Surface Reaction of Ozone at High Concentration with Isotactic And Syndiotactic Polypropylene

The surface reaction of isotactic and syndiotactic polypropylene (I-PP and S-PP) films with ozone was studied with FT-IR spectroscopy with differential scanning calorimetry (DSC) and making use of 2,2,4-trimethylpentane as a model compound of PP chain segment. I-PP and S-PP were found reactive toward ozone, and it was found that I-PP being more crystalline than S-PP, reacts more slowly with O₃. In fact, the pseudo first rate constant of I-PP with ozone was k’_I-PP = 8.0 × 10^?6 s^?1 while that of S-PP with ozone k’_S-PP = 1.3 × 10^?5 s^?1. However, the DSC study has shown that the ozone attack on I-PP or S-PP films is not selective and simultaneously destroys the amorphous and the crystalline phases. The ozone treated I-PP and S-PP films are much less resistant to the combined thermal and oxidative degradation reaction than the unexposed films. Thus, ozone is a naturally occurring pollutant at the soil level which accelerates the ageing of I-PP and S-PP materials.     

Chemiluminescence in the ozonation of C60 aqueous dispersions

Two types of chemiluminescence (CL) arising upon ozonation of crystalline, amorphous, and molecular aqueous dispersions of C₆₀ prepared in different ways were discovered and studied. The weak long-wavelength CL-1 (λ_max > 650 nm) is due to thermocatalytic decomposition of ozone on the surface of fullerene micro- and nanoparticles. The bright short-wavelength CL-2 (λ_max = 570 nm) is caused by generation of electronically excited states of the products of C₆₀ oxidation with ozone. CL-1 appears upon ozonation of aqueous dispersions of C₆₀ consisting of surface-hydrated crystalline micro- and nanoparticles by low concentrations of ozone. CL-2 is exhibited upon ozonation of nano-sized C₆₀ aqueous dispersions and colloid solutions, which contain C₆₀ molecules surrounded by a strong aqueous shell and their associates, by higher concentrations of ozone. Owing to shielding by the hydration shell, C₆₀ fullerene in aqueous dispersions is much less reactive towards ozone and forms oxidation products of different composition as compared with C₆₀ in organic solvents.     

Photochemical production of ozone in marine boundary layer in the sea of Japan: Results of the Rishiri Fall Experiment campaign

The Rishiri Fall Experiment (RISFEX ) campaign was performed in September 2003 at Rishiri island (45.07 N, 141.12 E, and 35 m asl) in the sea of Japan to investigate photochemical production of ozone in the marine boundary layer. Total peroxy radicals RO _x (HO₂ + RO₂) and NO _x (NO + NO₂) were measured together with other chemical species and physical parameters relevant to ozone production. The ozone production rate (P(O₃)) was estimated from measured peroxy radicals and was found to be highly variable between days, with 30-min averaged midday values varying from 0.2 to 1.7 ppbv/h (ppbv refers to part per billion by volume). The daytime mean P(O₃) for the air masses from relatively clean NE sector is close to zero, but significantly higher for air masses from more polluted W and SE sector, suggesting the impact of transport of pollutants on the remote local ozone production. The experimentally determined P(O₃) is compared with those derived from a time-dependent box model based on Regional Atmospheric Chemistry Modeling (RACM), and both the methods give the results generally in agreement. The model calculation shows that HO₂ + NO reaction contributes most to ozone production, ca. 60% at midday, followed by the reactions of CH₃O₂ and ISOP (peroxy radicals formed from isoprene) with NO which account for ca. 13% and 10% to ozone production, respectively, at noon. Sensitivity analysis indicates that the ozone production during the measurement period is within NO _x -limited regime.     

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.     

Model Studies on the Ozone-Mediated Synthesis of Cobalt Oxide Nanoparticles from Dicobalt Octacarbonyl in Ionic Liquids

Low-temperature synthesis in ionic liquids (ILs) offers an efficient route for the preparation of metal oxide nanomaterials with tailor-made properties in a water-free environment. In this work, we investigated the role of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C₄C₁Pyr][NTf₂] in the synthesis of cobalt oxide nanoparticles from the molecular precursor Co₂(CO)₈ with ozone. We performed a model study in ultra-clean, ultrahigh vacuum (UHV) conditions by infrared reflection absorption spectroscopy (IRAS) using Au(111) as a substrate. Exposure of the pure precursor to ozone at low temperatures results in the oxidation of the first layers, leading to the formation of a disordered Co_xO_y passivation layer. Similar protection to ozone is also achieved by deposition of an IL layer onto a precursor film prior to ozone exposure. With increasing temperature, the IL gets permeable for ozone and a cobalt oxide film forms at the IL/precursor interface. We show that the interaction with the IL mediates the oxidation and leads to a more densely packed Co_xO_y film compared to a direct oxidation of the precursor.     

