Final Oxidation Products Research Articles

Mesoporous nanoplate multi-directional assembled Bi2WO6 for high efficient photocatalytic oxidation of NO

Herein, a mesoporous nanoplate multi-directional assembled Bi2WO6 architecture was successfully prepared and applied for the photocatalytic removal of NOx pollutants at low concentrations under visible light and simulated solar light irradiation. Bi2WO6-180-C synthesized at a hydrothermal temperature of 180 °C with calcination exhibited an excellent conversion efficiency in the photocatalytic oxidation of gaseous NO. The crystallinity, morphology, specific surface area, pore environment, light absorption, and separation of photogenerated electrons and holes were investigated by various techniques; the excellent photocatalytic performance of Bi2WO6-180-C was attributed to its special hierarchical mesoporous structure with an appropriate pore size and interconnected porous network, which imparted good gas permeability and fast mass transfer of reaction intermediates and final products of NO oxidation. Furthermore, hierarchical mesoporous Bi2WO6 showed excellent photocatalytic durability and reusability.

Investigation of 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone-based catalyst in the reaction of liquid-phase oxidation of inorganic sulfides

ABSTRACTIn this paper, the intermediate and final reaction products of catalytic oxidation of inorganic sulfides in the presence of oxygen dissolved in the kerosene fraction and 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone were investigated. The thiosulfate and sulfate are major products of the oxidation of sodium sulfide under these conditions. The intermediate and final products in the catalytic oxidation of sulfide sulfur do not affect the rate of its oxidation. The yield of catalytic oxidation products depends on the nature of the sulfide and on the pH of the solution. The catalytic cycle for sulfide oxidation in the presence of 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone is shown. The role of 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone is to create a new and a more effective way of electron transfer from the reducing agent (sulfide) to the oxidant (oxygen).

Antibiotics abatement in synthetic and real aqueous matrices by H2O2/natural magnetite

The removal of micropollutants in wastewater treatment plants (WTTPs) is a challenging issue which requires the development of effective but also green and low-cost strategies. In this work, we explore the capability of naturally-occurring magnetite combined with H2O2 for the degradation of the highly persistent antibiotic sulfamethoxazole (SMX). A complete operating condition study has been performed to evaluate the effect of initial pH (3–7), temperature (15–50°C), magnetite concentration (0.5–2gL−1) and H2O2 dose (12.5–100mgL−1), using an initial SMX amount of 5mgL−1. Remarkably, complete removal of the target pollutant and the aromatic intermediates was achieved operating under ambient-like conditions (25°C) and circumneutral pH (pH0=5) using the stoichiometric dose of H2O2 (25mgL−1) and a catalyst load of 1gL−1. The mineralization yield was above 50%, being the final oxidation products short-chain organic acids. The oxidation pathway of SMX was accordingly proposed. The stability of magnetite was confirmed upon three sequential runs, where a similar catalytic activity and negligible iron leaching (<0.15%wt) were observed. As a proof of concept, the performance of the catalytic system was also evaluated in different real aqueous matrices, such as WWTP effluent, surface water and hospital wastewater. Although the catalyst did not show any sign of deactivation, partial inhibition of the oxidation reaction was observed due to scavenging effects.

Preparation of magnesium aluminate spinel by self-propagating high-temperature synthesis metallurgy methods

Experimental data are presented on the high-temperature synthesis of cast inorganic materials in the MgO–Al2O3 system. Experiments were carried out in multipurpose self-propagating high-temperature synthesis (SHS) reactors at an argon pressure p = 5 MPa. The starting mixtures used in the experiments consisted of molybdenum(VI) and magnesium(II) oxides and aluminum. It has been shown that, varying synthesis parameters, one can control the phase composition and microstructure of the final oxide products. We have optimized synthesis conditions for the preparation of single-phase magnesium aluminate spinel, MgAl2O4. The SHS products have been characterized by X-ray diffraction and local microstructural analysis.

Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation of 1,3-Dimethylthiourea by Acidic Bromate.

