H2O2 Decomposition Rate Research Articles

Climate Change and Modern Human Evolution

Catalytic diuron degradation in soil by modified Fenton or Fenton-like reaction has been studied and a kinetic model including the rates of all physical and chemical processes involved in both aqueous and soil phases has been developed and validated.The soil selected, a sandy clay loam one, was artificially spiked with a solution of diuron dissolved in methanol, obtaining a final diuron concentration of 0.167 mmol kg−1. Diuron oxidation experiments were performed in a batch reactor in both aqueous phase and slurry system at different concentrations of H2O2, trisodium citrate (CT) as chelant, and Fe(III) as catalyst.Because of the neutral pH achieved by adding CT, the oxidation rate of CT and H2O2 decomposition in the aqueous phase has been found negligible. On the contrary, a significant unproductive decomposition of H2O2 by the soil was observed. Diuron oxidation rate was strongly dependent on the iron concentration and, in lower extent, on the H2O2 concentration, in both aqueous phase and slurry system.A kinetic model, including diuron desorption, CT adsorption, H2O2 decomposition by soil, and diuron oxidation in both soil and aqueous phase was proposed. The kinetic parameters were obtained by fitting the experimental data to this model. The predicted values of diuron abatement, in both soil and aqueous phases, and the H2O2 simulated conversion values were in good agreement with the experimental ones. Moreover, the obtained results suggest that kinetic of diuron desorption to the aqueous phase was enhanced due to the chemical reaction.

Kinetics and efficiency of H2O2 activation by iron-containing minerals and aquifer materials

To gain insight into factors that control H2O2 persistence and OH yield in H2O2-based in situ chemical oxidation systems, the decomposition of H2O2 and transformation of phenol were investigated in the presence of iron-containing minerals and aquifer materials. Under conditions expected during remediation of soil and groundwater, the stoichiometric efficiency, defined as the amount of phenol transformed per mole of H2O2 decomposed, varied from 0.005 to 0.28%. Among the iron-containing minerals, iron oxides were 2–10 times less efficient in transforming phenol than iron-containing clays and synthetic iron-containing catalysts. In both iron-containing mineral and aquifer materials systems, the stoichiometric efficiency was inversely correlated with the rate of H2O2 decomposition. In aquifer materials systems, the stoichiometric efficiency was also inversely correlated with the Mn content, consistent with the fact that the decomposition of H2O2 on manganese oxides does not produce OH. Removal of iron and manganese oxide coatings from the surface of aquifer materials by extraction with citrate–bicarbonate–dithionite slowed the rate of H2O2 decomposition on aquifer materials and increased the stoichiometric efficiency. In addition, the presence of 2 mM of dissolved SiO2 slowed the rate of H2O2 decomposition on aquifer materials by over 80% without affecting the stoichiometric efficiency.

Use of EIS to Measure the Rate of H2O2 Decomposition on a Bulk Magnetite Electrode in Alkaline Solution

The new generation of supercritical cooled water reactors (SCWR) are susceptible to particulate fouling as a result of corrosion product sedimentation. Iron oxides are a major component of corrosion products and are also known to catalyze hydrogen peroxide decomposition. This work aimed to investigate the rate of H2O2 decomposition on the surface of a magnetite bulk electrode by using electrochemical impedance spectroscopy. A magnetite bulk electrode was immersed in a suspension of various concentrations of magnetite particles and initial H2O2 concentration of 10−2 M. It was observed that the electrochemical response of the magnetite surface (which is partially oxidized to γ − Fe+3 species) is a function of H2O2 concentration. Therefore, at different time intervals EIS was used to obtain charge transfer resistance as a proxy variable for hydrogen peroxide concentration. These measurements were compared to results obtained by permanganate titration. It was observed that the changes of decomposition current density extracted from the EIS data fitting process for various conditions were in good agreement with the titration results. H2O2 decomposition in the presence of iron oxide particles was found to be a second-order reaction with rate constants of 0.015 and 0.017 min−1g−1L (obtained from EIS and titration methods, respectively).

