities of micro amount of Ir(III) in oxidation of D(-) Galactose by N-bromosuccinimide in acidic homogeneous medium

It has been investigated how iridium(III) catalyses the oxidation of D(-)Galactose by N-bromosuccinimide (NBS) in an aqueous perchloric acid solution at 308 K. NBS kinetics is first-order, while galactose kinetics is zero-order. As a function of [Ir(III)], the reactions demonstrate first order at lower [Ir(III)] and zero-order behaviour at higher [Ir(III)]. On the rate of oxidation, inverse fractional-order has been reported in [H+], [Cl-] and [succinimide]. There is no difference in the rate of oxidation with changes in the ionic strength of the medium or with the addition of Hg(OAc)2 (a Br-ion scavenger). Galactonic acid has been identified as the major oxidation product of the process. It is possible to compute the activation parameters by utilizing the rate constants observed at four distinct temperature levels. For the sake of this research, it is hypothesised that HOBr and [IrCl5H2O]2-are both reactive species oxidants (i.e. NBS) as well as catalysts. It is very probable that the reaction mechanism for the oxidation of galactose by NBS is supported by current kinetic data, reaction stoichiometry, and product analysis.

Toward real applicability of electro-ozonizers: Paying attention to the gas phase using actual commercial PEM electrolyzers technology

This work focuses on increasing the TRL of electro-ozonizer technology by evaluating the effect of electrolyte composition and operation conditions on the production of ozone, using an actual commercial cell, CONDIAPURE®, in conditions similar to what could be expected in a real application. Not only is attention paid to the changes in the concentration of ozone in the liquid phase, but also to those observed in the gas phase. The electrolyte and its recirculation flowrate, as well as operation temperatures and pressures are found to have significant influence on production rates. The most efficient way to produce ozone is operating at low temperatures and high pressures. In this work, 0.25 and 0.21 mg O3/min were obtained operating at 10 A in electrolytes consisting of aqueous solutions of perchloric and sulfuric acid, respectively, in tests carried out at 13 °C and 2 bars of gauge pressure. The negative effect of scavengers that appear electrochemically along the production of ozone is very important and seems to be partially compensated when organics are present in the solution due to the competition between the reaction of these scavengers with ozone or organics.

Spectroelectrochemical and DFT approaches to the study of croconic acid adsorption at gold electrodes in acidic solutions

• Croconate anions adsorb at Au electrodes in croconic acid-containing solutions. • Croconate species bons in a bidentate configuration with O atoms on top positions. • Adsorption occurs with the molecular plane (quasi) normal to the metal surface. • Adsorption causes significant changes on the geometry and symmetry of croconate. • Collective vibrations broaden and split croconate bands at high coverage. The adsorption of species coming from croconic acid (4,5-dihydroxy-4-cyclopentene-1,2,3-trione, H 2 C 5 O 5 , CA) at gold electrodes was studied spectroelectrochemically in aqueous perchloric acid solutions. Voltammetric experiments suggest the existence of reversible adsorption processes in the potential range between 0.30 and 0.80 V vs RHE. Surface-Enhanced Infrared Reflection Absorption Spectroscopy experiments under Attenuated Total Reflection conditions (ATR-SEIRA) show potential-dependent adsorbate bands in the latter potential range that, according to Density Functional Theory calculations, can be assigned to adsorbed croconate. Calculated optimized geometry corresponds to bonding of croconate species to the gold surfaces involving two oxygen atoms in a bidentate configuration, with the molecular plane perpendicular to the metal surface for low and high crocoanate coverage. For intermediate coverage, lateral repulsions between neighbor croconate adsorbates give rise to the tilting of the molecular plane. The broadening and splitting at high electrode potentials of the C O stretching bands for adsorbed croconate can be explained by invoking the existence of collective vibrational modes appearing at high coverage. The cyclic voltammograms recorded in the CA-containing solutions also show the existence of reversible redox processes at potentials below 0.30 V involving adsorbed species, which are detected in the collected ATR-SEIRA spectra.