The mechanism of oxidation of the well-known radical scavenger dimethylthiourea, DMTU, by acidic bromate was studied. The stoichiometry of the reaction is 4:3: 4BrO3- + 3CS(NHMe)2 + 3H2O → 3SO42- + 3CO(NHMe)2 + 6H+ + 4Br-. In excess acidic bromate, the reaction stoichiometry is 8:5: 8BrO3- + 5CS(NHMe)2 + H2O → 5SO42- + 5CO(NHMe)2 + 4Br2 + 2H+. In excess bromate, the reaction displays well-defined clock reaction characteristics in which initially there is a quiescent period before formation of bromine. The direct reaction of aqueous bromine with DMTU, with a bimolecular rate constant of k = (1.95 ± 0.15) × 105 M-1 s-1, is much faster than reactions that form bromine such that formation of bromine indicates complete consumption of DMTU. ESI spectrometry showed evidence for an oxidation pathway that passes through the sulfenic, sulfinic, and sulfonic acids before formation of sulfate. In contrast to the oxidation of tetramethylthiourea, these oxoacid intermediates are not as abundant or as stable. The final product of oxidation was dimethylurea, the desulfurized DMTU. EPR spectroscopy implicates more than one set of radical species. The absence of the dimeric DMTU species, even in excess reductant indicates negligible formation of thiyl radicals. This also precludes substantial formation of the sulfenic acid intermediate which would form the dimer from a condensation-type reaction with unreacted DMTU. A 20-step reaction mechanism network was modeled which gave a reasonable fit with experimental data.

Hyperuricemia, Type 2 Diabetes Mellitus, and Hypertension: an Emerging Association.

Uric acid is the final oxidation product of purine metabolism in circulation and has been associated with the occurrence of gout and kidney stones. Type 2 diabetes mellitus and hypertension are two important public health challenges, and both are linked to increased risk of cardiovascular events. Hyperuricemia has recently emerged as an independent risk factor in the development of type 2 diabetes mellitus and hypertension through several proposed mechanisms. Few clinical trials investigated the use of uric acid lowering agents in the management of these two disease entities; however, their results provided encouraging evidence to a potential role for these agents in fighting disease burden. Larger randomized controlled trials are therefore warranted to establish the role of uric acid as a promising target for novel therapeutic interventions in the management of type 2 diabetes mellitus and hypertension.

Effects of a NiFe co-deposited layer on α-Al2O3 formation by oxidation of a β-NiAl alloy

Effects of Ni metal, Fe metal or NiFe alloy deposits on the oxidation behavior and oxidation products of a β-NiAl alloy at 1000°C in air were studied. The surface morphologies of the deposited layers and oxide scales were examined by using field emission scanning electron microscope (FE-SEM) and transmission electron microscopy (TEM). The chemical compositions of the deposited layers were determined before and after oxidation by using energy dispersive X-ray (EDX). The deposited layer and the resultant oxidation products were identified by using X-ray diffractometer (XRD). The chemical composition of the deposited layers was found to affect the morphology of the deposits and the final oxidation products. By oxidation at 1000°C in air, θ-Al2O3 was detected for bare, Ni-coated and Ni-rich coated (Ni17.7at.%Fe) samples, but was not detected for Fe-coated and Fe-rich coated (Ni72 at.%Fe) samples at all oxidation times. The oxidation mass gain after 100h on Fe-coated sample was the highest among the coated samples. TEM Cross-sectional images revealed that the grain size of α-Al2O3 on both Fe coated and Fe-rich NiFe coated samples were the smallest among the coated samples. XRD and EDX point analysis confirmed the formation of different multilayered oxide scales on oxidized samples, NiO/NiAl2O4/Al2O3 on Ni coated, complex spinel Ni(Fe)Al2O4/Al2O3 on Ni-rich NiFe coated, Fe2O3/(Fe, Ni, Al)2O3/α-Al2O3 on Fe-rich NiFe coated and Fe2O3/α-Al2O3 on Fe-coated samples, respectively. Introducing Fe or Fe-rich NiFe coating layer prior to the oxidation of a NiAl alloy resulted in suppression of θ-Al2O3 formation and finer grains of α-Al2O3, which accelerated the growth rate of α-Al2O3 scale. Up to 72at.% of Fe in NiFe coating was found to be beneficial as an oxidation pretreatment for NiAl alloys to obtain a better high temperature oxidation resistance.

