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.     

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.     

Mechanism and kinetics of the reaction of ozone with sodium chloride in aqueous solutions

It is shown experimentally that Cl⁻ appreciably accelerates ozone decomposition in water (τ_1/2 = 1.5 h versus 6 h in pure water). The decomposition of ozone in NaCl solutions includes the reversible reaction of ozone with the chloride ion (O₃ + Cl⁻ → O₃⁻ + Cl) as the key step, which is followed by the development of a chain reaction in which chain propagation is performed alternately by the chlorine atom Cl and its monoxide ClO. The current concentrations of the chlorine atom are rather low ([Cl] ∼ 10⁻¹⁴ mol/l). The overall process is satisfactorily described by a first-order rate law with respect to ozone. The decomposition of ozone in aqueous solutions of NaCl is not accompanied by the formation of products other than oxygen. In particular, no noticeable amounts of hypochlorites and chlorates are observed. This is particularly significant for medicinal applications of ozonized isotonic solutions.     

The solubility of ozone and kinetics of its chemical reactions in aqueous solutions of sodium chloride

The solubility of ozone and the kinetics of its decomposition and interaction with chloride ions in a 1 M aqueous solution of NaCl at 20°C and pH 8.4–10.8 were studied. The ratio between the concentration of O₃ in solution and the gas phase was found to be 0.16 at pH 8.4–9.8. The concentration of dissolved ozone decreased sharply as pH increased to 10.8 because of a substantial increase in the rate of its decomposition. It was observed for the first time that the interaction of O₃ with Cl^? in alkaline media resulted in the formation of ClO ₃ ^? chlorate ions. The dependence of the rate of formation of ClO ₃ ^? on pH was determined; its maximum value was found to be 9.6 × 10^?6 mol l^?1 min^?1 at pH 10.0 and the concentration of ozone at the entrance of the reactor 30.0 g/m³. A spectrophotometric method for the determination of chlorate ions (concentrations 1 × 10^?5?3 × 10^?4 M) in aqueous solutions was suggested.     

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.     

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.     

Metastable intermediates in the formation of ozone by recombination

The rate of formation of ozone by O(³P) + O₂(³Σ_g⁻) recombination following an energy pulse such as flash photolysis or pulse radiolysis is typically only about half the rate of disappearance of O(³P). Measurements of the growth of the Hartley band of ozone under several experimental conditions are shown to be consistent with reaction of 0.62 of the available O(³P) to form a metastable state of ozone. Deactivation of the metastable state by ground state O₂ is slow (approximately 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹), but it is significant because of its large excess. Deactivation and decomposition of the metastable state by singlet molecular oxygen is rapid.     

3d Metal complexes with 2-hydroxy-3-methoxybenzaliminopropyl and 4-hydroxy-3-methoxybenzaliminopropyl immobilized on aerosil as catalysts of ozone decomposition

The composition and structure of M(II) (Mn, Co, Cu) complexes with Schiff bases (L1 = 2-hydroxy-3-methoxybenzaliminopropyl, L2 = 4-hydroxy-3-methoxybenzaliminopropyl) immobilized on Aerosil and their catalytic activity in ozone decomposition were studied. The formation of pseudotetrahedral bisligand complexes M(L1)₂ and pseudooctahedral complexes M(L2)₂ on the modified surface of Aerosil was confirmed by IR and ESR spectroscopy and by diffuse reflectance spectroscopy (DSR). The catalytic activity of isostructural complexes in ozone decomposition varies in the order Mn > Co > Cu, and M(L₂)₂ complexes are more active than M(L1)₂.     