Experimental, Monte Carlo and Molecular Dynamic Study on Corrosion Inhibition of Mild Steel by Pyridine Derivatives in Aqueous Perchloric Acid

The corrosion of mild steel in aqueous perchloric acid solution was studied in the presence and absence of four different pyridine derivatives. Electrochemical measurements point out that these molecules inhibit the corrosion of mild steel by acting as mixed inhibitors. The adsorbed molecules act as a barrier that prevents the oxidation of the metal and the hydrogen evolution reaction at the mild steel surface. Molecular insights vis-à-vis the corrosion process were acquired by the use of Density Functional Theory (DFT), Molecular Dynamics, and Monte Carlo calculations. Monte Carlo and Molecular Dynamic simulation were used to understand at the molecular level the adsorption ability of the studied molecules onto Fe(110) surface. The experimental results and theoretical calculations provided important support for the understanding of the corrosion inhibition mechanism expressed by the pyridine molecules.

The solubility of monazite (CePO4), SmPO4, and GdPO4 in aqueous solutions from 100 to 250 °C

Monazite (CePO4) is a light rare earth element (REE) phosphate occurring as accessory mineral in metamorphic, igneous and sedimentary rocks, and is also a common mineral in REE mineral deposits. Metasomatism of monazite yields important clues about fluid-rock interaction in the crust, in particular, because its compositional variations may enable us to determine conditions of mineralization. The thermodynamic properties of monazite have been determined using several calorimetric methods, but up to the present time only a few solubility studies have been undertaken, which test the reliability of both, the thermodynamic properties of the REE phosphates and associated REE aqueous species. In this study, we have measured the solubility of the monoclinic REE phosphate end-members CePO4, SmPO4, and GdPO4 in aqueous perchloric acid solutions at temperatures from 100 to 250 °C at saturated water vapor pressure (swvp). The solubility products (Ks0) were determined according to the reaction: REEPO4 = REE3+ + PO43−.▪Combining available calorimetric data for the REE phosphates with the REE aqueous species from the Supcrt92 (slop98.dat) dataset, yields several orders of magnitude differences when compared with our solubility measurements. We have investigated ways to reconcile these discrepancies and propose a consistent set of provisional thermodynamic properties for REE aqueous species and REE phosphates that reproduce our measured solubility values. To reconcile these discrepancies, we have used the GEMS code package and GEMSFITS for parameter optimization by adjusting the standard Gibbs energy of REE3+ and REEOH2+ at 25 °C and 1 bar. An alternative optimization could involve adjustment of the standard Gibbs energy of REEPO4(s) and REEOH2+. Independently of the optimization method used, this study points to a need to revise the thermodynamic properties of REEOH2+ and possibly other REE hydroxyl species in future potentiometric studies. These revisions will have an impact on calculated solubilities of REE phosphates and our understanding of the mobility of REE in natural hydrothermal fluids.

Investigation of selective leaching and kinetics of copper from malachite ore in aqueous perchloric acid solutions

ABSTRACTIn this study, the leaching kinetics of malachite in perchloric acid solutions was investigated. The dissolution behaviors of copper, zinc, and iron in the ore matrix were determined at different acid concentrations and reaction temperatures. It was observed that the concentration of perchloric acid had a major effect on the dissolution of copper, zinc, and iron. It was determined that the effect of temperature on the dissolution of these species was not as significant as concentration impact. The results obtained shown that copper in the ore matrix was completely leached while zinc and iron were partially dissolved in perchloric acid solutions. In addition, the effects of the acid concentration, reaction temperature, stirring speed, particle size, and solid-to-liquid ratio on the leaching of malachite were researched. In these experiments, it was observed that the leaching rate of copper increased with increasing solution concentration, stirring speed, and reaction temperature, and with decreasing solid-to-liquid ratio and particle size. A kinetic analysis was performed, and it was found that the rate of leaching reaction obeyed the mixed kinetic control model in the unsteady state. The activation energy of the leaching process was calculated to be 34.69 kJ/mol.