Mechanism of the Decomposition of Aqueous Hydrogen Peroxide over Heterogeneous TiSBA15 and TS-1 Selective Oxidation Catalysts: Insights from Spectroscopic and Density Functional Theory Studies

The Ti-based heterogeneous catalysts TiSBA15, BucapTiSBA15, TS-1, and [Ti,Al]-MFI were investigated with respect to controlling factors for the competitive decomposition of aqueous H2O2 during selective catalytic oxidations. DRUV–vis spectroscopy revealed that the titanium species in these materials exist mainly in isolated, tetrahedral coordination environments. The observed rates of H2O2 decomposition at 65 °C in acetonitrile decreased in the following order: BucapTiSBA15 > TiSBA15 and TS-1 > [Ti,Al]-MFI. The decompositions of H2O2 were also monitored in the presence of inorganic additives and Bronsted acids and bases, in benzene/aqueous biphasic solutions. Significant retardation of the decomposition rates with the KH2PO4 additive was found with TiSBA15, which suggests that the KH2PO4 stabilizer may be useful for optimization of hydrogen peroxide efficiency in catalytic oxidations. DRUV–vis spectroscopy was employed to identify possible catalytically active intermediates, proposed to be Ti(IV)(OOH) spe...

Selective decomposition of hydrogen peroxide in the epoxidation effluent of the HPPO process

This work describes the selective H2O2 decomposition in the exit stream of the epoxidation reactor employed in the Hydrogen Peroxide–Propylene Oxide (HPPO) process. Pd/Al2O3 and Pt/Al2O3 catalysts were tested. The effects of the reaction temperature and the pH of the solution on catalyst performance were investigated. It was found that the Pt catalyst is much more active than its Pd counterpart. An increase in the temperature and the pH of the solution resulted in an increase in the H2O2 decomposition rate; however, a parallel increase of by-products from PO was also observed. Working with a Pt/Al2O3 catalyst under optimized reaction conditions (333K, pH=7), hydrogen peroxide can be completely decomposed at reaction times of 120min with no by-products produced from propylene oxide.

Study of photocatalytic decomposition of hydrogen peroxide over ramsdellite-MnO2 by O2-pressure monitoring

Abstract The catalytic and photocatalytic activities of ramsdellite type manganese oxide, R-MnO2 were studied from the initial rate of decomposition of H2O2 in aqueous solution. The kinetic study was followed by the production of O2 via gas pressure monitoring (O2-monitored method), in the dark and under visible light irradiation (λ ≥ 400 nm), at 20 °C. Experimental data showed that the rate of H2O2 decomposition, under visible light irradiation and in the dark, obeys the first order kinetic law. While in the dark the H2O2 decomposition rate by mass unit was around 6.88 mmol g−1 s−1, under visible light irradiation the H2O2 decomposition rate achieved a maximal value of 15.13 mmol g−1 s−1. The increase in the H2O2 decomposition, by effect of the visible light, was observed in ranges of catalyst concentrations from 16 to 374 mg L−1. These results reflect the potential of R-MnO2 as a photoactive catalyst, being a consequence of presumed photoreduction of Mn4+centers.

Performances of Pd Nanoparticles on Different Supports in the Direct Synthesis of H2O2 in CO2-Expanded Methanol

