The role of platinum as the high voltage electrode in the enhancement of Fenton''s reaction in liquid phase electrical discharge

Pulsed electrical discharges in water produce a variety of oxidative and reductive species including hydroxyl radicals, hydrogen peroxide, and hydrogen. The reaction of ferrous ions with hydrogen peroxide (Fenton's reaction) provides additional hydroxyl radicals. Previous experiments with pulsed electrical discharges in water have shown that when ferrous sulfate is used as an electrolyte with a platinum high voltage electrode significantly higher organic compound degradation can be obtained in comparison to the case with an electrode made of nickel-chromium. In the work presented here, it is shown that particles emitted into solution from the platinum high voltage electrode enhance the production of hydroxyl radicals by forming a catalytic cycle between ferric and ferrous ions. The ferrous ions are converted to ferric ions by the Fenton's reaction utilizing hydrogen peroxide from the electrical discharge and the ferric ions are in turn converted to ferrous ions by reactions on the platinum particles emitted into solution from the high voltage electrode with molecular hydrogen formed by the electrical discharge. Based upon experiments with various scavengers it is concluded that the catalytic effect of the platinum particles is due to the presence of adsorbed hydrogen, while in contrast the nickel-chromium, which does not adsorb hydrogen, high voltage electrode and particles emitted by this electrode have no effect on the ferric ion regeneration.     

Formation of Hydroxyl Radicals from Hydrogen Peroxide and their Effect on Bleaching of Mechanical Pulps

The formation of hydroxyl radicals from hydrogen peroxide in alkaline solutions and under the conditions of hydrogen peroxide bleaching of pulps was investigated. The results lend support to the generally accepted view that the decomposition of alkaline hydrogen peroxide is catalyzed by redox processes involving transition metal ion species. The formation of hydroxyl radicals by one-electron reduction of hydrogen peroxide in this process is believed to be catalyzed primarily by mononuclear transition metal ion complexes, polynuclear species being far less efficient in this respect. It was found that a certain formation of hydroxyl radicals during alkaline hydrogen peroxide bleaching of pulp may have a beneficial effect on the final brightness. This finding is ascribed to the cleavage of crosslinks in the rigid lignin matrix which facilitates penetration of the bleaching reagent(s). Silicate does not appreciably suppress the formation of hydroxyl radicals in alkaline hydrogen peroxide solution. The stabilizing effect of this additive is probably due to deactivation of finely dispersed colloidal particles of metal hydroxides and hydrated oxides which decompose hydrogen peroxide to give mainly molecular oxygen and water.     

Greener method for high-quality polypyrrole

Conducting polypyrrole has been synthesized via a simple metal catalyzed process. The oxidative polymerization of pyrrole using hydrogen peroxide and a catalytic amount of iron(III) in an acidified aqueous medium afforded conducting polypyrrole in very good yield. The copper(II) or cerium(IV) catalyzed reactions under similar conditions gave poor yields. The iron(III) catalyzed reaction carried out in the absence of the acid produced low-quality polypyrrole that contain hydroxyl and carbonyl groups resulting from the nucleophilic attack of water or hydroxyl radicals.     

Aromatic Products from Reaction of Lignin Model Compounds with UV-Alkaline Peroxide

A series of guaiacyl and syringyl lignin model compounds and their methylated analogues were reacted with alkaline hydrogen peroxide while irradiating with UV light at 254 nm. The aromatic products obtained were investigated by gas chromatography-mass spectrometry (GC-MS). Guaiacol, syringol and veratrol gave no detectable aromatic products. However, syringol methyl ether gave small amounts of aromatic products, resulting from ring substitution and methoxyl displacement by hydroxyl radicals. Reaction of vanillin and syringaldehyde gave the Dakin reaction products, methoxy-1,4-hydroquinones, while reaction of their methyl ethers yielded benzoic acids. Acetoguaiacone, acetosyringone and their methyl ethers afforded several hydroxylated aromatic products, but no aromatic products were identified in the reaction mixtures from guaiacylpropane and syringylpropane. In contrast, veratrylpropane gave a mixture from which 17 aromatic hydroxylated compounds were identified. It is concluded that for phenolic lignin model compounds, particularly those possessing electron-donating aromatic ring substituents, ring-cleavage reactions involving superoxide radical anions are dominant, whereas for non-phenolic lignin models, hydroxylation reactions through attack of hydroxyl radicals prevail.     