Study on catalytic mechanisms of Fe3O4-rGOx in three typical advanced oxidation processes for tetracycline hydrochloride degradation

This study explored the catalytic mechanism and performance impacted by the materials ratio of Fe₃O₄-GO_x composites in three typical advanced oxidation processes (AOPs) of O₃, peroxodisulfate (PDS) and photo-Fenton processes for tetracycline hydrochloride (TCH) degradation. The ratio of GO in the Fe₃O₄-GO_x composites exhibited different trends of degradation capacity in each AOPs based on different mechanisms. Fe₃O₄-rGO_20wt% exhibited the optimum catalytic performance which enhanced the ozone decomposition efficiency from 33.48% (ozone alone) to 51.83% with the major reactive oxygen species (ROS) of O₂^??. In PDS and photo-Fenton processes, Fe₃O₄-rGO_5wt% had the highest catalytic performance in PDS and H₂O₂ decomposition for SO₄^??, and ^?OH generation, respectively. Compared with using PDS alone, PDS decomposition rate and TCH degradation rate could be increased by 5.97 and 1.73 times under Fe₃O₄-rGO_5wt% catalysis. In the photo-Fenton system, Fe₃O₄-rGO_5wt% with the best catalyst performance in H₂O₂ decomposition, and TCH degradation rate increased by 2.02 times compared with blank group. Meantime, the catalytic mechanisms in those systems of that the ROS produced by conversion between Fe²⁺/Fe³⁺ were also analyzed.     

Cement-containing catalysts of ozone decomposition based on iron oxides

Cement-containing catalysts of ozone decomposition were synthesized on the basis of iron oxides obtained by ozonation of iron-containing aqueous solutions. X-ray diffraction analysis and Mössbauer spectroscopy showed that α-Fe₂O₃ occurs in the catalyst as highly dispersed nanoparticles. The catalysts obtained are efficient in the reaction of ozone decomposition and are as active as the best representatives of cement-containing catalysts of the GTT type.     

Photocatalytic performance of Pt-loaded TiO2 in the decomposition of gaseous ozone

Gas-phase catalytic and photocatalytic decomposition of ozone (O₃) was investigated using TiO₂ and Pt-loaded TiO₂ (Pt/TiO₂) at room temperature and atmospheric pressure. The nominal weight loading of Pt was less than 1 wt.%. Results of this study indicate that both the overall conversion of O₃ to O₂ and other products with UV irradiation and without UV irradiation (dark reaction) can be improved by using Pt-loaded TiO₂. Photocatalytic conversion of O₃ on pure TiO₂ decreased with increasing water vapor. In contrast, Pt/TiO₂ was active for the decomposition of ozone under the humidity condition at room temperature.     

Oxidative decomposition of oxalate ion with ozone in aqueous solution

The oxidation of oxalate ions with ozone in aqueous solution has been studied, and the effects of pH, temperature, and reactant concentrations on the reaction rate and efficiency have been estimated. The oxidative decomposition is most effective in alkaline medium (pH ≥ 10) at 50°C. Under these conditions, the consumption of ozone is 0.6±0.1 g per gram of oxalate or 1.1±0.1 mol per mole of oxalate, which corresponds to the stoichiometry (COO^–)₂ + O₃ + H₂O → 2CO₃^2– + O₂ + 2H⁺.     

Effect of silver and copper ions on the decomposition of ozone in water

Features of the kinetics of ozone decomposition in water at pH 2 are studied depending on the concentration of silver and copper ions that are present. The existence of a critical concentration of metal ions (??3?6 × 10^?6 M) is established, below which ions slow the rate of ozone decomposition and above which the accelerate the process. It is concluded that the first region is due to the capture of hydroxyl and other radicals by metal ions, inhibiting the chain of ozone decomposition in water. A further increase in the concentration of ions leads to dominance of their direct interaction with molecules of ozone. A mechanism for the process is proposed and the rate constants of reaction of ozone with silver ions and copper are calculated (0.033 and 0.06 M^?1 s^?1, respectively).     