Catalysts based on Pd supported on SiO2, SBA-15, γ-Al2O3 and N-CNT were investigated for the direct H2O2 synthesis and decomposition/hydrogenolysis in CO2-expanded methanol in batch and semi-batch reactors working at room temperature and a pressure of 6.5 bar. The order of reactivity for the synthesis of H2O2 per g of Pd or for the rate of H2O2 decomposition, or the selectivity to H2O2 does not correlate with the acidity of the support. A relation was observed with the Pd particle sizes, i.e. smaller particles lead to a higher specific activity, but the sample supported on carbon nanotube shows an order of magnitude higher specific activity per g of Pd, indicating the presence of an additional factor attributed to the interaction with the carbon support which determines an intrinsic higher reactivity. However, this higher reactivity corresponds also to a higher activity in the consecutive conversion of H2O2, probably by hydrogenolysis reaction. A rough relation between activity in H2O2 synthesis and in H2O2 conversion was observed in the samples with the different supports, indicating the similar nature of the active sites responsible for the two reactions. Finally, the analysis of the recyclability of the catalysts and transmission electron microscopy (TEM) characterization data after the catalytic tests indicate that the use of CO2-expanded methanol allows improving the catalytic performances in H2O2 direct synthesis due to the enhanced solubility of H2 and O2, but induces a fast catalyst deactivation due to an enhanced mobility and sintering of the supported Pd particles. The effect is present in all the four type of support used.

Enhancement of Epoxidation Efficiencies for Ta-SBA15 Catalysts. The Influence of Modification with –EMe3 (E = Si, Ge, Sn) Groups

Site-isolated Ta(V) centers were introduced onto the surface of a mesoporous SBA-15 support via the thermolytic molecular precursor method. After thermal treatment under oxygen, the resulting Si-OH and Ta-OH sites of TaSBA15-O(2)were modified with a series of trimethyl group 14 species, Me(3)E-, by treatment with Me(3)E-NMe(2) (E = Si, Ge, Sn) reagents. The resulting surface-modified catalysts (Me(3)E)(cap)TaSBA15 exhibit a significantly increased rate of cyclohexene epoxidation with H(2)O(2) as an oxidant, and provided a decreased amount of allylic oxidation products with respect to the unmodified material, TaSBA15-O(2). The rate of nonproductive H(2)O(2) decomposition, as monitored via (1)H NMR spectroscopy, significantly decreased after the surface modification. The structure of the TaSBA15 catalysts and potential Ta(V) epoxidation intermediates (formed upon treatment of Ta(V) materials with H(2)O(2)) were probed using UV-visible absorbance and diffuse-reflectance UV-visible spectroscopy. A Ta(V)(η(2)-O(2)) intermediate species is proposed for the TaSBA15-O(2), (Me(3)Si)(cap)TaSBA15, and (Me(3)Ge)(cap)TaSBA15 catalysts, while intermediate species for the (Me(3)Sn)(cap)TaSBA15 catalysts could not be characterized.

A study of the relative importance of the peroxiredoxin-, catalase-, and glutathione-dependent systems in neural peroxide metabolism

Cells are endowed with several overlapping peroxide-degrading systems whose relative importance is a matter of debate. In this study, three different sources of neural cells (rat hippocampal slices, rat C6 glioma cells, and mouse N2a neuroblastoma cells) were used as models to understand the relative contributions of individual peroxide-degrading systems. After a pretreatment (30min) with specific inhibitors, each system was challenged with either H2O2 or cumene hydroperoxide (CuOOH), both at 100μM. Hippocampal slices, C6 cells, and N2a cells showed a decrease in the H2O2 decomposition rate (23–28%) by a pretreatment with the catalase inhibitor aminotriazole. The inhibition of glutathione reductase (GR) by BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea) significantly decreased H2O2 and CuOOH decomposition rates (31–77%). Inhibition of catalase was not as effective as BCNU at decreasing cell viability (MTT assay) and cell permeability or at increasing DNA damage (comet test). Impairing the thioredoxin (Trx)-dependent peroxiredoxin (Prx) recycling by thioredoxin reductase (TrxR) inhibition with auranofin neither potentiated peroxide toxicity nor decreased the peroxide-decomposition rate. The results indicate that neural peroxidatic systems depending on Trx/TrxR for recycling are not as important as those depending on GSH/GR. Dimer formation, which leads to Prx2 inactivation, was observed in hippocampal slices and N2a cells treated with H2O2, but not in C6 cells. However, Prx-SO3 formation, another form of Prx inactivation, was observed in all neural cell types tested, indicating that redox-mediated signaling pathways can be modulated in neural cells. These differences in Prx2 dimerization suggest specific redox regulation mechanisms in glia-derived (C6) compared to neuron-derived (N2a) cells and hippocampal slices.