Kinetic and Mechanistic Aspects of Oxidation of Aminotriazole Formamidine by Cerium(IV) in Aqueous Perchloric and Sulfuric Acid Solutions: A Comparative Study

The kinetics of the oxidation of an aminotriazole formamidine derivative, N,N-dimethyl-N′-(4H-1,2,4-triazol-3-yl) formamidine (ATF) by cerium(IV) has been studied spectrophotometrically in aqueous perchloric and sulfuric acid solutions at constant ionic strength of 1.0 mol·dm−3. In both acids, the reaction shows first order kinetics with respect to [Ce(IV)], whereas the orders with respect to [ATF] are less than unity. The reaction exhibits negative fractional order kinetics with respect to [H+]. The rates of reaction are not significantly affected by variations of either ionic strength or relative permittivity of the reaction’s media. Addition of cerium(III) product does not affect the rates. Plausible mechanistic schemes for the reactions have been proposed. In both cases, the final oxidation products were identified as aminotriazole, dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate in perchloric acid solution is about sixfold higher than that in sulfuric acid solution. The effect of temperature on the rates has also been studied and activation parameters have been evaluated and discussed. The rate laws associated with the reaction mechanisms are derived.

Synthesis of graphite oxide by electrochemical oxidation in aqueous perchloric acid

In this research a graphite oxide (GO) was synthesized by electrochemical oxidation of natural graphite in aqueous solution of perchloric acid. The process of anodic oxidation of graphite was performed by linear sweep voltammetry (LSV) from the rest potential of electrode to 1.4 V. In consequence of the electrochemical treatment graphite was fully transformed yielding GO. Formation of GO was proved by X-ray diffraction (XRD) and Raman spectroscopy analysis. The synthesis product was also characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).

The mediatory activity of meso-tetraphenylporphyrin iron(III) complex immobilized in Nafion film on a Pt electrode in the oxidation of 1,2- and 1,4-hydroquinones

This paper presents the results of an investigation of the properties of a modified platinum electrode with meso-tetraphenylporphyrin iron(III) complex immobilized in Nafion film and its catalytic activity in the electrochemical oxidation of selected hydroquinone and catechol derivatives. The redox activity of iron complexes of porphyrins was characterized in aqueous solutions of perchloric acid by means of cyclic voltammetry and differential pulse voltammetry. Both the increase in the anodic peak currents of the investigated compounds during oxidation on the platinum electrode modified with meso-tetraphenylporphyrin iron(III) complex immobilized in Nafion film (FeTPhP/Nafion/Pt) and the considerable decrease in the cathodic peak currents related to the porphyrine complexes reduction point to mediatory activity. The increase in the oxidation currents observed during the preparative electrolyses indicates that the modified platinum electrode, FeTPhP/Nafion/Pt, exhibits catalytic properties. The preparative electrooxidation of the investigated 1,2- and 1,4-hydroquinone derivatives showed that over 90% conversion of the substrate occurs in the shortest time on platinum modified with iron complex of porphyrin immobilized in Nafion film.

Kinetics and Mechanistic Study of Oxidation of Pyridine Derivative by Cerium(IV) in Aqueous Perchloric Acid

The kinetics of oxidation of N, N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F) by cerium(IV) was studied spectrophotometrically in aqueous perchloric acid solutions at a constant ionic strength of 1.0 mol dm-3 and at 20°C. The reaction showed first order dependence with respect to [Ce(IV)] and less than unit order with respect to [Py-F]. The reaction exhibited negative fractional-first order kinetics with respect to [H+]. The rate of reaction was not significantly affected by variation of either ionic strength or dielectric constant of the reaction medium. Addition of cerium(III) product did not affect the reaction rate. A suitable mechanistic scheme for the oxidation reaction has been proposed. The final oxidation products were identified as 2-aminopyridine, dimethylamine and carbon dioxide. The activation parameters have been evaluated and discussed. The rate law associated with the reaction mechanism was derived.

