The ozonization of sodium lignosulfonate in the presence of hydrogen peroxide

The kinetics of ozonization of sodium lignosulfate (LS) in the presence of H₂O₂ was studied. The effective rate constants for the oxidation of LS and the total ozone consumption were determined. The k _eff = 30 ± 8 M^?1 s^?1 value was found to be independent of the concentration of H₂O₂. The total ozone consumption decreased as the concentration of H₂O₂ increased from 1.0 × 10^?4 to 1.0 × 10^?3 M because of the participation of the radicals generated in the O₃ + H₂O₂ reaction in LS transformations. The kinetic and UV and IR spectroscopy data allowed the conclusion to be drawn that the destruction of the LS aromatic system in the LS + O₃ + H₂O₂ reaction was caused by the interaction of LS with O₃, whereas radicals generated in this system contributed to deeper destruction of LS in the interaction of aliphatic LS macromolecule fragments with low-molecular-weight polymer oxidation products. The depth of polymer oxidation could be changed by varying the content of hydrogen peroxide in the system for LS ozonization.     

Kinetics of Active Oxygen Species with Implications for Atmospheric Ozone Chemistry

Photochemical processes involving singlet oxygen (O₂(a¹Δ)), oxygen atoms_, and ozone are critical in determining atmospheric ozone concentrations. Here we report on kinetic measurements and modeling that examine the importance of the reactions of vibrationally excited ozone. Oxygen atoms and O₂(a¹Δ) were produced by UV laser photolysis of ozone. Time‐resolved absorption spectroscopy was used for O₃ concentration measurements. It was found that vibrationally excited ozone formed by O + O₂ + M → O₃(ν) + M recombination reacts effectively with O₂(a¹Δ) and O atoms. The reaction O₃(υ) + O₂(a¹Δ) → O + 2O₂ results in a reduction of the ozone recovery rate due to O atom regeneration, whereas the reaction O₃(υ) + O → 2O₂ removes two odd oxygen species, resulting in incomplete ozone recovery. The possible impact of these reactions on the atmospheric O₂(a¹Δ) and O₃ budgets at altitudes in the range of 80–100 km is considered.     

Atrazine and Parathion-Methyl Removal by UV And UV/O3 in Drinking Water Treatment

Abstract

The degradation of atrazine and parathion-methyl by UV-light in the presence of O₂(UV/O₂) and by a combination of UV-light and ozone in the presence of O₂(UV/O₂/O₃) was studied at a pilot plant for drinking water treatment. The photolysis rate of parathion-methyl increased with UV/O₂/O₃ compared to the treatment with UV/O₂ only, while the photodecomposition rate of atrazine was not enhanced by the UV/O₂/O₃ combination under the working conditions applied.

In field experiments with a large-scale plant the degradation of atrazine and desethylatrazine was studied at a drinking water supply. The applied ozone dose rates were smaller and the residence time of the liquid phase in the UV-reaction unit was shorter than in the pilot plant. The degradation rate of both atrazine and desethylatrazine increased with increasing ozone dose rates and increasing radiant power. At a continuous flow rate of 70 m³/h of contaminated raw water atrazine could be degraded below the threshold limit for pesticides (0.1[ugrave]g/L) at optimum operation conditions, whereas the resulting desethylatrazine concentration exceeded this limit. At a continuous flow rate of 30 m³/h desethylatrazine could be degraded below the threshold limit, too.     

Ozone production and losses in N<Subscript>2</Subscript>/O<Subscript>2</Subscript> mixtures in an ozone generator

Nonunique ozone concentrations at the output of an ozone generator under identical external conditions of barrier discharge activation of N₂/O₂ mixtures but with different prehistories of operating practice and employed gas mixtures are investigated theoretically. An analytical approach is developed to determine the ozone yield with regard for its heterogeneous loss. Plasma-chemical and electron kinetics in the N₂/O₂-mixtures are calculated numerically. The results of numerical calculations are compared to experimental data obtained by the authors. It is noted that the heterogeneous loss of ozone is the probable reason for the observed variety of behavior of О₃ concentrations, depending on prehistory of ozone generator operation, along with the N₂ and O₂ gas flow rates and the specific active power.     