Catalase Activity of Cytochrome c Oxidase Assayed with Hydrogen Peroxide-Sensitive Electrode Microsensor

An iron-hexacyanide-covered microelectrode sensor has been used to continuously monitor the kinetics of hydrogen peroxide decomposition catalyzed by oxidized cytochrome oxidase. At cytochrome oxidase concentration ~1 µM, the catalase activity behaves as a first order process with respect to peroxide at concentrations up to ~300-400 µM and is fully blocked by heat inactivation of the enzyme. The catalase (or, rather, pseudocatalase) activity of bovine cytochrome oxidase is characterized by a second order rate constant of ~2·10(2) M(-1)·sec(-1) at pH 7.0 and room temperature, which, when divided by the number of H2O2 molecules disappearing in one catalytic turnover (between 2 and 3), agrees reasonably well with the second order rate constant for H2O2-dependent conversion of the oxidase intermediate F(I)-607 to F(II)-580. Accordingly, the catalase activity of bovine oxidase may be explained by H2O2 procession in the oxygen-reducing center of the enzyme yielding superoxide radicals. Much higher specific rates of H2O2 decomposition are observed with preparations of the bacterial cytochrome c oxidase from Rhodobacter sphaeroides. The observed second order rate constants (up to ~3000 M(-1)·sec(-1)) exceed the rate constant of peroxide binding with the oxygen-reducing center of the oxidized enzyme (~500 M(-1)·sec(-1)) several-fold and therefore cannot be explained by catalytic reaction in the a(3)/Cu(B) site of the enzyme. It is proposed that in the bacterial oxidase, H2O2 can be decomposed by reacting with the adventitious transition metal ions bound by the polyhistidine-tag present in the enzyme, or by virtue of reaction with the tightly-bound Mn2+, which in the bacterial enzyme substitutes for Mg2+ present in the mitochondrial oxidase.

Magnetic minerals from volcanic Ultisols as heterogeneous Fenton catalysts

This study was devoted to the evaluation of the effectiveness of Fenton catalysts, based on magnetically-concentrated portions of iron oxide-rich sand fractions from two magnetic Ultisols, derived from volcanic materials of southern Chile. The samples were labeled according to the municipality where the sample sites are geographically located, namely Metrenco and Collipulli, and were characterized with Mossbauer spectroscopy at 298 K and saturation magnetization (σ) measurements. Mossbauer data revealed a complex magnetic hyperfine structure for these magnetic portions from both soil-sand materials, suggesting relatively complex mineral assemblages. The monitored rate of H2O2 decomposition via heterogeneous Fenton reaction revealed that materials from the Collipulli soil are more efficient Fenton catalyst than are those from the Metrenco soil. The reasons for these differences are from now on being explored on basis of a more detailed chemical investigation of these samples.

Degradation of 2, 4-D acid using Mn2+ as catalyst under UV irradiation

In this paper, the oxidative degradation of 2, 4-dichlorophenoxyacetic acid (2, 4-D) using Mn2+/H2O2 reagent under UV irradiation was studied. The results show that 2, 4-D was degraded more completely in Mn2+/H2O2 solution than traditional Fenton solutions. The effects of the concentration of Mn2+, H2O2 and pH were also investigated. And under the optimal condition of \( c_{Mn^{2 + } } \) 1.48×10−4 mol/L, \( c_{H_2 O_2 } \) 8.99×10−5 mol/L and pH 3.38, the formation of ·OH was the most, both the decomposition rate of H2O2 and the degradation rate of 2, 4-D were the fastest. In addition, the photoreaction process was monitored using spin-trapping electron paramagnetic resonance (EPR), and the results indicated that the oxidative process was predominated mainly by the hydroxyl radical (·OH) gennerated in the system.

