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1.
Reactions with hydrogen peroxide on silver in alkaline solutions with H2O2 concentration 5 × 10?7 mol/ml have been studied with the ring-disk electrode. The amount of oxygen formed on the disk as the result of catalytic decomposition of hydrogen peroxide and its oxidation was established on the ring-electrode made from pyrographite. The rate constants of H2O2 electrochemical reduction (k3), its oxidation (k2) and catalytic decomposition (k4) and their dependence on potential have been evaluated. The constant k4 scarcely depends on potential; it is ca 10?2 cm/s.  相似文献   

2.
Diazinon is a widely used organophosphorus insecticide that is an important pollutant in aquatic environments. The chemical removal of diazinon has been studied using UV radiation, ozone, Fenton's reagent, UV radiation plus hydrogen peroxide, ozone plus hydrogen peroxide and photo‐Fenton as oxidation processes. In the photodegradation process the observed quantum yields had values ranging between 2.42 × 10?2 and 6.36 × 10?2 mol E?1. Similarly, the ozonation reaction gave values for the rate constant ranging between 0.100 and 0.193 min?1. In the combined systems UV/H2O2 and O3/H2O2 the partial contributions to the global oxidation reaction of the direct and radical pathways were deduced. In the Fenton's reagent and photo‐Fenton systems, the mechanism of reaction has been partially discussed, and the predominant role of the radical pathway pointed out. Additionally, the rate constant for the reaction between diazinon and the hydroxyl radicals was determined, with the value 8.4 × 109 L mol?1 s?1 obtained. A comparison of the different oxidation systems tested under the same operating conditions revealed that UV radiation alone had a moderate oxidation efficiency, which is enhanced in the case of ozone, while the most efficient oxidant is the photo‐Fenton system. Copyright © 2007 Society of Chemical Industry  相似文献   

3.
The aim of the present study was to evaluate the concentration of sodium pyruvate in growth media by using the most-probable number method to decompose carried-over liquid hydrogen peroxide (H2O2) without negative influences on correct enumeration of Geobacillus stearothermophilus spores. An equivalent molar ratio of sodium pyruvate and H2O2 was verified to be sufficient for a complete decomposition. The results showed that by exposition of G. stearothermophilus spores in different liquid hydrogen peroxide and by carry-over of concentrations ranging from 3.56 · 10−6 up to 1.69 · 10−4 mol, a sodium pyruvate concentration of 0.05 mol L−1 in growth media was most efficient for the recovery of spores.  相似文献   

4.
Several advanced oxidation processes for the destruction of cyanide contained in waste waters from thermoelectric power stations of combined‐cycle were studied. Thus, oxidation processes involving ozonation at basic pH, ozone/hydrogen peroxide, ozone/ultraviolet radiation and ozone/hydrogen peroxide/ultraviolet radiation have been carried out in a semi‐batch reactor. All these methods showed that total cyanide can be successfully degraded but with different reaction rates, and the decrease in the total cyanide concentration can be described by pseudo‐first order kinetics. The influence of pH and initial concentration of hydrogen peroxide was studied to find the optimal conditions of the oxidation process. Experimental results of the single ozone treatment indicated that total cyanide is destroyed more rapidly at higher pH (12), while ozonation combined with H2O2 and/or UV is faster at pH 9.5. The optimum concentration of H2O2 was 20.58 × 10?2 M because an excess of peroxide decreases the reaction rate, acting as a radical scavenger. The total cyanide degradation rate in the O3/H2O2(20.58 × 10?2 M ) treatment was the highest among all the combinations studied. However, COD reduction, in the processes using UV radiation such as O3/UV or O3/H2O2/UV was about 75%, while in the processes with H2O2 and/or O3/H2O2 was lower than 57% and was insignificant, when using ozone alone. Copyright © 2003 Society of Chemical Industry  相似文献   

5.
Methyl methacrylate (MMA) was successfully grafted onto rubber‐wood fiber in a free‐radical solution polymerization initiated by ferrous ion and hydrogen peroxide. The effects of the reaction parameters (reaction temperature, reaction period, influence of hydrogen peroxide, ferrous ammonium sulfate, and monomer concentrations) were investigated. The grafting percentage showed dependency on H2O2, Fe2+, and monomer concentrations, as well as reaction temperature and reaction period. The optimum reaction temperature was determined to be about 60°C and the reaction period was 60 min. The optimum concentration of H2O2 was 0.03M and optimum amounts of Fe2+ and MMA were 0.26 mmol and 2.36 × 10?2 mol, respectively. Poly(methyl methacrylate) (PMMA) homopolymer was removed from the graft copolymer by Soxhlet extractor using acetone. The presence of PMMA on the fiber was shown by FT‐IR spectroscopy and gravimetric analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2499–2503, 2003  相似文献   