Oxidation of alginate and pectate biopolymers by cerium(IV) in perchloric and sulfuric acid solutions: A comparative kinetic and mechanistic study

The kinetics of oxidation of alginate (Alg) and pectate (Pec) carbohydrate biopolymers was studied by spectrophotometry in aqueous perchloric and sulfuric acid solutions at fixed ionic strengths and temperature. In both acids, the reactions showed a first order dependence on [Ce(IV)], whereas the orders with respect to biopolymer concentrations are less than unity. In perchloric acid, the reactions exhibited less than unit orders with respect to [H+] whereas those proceeded in sulfuric acid showed negative fractional-first order dependences on [H+]. The effect of ionic strength and dielectric constant was studied. Probable mechanistic schemes for oxidation reactions were proposed. In both acids, the final oxidation products were characterized as mono-keto derivatives of both biopolymers. The activation parameters with respect to the slow step of the mechanisms were computed and discussed. The rate laws were derived and the reaction constants involved in the different steps of the mechanisms were calculated.

Acid‐catalyzed hydrolysis of 5‐substituted‐1H,3H‐2,1,3‐benzothiadiazole 2,2‐dioxides (5‐substituted benzosulfamides): kinetic behavior and mechanistic interpretations

The acid‐catalyzed hydrolysis of a series of 5‐substituted‐1H,3H‐2,1,3‐benzothiadiazole 2,2‐dioxides has been investigated in aqueous solutions of sulfuric, perchloric, and hydrochloric acid at 85.0 ± 0.05 °C. Analysis of the kinetic data by the excess acidity method, Arrhenius parameters, the order of the catalytic effects of strong acids, the kinetic deuterium isotope effect, and the substituent effect have indicated that the hydrolysis of 5‐substituted benzosulfamides 1a, 1b, 1c, 1d occur with a mechanistic switchover from A2 to A1 in the studied range: an A2 mechanism in low acidity regions and an A1 mechanism in high acid concentrations. Copyright © 2015 John Wiley & Sons, Ltd.

Photochemical characterization of uranyl interaction with acetic acid

Aqueous perchloric acid solutions containing 1 × 10−4 M of U(VI) and acetic acid at different concentrations (from 0 up to 0.6 M) are studied by time-resolved laser-induced luminescence spectroscopy (TRLLS) at pH 1.5, 2.0 and 2.5. The quenching of uranyl luminescence is observed. The graphs giving U(VI) luminescence intensity, as a function of dissociated and non-dissociated acetic acid form concentrations are constructed at the different pH values to point out the interacting ligand species. Acetate ions are demonstrated to be responsible for the luminescence quenching. Stern–Volmer analysis gives the dynamic quenching rate constant value (kq) (1.0 ± 0.2) × 109 L M−1 s−1 at ionic strength (μ) 0.05 M (pH 2.0). The bimolecular excited-state process is shown to be diffusion-controlled as kq is practically identical to the diffusion rate constant as calculated for uranyl and acetate species. With an increase of acetate concentration (from 1 × 10−4 M), static quenching occurs in addition to the dynamic quenching. The formation of a non-luminescent complex between uranyl and acetate is supported (with 1:1 stochiometry). The stability constant values for the first complex species (UO2CH3COO+) are obtained at different ionic strengths. Extrapolation to μ = 0 by the specific ion interaction theory (SIT) gives log β1° = 2.95 ± 0.08 at 293 K. From 1.5 × 10−3 M of acetate concentration, the decay curves became biexponential and shorter lifetime appears. The U(VI) luminescence intensity is not decreased anymore and the bathochromic shift of peak maxima is observed. Most probably, this indicates the formation of the second complex species of U(VI) with two acetate ligands. These species give luminescence emission.

Experimental study of ZrO2(c) solubility in water and aqueous perchloric acid solutions at 150 and 250°C

Experimental study of ZrO2(c) solubility in water and aqueous perchloric acid solutions at 150 and 250°C

A spectroscopic and ab initio study on Bi(III) complex formation with 3-mercaptopropanesulfonic acid