Ultraviolet radiation from the pulsed corona discharge in water

Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water with needle-plate electrode geometry (∼1–3 J pulse−1) was performed using the potassium ferrioxalate actinometry. Photon flux J190–280 and radiant energy Q190–280 of the UV light emitted from the discharge at spectral region 190–280 nm was determined in dependence on the applied voltage (17–29 kV, positive polarity) and the solution conductivity (100–500 µS cm−1). The intensity of the UV radiation strongly increased with increasing water conductivity and applied voltage. Depending on the applied voltage the determined photon flux varied by more than two orders of magnitude within the range of solution conductivities 100–500 µS cm−1. It was found that photon flux from the discharge may be directly related to the discharge pulse mean power Pp as J190–280 = 44.33 (quanta pulse−1). A significant role of UV radiation in the production of hydrogen peroxide and bacterial inactivation by the corona discharge in water has been identified. As the solution conductivity increased the yield of H2O2 produced by the discharge decreased due to increasing photolysis of H2O2 accounting for up to 14% of the total decomposition rate of H2O2. As regards bactericidal effects, it was estimated that the UV radiation contributes about 30% to the overall inactivation of Escherichia coli.

Rates of Trace Mineral-Catalyzed Decomposition of Hydrogen Peroxide

Rapid hydrogen peroxide ( H2 O2 ) decomposition is a significant limitation of catalyzed H2 O2 propagations (i.e., modified Fenton’s reagent) for the remediation of contaminated soil and groundwater by in situ chemical oxidation. Rates of H2 O2 decomposition mediated by seven trace minerals and four iron and manganese oxides were evaluated in batch reactors containing slurries of H2 O2 and each of 11 minerals. At pH 3, the dominant catalysts in the decomposition of H2 O2 on a per surface area basis were the manganese and iron oxides pyrolusite, goethite, and hematite, while decomposition rates in the presence of the manganese oxyhydroxide manganite and the trace mineral siderite were one to two orders of magnitude lower. At pH 7, the dominant catalysts were hematite and pyrolusite, and decomposition rates were one to two orders of magnitude lower in the presence of goethite, manganite, and siderite. The trace minerals anatase, bauxite, cuprite, ilmenite, magnesite, and willemite provided the least activit...

Phosphatidylcholine Vesicle-Mediated Decomposition of Hydrogen Peroxide

The decomposition of hydrogen peroxide (H2O2) was examined in aqueous solution (50 mM Tris-HCl buffer, pH 7.4, containing 100 mM NaCl) at 25 degrees C in pure buffer or in the presence of either vesicles or micelles formed from various phosphatidylcholines (PCs). In the absence of PCs, more than 90% of the initially added H2O2 (1.0 mM) remained intact after incubation for 120 h. The effect of the PCs on the decomposition of H2O2 was studied by using different PCs that varied in terms of number of carbon atoms in the two acyl chains n as well as in terms of the degree of unsaturation. PCs with short hydrocarbon chains (n = 4, 6-8) were dissolved in the buffer solution in the form of nonassociated monomers or as micelles in equilibrium with monomers at a fixed PC concentration of 10 mM. The presence of these short-chain PCs slightly enhanced the H2O2 decomposition rate. Micelles formed by non-lipid detergents (sodium cholate, Triton X-100, and sodium dodecylsulfate) had a similar effect. In marked contrast, PCs with long hydrocarbon chains (n > or = 10) dispersed in buffer solution as vesicles (liposomes) significantly enhanced the rate of H2O2 decomposition, with the most effective PC being 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at 25 degrees C. This indicates that the packing density of the PC molecules influences the reactivity, presumably through the direct interaction of the PC assemblies with H2O2 molecules. Furthermore, in the case of vesicles formed from PCs with unsaturated acyl chains (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC; 1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC), carbon-carbon double bond oxidation did not occur extensively under the conditions used. This indicates that the observed effect of PCs on the decomposition of H2O2 is indeed related to the assembly structure (vesicle vs micelles vs monomers) and is clearly not related to the presence of unsaturated hydrocarbon chains. Fluorescence polarization measurements of two fluorescent probes embedded either in the acyl chain region of the vesicles (DPH, 1,6-diphenyl-1,3,5-hexatriene) or on the surface of the vesicles (TMA-DPH, 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide) show that the presence of H2O2 leads to a decrease in the fluidity of the lipid-water surface and not to a change in the fluidity of the hydrophobic region of the vesicle bilayer. This indicates that the decomposition of H2O2 is triggered through interactions between H2O2 and the polar head group area of PC vesicles.