Stabilization of hydrogen peroxide using tartaric acids in Fenton and Fenton-like oxidation

The stabilization of hydrogen peroxide is a key factor in the efficiency of a Fenton reaction. The stability of hydrogen peroxide was evaluated in a Fenton reaction and Fenton-like reactions in the presence of tartaric acid as a stabilizer. The interactions between ferrous or ferric iron and tartaric acid were observed through spectroscopic monitoring at variable pH around pKa1 and pKa2 of the stabilizer. Ferric iron had a strong interaction with the stabilizer, and the strong interaction was dominant above pKa2. At a low pH, below pKa1, the stabilizing effect was at its maximum and the prolonged life-time of hydrogen peroxide gave a higher efficiency to the oxidative degradation of nitrobenzene. In Fenton-like reactions with hematite, the acidic conditions caused dissolution of iron from an iron oxide, and an increase in iron species was the result. Tartaric acid showed a stabilizing effect on hydrogen peroxide in the Fentonlike system. The stabilization by tartaric acid might be due to an inhibition of catalytic activity of dissolved iron, and the stabilization strongly depends on the ionization state of the stabilizer.     

2，4-二氯苯氧乙酸臭氧化过程中过氧化氢的生成

引言2,4-二氯苯氧乙酸(2,4-D,又名2,4-滴)是一种广泛使用的除草剂[1],应用历史较长,是我国主要的除草剂品种之一,用量也比较大。2,4-D属于苯氧羧酸类除草剂的一种,可有效去除阔叶杂草,目前仍广泛用于农作物除草和草坪养护[2]。2,4-D的水溶性较高,挥发性较低,在自然界中难以生物     

Oxidation of several chlorophenolic derivatives by UV irradiation and hydroxyl radicals

The oxidation of some chlorophenols: 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,6‐trichlorophenol, 2,3,4,6‐tetrachlorophenol, tetrachlorocatechol (3,4,5,6‐tetrachloro‐2‐hydroxy phenol) and 4‐chloroguaiacol (4‐chloro‐2‐methoxy phenol) has been studied via single photodecomposition produced by polychromatic UV irradiation, oxidation by hydroxyl radicals generated by Fenton's reagent (hydrogen peroxide plus ferrous ions), and degradation by hydroxyl radicals produced by combinations of UV irradiation plus hydrogen peroxide, and UV irradiation plus hydrogen peroxide and ferrous ions (photo‐Fenton system). These organics have been selected as models of chloro‐phenolic derivative pollutants present in wastewaters and groundwaters. The degradation levels obtained in each process are reported. The quantum yields in the single photodecomposition reaction and the rate constants between the chlorophenols and the hydroxyl radicals in the reaction with Fenton's reagent are determined. Finally, the additional contributions to the photodecomposition promoted by the radical reaction in the combined UV/H₂O₂ and photo‐Fenton systems are also evaluated. © 2001 Society of Chemical Industry     

QUANTITATION OF PROTEIN DAMAGE IN METAL ION-CATALYZED OXIDATION SYSTEMS

The loss of enzymatic activity of lactate dehydrogenase was studied in several ascorbate, iron and hydrogen peroxide metal catalyzed oxidation solutions in which the initial concentration of each reactant was varied independently. Nonmonotonic concentration dependencies of enzymatic inactivation were observed for all three reactants. with minimum activity levels occurring in the 0·1 to 8 mM range. A first effort has been made to predict these concentration dependencies with a mathematical simulation model. The model consisted of the most commonly reported reactions and assumed that protein damage occurred through reaction with the hydroxyl radical. The simulation predicted nonmonotonic concentration dependencies of enzyme inactivation on each of the reactants. The predicted concentrations of the minima differed from the experimentally observed points by a factor of 2 to 4. Mathematically the minima occurred because each reactant was reported to react with hydroxyl radicals and form less reactive compounds. The plausibility that competition caused or contributed to the extrema was further explored with experimental competition studies between peroxide and the radical scavenger dimethylsulfoxide. A point of maximum hydroxyl radical formation was observed with increasing peroxide concentration. This maxima corresponded to the point of maximum lactate dehydrogenase damage observed with increasing peroxide concentration.     