6.
Electrogenerated Chemiluminescence (ECL) involves applying a certain electric potential to a chemical reaction, resulting in the oxidation or reduction of the substance which reacts to produce light. We determined the amount of glucose by its reaction to glucose oxidase (GO X ) on the surface of the proposed modified electrode, which results hydrogen peroxide (H2O2) as side product. After that the reactions between luminol and H2O2 under oxidizing conditions generate dependent light which can be used to analyze. In the current article at first we proposed a convenient method to obtaining a self-assembly modified electrode. A nano based modified glassy carbon (GC) electrode (Glucose oxidase/Ag nanoparticles/cysteamine (CA)/p-aminobenzene sulfonic acid/GC electrode) was prepared, and the ECL behavior of luminol in the presence of glucose was examined. Compared to the bare GC electrode, the modified electrode incorporating glucose oxidase significantly enhanced the response of the ECL biosensor to glucose due to the enhanced specificity of the modified surface to enzymatic reaction, and the sensitivity of the luminol ECL reaction. Under optimal conditions, the electrode was established to respond linearly to glucose in the concentration range 5.0×10?7 to 8.0×10?3 mol/L, and the detection limit was established to be a glucose concentration of 4.0×10?8 mol/L.  相似文献   

7.
The reactivity of sodium azide, activated sodium azide and hydrazinium azide towards various dioxygenyl salts was studied. Under no circumstances the formation of dioxygenyl azide, O2N3, could be observed. This is in agreement with high level quantumchemical ab initio computations at correlated level (MP2, PMP2, CISD), predicting the decomposition of hypothetical O2+(g)/N3(g) to be thermodynamically highly favorable (MP2: −326; PMP2: −328; CISD; −369 [kcal/mol]). The combustion of O2BF4 with either N2H5N3 (spontaneous reaction on contact in a coaxial solid-propellant system) or NaN3 (safe to handle, highly exothermic reaction after ignition) is discussed in terms of high-energy-density materials (HEDM).   相似文献   

8.
Enzymatic hydrolysis and fermentation methods were evaluated on alkaline peroxide pretreated shea tree sawdust conversion to ethanol. Optimum pretreatment conditions of 120 °C reaction temperature, 30 min reaction time, and 20 mL L?1 of water hydrogen peroxide concentration (1%(v/v)H2O2) solubilized 679 g kg?1 of hemicellulose and 172 g kg?1 of lignin. 617 g kg?1 cellulose was retained in the solid fraction. The maximum yield of reducing sugar with optimized enzyme loadings by two enzyme preparations (cellulase and β-glucosidase) was 165 g kg?1 of dry biomass. The ethanol yield was 7.35 g L?1 after 72 h incubation period under the following conditions: 2% cellulose loading, enzyme concentration was 25 FPU (g cellulose)?1 loading, yeast inoculums was 10% (v/v), 32 oC, and pH 4.8. The pretreatments gave information about the hindrances caused by lignin presence in lignocellulosic materials and that hemicelluloses are better hydrolyzed than lignin, thereby enhancing enzymatic digestibility of the sawdust material.  相似文献   

9.
An electrochemical hydrogen peroxide biosensor was designed by immobilizing horseradish peroxidase (HRP) on Ag nanoparticles/cysteamine/p-aminobenzene sulfonic acid/glassy carbon (GC) electrode. Ag nanoparticles can act as tiny conduction centers on electrodes that adsorb redox enzymes, facilitating the transfer of electrons with no requiring any loss of biological activity. The forerunner film was first electropolymerized on the glassy carbon electrode with p-aminobenzene sulfonic acid (p-ABSA) by cyclic voltammetry. The cysteamine (CA) was bound on the surface of the film by electrostatic force, then Ag nanoparticles were immobilized on the cysteamine monolayer, and lastly HRP was adsorbed onto the surfaces of the Ag nanoparticles. A dramatic decrease in the overvoltage of H2O2 was observed with improved sensitivity, which makes the modified electrodes of great promise for oxidase-based amperometric biosensors. The biosensor responded to H2O2 in the linear range from 1.2×106 mol/L to 9.8×103 mol/L with a detection limit of 1.1×108 mol/L. Moreover, the obtained biosensor exhibited good accuracy and high sensitivity.  相似文献   