Production and decomposition dynamics of hydrogen peroxide in freshwater

Environmental context. Hydrogen peroxide (H2O2) is the most stable reactive oxygen species (ROS) formed through irradiation of chromophoric dissolved organic matter (CDOM) in freshwater. It can act as a reductant or as an oxidant and decays largely through interaction with microorganisms via unknown mechanisms. In this way it can affect biological and chemical processes in natural waters and thus shape the ecosystem biogeochemistry. Abstract. Hydrogen peroxide (H2O2) is widely recognised as the most stable of the reactive oxygen species produced by solar radiation-driven photochemical reactions in natural waters. H2O2 concentrations were determined in a shallow fresh water system (water of Leith, Dunedin, New Zealand) by flow-injection analysis (FIA) using an acridinium ester chemiluminescent reaction system. Daytime measurements of H2O2 concentration showed a rapid increase from early morning (15 nM) to 1300 hours (491 nM), consistent with photochemical formation, lagging maximum solar irradiance by ~1.5 h. The wavelength dependency of H2O2 formation was studied and it was shown that UV-B, UV-A and PAR contributed 40, 33 and 27%, respectively. The average formation rate was 339 nM h–1 during springtime. The influence of biotic communities on the rate of H2O2 decomposition was also studied and the majority of decomposition was due to particles smaller than 0.22 μm. The overall first order decay rate constant was of the order of 7.1 h–1. The bacterial and algal communities in the water column and on the riverbed were primarily responsible for the decomposition of H2O2.

Formation from direct oxidation of H2 and destruction by decomposition/hydrogenation of H2O2 over Pd/C catalyst in aqueous medium containing different acids and halide anions

Abstract Direct oxidation of H2 by O2 to H2O2 and decomposition/hydrogenation of H2O2 (at 27 °C and atmospheric pressure) over Pd/C catalyst in an aqueous acidic reaction medium have been thoroughly investigated using different mineral acids (viz. 0.1N H2SO4, H3PO4, H3BO3, HNO3, HCl, HBr or HI) and/or halide anions (viz. F−, Cl−, Br− or I−), covering their wide concentration range (0–24 mmol/dm3), in the reaction medium. In the absence of any externally added halide, appreciable H2O2 formation in the H2 oxidation occurred only when the medium contained HCl. However, the rates of H2O2 decomposition and hydrogenation are greatly reduced because of the presence of any acid; the influence on the H2O2 decomposition was, however, much larger for the halo acids. In the presence of acid (0.1N H3PO4 or H2SO4), the H2-to-H2O2 formation reaction is greatly enhanced by the externally added halide anions up to their optimum concentrations. However, above the optimum halide anion concentration, it is inhibited more than the H2-to-water formation (parallel) reaction, causing a decrease in both the H2O2 yield and selectivity. Whereas, the H2 conversion and H2O2 destruction activities of the catalyst are decreased continuously with increasing the halide anion (except F−) concentration. Among the halides, chloride is the best halide promoter for Pd/C catalyst in the H2-to-H2O2 oxidation. At the optimum Cl− concentration (5.4 mmol/dm3), both the H2 conversion and H2O2 yield are passed through a maximum and the H2O2 decomposition is greatly inhibited with increasing the phosphoric acid concentration. In the absence of either the chloride anions or the acid (or both) in the reaction medium, only a little or no H2O2 is formed in the H2 oxidation and also the rate of H2O2 destruction is very fast, particularly in the presence of H2; the rapid destruction of H2O2 is mainly due to its decomposition rather than its hydrogenation. The best H2-to-H2O2 oxidation results are obtained at the optimum concentrations of both the acid and halide anions. In the presence of acid and chloride (or bromide) promoter, the H2O2 hydrogenation dominates the H2O2 destruction and hence the net H2O2 formation is mainly controlled by the H2O2 hydrogenation.

