Indirect electrosynthesis of peracetic acid using hydrogen peroxide generated in situ in a gas diffusion electrode

Indirect electrochemical oxidation of acetic to peracetic acid in aqueous solutions using hydrogen peroxide generated in situ from O₂ in a gas diffusion electrode was studied. The use of sulfuric acid and ammonium molybdate as catalysts accelerated the formation of peracetic acid during the electrolysis, and the use of both catalysts allowed us to prepare 0.02 M solutions. The limiting stage of the electrosynthesis of peracetic acid was the chemical interaction of the substrate with the generated H₂O₂. The desired product mainly formed during the storage of the reaction mixture after the electrosynthesis. In electrolytes with more than 3.5 M acetic acid, the electrochemical activity of the gas-diffusion cathode decreased.     

Electrosynthesis of Н<Subscript>2</Subscript>О<Subscript>2</Subscript> from О<Subscript>2</Subscript> in a Gas-Diffusion Electrode Based on Mesostructured Carbon CMK-3

Mesostructured carbon CMK-3 (Carbon Mesostructured by KAIST) synthesized by the template method is studied as the electrocatalyst for electrosynthesis of Н₂О₂ from О₂ in a gas-diffusion electrode (GDE) in alkaline and acidic solutions. The texture characteristics of the original material and its mixture with hydrophobizer (polytetrafluoroethylene) are studied by the method of low-temperature nitrogen adsorption. The rate constants for hydrogen peroxide decomposition on these materials in alkaline and acidic solutions are calculated. Kinetic parameters of oxygen reduction in alkaline and acidic solutions are determined as well as the capacitance of gas-diffusion electrodes based on mesocarbon. The selectivity of the electrocatalyst is estimated by finding the current fracture γ consumed in oxygen reduction to hydrogen peroxide. Data on the kinetics of hydrogen peroxide accumulation during electrosynthesis of Н₂О₂ from О₂ are obtained. The acidic solution of hydrogen peroxide with the concentration more than 3 M is obtained with the current efficiency higher than 80%.     

Peroxide Coordination of Tellurium in Aqueous Solutions

Tellurium–peroxo complexes in aqueous solutions have never been reported. In this work, ammonium peroxotellurates (NH₄)₄Te₂(μ‐OO)₂(μ‐O)O₄(OH)₂ ( 1 ) and (NH₄)₅Te₂(μ‐OO)₂(μ‐O)O₅(OH)?1.28 H₂O?0.72 H₂O₂ ( 2 ) were isolated from 5 % hydrogen peroxide aqueous solutions of ammonium tellurate and characterized by single‐crystal and powder X‐ray diffraction analysis, by Raman spectroscopy and thermal analysis. The crystal structure of 1 comprises ammonium cations and a symmetric binuclear peroxotellurate anion [Te₂(μ‐OO)₂(μ‐O)O₄(OH)₂]^4?. The structure of 2 consists of an unsymmetrical [Te₂(μ‐OO)₂(μ‐O)O₅(OH)]^5? anion, ammonium cations, hydrogen peroxide, and water. Peroxotellurate anions in both 1 and 2 contain a binuclear Te₂(μ‐OO)₂(μ‐O) fragment with one μ‐oxo‐ and two μ‐peroxo bridging groups. ¹²⁵Te NMR spectroscopic analysis shows that the peroxo bridged bitellurate anions are the dominant species in solution, with 3–40 %wt H₂O₂ and for pH values above 9. DFT calculations of the peroxotellurate anion confirm its higher thermodynamic stability compared with those of the oxotellurate analogues. This is the first direct evidence for tellurium–peroxide coordination in any aqueous system and the first report of inorganic tellurium–peroxo complexes. General features common to all reported p‐block element peroxides could be discerned by the characterization of aqueous and crystalline peroxotellurates.     