Rate coefficient for the reaction of CCl3 radicals with ozone

The rate coefficient for the reaction of CCl₃ radicals with ozone has been measured at 303 ± 2 K. The CCl₃ radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl₃ concentration was monitored with a photoionization mass spectrometer. Addition of the O₃–O₂ mixture to this system caused a decay of the CCl₃ concentration because of the reactions of CCl₃ + O₃ → products (5) and CCl₃ + O₂ → products (4). The decay of signals from the CCl₃ radical was measured in the presence and absence of ozone. In the absence of ozone, the O₃–O₂ mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl₃ + O₂ could be determined separately, the absolute rate coefficient for reaction ( 5 ) was obtained from the competition among these reactions. The rate coefficient determined for reaction ( 5 ) was (8.6 ± 0.5) × 10^?13 cm³ molecule^?1 s^?1 and was also found to be independent of the total pressure (253–880 Pa of N₂). This result shows that the reaction of CCl₃ with O₃ cannot compete with its reaction with O₂ in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003     

Elektrochemische Methode zur quantitativen und kontinuierlichen Bestimmung von Ozon in Gasgemischen

The method is based on the measurement of the diffusion controlled limiting current obtained with the cathodic reduction of ozone according to O₃ + 2H⁺ + 2e^? → H₂O + O₂ in sulphuric acid. The electrolyte is vigorously mixed with the gas containing ozone and circulated through the electrolytic cell by the ascending gas flow operating as a gas-lift pump. The solution saturated with ozone moves along a cylindric electrode consisting of a smooth platinum foil in laminar flow. A constant potential is maintained at the electrode by means of a potentiostat in such a way, that the electrochemical reaction is proceeding under limiting current conditions. A lead anode of high capacitiy is used as a counter- and reference electrode. The current recorded continuously is directly proportional to the concentration of ozone in gas.     

Metal oxide semiconductor sensors for determination of reactive gas impurities in air

Characteristics of metal oxide semiconductor sensors intended for measuring O₃, NO _x , Cl₂, C1O₂, and HCl microconcentrations were discussed. Specific features of detection of these microimpurities with semiconductor sensors were determined. The size of signal generated by sensors with WO₃-, ZnO-, and In₂O₃-based sensing layers was examined in relation to the O₃, NO _x , Cl₂, C1O₂, and HCl concentration. The sensitivities exhibited by the semiconductor sensors with respect to target impurities make them suitable for measuring their maximum permissible concentrations in sanitary zones and for monitoring background ozone level in atmosphere. Examples of application of gas analyzers based on semiconductor sensors in determination of gas impurities in the open atmosphere were given.     

The sensor properties of Fe2O3 · In2O3 films: The detection of low ozone concentrations in air

The detection of low ozone concentrations in air (no higher than 120 ppb) using semiconducting films based on Fe₂O₃ · In₂O₃ obtained by laser ablation of the corresponding targets onto alumina substrates was studied. The temperature of the substrate during film deposition influenced their sensor properties. Temperature effects on the sensitivity of the films with respect to ozone were studied over the temperature range 200–380°C. Maximum sensitivity was reached at 250°C irrespective of the temperature of film deposition. The dependence of film sensitivity on the concentration of ozone in air was determined. At equal ratios between In₂O₃ and Fe₂O₃, the sensitivity of the sensor films prepared by laser ablation was much higher than that of thick-film sensors obtained from aqueous metal oxide suspensions by the stenciling technique. Possible reasons for the effects observed were considered.     

An Ozone Generator of Miniaturization and Modularization with the Narrow Discharge Gap

The method of ionization discharge has a key action on the process of the ionization and decomposition of O₂ molecule as well as the re-decomposition of O₃ molecule. In this paper, an ozone generation of miniaturization which was fabricated by stacking discharge modules with rectangle is introduced, only volume of 23.0×53.0×42.0 cm³ for ozone production capacity of 1 kg/hr. In addition, the ozone concentration and its production efficiency are significantly improved in comparison with a conventional ozone generator, which have the highest ozone concentration of 308 g/Nm³ and the production efficiency of 118 g/kWh at ozone concentration of 200 g/Nm³.     

A study of the cathodic reduction of ozone at the rotating disc electrode in acid electrolyte

The cathodic reduction of ozone according to O₃+2H⁺+2e^?→H₂O+O₂ was studied at a rotating disc electrode consisting of bright platinum in 1 M HClO₄ at 20°C. The current-potential curves obtained potentiostatically are determined by slow charge transfer in the range of low polarization (Tafel region) and diffusion as rate controlling step at high overvoltage. From the exchange current densities (i₀), obtained by extrapolation of Tafel lines to the reversible potentials, the heterogeneous rate constant k was evaluated giving an average value of 2.5×10^?7 cm s^?1. Likewise the diffusion coefficient (D_O3=1.7×10^?5 cm² s^?1) was calculated from the limiting currents measured at various partial pressures of ozone and different values of rotation rate. An equation for the total current-polarization curve was developed. The computed curves are in good agreement with the data which were obtained experimentally.     