Ozone generation on the lead dioxide electrodes in a sulfuric acid solution at potentials of 2 to 3 V

The electrochemical synthesis of ozone is studied on lead dioxide electrodes in sulfuric acid solutions. The two maximums of the current efficiency for ozone (CEO) observed at 2–3.5 V are largely due to the participation of various chemisorbed particles in the ozone synthesis. In the vicinity of the first CEO maximum at lead dioxide, ozone forms only in a discharge of water molecules with the participation of adsorbed oxygen-containing radicals. In the potential range of the second maximum, the adsorbed anion radicals, e.g., ·HSO₄ and ·SO₄, also take part in the reaction of ozone generation. At the electrode not subjected to anodic polarization, CEO is considerably higher than that on the preliminarily polarized electrode. On the basis of the experimental data, schemes for the ozone evolution at PbO₂ in sulfuric acid at 2 to 3 V are proposed.     

Semiconductor Sensors for Studying the Heterogeneous Destruction of Ozone at Low Concentrations

Prospects for the use of semiconductor resistive sensors in studies of the heterogeneous destruction of ozone at low concentrations (5–400 μg/m³) were shown. The influence of various factors (sensor temperature, gas flow rate, ozone concentration) on the results of ozone concentration measurements with sensors of various types was studied. Methods for forming a sensitive layer of In₂O₃(3% Fe₂O₃) sensors with specified parameters of calibration curves were proposed. The optimum conditions for the operation of sensors in a flow mode were formulated. The results of the study of heterogeneous destruction of ozone on microfiber polymer and natural disperse (sand, coals) materials obtained by the developed method were presented.     

Effect of atmospheric pressure on ozone cracking of rubber

Ozone chamber testing of rubbers occupies a prominent place in the field of polymeric degradation testing. In such testing the rate of ozone cracking of rubber vulcanizates is a function of the rate of collision of ozone molecules with the rubber surface, all other factors constant. However, the conventional mode of expression of the ozone concentration in chamber testing is on a volume O₃ per volume air basis, i.e. parts O₃ per hundred million (10⁸) air by volume, abbreviated by pphm.In this paper we show that at equal ozone concentrations expressed as pphm, cracking rate is a function of the ambient atmospheric pressure (in the chamber). Thus variations in ozone test results may occur in intra- or inter-laboratory testing if ambient atmospheric pressure at the time or place of test is sufficiently different. A mode of expression that avoids this is recommended, i.e. the partial pressure of O₃ in mPa.     

Surface Modification of (001) Facets Dominated TiO2 with Ozone for Adsorption and Photocatalytic Degradation of Gaseous Toluene

This study investigated the positive effect of surface modification with ozone on the photocatalytic performance of anatase TiO₂ with dominated (001) facets for toluene degradation. The performance of photocatalyst was tested on a home-made volatile organic compounds degradation system. The ozone modi cation, toluene adsorption and degradation mechanism were established by a combination of various characterization methods, in situ diffuse reflectance infrared fourier transform spectroscopy, and density functional theory calculation. The surface modi cation with ozone can significantly enhance the photocatalytic degradation performance for toluene. The abundant unsaturated coordinated 5c-Ti sites on (001) facets act as the adsorption sites for ozone. The formed Ti-O bonds reacted with H₂O to generate a large amount of isolated Ti_5c-OH which act as the adsorption sites for toluene, and thus significantly increase the adsorption capacity for toluene. The outstanding photocatalytic performance of ozone-modified TiO₂ is due to its high adsorption ability for toluene and the abundant surface hydroxyl groups, which produce very reactive OH radicals under irradiation. Furthermore, the O₂ generated via ozone dissociation could combine with the photogenerated electrons to form superoxide radicals which are also conductive to the toluene degradation.     

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.     

Isomeric structures of protonated ozone: A theoretical study

Ab initio molecular orbital calculations have been used to determine the structure of protonated ozone. Four stable minima were found on the O₃H⁺ singlet potential energy surface. Three forms correspond to ozone protonated at the central oxygen (C_2v) or at the terminal oxygen (two C_s isomers, E and Z). The fourth isomer (C_s) is a derivative of trioxirane. The most stable structure is the planar E form I. The proton affinity of ozone (to give I) is given as 123.6 kcal/mole (MP2/6-31G*//4-31G). The energy difference between I and protonated trioxirane VI is greater than that between ozone and trioxirane.     

The solubility and kinetics of decomposition of ozone in aqueous solutions of nitrates

The influence of the concentration of NaNO₃ on the solubility of ozone in water was studied at 20, 30, and 40°C. The solubility coefficients of ozone were calculated, and the Henry constants and Sechenov coefficients determined. The Sechenov coefficients (K _c ) were found to decrease insignificantly as the temperature increased. The kinetics of dissolved O₃ transformations was analyzed. The decomposition of ozone was described by a pseudofirst-order equation with respect to salt concentration. The rate constant (k _c ) for the decomposition of ozone in the presence of NaNO₃ was found to be 3.5 × 10^?4 l mol^?1 s^?1.     

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.     

Ozone decomposition in concentrated aqueous solutions of salts

Effect of high concentrations of electrolytes (Na₂SO₄, NaCl, and NaNO₃) on the rate of ozone decomposition in water was studied. The conversion kinetics of O₃ dissolved in these solutions was analyzed. The rate constants of ozone decomposition were determined.     