Ni-Co oxide formation with Cu assisted method on Ni foam: Unexpected higher areal capacitance of inner layer with naturally formed nanotubes

Ni Foam substrate directly serves as the Ni source for the final Ni-Co oxide product with a Cu assisted chemical method. Especially, after shaking off top layer of Ni-Co oxide grown on Ni Foam, the sample unexpectedly exhibits a greatly enhanced areal capacitance from 4.17 to 11.44 F cm−2 (1 mA cm−2). Finer structures including oxide nanotubes are interestingly found underneath the top layer, which may account for this extraordinary phenomenon.

Non‐enzymatic Electrochemical Sensor for the Simultaneous Determination of Xanthine, its Methyl Derivatives Theophylline and Caffeine as well as its Metabolite Uric Acid

AbstractXanthine and its methyl derivatives, theophylline and caffeine are purines which find important roles in biological systems. The simultaneous voltammetric behaviour of these purines has been studied on a glassy carbon electrode modified with an electropolymerised film of para amino benzene sulfonic acid. Well defined and well separated peaks were obtained for the oxidation of xanthine, theophylline and caffeine on the polymer modified electrode in the square wave mode. The experimental requirements to obtain the best results for individual as well as simultaneous determination were optimised. The signal for the electro‐oxidation was found to be free of interferences from each other in the range 0.9 – 100 μM in the case of xanthine and from 10–100 μM in the case of theophylline and caffeine with detection limits 0.35 μM, 7.02 μM and 11.95 μM respectively. The simultaneous determination of uric acid, the final metabolic product of xanthine oxidation in biological systems could also be accomplished along with xanthine, theophylline and caffeine atphysiological pH. The mechanistic aspects of the electro‐oxidation on the polymer modified electrode was also studied using linear sweep voltammetry. Chronoamperometry was employed to determine the diffusion coefficient of these xanthines. The developed sensor has been successfully demonstrated to be suitable for the determination of these compounds in real samples without much pre‐treatment.

Effect of antigen stimulation on the oxidative stress parameters in sperm of outbred and inbred rabbits

ABSTRACTThe presence of an increased oxidative stress during antigen stimulation was established in the sperm of inbred rabbits by evaluation of the level of real-time free radical formation (ROS and Asc•), final products of oxidation of lipids (MDA) and the activities of antioxidant defence enzymes superoxide dismutase (SOD) and catalase (CAT). There was not a significant difference between levels of ROS, Asc• and MDA in inbred and outbred rabbits before immunization. The immune response, represented by levels of ROS and Asc• of inbread and outbread rabbits were statistically significantly higher compared to those before immunization (p = 0.0001 and p = 0.00001) Moreover, the levels of ROS in the sperm of inbread rabbits were statistically significantly higher compared to outbread rabbits (p < 0.05). Oxidative stress was accompanied by an adaptive increase of SOD and CAT activities during the immune response, compared to those before immunization. Furthermore, the increased SOD and CAT activities appeared to be sufficient to inactivate the oxidative stress. We measured reduced levels of ROS, Asc• and MDA 30 days after immunization. When immune response reduced, the observed SOD and CAT activities tended to return to the values before immunization. That might have been connected with the decreased oxidative burden. However, CAT activities remained about 1.5 times higher than that before immunization. In conclusion, our results indicate that the administered antigen stimulation induces oxidative stress in both groups inbred and outbred rabbits.

