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Hydrogen peroxide was detected during the ozonation of para-chlorophenol (4-CP) in aqueous solutions. Its formation and influence on the reaction mechanism were examined. Semi-batch experiments showed that hydrogen peroxide was formed during the direct reaction between molecular ozone and 4-CP. The detected hydrogen peroxide could reach 12.3% of the initial mole concentration of 4-CP. Hydrogen peroxide reacts with ozone in neutral pH and leads to the appearance of the powerful oxidant, OH* radicals. An O(3)/OH* probe compound, succinate was then developed, and also included in the 4-CP solution matrix. The disappearance of succinate with time shows the amount of OH radicals. With enough tert-butanol inhibiting the OH* radical oxidation, results showed that 4-CP was transformed to para-quinone by ozone, and subsequently destroyed to formic acid and oxalic acid. Without scavengers of inactivation the OH* radicals, 4-CP was destroyed to low molecular weight acid.
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PMID:The formation and influence of hydrogen peroxide during ozonation of para-chlorophenol. 1693 86

Clostridium acetobutylicum, an obligatory anaerobe, is able to grow microoxically with the accumulation of two functionally unknown O2-induced proteins identified by two-dimensional electrophoresis. One was determined to be a novel type rubrerythrin-like protein, named rubperoxin (Rpr) in this study, that conserves one rubredoxin-type Fe(SCys)(4) site per polypeptide in the N-terminus. Recombinant rubperoxin expressed in E. coli purified in its oxidized form is a dimer with optical absorption maxima at 492, 377, and 277nm. Reduced rubperoxin is rapidly and fully oxidized by a half molar ratio of H2O2 per mole protein, and slowly oxidized by t-butyl hydroperoxide and O2. Cell-free extracts from microoxically grown cells efficiently reduce rubperoxin when NAD(P)H is used as the electron donor (preferentially reduced by NADH). These results strongly suggest that rubperoxin is involved in NAD(P)H-dependent H2O2 detoxification in vivo.
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PMID:An O2-inducible rubrerythrin-like protein, rubperoxin, is functional as a H2O2 reductase in an obligatory anaerobe Clostridium acetobutylicum. 1748 86

Bimetallic nanoparticles consisting of gold and platinum were prepared by a citrate reduction method and complementarily stabilized with pectin (CP-Au/Pt). The percent mole ratio of platinum was varied from 0 to 100%. The CP-Au/Pt were alloy-structured. They were well dispersed in water. The average diameter of platinum nanoparticles (CP-Pt) was 4.7 +/- 1.5 nm. Hydrogen peroxide (H(2)O(2)) was quenched by CP-Au/Pt consisting of more than 50% platinum whereas superoxide anion radical (O(2)(-)) was quenched by any CP-Au/Pt. The CP-Au/Pt quenched these two reactive oxygen species in dose-dependent manners. The CP-Pt is the strongest quencher. The CP-Pt decomposed H(2)O(2) and consequently generated O(2) like catalase. The CP-Pt actually quenched O(2)(-) which was verified by a superoxide dismutase (SOD) assay kit. This quenching activity against O(2)(-) persisted like SOD. Taken together, CP-Pt may be a SOD/catalase mimetic which is useful for medical treatment of oxidative stress diseases.
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PMID:Platinum nanoparticle is a useful scavenger of superoxide anion and hydrogen peroxide. 1751 33

Horseradish peroxidase (HRP) was used to catalyze the oxidation of bisphenol A (BPA) in a reverse micelle system consisting of water, sodium bis(2-ethylhexyl)sulfosuccinate (AOT) as the surfactant, and n-octane as the organic solvent phase. In order to achieve maximal BPA transformation, a water-to-surfactant molar ratio greater than 15 was required, above which no further increase in conversion was observed. BPA transformation was catalyzed in the reverse micelle system over a pH range of 6-9 with an optimum at pH 7 and was enhanced with increasing temperatures up to 40 degrees C. The stoichiometric ratio of moles of bisphenol A transformed per mole of peroxide consumed was 0.46 when the initial BPA concentration was 0.01 mM, which is significantly less than the theoretical value of 2 based on the known catalytic cycle of the enzyme. However, the stoichiometric ratio increased and approach the theoretical value with higher BPA concentrations. Over the course of the catalytic reaction, the enzyme became inactivated. Hydrogen peroxide strongly inhibited the enzyme and, thus, when the oxidant was present in quantities in excess of the stoichiometric amount, BPA transformation was significantly reduced.
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PMID:Biocatalytic oxidation of bisphenol A in a reverse micelle system using horseradish peroxidase. 1792 23