Boosting Hydrogen Peroxide Electrosynthesis via Modulating the Interfacial Hydrogen-Bond Environment

Designing highly efficient and stable electrode-electrolyte interface for hydrogen peroxide (H₂O₂) electrosynthesis remains challenging. Inhibiting the competitive side reaction, 4 e⁻ oxygen reduction to H₂O, is essential for highly selective H₂O₂ electrosynthesis. Instead of hindering excessive hydrogenation of H₂O₂ via catalyst modification, we discover that adding a hydrogen-bond acceptor, dimethyl sulfoxide (DMSO), to the KOH electrolyte enables simultaneous improvement of the selectivity and activity of H₂O₂ electrosynthesis. Spectral characterization and molecular simulation confirm that the formation of hydrogen bonds between DMSO and water molecules at the electrode-electrolyte interface can reduce the activity of water dissociation into active H* species. The suitable H* supply environment hinders excessive hydrogenation of the oxygen reduction reaction (ORR), thus improving the selectivity of 2 e⁻ ORR and achieving over 90 % selectivity of H₂O₂. This work highlights the importance of regulating the interfacial hydrogen-bond environment by organic molecules as a means of boosting electrochemical performance in aqueous electrosynthesis and beyond.     

Peroxo derivatives of hydroxyapatite and calcium hydrophosphate

Hydroxyapatite and calcium hydrophosphate peroxo solvates were synthesized and characterized by IR spectroscopy, powder X-ray diffraction, and TGA to be used as biocompatible and antibacterial medicaments in manufacturing calcium phosphate bioceramics for implantations in orthopedics and dentistry. A wide range of hydrogen peroxide percentages in stable mixtures of mCa₅(PO₄)₃(OH) + nCaHPO₄ · H₂O₂ · H₂O (ranging from 0.5 to 18%) allows composites to be prepared with a tailored active oxygen content.     

Electrosynthesis of hydrogen peroxide from oxygen in a gas-diffusion electrode in solutions of mineralized exometabolites

The electrosynthesis of H₂O₂ in aqueous solutions (pH 1–9) of mineralized liquid and solid bio-wastes (exometabolites) for their processing in closed life-support systems was studied. It was shown that H₂O₂ can be obtained in these solutions by electrochemical reduction of oxygen in carbon black gas diffuse electrodes to concentrations of over 2 M with current efficiency 80%. The composition of the solution was found to affect the accumulation of H₂O₂ during the synthesis. The solutions can be concentrated further to 19 M H₂O₂. The results showed that the electrolytic method is promising for preparing H₂O₂ for closed life-support systems.     

High‐Yield Electrosynthesis of Hydrogen Peroxide from Oxygen Reduction by Hierarchically Porous Carbon

H₂O₂ production by electroreduction of O₂ is an attractive alternative to the current anthraquinone process, which is highly desirable for chemical industries and environmental remediation. However, it remains a great challenge to develop cost‐effective electrocatalysts for H₂O₂ synthesis. Here, hierarchically porous carbon (HPC) was proposed for the electrosynthesis of H₂O₂ from O₂ reduction. It exhibited high activity for O₂ reduction and good H₂O₂ selectivity (95.0–70.2 %, most of them >90.0 % at pH 1–4 and >80.0 % at pH 7). High‐yield H₂O₂ generation has been achieved on HPC with H₂O₂ concentrations of 222.6–62.0 mmol L^?1 (2.5 h) and corresponding H₂O₂ production rates of 395.7–110.2 mmol h^?1 g^?1 at pH 1–7 and ?0.5 V. Moreover, HPC was energy‐efficient for H₂O₂ production with current efficiency of 81.8–70.8 %. The exceptional performance of HPC for electrosynthesis of H₂O₂ could be attributed to its high content of sp³‐C and defects, large surface area and fast mass transfer.     