OXIDATIVE EPOXIDATION OF OLEOX AND VEGETABLE OILS

We have studied the oxidative epoxidation product of ethoxylated oleic acid (oleox) and tonnage vegetable oils: sunflower, corn, rapeseed and flax. The oxidation was carried out using hydrogen peroxide, peracetic acid and performic, which were obtained in situ using the appropriate acids and concentrated aqueous solution of hydrogen peroxide. The kinetics of oxidation was evaluated on the accumulation of the peroxide compounds, the iodine value and the number of refractive index. The final oxidation products were examined for the content of epoxy and aldehyde groups. It was shown that at the epoxidation of oleox with superoxide acids the intermediates of formic acid formed and loss faster than similar products of acetic acid. It is reflected on the character of changes in the values of iodine and peroxide value at the initial step of the process. As a result of the decomposition of the hydroperoxide derivatives the oleox aldehydes and epoxides are formed. The total content of oxidation products is changed from 3.71 to 3.84 %. It was experimentally shown that the oleox oxidation at temperatures of 55 and 65 °C did not substantially affect the dynamics of change in the number of iodine. The content of aldehyde groups in the oxidation products obtained at these temperatures is reduced. It was concluded that the oleox oxidation necessary to carry out at temperatures above 45-50 °C. It allows to obtaine the maximum content of reactive groups in the modified product. At vegetable oils oxidation study, it was found that the linseed oil has the highest oxidation rate, which contains the greatest amount of linolenic acid (46%), that probably initiates the oxidation processes. The degree of epoxidation of vegetable oils is much lower than that of oleox, probably due to a high degree of oxidation of unsaturated bonds in oils containing large amounts of polyunsaturated acids, which are the "catalysts" of the oxidation process. Relatively high levels of aldehyde and epoxy groups in sunflower oil oxidation products allows us to speak about the prospects of getting on its base materials for tanning fat.Forcitation:Chursin V.I. Oxidative epoxidation of oleox and vegetable oils. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 3. P. 83-89.

The effect of aluminum additions on the oxidation resistance of U3Si2

The effect of aluminum additions to U3Si2 is investigated as a means to improve the oxidation resistance of this nuclear fuel form. Four U-Si-Al compositions have been synthesized and characterized using scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. The onsets of breakaway oxidation are identified in air thermal ramp tests using thermogravimetric analysis. The final oxidation products following 1000° C air exposure are identified using x-ray diffraction and compared to those of UO2 and U metal oxidized in the same manner. Thermogravimetric data acquired in this study indicates that increasing amounts of Al in U3Si2 further delays the onset of breakaway oxidation, providing enhanced oxidation resistance in air. Al2O3 formation on U3Al2Si3 is observed following a heat treatment performed at 500° C in air, demonstrating the potential of Al additions to improve the oxidation resistance of U3Si2.

Kinetics and Mechanism of Permanganate Oxidations of Isosorbide in Different Acidic Media

The oxidation kinetics of isosorbide (S) by potassium permanganate in both perchloric and sulfuric acid solutions was investigated spectrophotometrically at a constant ionic strength of 2.0 mol·dm−3 and at 25 °C. In both acids, the oxidation reactions showed a first-order dependence on \([{\text{MnO}}_{4}^{ - }]\), apparent a less than unit-order dependence with respect to [S] and a fractional-second-order dependence with respect to [H+]. Variation of either the ionic strength or dielectric constant of the reactions media did not significantly affect the oxidation rates. In both acids, the final oxidation product of isosorbide was identified by both spectroscopic and chemical tools as the corresponding monoketone derivative, namely (1S,4S,5R)-4-hydroxy-2,6-dioxabicyclo[3.3.0] octan-8-one. Under comparable experimental conditions, the oxidation rate of isosorbide in perchloric acid was lower than that in sulfuric acid. The oxidation mechanism describing the kinetic results was proposed and the rate law expression was derived. The activation parameters of the second-order rate constants were computed and are discussed.