Kinetics of the Reaction of Ozone with tert-Butanol

The kinetics of tert-butanol (ROH) oxidation by ozone in CCl₄ and H₂O solutions at 295 K is studied by spectrophotometry under batch conditions. The rate-limiting step of the process in both solvents is the reaction of ozone with the monomeric form of ROH. In H₂O, the hydrated molecules of ROH and ozone react with each other. In CCl₄, the association of ROH molecules, which changes the kinetics and mechanism of the process, should be taken into account. The reaction kinetic parameters and the dimerization constant of ROH in CCl₄ are determined.     

Characteristics of the Discharge and Ozone Generation in Oxygen-Fed Coaxial DBD Using an Amplitude-Modulated AC Power Supply

In this study, a traditional tubular reactor and an amplitude-modulated AC power supply were employed to develop a unique practical ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. The characteristics regarding discharge and ozone generation in oxygen were experimentally investigated in detail. The amplitude-modulated AC waveform consisted of T_ON (burst of four consecutive AC cycles) and T_OFF with a duty cycle of 0.4. The experimental results show that a unique ozone generator can be developed through changing the applied voltage amplitude when an amplitude-modulated AC power supply producing periodic bursts of several consecutive AC cycles during the T_ON period is used. A quite high and stable ozone yield of 165?±?16 g/kWh was achieved and a wide range of ozone concentrations could be obtained. Moreover, we observed a very interesting phenomenon that the discharge energy and voltage peak for every AC cycle showed some difference, resulting from the accumulation and release of charge on the dielectric. The first AC cycle had the highest discharge energy and positive voltage peak as well as the lowest negative voltage peak, which was particularly obvious at a high energy density. Additionally, water cooling of the grounded electrode seemed to have a small influence on the basic electrical characteristics of the discharge and had a positive effect on the concentration and yield of ozone due to a reduction in gas temperature in the discharge gap.     

Efficient ozone decomposition over bifunctional Co3Mn-layered double hydroxide with strong electronic interaction

Ground-level ozone is one of the primary pollutants detrimental to human health and ecosystems. Catalytic ozone decomposition still suffers from low efficiency and unsatisfactory stability. In this work, we report a manganese-based layered double hydroxide catalyst (Co₃Mn-LDH), which exhibited a superior ozone decomposition performance with the efficiency of 100% and stability over 7 h under a GHSV of 2,000,000 mL g^?1h^?1 and relative humidity of 15%. Even when the relative humidity increased to 50%, the ozone decomposition also reached 86%, which significantly exceeds as-synthesized MnO₂ and commercial MnO₂ in performance. The catalytic mechanism was studied by H₂-TPR, FT-IR and XPS. The excellent performance of Co₃Mn-LDH can be attributed to its abundant surface hydroxyl groups that ensured the preferentially surface enrichment of ozone, as well as the cyclic dynamic replenishment of electrons between multivalent Co²⁺/Co³⁺, Mn²⁺/Mn³⁺/Mn⁴⁺ and oxygen species that endowed the stable ozone decomposition. This work offers new insights into the design of efficient catalysts for ozone pollution control.     

Ozone solubility in concentrated aqueous solutions of salts

The effect exerted by the concentration of salts (NaCl, Na₂SO₄, and NaNO₃) on the ozone solubility in aqueous solution at 20, 30, and 40°C was studied. The solubility coefficients of ozone were calculated. The Henry constants and the Sechenov coefficients were determined.     

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.     

A pathway of free radical generation via copper corrosion and its application to oxygen and ozone activation for the oxidative destruction of organic pollutants

This study investigated the commercially available zero-valent copper powder and copper foil to activate molecular oxygen (O₂) and ozone for the degradation of organic pollutants. Under aerobic atmospheric conditions, copper powder effectively removed 50 mg/L of acetaminophen (ACT) within 2 h, though the degradation rate using the foil was less than 20% of the powder. However, copper foil activated ozone to effectively degrade ACT. The total organic carbon (TOC) removal reached a high of 58.3% at a catalyst concentration of 40 g/L, but only 26.8% with ozone alone. The initial solution pH and dosage of copper foil were key operational parameters affecting the ozone activation process. H₂O₂ and Cu(I) were important intermediates in the process as hydroxyl radicals (^·OH) were identified via EPR (electron paramagnetic resonance) experiments and free radical scavengers. The generation of ^·OH was attributed to a Fenton-like reaction between Cu(I) and H₂O₂; this free-radical generation mechanism differs from typical transition metal oxide catalysts. This study outlines a promising approach to significantly increase the generation of ^·OH and effectively remove refractory organic compounds. Furthermore, these copper products are applied in structural components of practical water treatment. Thus, the study of corrosion resistance to oxygen and ozone in aqueous solution have both a practical and theoretical significance. It was determined that copper products were resistant to oxygen corrosion in aqueous solution, but not resistant to ozone corrosion.