On the stability of Al<Subscript>13</Subscript> Keggin cation in aqueous hydrogen peroxide solutions

We report the first attempt to study the behavior of the [AlO₄Al1₂(OH)₂₅(H₂O)₁₁]⁶⁺ (Al₁₃) Keggin cation (KC) in water–peroxide solutions. Addition of hydrogen peroxide into an aqueous solution containing the Al₁₃ KC reduces pH due to the acidity of hydrogen peroxide. According to the ²⁷Al NMR studies of water–peroxide solutions prepared just before the NMR experiment, with their pH adjusted to the initial value of 5.5 with aqueous NaOH, the Al₁₃ KC concentration decreases immediately once hydrogen peroxide is added to the initial system. Addition of 18.2 wt % hydrogen peroxide to the initial 0.88 mM Al₁₃ solution gives rise to a fourfold decline in Al₁₃ polyoxo cation concentration to 0.22 mM. Then, the KC concentration in the test system remains unchanged for 1 week. Large hydrogen peroxide amounts (27.9 wt % or higher) added to the initial system almost completely degrade the KC. Sodium sulfate added to the initial water–peroxide solution of Al₁₃ chloride where the hydrogen peroxide concentration is 5.5 wt % precipitates the earlier described Al₁₃ sulfate [AlO₄Al₁₂(OH)₂₅(H₂O)₁₁](SO₄)₃ · 16H₂O, where the aluminum polyoxo cation does not contain coordinated hydrogen peroxide molecules, peroxo or hydroperoxo groups as shown by X-ray diffraction.     

Hydrogen Peroxide Solvates of 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane

Two polymorphic hydrogen peroxide solvates of 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20; wurtzitane is an alternative name to iceane) were obtained using hydrated α‐CL‐20 as a guide. These novel H₂O₂ solvates have high crystallographic densities (1.96 and 2.03 g cm^?3, respectively), high predicted detonation velocities/pressures (with one solvate performing better than ?‐CL‐20), and a sensitivity similar to that of ?‐CL‐20. The use of hydrated materials as a guide will be important in the development of other energetic materials with hydrogen peroxide. These solvates represent an area of energetic materials that has yet to be explored.     

Formation of peracids from corresponding organic acids under oxygen electroreduction in gas-diffusion electrode

The effect of conditions of electrolysis in aqueous solutions of (K₂SO₄ + H₂SO₄) electrolytes was studied in the presence of formic, acetic, and butyric acids on the formation of the corresponding peracids under oxygen electroreduction in carbon black gas-diffusion electrodes. In the presence of organic acids with the concentration of 1.5–4.7 M, as dependent in the electrolysis conditions, the current efficiency of H₂O₂ formation decreases from 70 to 13 % and its concentration drops from 2.3 to 0.4 M. Electrolysis under constant current (50–100 mA/cm²) results in formation of peracids with the concentration of up to 7.5 mM. No direct dependence of the concentration of peracids on the concentration of the obtained H₂O₂ is observed. The presence of tetrabutylammonium bromide in the solution inhibits significantly peracid formation. It is assumed that synthesis of peracids occurs partly on the surface of carbon black through activation of the adsorbed acid by a hydrogen cation and further interaction with the active form of oxygen obtained under oxygen reduction or decomposition of H₂O₂.     

New peroxo derivatives of synthetic montmorillonite structures

New peroxo derivatives of montmorillonite (MT) minerals (cationic clay structures) were prepared. Conditions were found for the synthesis of stable (for 2 years) peroxide varieties of such structures containing high active oxygen percentages (15 wt % O_act or 32 wt % H₂O₂). A scenario for hydrogen peroxide sorption by cationic clays was proposed.     

Electrochemical Peroxidase‐Catalase Clark‐Type Biosensor: Computed and Experimental Response

A bioelectrode containing immobilized catalase and peroxidase was built using a Clark‐type oxygen electrode. The bioelectrode responded to hydrogen peroxide (H₂O₂) as well as to acetaminophen (Ac). The sensitivity of the bioelectrode for H₂O₂ was 0.35 mM O₂/mM H₂O₂ and for Ac it was 0.23–1.05 µM O₂/µM Ac at pH 6.6 and 25 °C. The limit of detection of Ac varied from 12 to 44 µM. The half‐time of the bioelectrode response to hydrogen peroxide was 36 s. The modeling of the bioelectrode action was performed digitally at transition and steady‐state conditions using finite difference technique. The calculated half‐time of the bioelectrode response to hydrogen peroxide was 53 % larger and the steady‐state response 11 % less than experimentally determined. The response to Ac was 2–3 times smaller in comparison to the experimental values. The calculated response change correlated with the experimentally determined when the catalase and peroxidase concentrations in the biocatalytical membrane changed 3–4 orders of magnitude. The simulations of the bioelectrode response revealed that the bioelectrode acts in diffusion limiting conditions at almost all enzymes concentrations. The model appears to be promising for optimization of the bioelectrode response.     