Photoinduced organic oxidation with iron (hydr)oxides in aqueous suspension has been argued with respect to two principal mechanisms: (a) photoinduced ligand-to-metal charge transfer within a surface complex and (b) semiconductor photocatalysis. In this work, the photodegradation of azo dye orange II with UV light (lambda > or = 320 nm) in the aerated aqueous suspensions of haematite, maghemite, magnetite, goethite, lepidocrocite, and feroxyhite at an initial pH of 6.5 has been examined. The results showed that (1) all of the catalysts were effective at initiating dye photodegradation but the iron oxides appeared to be more active than the iron hydroxides; (2) the photodissolution of different iron phases and the dye photolysis in the dissolved iron solutions were very slow; (3) the initial rate of dye loss was proportional to the initial amount of adsorption, implying dye photodegradation on the catalyst surface; and (4) upon addition of H2O2, AgNO3, and NaF to the suspension, the rate of dye photodegradation was significantly enhanced with all the catalysts. In the presence of H2O2, less than 50% of the total rate enhancement was ascribed to the photo-Fenton reaction in solution and the dark Fenton reactions in solution and on the catalyst. In the presence of AgNO3, about 1 mole of silver particles was produced by consuming 3 moles of the dye substrate. In the presence of NaF, hydroxyl radicals were detected by an ethanol scavenger, whereas such radicals were not found in the absence of NaF. Moreover, under visible-light irradiation (lambda > or = 450 nm), the dye degradation was much slower than that under UV irradiation, but the reaction was also accelerated by the addition of NaF and AgNO3. The results suggest that mechanism b, not mechanism a, is operative for dye photodegradation occurring on the iron (hydr)oxides. A detailed discussion of all possible pathways is given in the text.
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PMID:Photoinduced degradation of orange II on different iron (hydr)oxides in aqueous suspension: rate enhancement on addition of hydrogen peroxide, silver nitrate, and sodium fluoride. 1805 20

In this work, an indirect method for estimating the total amount and concentration of oxidative radicals in aqueous and slurry-phase Fenton's systems was developed. This method, based on the use of benzoic acid as probe compound, was applied for evaluating the effect of the operating conditions on the radicals amount produced, their production efficiency (i.e. moles of radicals generated per mole H2O2 and their concentration. A Rotatable Central Composite design (RCC) was used to select the operating conditions in order to get a statistically meaningful data set. Hydrogen peroxide and ferrous ion concentrations ranged between 0.2-1mM and 0.2-0.5mM, respectively; humic acid concentration between 0 and 15mg/L, whereas the soil/water weight ratio in slurry-phase systems between 1:10 and 9:10. The probe compound concentration was 9 or 0.1mM in experiments aimed to evaluate the total amount or concentration of oxidative radicals, respectively. The obtained results indicated that the amount of radicals generated in both aqueous and soil slurry Fenton's system increased with higher H2O2 concentration and, more specifically, that their production efficiency increased with increasing Fe(II):H2O2 molar ratio. Addition of dissolved organic compounds as humic acid did not notably affect the oxidative radicals amount and concentration. On the contrary, a one order of magnitude reduction in both radicals amount generated and concentration was observed when soil was added to the reaction environment.
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PMID:Influence of the operating conditions on highly oxidative radicals generation in Fenton's systems. 1846 91

4-(Hydroxymethyl)phenyl benzyl selenoxide (4) sequestered in a halide-permeable, Class II xerogel formed from 10/90 (mol/mol) 3-aminopropyltriethoxysilane/tetraethoxysilane catalyzes the bromination of organic substrates (4-pentenoic acid, 3,5-dihydroxybenzoic acid, 1,3,5-trimethoxybenzene, N-phenylmorpholine, and N,N-dimethylaniline) with NaBr and H2O2. Catalyst performance (reaction rate) when sequestered within the halide-permeable xerogel is 23-fold greater in comparison to xerogel-free catalyst in solution. The catalyst is easily separated from the reaction mixture via filtration and the recovered catalyst can be reused without loss of activity through formation of the first 80 mol of product per mole of catalyst.
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PMID:A xerogel-sequestered selenoxide catalyst for brominations with hydrogen peroxide and sodium bromide in an aqueous environment. 1867 30