Influence of surface texture and acid–base properties on ozone decomposition catalyzed by aluminum (hydroxyl) oxides

The decomposition of aqueous ozone in the presence of three aluminum (hydroxyl) oxides was studied, respectively. It was hypothesized that surface hydroxyl groups and acid–base properties of aluminum (hydroxyl) oxides play an important role in catalyzed ozone decomposition. The variables investigated were oxide dose, aqueous pH, presence of inorganic anions (sulfate and nitrate), the effect of tert-butyl alcohol (TBA) and surface hydroxyl groups density of the three aluminum (hydroxyl) oxides. All three aluminum (hydroxyl) oxides tested, i.e. γ-AlOOH (HAO), γ-Al₂O₃ (RAO) and α-Al₂O₃ (AAO), enhanced the rate of ozone decomposition. The net surface charge of the aluminum (hydroxyl) oxides favored in catalyzed ozone decomposition. The greatest effect on catalyzed ozone decomposition was observed when the solution pH was close to the point of zero charge of the aluminum (hydroxyl) oxide. Sulfate and nitrate were substituted for the surface hydroxyl groups of the aluminum (hydroxyl) oxides, which then complexed with Al³⁺ in a ligand exchange reaction. Therefore, inorganic anions may be able to inhibit catalyzed ozone decomposition. It was confirmed that surface hydroxyl groups were important for ozone decomposition with aluminum (hydroxyl) oxides as catalysts. TBA inhibited ozone decomposition in the presence of HAO, RAO and AAO. It was also tested whether aluminum (hydroxyl) oxides catalyzed ozone-transformed hydroxyl radicals. The relationship between surface hydroxyl groups and the ratio of hydroxyl radical concentration to ozone concentration (R_ct) was investigated quantitatively. Higher density of surface hydroxyl groups of the aluminum oxide tested was favorable for the decay of ozone into hydroxyl radicals.     

绿色化制备硫酸铁铵条件的探讨

用铁粉和稀硫酸反应制备硫酸亚铁,再用双氧水作氧化剂、铁氰化钾作指示剂制备硫酸铁,最后加入饱和硫酸铵,经过蒸发、冷却、结晶、抽滤制得硫酸铁铵产品。确定了硫酸浓度为3 mol/L,搅拌速度为870 r/min,制备硫酸亚铁反应温度为95℃,制备硫酸铁铵反应温度为45℃和制备硫酸铁铵溶液酸度为pH≤0.5的最佳条件。     

Electrochemical oxidation of Crystal Violet in the presence of hydrogen peroxide

BACKGROUND: The combination of electrochemical oxidation using a Ti/RuO₂? IrO₂ anode with hydrogen peroxide has been used for the degradation of Crystal Violet. The effect of major parameters such as initial pH, hydrogen peroxide concentration, current density, electrolyte concentration and hydroxyl radical scavenger on the decolorisation was investigated. RESULTS: The decolorisation rate increased with initial pH and hydrogen peroxide concentration, but decreased with electrolyte and radical scavenger concentration. The decolorisation rate increased with current density, but the increase became insignificant after current density exceeded 47.6 mA cm^?2. On the other hand, hydrogen peroxide decomposition rate increased with initial pH and current density, but decreased with electrolyte and radical scavenger concentration. The amount of hydrogen peroxide decomposed during 30 min reaction increased linearly with hydrogen peroxide dosage. The main intermediates were separated and identified by gas chromatography–mass spectrometry (GC–MS) technique and a plausible degradation pathway of Crystal Violet was proposed. At neutral pH, the electrochemical process in the presence of hydrogen peroxide was more efficient than that in the presence of Fenton's reagent (electro‐Fenton process). CONCLUSION: The anodic oxidation process could decolorise Crystal Violet effectively when hydrogen peroxide was present. Almost complete decolorisation was achieved after 30 min reaction under the conditions 2.43 mmol L^?1 hydrogen peroxide, 47.6 mA cm^?2 current density and pH₀ 7, while 62% COD removal efficiency was obtained when the reaction time was prolonged to 90 min. Copyright © 2010 Society of Chemical Industry     

Comparison of Fe2+?H2O2 and Fe3+?H2O2 initiation systems in graft copolymerization of cellulosic materials

Studies were carried out on decomposition of hydrogen peroxide by ferrous and ferric ions adsorbed on cellulosic materials (SP, SCP), scission of the cellulose chain and formation of grafts by graft copolymerization. As a result, it was found that the activity of ferrous ion is always higher than that of ferric ion, but there exists a common relation between the amount of decomposition of hydrogen peroxide and the number of grafts for all cellulose samples and kinds of metallic ions, and it was inferred that essentially, copolymerization takes place by the same mechanism irrespective of the kind of metallic ions. Consequently, it can be considered that the difference in degree of activity between ferrous ion and ferric ion is due to the difference in the decomposition mechanism of hydrogen peroxide by these metallic ions and it is assumed that the high activity of ferrous ion in graft copolymerization is due to the high hydrogen peroxide decomposition effect.     