Effect of trialkylammonium salts and current density on the electrosynthesis of hydrogen peroxide from oxygen in a gas-diffusion electrode in acid solutions

The influence exerted by the nature of cation of a supporting electrolyte and by the current density on the electroreduction of oxygen to hydrogen peroxide in acid K₂SO₄ solutions (pH 0.9–1.4) in gas-diffusion hydrophobized carbon black electrodes with varied electrolyte porosity was studied.     

A new process for preparing dialdehyde by catalytic oxidation of cyclic olefins with aqueous hydrogen peroxide

A. novel peroxo-niobophosphate was synthesized for the first time and used as a catalyst in the oxidation reaction of cyclic olefins with aqueous hydrogen peroxide to prepare dialdehy-des. The catalyst was characterized by elemental analysis, thermographic analyses, IR, UV/vis, 31P NMR and XPS spectra as [ π-C5H5N(CH2 )13 CH3 ]2 [ Nb4O6 (O2 )2 (PO4 )2 ] ·6H2O (PTNP). It showed high selectivity to glutaraldehyde in the catalytic oxidation of cyclopentene with aqueous hydrogen peroxide in ethanol.     

Effect of the hydrogen peroxide concentration in stereospecific oxidation of alkanes by models of non-heme oxygenases

The biomimetic oxidation of alkanes (cyclohexane, adamantane, cis-1,2-dimethylcyclohexane) with hydrogen peroxide catalyzed by Fe(II) complexes containing tetradentate nitrogen ligands (M = [Fe(bpmen)(MeCN)₂](ClO₄)₂ (bispicolyl-1,2-dimethylethylenediamine), [Fe(bpen)(MeCN)₂](ClO₄)₂ (bispicolylethylenediamine), and [Fe(tpcaH)(MeCN)₂]₂(ClO₄)₄ (tripyridylcarboxamide) is studied. The effects of the hydrogen peroxide concentration on the alcohol/ketone (A/K) ratio and on the regioselectivity of oxidation (3/2) are discovered. Rather high stereospecificity (RC = 96–99%) persisting at high hydrogen peroxide concentrations is hardly consistent with the participation of the HO^. radical, inferred from the rather low regioselectivity and low A/K ratio observed under these conditions. The molecular mechanism of oxygen transfer from hydrogen peroxide, which was earlier proved reliably for low concentrations of hydrogen peroxide ([H₂O₂]/[M] ? 10), can be applied to high peroxide concentrations ([H₂O₂]/[M] > 10) if a new ferryl species containing two equivalents of the oxidant is assumed to be involved in the process. This assumption is confirmed by the direct stereospecific formation of alkyl hydroperoxide from alkane at a high concentration of hydrogen peroxide.     

Catalytic cross-coupling of aniline by pyrite and dissolved oxygen under alkaline conditions

Pyrite catalyzes oxidation of various organic contaminants by dissolved oxygen (DO) under acidic conditions; however, the catalytic mechanism under alkaline conditions is still not clear. In this study, we observe increased oxidation rates of aniline with increasing pHs (7.0–11.0). Electron paramagnetic resonance (EPR) analysis and quenching experiments rule out contributions of •OH, O₂^•−, ¹O₂ and Fe (IV) to aniline oxidation and suggest that the Fe (III)–OOH peroxo and/or H₂O₂ are the primary oxidative species in the oxidation of aniline at pH 11.0. In addition, 200 mg L⁻¹ H₂O₂ does not apparently increase the oxidation rate of aniline, which also rules out the predominant contribution of the produced H₂O₂ to aniline oxidation. We therefore suggest that the Fe (III)–OOH peroxo is indeed the primary oxidative species in the pyrite–DO system under alkaline conditions. Analyses of solid total organic carbon (TOC), gas chromatography–mass spectrometry and Fourier-transform infrared spectroscopy further reveal that more than 83.3% aniline has been polymerized to polyaniline, instead of being mineralized into CO₂ and H₂O, indicating that H-abstraction from aniline by the Fe (III)–OOH peroxo is an important step in the oxidation of aniline under alkaline conditions. This study provides new insight into the oxidative species in the pyrite–DO system, and opens a new door for organic degradations under alkaline conditions.     