Hydrogen peroxide, m a mixture that is 0.1M in manganese(II) sulphate and sulphuric add and exposed to light from a tungsten lamp, decomposes slowly at room temperature in a nitrogen atmosphere. At 75 degrees the reaction is fairly rapid in the dark (about 20-25% in 4 hr) and about 60% faster in light. Presence of oxalic add has little effect on the rate of disappearance of peroxide, the overall reaction corresponding to H(2)C(2)O(4) + H(2)O(2) --> 2CO(2) + 2H(2)O. In the presence of oxygen [and manganese(II)] this reaction does not take place; instead, hydrogen peroxide is formed and oxalic add disappears in equimolar amounts. The extent of all reactions greatly increases with increasing concentration of manganese. Acrylonitrilc acts as a retarder. Conditions m the presence of mangancse(II) are described, under which oxalic add can be oxidized quantitatively by oxygen to carbon dioxide with formation of an amount of hydrogen peroxide equimolar to the oxalic add oxidized. Reaction mechanisms are proposed to account for the fact that in the absence of oxygen 1 mole of peroxide disappears and in the presence of oxygen 1 mote of peroxide is formed for each mole of oxalic add reacted.
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PMID:Formation of hydrogen peroxide upon oxidation of oxalic acid in presence and absence of oxygen-II Oxygen as oxidant. 1896 Nov 68

A Fe-containing metal-organic framework, Fe-MOF-74, was solvothermally synthesized using FeCl2.4H2O and 2,5-di-hydroxy-1,4-benzenedicarboxylic acid. Characterization was conducted by XRD, BET surface area measurement, FT-IR spectroscopy, TGA, and elemental analysis, which confirmed successful preparation of Fe-MOF-74 having an identical framework structure to that reported for MOF-74. Fe-MOF-74 was found to be an effective heterogeneous catalyst for the hydroxylation of phenol using H2O2 as an oxidant; 60% phenol conversion was achieved at 20 degrees C in water with 68 and 32% selectivity to catechol and hydroquinone, respectively. The effect of temperature, phenol/H2O2 mole ratio, catalyst quantity, and solvent on catalytic performance was discussed, and a reaction mechanism is proposed based upon the experimental results.
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PMID:Solvothermal synthesis of Fe-MOF-74 and its catalytic properties in phenol hydroxylation. 2035 23

This study was based on the purpose of investigating the reaction rules of formaldehyde (HCHO) as an intermediate product in the degradation of many other organic wastewaters. The process conditions of UV-Fenton method for the degradation of the low concentrations of HCHO were studied in a batch photochemical reactor. The results showed that, when the original HCHO concentration was 30 mg/L, at an operating temperature of 23 degrees C, pH = 3, an H202 dosage of 68 mg/L, and an H2O2-to-Fe2+ mole ratio (H2O2:Fe2+) of 5, 91.89% of the HCHO was removed after 30 minutes. The degradation of HCHO in the UV-Fenton system was basically in accordance with the exponential decay. The kinetic study results showed that the reaction orders of HCHO, Fe2+, and H2O2 in the system were 1.054, 0.510, and 0.728, respectively, and the activation energy (Ea) was 9.85 kJ/mol. The comparison of UV/H2O2, Fenton, and UV-Fenton systems for the degradation of HCHO, and the results of iron catalyst tests showed that the mechanism of UV-Fenton on the degradation of HCHO was through a synergistic effect of Fe2+ and UV light to catalyze the decomposition of H2O2. The introduction of UV irradiation to the Fenton system largely increased the degradation rate of HCHO, mainly as a result of the accelerating effect on the formation of the Fe2+/Fe3+ cycle. The reaction products were analyzed by gas chromatography-mass spectrometry and a chemical oxygen demand (COD) analyzer. The effluent gases also were analyzed by gas chromatography. Based on those results, the reaction pathways of HCHO in the UV-Fenton system were proposed. The qualitative and quantitative analysis of the reaction products and the COD showed that the main intermediate product of the reaction was formic acid, and the further oxidation of it was the rate-limiting step for the degradation of HCHO.
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PMID:Kinetics and reaction pathways of formaldehyde degradation using the UV-fenton method. 2165 93


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