Studies of the initiation mechanism of ferric ion–hydrogen peroxide systems in graft copolymerization on cellulose

The decomposition of hydrogen peroxide by ferric ion adsorbed on cellulose, the lowering of the degree of polymerization of cellulose, and the graft copolymerization in the systems containing methyl methacrylate were studied. As the amount of ferric ion adsorbed on cellulose and the concentration of hydrogen peroxide became higher, the amount of decomposition of hydrogen peroxide and the number of scissions of cellulose chains with higher rates at the initial stage of reaction were both observed to increase. It was recognized that the graft copolymerization was hardly initiated, while such initial reactions were proceeding. Assuming that the hydrogen peroxide decomposed with a higher rate was indifferent to the initiation reaction, a certain relationship was found between the amount of ferric ion adsorbed on cellulose ànd the initiation efficiency of hydrogen peroxide in graft copolymerization.     

Influence of surface texture and acid–base properties on ozone decomposition catalyzed by aluminum (hydroxyl) oxides

The decomposition of aqueous ozone in the presence of three aluminum (hydroxyl) oxides was studied, respectively. It was hypothesized that surface hydroxyl groups and acid–base properties of aluminum (hydroxyl) oxides play an important role in catalyzed ozone decomposition. The variables investigated were oxide dose, aqueous pH, presence of inorganic anions (sulfate and nitrate), the effect of tert-butyl alcohol (TBA) and surface hydroxyl groups density of the three aluminum (hydroxyl) oxides. All three aluminum (hydroxyl) oxides tested, i.e. γ-AlOOH (HAO), γ-Al₂O₃ (RAO) and α-Al₂O₃ (AAO), enhanced the rate of ozone decomposition. The net surface charge of the aluminum (hydroxyl) oxides favored in catalyzed ozone decomposition. The greatest effect on catalyzed ozone decomposition was observed when the solution pH was close to the point of zero charge of the aluminum (hydroxyl) oxide. Sulfate and nitrate were substituted for the surface hydroxyl groups of the aluminum (hydroxyl) oxides, which then complexed with Al³⁺ in a ligand exchange reaction. Therefore, inorganic anions may be able to inhibit catalyzed ozone decomposition. It was confirmed that surface hydroxyl groups were important for ozone decomposition with aluminum (hydroxyl) oxides as catalysts. TBA inhibited ozone decomposition in the presence of HAO, RAO and AAO. It was also tested whether aluminum (hydroxyl) oxides catalyzed ozone-transformed hydroxyl radicals. The relationship between surface hydroxyl groups and the ratio of hydroxyl radical concentration to ozone concentration (R_ct) was investigated quantitatively. Higher density of surface hydroxyl groups of the aluminum oxide tested was favorable for the decay of ozone into hydroxyl radicals.     

The formation in wool of copolymers of butadiene with acrylonitrile and methyl acrylate by iron salt-hydrogen peroxide initiation

The formation in wool of graft copolymers of butadiene with acrylonitrile and methyl acrylate has been studied, using the ferrous ion–hydrogen peroxide system as initiator and a heterogeneous liquid phase consisting of a dilute hydrogen peroxide solution and a monomer mixture. The effects of time and temperature, and the pH and concentrations of the ferrous ion and peroxide solutions, on the polymer add-on are discussed. The dependence of the composition of the graft copolymer on that of the monomer mixture has been determined. Certain features of the kinetics of the reaction are discussed.     

