Some aspects of the ozone degradation of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVAL) forms a strong hydrogen-bond complex with ozone. The interaction energy is of the order of 47.3 kJ/mol as calculated from the blue shift undergone by the ozone absorption band in the UV after its complexation with PVAL. This fact may have many important practical implications in the application of PVAL in wastewater treatment both in terms of O₃ dissolution and persistence in water. Furthermore, PVAL is easily biodegradable but it is also slowly degraded by ozone. It is shown by viscometry, electrical conductimetry and by pH measurements that PVAL is degraded by ozone attack with extensive chain breaking. By FT-IR spectroscopy it has been shown that the final product is a PVAL oligomer with numerous ketonic groups along the main oligomer backbone and with carboxylic end groups. A mechanism of ozone degradation of PVAL has been presented and discussed. The chain scission is based on the ozone oxidation of the alcoholic groups of PVAL with formation of ketonic groups which in turn are the source of a keto-enol tautomerism which leads to random chain scission by further O₃ attack. Viscometric measurements show that the main viscosity drop of PVAL is achieved when a nominal stoichiometric ratio of O₃/PVAL < 0.05 is reached which means one ozone molecule for every >20 PVAL monomeric units. For comparison PVAL has been oxidized also with paraperiodic acid.Ozonized PVAL has been studied by thermal analysis (TGA, DTG and DTA) in comparison to a reference untreated PVAL under N₂. The oxidation of PVAL causes its complete amorphization since the crystalline melting point of PVAL at 235 °C is no longer detectable in the case of ozonized PVAL. In any case ozonized PVAL shows a better thermal stability which can be confirmed for instance by a higher maximum decomposition rate temperature as measured by DTG. This result is in agreement with theoretical calculations made by group increments according to Van Krevelen's method which predicts a higher decomposition temperature for a PVAL having ketonic groups in place of alcoholic moieties in the main polymer backbone.     

臭氧与二乙胺和三乙胺气相反应的速率常数

利用自制的烟雾箱系统研究了臭氧与二乙胺和三乙胺的气相反应动力学. 实验过程中保证二乙胺和三乙胺浓度远远大于臭氧浓度, 使得实验在准一级条件下进行. 加入环己烷以消除实验过程中可能产生的OH自由基对反应的影响. 在(298±1) K和1.01×105 Pa条件下, 测得臭氧与二乙胺和三乙胺反应的绝对速率常数值分别为(1.33±0.15)×10^-17和(8.20±1.01)×10^-17 cm³·molecule^-1·s^-1. 与文献中已有的其它胺类的臭氧反应数据比较后发现, 臭氧与胺的反应可以用亲电反应机制来解释. 另外, 通过对比发现, 臭氧与三取代的烷基胺类的反应速率要远远大于其与二取代的烷基胺类的反应速率. 这在一定程度上可有助于解释外场观测到的气溶胶相中二烷基胺盐较多的事实. 利用测得的速率常数和大气中臭氧浓度, 还估算了二乙胺和三乙胺与臭氧反应的大气寿命. 结果显示, 与臭氧的反应是二乙胺和三乙胺在大气中的一种重要的消除途径, 尤其是在污染严重地区.     

Studies on Oxidants' Generation in a Foaming Column with a Needle to Dielectric Covered Plate Electrode

The generation of oxidative products in the newly investigated foaming system was improved by a discharge between a high voltage multineedle electrode and a dielectric covered plate electrode. A uniformity of the discharge was observed. The presence of alumina dielectric seems to be responsible of the homogenous spatial distribution of the discharge. The absolute power and energy of the discharge was determined. Besides, in larger gap space the foam quality was improved.This way of oxidant's generation, which might be prospective for the treatment of exhaust gas and wastewater, has not been investigated by the other researchers' groups as yet. During the laboratory test 875 ppm of gaseous ozone, 0.5 mg/l of dissolved ozone and 62 mg/l of hydrogen peroxide was obtained at 14 kV of applied voltage and 5 l/min of oxygen gas flow in the present configuration used for the discharge generation. The average yield of gaseous ozone production ranged 55 gO₃/kWh.     

玻璃纤维表面的乙烯基单体接枝聚合

用玻璃纤维表面处理剂ＭＡＣ处理玻璃纤维后，再进行臭氧处理，使玻璃纤维的表面产生活性中心，引发苯乙烯、甲基丙烯酸甲酯、及丙烯酸等乙烯基单体在玻璃纤维表面上接枝聚合。接枝纤维的密度减小，对水的浸润性下降，红外光谱及扫描电镜观察证明玻璃纤维表面上接枝聚合物的存在。     

Nonempirical Description of the Atmospherically Important Anionic Species. II. Hydrated Ozone Anions

Ozone–water clusters are nonempirically modeled in the complete active space self-consistent field approximation (CASSCF) with the energetic estimates obtained at the multiconfiguration quasidegenerate perturbation theory level (MCQDPT) with 6–31++G** basis set. Coordination of a neutral ozone molecule to small water clusters is either surface or interior, with the binding energy of the order of a weak hydrogen bond. Upon localization of an excess electron, the hydration of ozone becomes strong. The adiabatic affinities of water–ozone clusters and the energies of electron detachment from their anions, depending on the number of water molecules, estimate the electron hydration and vertical electron detachment thresholds of water or ice that superficially coordinates minor amounts of ozone.     