Influence of Power Modulation on Ozone Production Using an AC Surface Dielectric Barrier Discharge in Oxygen

The measurements of electro-optical discharge characteristics and concentration of produced ozone were performed to evaluate the efficiency of ozone production in an AC surface dielectric barrier discharge (SDBD) in pure oxygen at atmospheric pressure. The discharge was driven in an amplitude-modulated regime with a driving AC frequency of 1 kHz, variable discharge duty cycle of 0.01–0.8 and oxygen flow rate of 2.5–10 slm. We observed asymmetric SDBD behaviour as evidenced by the variation in the ratio of the O^I/O₂ ⁺ emission intensities registered during the positive/negative half-periods and complemented by the transferred charge measurements through the Lissajous figures. We also found a strong dependence of O₃ concentration on the discharge duty cycle. The highest calculated ozone production yield reached 170 g/kWh with a corresponding energy cost of about 10 eV/molecule when combining the lowest inspected duty cycle with the lowest AC high voltage amplitude.     

Product Determination of Gaseous Radical Reactions Using Matrix Isolation-Ftir Detection

The matrix isolation technique with Fourier transform infrared detection has been applied to determine the products of gaseous radical reactions. The gas phase reactions were carried out in a discharge flow system and about 1% of the gas mixture was deposited onto a low temperature target through a pinhole. A differential pumping scheme was employed to maintain the pressure of the cryosystem below 10^?5 torr while that of the flow system was kept at about 2 torr. Species including HO₂ (from the H+O₂ reaction), ClO₂ (from the Cl+O₂ reaction) and ClO (from the Cl+O₃ reaction) have been produced in the gas phase and were successfully trapped in matrices and detected with an FTIR spectrometer. In addition, both HCl and HOCl have been detected as the reaction products from the gaseous ClO+HO₃ reaction. The production of HCl from the ClO+HO₂ reaction may have a significant impact on catalytic ozone destruction in the atmosphere.     

Molar absorption coefficient of ozone in aqueous solutions

The value of the molar absorption coefficient of ozone in aqueous solutions (2992 ± 71 M^–1 cm^–1 at 260 nm) is found based on the determination of ozone concentration by iodometry. This value is confirmed by the results of determination of O₃ concentration by reaction with the bromide ion and virtually coincides with the maximum absorption coefficient of ozone in the gas phase in the region the Hartley band. In the determinations of ozone concentration in aqueous solutions by direct spectrophotometry, we recommend the value of the molar absorption coefficient ε(О₃)₂₆₀ = 3000 M^–1 cm^–1.     

Photolysis of ozone in the ultraviolet region. Reactions of O(1D), O2(1Δg) and O≠2

Reactions of O(¹D) and O₂(¹Δ_g) with ozone have been observed time resolved by the detection of the product O³P) and their rate constants have been determined. It is found that vibrationally excited molecular oxygen, O^≠₂, also produces O(³P) in reaction with ozone. These observations are supported by the results of quantum yield determinations of the ozone decomposition in UV-photolysis.     

Deactivation of vibrationally excited ozone by O(3P) atoms

Using laser-induced fluorescence of ozone (to measure the rate of disappearance of O₃²) and NO₂ titration (to determine O atom concentrations), we have determined bimolecular rate constants for the deactivation by O(³P atoms) of ozone in excited stretching and bending modes. These experiments do not distinguish between deactivation by (a) the exchange of vibrational and translational energy or (b) the chemical reaction O₃ + O → 2O₂. If the non-reactive pathway (a) is assumed to dominate, then O(³P) is 150 times more effective than O₂ in deactivating O²₃. If chemical reaction (b) is dominant, the bimolecular rate constant for O²₃ + O(³P) is larger by a factor of 150–1500 than that for ground-state ozone.     

The Heterogeneous Reaction of Ozone on Carbonaceous Surfaces

Ozone, O₃, reacts with a carbon sample at room temperature. Clean carbon samples show a half to one and a half order of magnitude increased initial rate constant (k₀) for O₃ loss relative to repetitively exposed carbon samples. The ozone loss rate and therefore the rate constant reaches steady state (k_ss) on the time scale of tens of minutes, upon exposure to a characteristic dose of 8 × 10¹⁷ molecules for a 30-mg carbon sample independent of the flow rate. This characteristic dose closely corresponds to a monolayer of adsorbed ozone molecules on the carbon sample. Both k₀ and k_ss decrease with increasing flow rate of O₃ into the reactor, and the loss rate is found to depend on [O₃]. When the loss rate is plotted against the steady state concentration of O₃, a saturation plot results which is proportional to the surface coverage, θ, at a given [O₃].This interpretation rests upon a Langmuir type kinetics model with an assumed first-order dependence of the loss rate constant. The “sticking coefficients” track the rate constants and are on the order of 10^?3 to 10^?5 depending on the carbon sample, dose, and flow rate. Furthermore, k_o depends on the length of the dark period (absence of O₃ exposure) and is larger the longer time the sample has had to recuperate from previous O₃ exposures up to a period of 150 s. This surface relaxation is thought of as a time-dependent change in surface coverage taking place in the dark period and is therefore an indication of a slow surface diffusion/reaction that can be separated from the adsorption-desorption kinetics. The mass balance shows that for every ozone molecule that is lost on the surface, an oxygen molecule is found. This adsorbed odd oxygen is then responsible for product formation, which comprises the volatile components CO and CO₂ to an extent of 20 to 40% of the odd oxygen deposited on the surface. The difference is thought to be in a preoxidized state on the carbon sample, which evolves CO and CO₂ upon heat treatment.     