10.
For the preparation of a heterogenized N,N′‐bis(acetylacetone)ethylenediamine cobalt(II) Schiff base complex, first crosslinked polymer beads were prepared by the suspension copolymerization of styrene (48.97 mmol, 5.1 g), allyl chloride (48.97 mmol, 3.746 g), and divinyl benzene (DVB; 1.75 mmol, 0.228 g) in the presence of azobisisobutyronitrile (0.9 × 10?3 mmol, 0.15 g) as an initiator at 23 ± 0.1°C under an inert atmosphere. The copolymerization of styrene, allyl chloride in the presence of gelatin (0.75 g), bentonite (2.0 g), and boric acid (2.5 g) produced beads of different crosslinked densities corresponding to the concentration of DVB in the reaction mixture. The amount of allyl chloride in the prepared beads varied from 5.40 to 7.40 mmol g?1 of beads with the amount of DVB varying from 2.0 to 0.8 mmol in the reaction mixture. A quadridentate Schiff base (acen) was prepared with ethylenediamine (5.0 mmol, 0.3 g) and acetylacetone (10.0 mmol, 1.0 g), and it was used to obtain a homogenized and heterogenized Co(II)(acen)2 complex. The extent and arrangement of the Schiff base (acen) in the crosslinked beads depended on the availability of DVB in the reaction mixture. The amount of DVB in the reaction mixture influenced the extent of cobalt(II) ion loading, the degree of swelling, the porosity, and the pore size in the prepared beads. The beads (type IV) prepared with 1.75 mmol (0.228 g) of DVB in the reaction mixture showed a degree of swelling of 9.65% and efficiencies of loading and complexation for cobalt(II) ions of 49.4 and 85%, respectively, in comparison with beads obtained at other concentrations of DVB in the reaction mixture. The structure of free and polymer‐supported Co(II)(acen)2 complexes was verified with IR, UV, and magnetic measurements, which suggested a square planar geometry for the complexes under both conditions. The catalytic activities of the homogenized and heterogenized Co(II)(acen)2 complexes were compared by the evaluation of the rate constant (k) for the decomposition of hydrogen peroxide. The heterogenized Co(II)(acen)2 complex showed a high catalytic activity for the decomposition of hydrogen peroxide (k = 2.02 × 10?4 s?1) in comparison with the homogenized Co(II)(acen)2 complex (k = 4.32 × 10?6 s?1). The energy of activation for the decomposition of hydrogen peroxide with the heterogenized Co(II)(acen)2 complex was low (38.52 kJ mol?1) in comparison with that for the homogenized complex (73.44 kJ mol?1). In both cases, the rate of decomposition of hydrogen peroxide was directly proportional to the concentration of hydrogen peroxide and cobalt(II) ions. On the basis of experimental observations, a rate expression for the decomposition of hydrogen peroxide was derived. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1398–1411, 2003  相似文献   

11.
Ozone/hydrogen peroxide batch treatment was utilized to study the degradation of the steroidal hormone estrone (E1). The competition kinetics method was used to determine the rate constants of reaction for direct ozone and E1, and for hydroxyl radicals and E1 at three pH levels (4, 7, and 8.5), three different molar O3/H2O2 ratios (1:2, 2:1, and 4:1) and a temperature about 20°C. The average second-order rate constants for direct ozone-E1 reaction were determined as 6.2?×?103?±?3.2?×?103 M?1s?1, 9.4?×?105?±?2.7?×?105 M?1s?1, and 2.1?×?107?±?3.1?×?106 M?1s?1 at pH 4, 7, and 8.5, respectively. It was found that pH had the greatest influence on the reaction rate, whereas O3/H2O2 ratio was found to be slightly statistically significant. For the hydroxyl radical-E1 reaction, apparent rate constants ranged from 1.1?×?1010 M?1s?1 to 7.0?×?1010 M?1s?1 with an average value of 2.6?×?1010 M?1s?1. Overall, O3/H2O2 is shown to be an effective treatment for E1.  相似文献   