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     

Effect of Cl− anions on photocatalytic decomposition of gaseous ozone over Au @ Ag/TiO2 catalyst

Au core Ag shell composite structure nanoparticles were prepared using a sol method. The Au core Ag shell composite nanoparticles were loaded on TiO₂ nanoparticles as support using a modified powder–sol method, enabling the generation of Au @ Ag/TiO₂ photocatalysts for photocatalytic decomposition and elimination of ozone. The sols were characterized by means of ultraviolet–visible light (UV–Vis) reflection spectrometry, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The activity of the Au @ Ag/TiO₂ photocatalysts for photocatalytic decomposition and elimination of ozone was evaluated and the effect of Cl^? anions on the photocatalytic activity of the catalysts was highlighted. Results showed that Au @ Ag/TiO₂ prepared via the modified powder–sol route in the presence of an appropriate amount of NaCl solid as demulsifier had better activity in the photocatalytic decomposition and elimination of ozone. At the same time, Au @ Ag/TiO₂ catalysts had better ability to resist poisonous Cl^? anions than conventional Au/TiO₂ catalyst. The reasons could be, first, that NaCl was capable of reducing the concentration of free Ag⁺ by adsorption on the surface of Ag particles forming AgCl and enhancing the formation of Au core Ag shell particles, leading to a better resistance to Cl^? anions of the catalysts, and, second, AgCl took part in the photocatalytic decomposition of ozone together with Au @ Ag/TiO₂ catalysts and had a synergistic effect on the latter, resulting in better photocatalytic activity of Au @ Ag/TiO₂ catalysts.     

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.     

Free-radical chain decomposition of ozone initiated by di(tert-butyl) trioxide

Di(tert-butyl) trioxide in a solution of CFCl₃ (Freon-11) at –23 °C exists in equilibrium with the tert-butoxyl and tert-butylperoxyl radicals virtually without irreversible decomposition. The above radicals decompose ozone to dioxygen with a high effective rate constant, which is proprotional to the square root of the Bu^tOOOBu^t concentration. The kinetic scheme describing the found relationships was proposed.     

Decomposition of Cyanogen Chloride by Using a Packed Bed Plasma Reactor at Dry and Wet Air in Atmospheric Pressure

The decomposition rate of CNCl in a BaTiO₃-filled Packed Bed Plasma Reactor was studied as a function of AC input power, power frequency, residence time in the reactor, and inlet flow rate. The decomposition rate was compared with those of CH₃CN and CCl₂CHCl. Under the condition of 6.7 Wh/m³ specific energy den- sity, the decomposition rate of CNCl was found to be 50%, which is lower than those of CH₃CN and CCl₂CHCl at the same or similar conditions. At a higher frequency of the power input system, the decomposition rate of inlet gas becomes lower due to a decrease in field strength for the same level of power. And, under the same level of input power, a higher decomposition rate was obtained at an increased residence time. The relation between gas decomposition rates stemmed from the electron–molecule collision and bounding energy within the molecule. The decomposition ratio of CNCl was lower than those of CCl₂CHCl and CH₃CN because the bond strength of the weakest bond in the molecule is higher. In order to test the decomposition efficiency of CNCl with catalytic packing material in a plasma reactor, the catalyst of γ-Al₂O₃ and Pt/γ-Al₂O₃ was packed in the packed bed plasma reactor. Although byproducts were formed, the plasma-catalyst hybrid reactor containing Pt/γ-Al₂O₃ showed a higher efficiency in CNCl decomposition as shown in the decomposition rate of above 99% in 0.3 kWh/m³.     

Primary stage of the reaction between ozone and chloride ions in aqueous solution: Oxidation of chloride ions with ozone through the mechanism of oxygen atom transfer

Relying on experimental data on products and the kinetic features of the complex reaction between O₃ and Cl⁻(aq), we establish that the primary stage of the reaction proceeds via a mechanism in which an oxygen atom is transferred from an ozone molecule to a chloride ion. Analyzing the thermodynamic parameters of the primary stage, we conclude that a long-lived intermediate complex of a chloride ion and ozone is initially formed. The mechanism of acid catalysis in the reaction between O₃ and Cl⁻(aq) is described as the formation of a protonated intermediate complex, HO₃Cl, in the acidic medium and its rapid decomposition toward the formation of products.     

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.