Electrosynthesis of highly porous NiO nanostructure through pulse cathodic electrochemical deposition: heat-treatment (PCED-HT) method with excellent supercapacitive performance

A highly porous NiO nanostructure is prepared through a pulse cathodic electrochemical deposition/heat-treatment (PCED-HT) method. Based on the method first a hydroxide precursor was deposited from an additive-free 0.005 M Ni(NO3)2 through a pulse–base-electro-generation procedure. The pulsed deposition experiments were performed at ton = 1 s, toff = 1 s, ipeak = 50 mA cm−2, T = 80 °C and 30 min. The green hydroxide powder was then calcined at 500 °C for 3 h and to obtain a black oxide powder. The mechanisms for the deposition of the nickel hydroxide precursor during the PCED step, as well as that of the formation of the final oxide product during the HT step were studied. The structural and morphological properties of the product were evaluated through XRD, IR and SEM. The results revealed the precursor and the product to be porous β-nickel hydroxide and porous cubic crystalline nickel oxide nanostructures, respectively. The super-capacitive performance NiO-based electrode was evaluated by cyclic voltammetry and the galvanostatic charge–discharge techniques in 1 M KOH electrolyte. It was observed that the fabricated porous NiO electrode exhibits capacitive behavior of low ΔEp value of 32 mV and width potential window (ΔV = 0.8 V), and is capable to deliver high specific capacitance of 1056.4 F g−1 and capacity retention of 89.7% after 3000 GCD cycles at current load of 3 A g−1, and energy density and power density as high as 82.3 Wh/Kg and 0.60 W/g, respectively.

Silver(I) and Copper(II) Catalysis for Oxidation of Histidine by Cerium(IV) in Acid Medium: A Comparative Kinetic Study

The catalytic effect of silver(I) and copper(II) ions on the oxidation of histidine by cerium(IV) in aqueous sulfuric acid solutions was studied spectrophotometrically at a constant ionic strength of 3.0 mol dm−3 and at 25°C. In both uncatalyzed and metal ions-catalyzed paths, the reactions exhibited first-order kinetics with respect to [Ce(IV)] and [catalyst], and fractional first-order dependences with respect to [His] and [H+]. The oxidation rates increased as the ionic strength and dielectric constant of the reactions media increased. The catalytic efficiency of Ag(I) was higher than that of Cu(II). Plausible mechanistic schemes for both uncatalyzed and catalyzed reactions were proposed, and the rate laws associated with the suggested mechanisms were derived. In both cases, the final oxidation products of histidine were identified as 2-imidazole acetaldehyde, ammonium ion, and carbon dioxide. The activation parameters associated with the second-order rate constants were evaluated.

A Comparative Kinetic Study on the Efficacious Permanganate Oxidation of Fluorenes in Perchloric and Sulfuric Acid Media

Oxidation kinetics of fluorene (Fl) and its halogenated derivatives, namely, 2,7-dichlorofluorene (Fl-Cl), 2,7-dibromofluorene (Fl-Br) and 2,7-diiodofluorene (Fl-I), by permanganate ion in both perchloric and sulfuric acid media have been investigated using conventional spectrophotometric technique. In both acidic media, the reactions manifested first order kineticsin [permanganate] and less than unit order each in [reductants] and [acid]. Increasing ionic strength had no effect on the oxidation rates. Oxidation rates of fluorenes in perchloric acid were higher than those in sulfuric acid and the order of the oxidation rates was: Fl > Fl-I > Fl-Br > Fl-Cl. Final oxidation products were identified by GC/MS and FT-IR analyses in all cases as 9H-fluorenone derivatives. Reaction constants as well as activation parameters of the second order rate constants were also evaluated.

A Study of the Kinetics and Mechanism of Oxidation of Fluorene by Alkaline Hexacyanoferrate(III)

Kinetics of hexacyanoferrate (III) (HCF) oxidation of fluorene (Fl) in organic alkaline medium has been studied by spectrophotometric technique at a constant ionic strength of 0.15 mol dm-3 and at a temperature of 25°C. The reaction showed a first order kinetics with respect to [HCF] and fractional-first order dependences on both [Fl] and [OH-]. The oxidation rate was increased with the increase in the ionic strength of the reaction medium. The oxidation mechanism was suggested which involves formation of a 1:1 intermediate complex between fluorene and HCF species in a pre-equilibrium step. The final oxidation product of fluorene was identified by spectroscopic and chemical tools as 9H-fluorenone. The appropriate rate law expression was deduced and the reaction constants involved in the mechanism were evaluated. The activation parameters of the rate constant of the slow step along with the thermodynamic quantities of the equilibrium constants were evaluated and discussed.