12.
Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.  相似文献   

13.
Photocatalytic degradation of 4-chlrophenol (4-CP) using UVA-LED assisted persulfate and hydrogen peroxide activated by the nZVI (Nano Zero Valent Iron) in a batch photocatalytic reactor was investigated. The reaction involved a lab-scale photoreactor irradiated with UVA-LED light emitted at 390 nm. The efficiency of the reaction was evaluted in terms of 4-CP degradation and mineralization degree at different pH of solution, initial concentrations of nZVI, persulfate, hydrogen peroxide and 4-CP. In UVA-LED/H2O2/nZVI process, complete degradation of 4-CP (>99%) and 75% mineralization was achieved at pH of 3, hydrogen peroxide concentration of 0.75 mM, nZVI dosage of 1mM and initial 4-CP concentration of 25mg/L at the reaction time of 30 min. The optimum conditions obtained for the best 4-CP degradation rate were at an initial concentration of 25mg/l, persulfate concentration of 1.5mM, nZVI dosage of 1mM, pH of 3 and reaction time of 120min for UVA-LED/persulfate/nZVI process. It was also observed that the 4-CP degradation rate is dependent on initial 4-CP concentrations for both processes. The pseudo-first-order kinetic constant at 25mg/L initial concentration of 4-CP was found to be 1.4×10?1 and 3.8×10?2 in UVA-LED/H2O2/nZVI and UVA-LED/persulfate/nZVI processes, respectively. Briefly, the UVA-LED/H2O2/nZVI process enhanced the degradation rate of 4-CP by 3.67-times in comparison to UVA-LED/persulfate/nZVI process at 30min contact time, which serves as a new and feasible approach for the degradation of 4-CP as well as other organic contaminants containing wastewater.  相似文献   

14.
On the background of the direct adipic acid synthesis from cyclohexene and H2O2, a kinetic model was derived for the H2O2 decomposition catalyzed by sodium tungstate at high H2O2 concentrations and high temperatures. A perfluoroalkoxy (PFA) and a stainless steel micro‐flow capillary match commonly used microreactor materials. In the PFA capillary, the decomposition of hydrogen peroxide increased with residence time, reaction temperature and catalyst loading. The reaction order with respect to hydrogen peroxide and sodium tungstate was zero and one, respectively. Simulated data fit well with experimental data in the PFA capillary. While showing a similar trend as that in the PFA capillary, the stainless steel capillary exhibited much higher reaction rates. The steel surface participated in the decomposition process as a heterogeneous catalyst. Key influencing factors of the H2O2 decomposition provided some clues on the reaction mechanism of the adipic acid synthesis and its process optimization. © 2016 American Institute of Chemical Engineers AIChE J, 63: 689–697, 2017  相似文献   

15.
The effect of the reaction conditions on the grafting parameters during grafting of 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid onto sodium carboxymethylcellulose using H2O2/Fe+2 redox pair are studied at 30°C. The grafting ratio, add on, and conversion initially increase with the H2O2 concentration in the range of (10.0–15.0) × 10?2 mol dm?3. Thereafter, these parameters decrease with the H2O2 concentration. The grafting ratio, add on, and conversion increase when increasing the ferrous ion concentration from (0.5 to 4.0) × 10?2 mol dm?3 and decrease with a further increase in the concentration. It is observed that the grafting ratio and add on increase with the monomer concentration, whereas the conversion decrease. The hydrogen ions seem to be facilitating the grafting reaction up to a certain concentration and after this concentration seem to be retarding the process. The grafting ratio, add on, and conversion decrease with the sodium carboxymethylcellulose concentration. When increasing the time period from 60 to 90 min, the grafting parameters increase but decrease thereafter. Similarly, when increasing the temperature from 25 to 30°C, the grafting parameters increase and decrease thereafter. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4819–4825, 2006  相似文献   

16.
The ozonation of esculetin (6,7-dihydroxycoumarin), a major pollutant present in the wastewater generated in the cork industry, was accelerated at high pH, with apparent second-order rate constants in the range from 3.3 × 104 L/(mol·s) at pH=2 to 8.4 × 107 L/(mol·s) at pH=9. The acid-base equilibrium of esculetin was studied, resulting in a pKa value of 7.37. Taking into account this pKa, the rate constants for the reaction between ozone and the un dissociated and dissociated forms of esculetin were 3.0 × 104 and L/(mol·s) 6.67 × 108 L/(mol·s), respectively. Apparent first-order rate constants for the photolysis by UV irradiation were also evaluated, with values between 0.12 × 10?2 min?1 at pH=2 and 1.15 × 10?2 min?1 at pH=9, while the quantum yields for this photo-degradation reaction varied from 0.99 × 10?2 mol/Eins to 11.1 × 10?2 mol/Eins at these pHs. The Fenton's reagent system was used for the generation of hydroxyl radicals, and the rate constant for the reaction between esculetin and these radicals was determined to be 1.06 × 1010 L/(mol·s). Finally, several chemical oxidation systems were used in the degradation of this pollutant: single oxidants (ozone, UV irradiation) and advanced oxidation processes (Fenton's reagent, UV/H2O2, O3/H2O2, O3/UV, O3/H2O2 /UV, and photo-Fenton system). The results revealed that the most efficient methods in terms of esculetin removal were ozonation among the single oxidants, and the photo-Fenton system among the combined processes.  相似文献   