This article deals with complex formation of Bi(III) with 3-mercaptopropanesulfonic acid (H2MPS) in aqueous perchloric acid solutions, with synthesis and characterization of a solid 3-mercaptopropanesulfonate complex of bismuth(III). The stoichiometry and structures of Bi-MPS species in aqueous solution and of a solid complex have been studied by UV–Vis, 1H-NMR, ICP-AES, Raman, and EXAFS spectroscopic methods; the structures have also been simulated with DFT/PBE0 calculations. The Bi(III) LIII-edge EXAFS oscillation for a solid compound with the empirical formula [Bi(HMPS)2(ClO4)]0 was simulated with two Bi–S interatomic distances at 2.50 ± 0.01 Å, two Bi–O distances at 2.56 ± 0.02 Å and two Bi–O distances at 2.75 ± 0.02 Å. Implementation of the same approach for aqueous solutions on the assumption of S3BiO3 coordination at the H2MPS : Bi(III) mole ratio ≥ 3.0 revealed three Bi–S bonds at 2.53 ± 0.02 Å and three Bi–O bonds at 2.68 ± 0.02 Å, respectively. Optimized geometries, electronic structures of Bi(HMPS)3 and [Bi(HMPS)2ClO4]0, vibrational properties of [Bi(HMPS)2ClO4]0, and electronic absorption spectrum of Bi(HMPS)3 species obtained by DFT and TD–DFT modeling are consistent with empirical parameters. In the UV–Vis spectrum of Bi(HMPS)3 the LMCT and MLCT S2− ↔ Bi3+ band appears at 268 nm.

Synthesis, transport, and ionophore properties of α,ω-biphosphorylated azapodands: VIII. Solvent extraction of the metal ions with N,N′-bis(dioctylphosphorylmethyl)-1,8-diamino-3,6-dioxaoctane

Liquid extraction from the aqueous solutions of perchloric acid with neutral azapodand extractant N,N′-bis(dioctylphosphorylmethyl)-1,8-diamino-3,6-dioxaoctane has been highly efficient in the cases of uranyl ions and some metals of groups II and III. To estimate the synergic effect of organophosphorus extractants, the neutral extractant was applied in the mixture with an acidic component, bis(pentadecyl)phosphoric acid. The synergic effect has exclusively been observed in the extraction of zinc and cadmium ions.

Involvement of ·OH radicals in the mechanism of excitation of the uranyl ion in the chemiluminescent oxidation of U(IV) by atmospheric oxygen in aqueous solutions of perchloric acid

The chemiluminescence (CL) kinetics in U(IV) oxidation by atmospheric oxygen in aqueous HClO4 has been investigated. The CL quantum yield (ηCL, E/(mol U(IV))) in this reaction is 1.4 × 10−8. The elementary event generating the CL emitter, which is the electronically excited uranyl ion *(UO22+), is electron transfer from the uranyl ion UO2+ to the oxidizer (·OH radical). The Ag+ ion quenches CL, and the Cu2+ ion enhances CL.

Direct STM Elucidation of the Effects of Atomic-Level Structure on Pt(111) Electrodes for Dissolved CO Oxidation

We sought to establish a new standard for direct comparison of electrocatalytic activity with surface structure using in situ scanning tunneling microscopy (STM) by examining the electrooxidation of CO in a CO-saturated solution on Pt(111) electrodes with steps, with combined electrochemical measurements, in situ STM, and density functional theory (DFT). On pristine Pt(111) surfaces with initially disordered (111) steps, CO oxidation commences at least 0.5 V lower than that for the main oxidation peak at ca. 0.8-1.0 V vs the reversible hydrogen electrode in aqueous perchloric acid solution. As the potential was cycled between 0.07 and 0.95 V, the CO oxidation activity gradually decreased until only the main oxidation peak remained. In situ STM showed that the steps became perfectly straight. A plausible reason for the preference for (111) steps in the presence of CO is suggested by DFT calculations. In contrast, on a pristine Pt(111) surface with rather straight (100) steps, the low-potential CO oxidation activity was less than that for the pristine, uncycled (111) steps. As the potential was cycled, the activity also decreased greatly. Interestingly, after cycling, in situ STM showed that (111) microsteps were introduced at the (100) steps. Thus, potential cycling in the presence of dissolved CO highly favors formation of (111) steps. The CO oxidation activity in the low-potential region decreased in the following order: disordered (111) steps > straight (100) steps > (100) steps with local (111) microsteps ≈ straight (111) steps.