Oxidation of Acebutolol by Copper(III) Periodate Complex in Aqueous Alkaline Medium: A Kinetic and Mechanistic Approach

Illuminating the complex reactions of molecules in aqueous solution is one of the most important tasks of experimental studies of reaction dynamics. The oxidant diperiodatocuprate(III) (DPC) was used for the oxidation of acebutolol (ACBT) in aqueous alkaline medium, at an ionic strength of 0.30 mol·dm−3. The stoichiometry was found to be 1:2 ([ACBT]:[DPC]). The order of the reaction with respect to [DPC] was unity when [DPC] << [ACBT], while the orders with respect to [ACBT] and [OH−] were less than unity, whereas it was negative less than unity in [\( {\text{IO}}_{ 4}^{ - } \)] over the concentration range studied. The final products of oxidation were identified by GC–MS analysis. Based on the experimental observations, a plausible mechanism is proposed. The reaction constants involved in the different steps of the reaction mechanism were calculated. The activation parameters and the thermodynamic quantities were determined and discussed. Active species of diperiodatocuprate(III) was found to be monoperiodatocuprate(III), i.e. [Cu(H2IO6)(H2O)2]. An understanding of the mechanism allows the chemistry to be interpreted, understood and predicted.

Catalytic properties of CuMgAlO catalyst and degradation mechanism in CWPO of methyl orange

Cu-loaded MgAl hydrotalcite catalysts were synthesized by impregnation method and further used for catalytic wet peroxidation (CWPO) of methyl orange (MO) using hydrogen peroxide as oxidant. The synthesized catalysts have been characterized by XRD, FT-IR, SEM/EDS, TG/DTA, XPS, H2-TPR and BET. The characterizations showed that a good dispersion of Cu species inside the MgAl hydrotalcite supports, where Cu2+ and Cu+ species were coexistence, mainly existed as Cu2+↔Cu+ pairs. The CuMgAlO catalyst showed the highest catalytic activity due to the high content of Cu2+↔Cu+ pairs, stable performance during reuse for five cycles with fewer copper leaching. The degradation mechanism of MO was determined by UV-vis, ATR-FTIR and GC–MS. The hydroxyl radicals (HO) induced strong oxidizing effect, where the azo groups (NN−) double bonds would be first attacked by the hydroxyl radical and other free radicals. With the continuous oxidization, these intermediates could be oxidized to the final oxidation products, such as water and carbon dioxide.

Simultaneous removal of Hg0 and SO2 from flue gas using vacuum ultraviolet radiation combining with absorption of urea solution

A novel process on simultaneous removal of SO2 and Hg0 from flue gas using vacuum ultraviolet (VUV) radiation combining with absorption of urea solution was developed. Several process parameters (e.g., VUV radiated power, O2 content, solution pH, solution temperature, SO2 content, liquid-gas ratio, urea concentration and Hg0 content) of Hg0 removal process were studied and optimized in a semicontinuous and small-scale photochemical reactor. Products and intermediates of SO2 and Hg0 simultaneous removal were measured. Chemistry of Hg0 removal was also investigated initially. Results show that an increase in VUV radiated power, O2 content or liquid-gas ratio promotes Hg0 removal. Increasing solution temperature, SO2 content or Hg0 content reduces Hg0 removal efficiency. Increasing solution pH or urea concentration has a dual impact on Hg0 removal. SO2 reaches 100% removal efficiency under all test conditions. The highest simultaneous removal efficiency is 100% for SO2 and 98.1% for Hg0. Hg2+ and SO42− are the final products of Hg0 and SO2 oxidation, respectively. Ozone and hydroxyl free radicals are successfully captured. The ozone, oxygen atom and hydroxyl free radicals are proved to be the most important oxidants for oxidation removal of Hg0.