Amperometric determination of hydrogen peroxide in pickling baths for copper and copper alloys by flow injection analysis

The hydrogen peroxide is oxidized at + 1.5 V vs. SCE at a glassy carbon electrode of the wall-jet type. The samples are diluted about 100 times in a dispersion coil before entering the amperometric detector. The calibration curve is linear from 10^?4 to 1 M H₂O₂, when 5-μl samples are used. With 50-μl samples the detection limit decreases to 10^?6 M H₂O₂. Neither metal ions (Cu²⁺, Zn²⁺, Ni²⁺, Al³⁺) up to 0.5 M nor changes in the sulfuric acid concentration of the samples between 0.1 and 1 M interfere with the hydrogen peroxide determination. About 75 samples can be analyzed per hour.     

The role of peroxo complexes in the catalytic decomposition of H2O2 in the presence of Cu(II) hydroxides

The catalytic decomposition of hydrogen peroxide is studied in the presence of colloidal and silicagel-supported Cu(OH)₂. Copper peroxo complexes with different activities were identified. The reaction is molecular without radical formation. The mechanisms of H₂O₂ decomposition are discussed.     

Synergetic effect of Prussian blue film with gold nanoparticle graphite–wax composite electrode for the enzyme-free ultrasensitive hydrogen peroxide sensor

Enzyme-free amperometric ultrasensitive determination of hydrogen peroxide (H₂O₂) was investigated using a Prussian blue (PB) film-modified gold nanoparticles (AuNPs) graphite–wax composite electrode. A stable PB film was obtained on graphite surface through 2-aminoethanethiol (AET)-capped AuNPs by a simple approach. Field emission scanning electron microscope studies results in formation of PB nanoparticle in the size range of 60–80 nm. Surface modification of PB film on AET–AuNPs–GW composite electrode was confirmed by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy studies. Highly sensitive determination of H₂O₂ at a peak potential of ?0.10 V (vs. SCE) in 0.1 M KCl PBS, pH?=?7.0) at a scan rate of 20 mVs^?1 with a sensitivity of 23.58 μA/mM was observed with the modified electrode using cyclic voltammetry. The synergetic effect of PB film with AuNPs has resulted in a linear range of 0.05 to 7,800 μM with a detection limit of 0.015 μM for H₂O₂ detection with the present electrode. Chronoamperometric studies recorded for the successive additions of H₂O₂ with the modified electrode showed an excellent linearity (R ²?=?0.9932) in the range of 4.8?×?10^?8 to 7.4?×?10^?8 M with a limit of detection of 1.4?×?10^?8 M. Selective determination of H₂O₂ in presence of various interferents was successfully demonstrated. Human urine samples and stain remover solutions were also investigated for H₂O₂ content.     

Electrochemical characteristics of a platinum electrode modified with a matrix of polyvinyl butyral and colloidal Ag containing immobilized horseradish peroxidase

A new hydrogen peroxide biosensor was constructed, which consisted of a platinum electrode modified by a matrix of polyvinyl butyral (PVB) and nanometer-sized Ag colloid containing immobilized horseradish peroxidase (HRP), and using Co(bpy)₃³⁺ as mediator in the hydrogen peroxide solution. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The modified process was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The HRP immobilized on colloidal Ag was stable and retained its biological activity. The sensor displays excellent electrocatalytic response to the reduction of H₂O₂. Analytical parameters such as pH and temperature were also studied. Linear calibration for H₂O₂ was obtained in the range of 1×10^–5 to 1×10^–2 M under optimized conditions. The sensor was highly sensitive to H₂O₂, with a detection limit of 2×10^–6 M, and the sensor achieved 95% of steady-state current within 10 s. The sensor exhibited high sensitivity, selectivity and stability.