Gas‐Phase Reaction of Monomethylhydrazine with Ozone: Kinetics and OH Radical Formation

The gas‐phase reaction of monomethylhydrazine (CH₃NH? NH₂; MMH) with ozone was investigated in a flow tube at atmospheric pressure and a temperature of 295 ± 2 K using N₂/O₂ mixtures (3–30 vol% O₂) as the carrier gas. Proton transfer reaction–mass spectrometry (PTR‐MS) and long‐path FT‐IR spectroscopy served as the main analytical techniques. The kinetics of the title reaction was investigated with a relative rate technique yielding k_MMH+O3 = (4.3 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1. Methyldiazene (CH₃N?NH; MeDia) has been identified as the main product in this reaction system as a result of PTR‐MS analysis. The reactivity of MeDia toward ozone was estimated relative to the reaction of MMH with ozone resulting in k_MeDia+O3 = (2.7 ± 1.6) × 10^?15 cm³ molecule^?1 s^?1. OH radicals were followed indirectly by phenol formation from the reaction of OH radicals with benzene. Increasing OH radical yields with increasing MMH conversion have been observed pointing to the importance of secondary processes for OH radical generation. Generally, the detected OH radical yields were definitely smaller than thought so far. The results of this study do not support the mechanism of OH radical formation from the reaction of MMH with ozone as proposed in the literature.     

Ozonation of deciduous wood in the presence of hydrogen peroxide

The kinetic curves of the dependence of ozone specific absorption (Q _{r, sp} ) upon aspen wood ozonation in the presence and absence of hydrogen peroxide are obtained. It is established that the rate of ozone and Q _{r, sp} absorption increase in the O₃/H₂O₂ system. It is demonstrated by ESR, IR, and UV spectroscopy of diffuse reflection that wood ozonation in the O₃/H₂O₂ system results in the destruction of lignin aromatic and quinoid structures. The ozonation process in the presence of H₂O₂ is accompanied by destruction of the carbohydrate component of the lignocarbohydrate complex. We conclude that O₃/H₂O₂ can be used in the deep delignification of wood. It is shown that the presence of hydrogen peroxide upon ozonation increases the efficiency of the process, allowing its duration and total ozone consumption to be reduced.     

Interaction between gaseous ozone and crystalline potassium bromide

The formation of nonvolatile products of the oxidation of a bromide ion during the interaction between gaseous ozone and powdered crystalline KBr is studied. It is found that potassium bromate KBrO₃ is the main product of the reaction. The influence of major experimental factors (the duration of ozonation, the concentration of ozone, the humidity of the initial gas, and the temperature) on the rate of formation of bromate is studied. The effective constants of the formation of bromate during the interaction between O₃ and Br^– in a heterogeneous gas–solid body system and in a homogeneous aqueous solution are compared.     

Binary α-Fe2O3–Co3O4 nanostructures for advanced oxidation process: Role of synergy for enhanced catalysis

Iron and its binary oxides are meticulously exploited for environmental remediations. However, only limited studies have been carried out on the degradation of industrial organics by advanced oxidation process. In this study, iron oxide, cobalt oxide, and iron–cobalt binary oxides were synthesized by a modified hydrothermal method as heterogeneous Fenton-like catalysts for the removal of methylene blue (MB) from wastewaters. The oxide nanostructures were characterized by different analytical techniques. Studying the effects of various parameters such as catalyst dose, MB concentration, and H₂O₂ concentration, the reaction conditions were optimized to enhance the removal of MB dye. The results revealed that α-Fe₂O₃–Co₃O₄ shows much higher activity than both Co₃O₄ and α-Fe₂O₃ for the degradation of MB at room temperature and beyond. The binary α-Fe₂O₃–Co₃O₄ shows degradation efficiency of 96.4% at 65 °C within 60 min. Furthermore, the binary α-Fe₂O₃–Co₃O₄ catalyst retains its activity for up to four successive cycles. A probable mechanism is also proposed, involving the generation of ‧OH radical as well as Fe²⁺/Fe³⁺ or Co²⁺/Co³⁺ redox couple of the binary α-Fe₂O₃–Co₃O₄ catalyst.