17.
The influence of hydrogen peroxide on the chemistry of aqueous silicates was investigated by high-resolution 29Si-NMR and electrochemical methods. The observations indicate that dissolved silicates form labile complexes with radical H2O2-decomposition products, possibly O2·?. An important role of soluble silicates in peroxide bleaching liquors thus might be to affect the activity of free radical species which mediate H2O2 bleaching and decomposition reactions. Attempts to prepare the widely reported peroxysilicates from silicate/H2O2/NaOH mixtures resulted in the isolation of Na2O2·8H2O.  相似文献   

18.
This work evaluates Fenton oxidation for the removal of organic matter (COD) from cork‐processing wastewater. The experimental variables studied were the dosages of iron salts and hydrogen peroxide. The COD removal ranged from 17% to 79%, depending on the reagent dose, and the stoichiometric reaction coefficient varied from 0.08 to 0.43 g COD (g H2O2)?1 (which implies an efficiency in the use of hydrogen peroxide varying from 17% to 92%). In a study of the process kinetics, based on the initial rates method, the COD elimination rate was maximum when the molar ratio [H2O2]o:[Fe2+]o was equal to 10. Under these experimental conditions, the initial oxidation rate was 50.5 mg COD dm?3 s?1 with a rate of consumption of hydrogen peroxide of 140 mg H2O2 dm?3 s?1, implying an efficiency in the use of the hydrogen peroxide at the initial time of 77%. The total amount of organic matter removed by Fenton oxidation was increased by spreading the H2O2 and ferrous salt reagent over several fractions by 15% for two‐fractions and by 21% for three‐fractions. Copyright © 2004 Society of Chemical Industry  相似文献   

19.
Polyimides were prepared from diamines: 2,4,6-trimethyl-1,3-phenylenediamine (3MPDA) and 2,3,4,5-tetramethyl-1,4-phenylenediamine (4MPDA). 1,4-Bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 3,3′-4,4′-diphenylsulphone tetracarboxylic dianhydride (SO2PDA), 3,3′,4,4′-diphenylsulphide tetracarboxylic dianhydride (SPDA), pyromellitic dianhydride (PMDA), and 2,2′-bis(3,4-dicarboxyphenyl)hexafluoroisopropane dianhydride (6FDA) were used as dianhydride. The gas permeabilities of H2, O2 and N2 through the polyimides were measured at temperatures from 30 °C to 90 °C. The results show that as methyl and trifluoromethyl substitution groups densities increase from 7.73 × 10−3 mol cm−3 to 13.50 × 10−3 mol cm−3, the peameability of H2 increases 10-fold at 60% loss of permselectivity of H2/N2; however, the permeability of O2 increases 20-fold at 20% loss of permselectivity of O2/N2. For O2/N2 separation, PMDA-3MPDA has similar performance to 6FDA-3MPDA and 6FDA-4MPDA; all have higher permeabilities for O2 than normal polyimides, and the P(O2)/α(O2/N2) trade-off relationships lie on the upper bound line for polymers. © 1999 Society of Chemical Industry  相似文献   

20.
A new biosensor for the voltammetric detection of hydrogen peroxide was developed based on immobilization of catalase on a clinoptilolite modified carbon paste electrode using bovine serum albumin and glutaraldehyde. The biosensor response was evaluated according to electrode composition, reaction time, solution pH and temperature. The voltammetric signals were linearly in proportion to H2O2 concentration in the range 5.0 × 10−6–1.0 × 10−3 M with a correlation coefficient of 0.9975. The detection limit is 8.0 × 10−7 M and the relative standard deviation for 4.0 × 10−4 M hydrogen peroxide was 1.83% (= 6). The biosensor exhibited high sensitivity, and it was determined that it could be used for more than 2 months. In addition, the biosensor was successfully applied for the determination of hydrogen peroxide in milk samples.  相似文献   

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