Production of Hydroxyl Radicals from the Decomposition of Hydrogen Peroxide Catalyzed by Various Iron Oxides at pH 7

The hydroxyl radical (HO⋅), generated from the Fenton-like catalysis of hydrogen peroxide (H2O2), is the major reactant involved in the oxidation of toxic organic contaminants. This study evaluated the effects of H2O2 doses and types of iron oxides on the yields and production rates of HO⋅ radicals at molar ratio of H2O2/total iron oxide=0.2-9.7 and pH=7. The results showed that for both ferrihydrite and goethite, the yields and production rates of HO⋅ radicals were in the order of 10-12mM and 1-5×10-14mM/S, respectively, and irrelevant to the initial H2O2 dose. However, a higher H2O2 dose was required in aquifer sand to produce the same level of HO⋅ radicals. The molar transformation ratios of H2O2 to HO⋅ radicals for three different iron oxides all ranged from 10-15 to 10-13, and occurred at low H2O2 doses. The yield and production rate of HO⋅ radicals showed no significant correlation with the first-order decay constant of H2O2. This indicated that the rate of H2O2 decomposition was not a suitable para...

Influence of Surface Modification on Catalytic Activity of Activated Carbon Toward Decomposition of Hydrogen Peroxide and 2-Chlorophenol

The objective of this research was to investigate the influence of the activated carbons modified by chemical treatment on the surface catalyzed loss of H2O2 and 2-CP. The characteristics of the modified activated carbons were examined by several techniques including nitrogen adsorption, SEM, and EDS. The H2O2 decomposition rate would be suppressed significantly either by the change of surface properties modified with chemical treatment or the reduction of active sites occupied with the adsorption of 2-CP. In addition, the H2O2 decomposition rate with activated carbons within a specific time can be described by a second-order kinetic expression with respect to the concentration of GAC and H2O2 in the absence or presence of 2-CP. The catalytic activities of the three activated carbons toward 2-CP reduction followed the inverse sequence of those toward H2O2 loss, implying that acidic surface functional group could retard the H2O2 loss and reduce the effect of surface scavenging resulting in increasing the reduction efficiency of 2-CP. By the detection of chloride ions in reaction mixture, it can be demonstrated that the reduction of 2-CP was not only attributed to the advanced adsorption but also the oxidation of the 2-CP with effective radicals. The real oxidation efficiency of 2-CP for the activated carbon modified with hot nitric acid was observed between 0.04 and 0.01 (mol/mol), offering a comparable efficiency to that of the other oxidation system using metal oxide as catalyst.

Studies of several systems with air electrode electro-synthesizing H2O2 on the spot for degrading aniline in aqueous

A gas diffusion electrode (air electrode) with a high current efficiency of electro-synthesizing H2O2 using O2 in air was prepared. The several systems with air electrode as cathode of electro-synthesizing H2O2 on the reaction spot for degrading aniline in aqueous—electro-Fenton system, photo-excitation electro-H2O2 system and photo-electro-Fenton system, were developed. The rates of decomposition of H2O2 and mineralization of aniline were experimentally measured respectively under different conditions, and the results indicated there has an excellent parallel relation between decomposition rate of H2O2 and mineralization rate of aniline. Especially, photo-electro-Fenton system, where H2O2 is decomposed the fastest, is the best system of oxidizing and degrading organic toxicants. Compared photo-electro-Fenton system with photo-Fenton system, important role is revealed in the interface of air electrode. In this paper, the mineralization mechanism of aniline in the photo-electro-Fenton system was also discussed.