Performance evaluation of ozonation and an ozone/hydrogen peroxide process toward development of a new sewage treatment process—Focusing on organic compounds and emerging contaminants

Performance of ozonation and an ozone/hydrogen peroxide process under a new concept centering on ozonation and/or ozone/hydrogen peroxide processes in sewage treatment processes comprising only physical and chemical processes are discussed, with focus on the removal of matrix organic compounds and emerging contaminants. Matrix organic compounds of filtrated primary sewage effluents were removed to as low as 3.2 mgC/L in the ozone/hydrogen peroxide process at an ozone consumption of around 400 mg/L. Linear relationships between ozone consumption and removal amounts of organic compounds were observed, in which the amounts of ozone required to remove 1 mg of organic carbon were 9.5 and 8.3 mg (2.4 and 2.1 mol-O₃/mol-C) in ozonation and the ozone/hydrogen peroxide process, respectively. Ratios of hydroxyl radical exposure to ozone exposure were in the order of 10^–9 to 10^–8 for ozonation and 10^–7 to 10^–6 for the ozone/hydrogen peroxide process. Experiments and a kinetic evaluation showed that ozonation and/or the ozone/hydrogen peroxide process have high elimination capability for emerging contaminants, even in primary sewage effluent with the thorough removal of matrix organic compounds. Newly found reaction phenomena, the temporal increase and decrease of dissolved ozone and accumulation of hydrogen peroxide in the early stage of oxidation with the continuous feeding of hydrogen peroxide, were presented. Possible reaction mechanisms are also discussed.     

Copper‐Catalyzed Peroxide Oxidation Testing for Tetraphenylborate Decomposition

Abstract

A new processing option, copper‐catalyzed hydrogen peroxide oxidation of tetraphenylborate under alkaline conditions, was demonstrated in laboratory testing. Laboratory‐scale tests were conducted to evaluate the use of copper‐catalyzed hydrogen peroxide oxidation to treat simulants of the Savannah River Site tank waste. The oxidation process involves the reaction of hydrogen peroxide with a copper catalyst to form hydroxyl free radicals. With an oxidation potential of 2.8 volts, the hydroxyl free radical is a very powerful oxidant, second only to fluorine, and will react with a wide range of organic molecules. The goal is to oxidize the tetraphenylborate completely to carbon dioxide, with minimal benzene generation. Testing was completed in a lab‐scale demonstration apparatus at the Savannah River National Laboratory. Greater than 99.8% tetraphenylborate destruction was achieved in less than three weeks. Offgas benzene analysis by a gas chromatograph demonstrated low benzene generation. Analysis of the resulting slurry demonstrated >82.3% organic carbon destruction. The only carbon compounds detected were formate, oxalate, benzene (vapor), carbonate, p‐terphenyl, quaterphenyl, phenol, and phenol 3‐dimethylamino.     

聚合硫酸铁的生成机理

聚合硫酸铁的生成机理阮复昌，莫炳禄，公国庆，卢燕玲，张民权（华南理工大学化学工程研究所，广州５１０６４１）关键词聚合硫酸铁，无机絮凝剂，高效净水剂，生成机理１引言聚合硫酸铁是近几年发展起来的一种无机高分子絮凝剂。与传统的絮凝剂如三氯化铁、硫酸铝、氯化...     

Mechanism and kinetics of chlorine dioxide reaction with hydrogen peroxide under acidic conditions

The reaction of chlorine dioxide with hydrogen peroxide was studied in a well stirred batch reactor in a pH range of 3.60 to 5.07, which is of interest for commercial chlorine dioxide bleaching of chemical pulp. The reaction rate was determined by following the consumption of chlorine dioxide and hydrogen peroxide and the formation of chlorite. The rate equation was established. It was found that the concentration dependencies of chlorine dioxide, hydrogen peroxide and hydroxide ion were all first-order. A reaction mechanism compatible with the rate equation was proposed. Since it was found in previous work that chlorite in chlorine dioxide solution by the addition of small amount of hydrogen peroxide potentially led to a decrease in the formation of organically bound chlorine during chlorine dioxide bleaching, two methods were suggested to implement this technique in a bleach plant.     

Kinetics of hydrogen peroxide bleaching of ALCELL® derived pulp

In this study, a kinetic model of the final bleaching stage with hydrogen peroxide in a totally chlorine free (TCF) bleaching sequence for ALCELL® processed pulp was developed. The model was based on the rate of chromophore destruction characterized by the decrease in the light absorption coefficient of bleached pulp at 457 nm, C_K. Based on the fact that the chromophore destruction proceeds rapidly in an initial phase followed by a much slower reaction during which a “floor-level” chromophore concentration is approached asymptotically, we propose that the hydrogen peroxide stage of the ALCELL® derived pulp in the studied TCF sequence consists of two distinct phases. The initial phase is a very fast reaction. The rate equation of the second phase was determined as: which is valid in a pH range of 10.5 to 11.5 and a temperature range of 60 to 92.5°C.