A nanometer-ZnO catalyst to enhance the ozonation of 2,4,6-trichlorophenol in water

Removal of 2,4,6-trichlorophenol (TCP) from water has been accomplished through zinc oxide (ZnO) catalytic ozonation. In the presence of ZnO catalyst, aqueous ozone (O₃) can be described by a two-stage behavior, first involving a short-term rapid decomposition followed by a second slow decomposition. The low reaction rate (k_d2) of second stage for O₃-ZnO systems suggested that most of O₃ was transferred into OH radical by ZnO catalyst and was rapidly consumed during the first stage. The combined use of O₃ and ZnO catalyst leads to a conspicuous 99.8% of TCP conversion in 30 min which compares favorably to the hardly 75% reached in the absence of the catalyst. The high reactivity of hydroxyl radicals that were generated by O₃-ZnO during the oxidation process effectively degraded TCP. Without regard to the O₃ dose, the catalytic–oxidation kinetics of the process depends on the concentration of ZnO catalyst and size of ZnO particles. At the same concentration of three different ZnO size in batch tests, TCP degradation rates were in the order of nanometer > submicrometer > micrometer. The effect of pore diffusion on the rate of TCP–ZnO reactions was determined by examination of the effectiveness factor using different particle sizes of ZnO. Calculations show that the rate of TCP decomposition by nano-size ZnO was strongly controlled by surface reaction with little influence of pore diffusion, as indicated by the high effectiveness factors.     

Update of the anharmonic force field parameters of the ozone molecule

A new set of spectroscopic constants of the ¹⁶O₃ molecule (ω_i, x_ij, y_ijk, γ^DD, _i^X, β_ij^X,…), which determine vibrational dependence of band centres and rotational parameters, is derived from recent accurate analysis of high-resolution experimental ro-vibrational spectra through the theoretical approach based on second-order perturbation expansions in normal coordinates accounting for Darling–Dennison resonance interactions. These values are used to update empirical values of anharmonic coefficients (k_ijl, k_ijlm) of the potential function expansion in normal coordinates. Quadratic f_rr, f_r, f_rr′, f as well as cubic f_rst and quartic f_rstl force constants in internal (bond lengths, bond angle) coordinates are also derived. A detailed discussion is devoted to the accuracy of parameter determination for each of four steps of calculations. It is emphasised that the conventional method based on the inversion of formulae of the perturbation theory gives the largest uncertainties at the last step of calculations: the determination of the anharmonic force field in internal coordinates.     

Ozone production and de-NO x modeling in dry air electrical discharges

Numerical simulations are performed to assess the possibility of using different kinds of electrical discharges operating in dry air under normal conditions as ozone generators. The ozone production and NO_x destruction efficiency are investigated as a function of discharge parameters such as the reduced electric field, the energy deposition, and the electron density. The specific energy deposition becomes a key parameter to compare the different classes of ozonators. During the operative phase the electric discharge produces an appreciable amount of nitrogen oxides. Taking into consideration both the active phase of flue gas processing and the post-discharge phase it is possible to achieve a good NO_x-removal efficiency even for initial concentrations as high as 1000 ppm. The main processes and characteristic times are discussed.     

Ozone Degradation of Polycyclic Aromatic Hydrocarbons Adsorbed on Asbestos

Abstract

The polycyclic aromatic hydrocarbons (PAH) represent a major source of pollution. The adsorption properties of chrysotile give us a good application as an asbestos filter and the regeneration can be made by ozonolysis for a complete destruction to non toxic compounds.     

Biocidal action of ozone-treated polystyrene surfaces on vegetative and sporulated bacteria

Surfaces of materials can be modified to ensure specific interaction features with microorganisms. The current work discloses biocidal properties of polystyrene (PS) Petri-dish surfaces that have been exposed to a dry gaseous-ozone flow. Such treated PS surfaces are able to inactivate various species of vegetative and sporulated bacteria on a relatively short contact time. Denaturation of proteins seems likely based on a significant loss of enzymatic activity of the lysozyme protein. Characterization of these surfaces by atomic-force microscopy (AFM), Fourier-transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) reveals specific structural and chemical modifications as compared to untreated PS. Persistence of the biocidal properties of these treated surfaces is observed. This ozone-induced process is technically simple to achieve and does not require active precursors as in grafting.