The kinetics of ozone decomposition in water,the influence of pH and temperature

The influence of pH on the kinetics of ozone decomposition in water was studied. Over the pH range 1–8, the kinetics was well described by a second-order reaction equation. Starting with approximately pH 3, the pH dependence of the logarithm of the constant at 19°C corresponded to the equation logk= −2.66 + (0.49 ± 0.03)pH. The activation energy of ozone decomposition was found to be 76.0 ± 8.3 kJ/mol.     

The microwave influence on the electrolytic decomposition of KOH water solution

The effect of microwaves (MW) on the electrolytic process of 6 M KOH water solutions was investigated in the temperature range from 291 K to 337 K. At lower temperatures, microwaves facilitated electrolytic process, whereas the effect is reversed at higher temperatures.     

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).     

The mechanism of the acid-catalyzed decomposition of the farnesyl phosphates

The rates and (in some cases) products of the acid-catalyzed decomposition of (Z,E)- and (E,E)-farnesyl phosphate, (Z,E)- and (E,E) - 1,1 - dideutereofarnesyl phosphate, (Z)- and (E) - 6,7,10,11 - tetrahydrofarnesyl phosphate, and t-butyl phosphate have been studied in an attempt to determine whether (Z,E)-farnesyl phosphate ionizes with intramolecular assistance from the C-6/C-7 double bond or via an unassisted process leading to a simple allylic cation. Data in support of both possibilities are adduced, but it is concluded, primarily on the basis of the secondary deuterium kinetic isotope effects, that the ionization involves little, if any, assistance from the double bond.     

臭氧在金属氧化物上的分解机理

臭氧分解反应在环境科学中具有重要理论和实际意义。本文对近期相关文献进行了综述，对臭氧在固体催化剂表面上的吸附和分解过程进行了总结，并结合我们的实验对其分解机理进行了探讨。     

The influence of aluminum on the thermal decomposition of hexabromocyclododecane

The influence of aluminum on the thermal stability of hexabromocyclododecane (HBCD) was investigated. HBCD pyrolysis was carried out using thermogravimetric analyzers and a laboratory scale reactor. The identification of decomposition products was based on FTIR and gas-chromatographic/mass-spectrometric techniques. The results obtained confirmed that the presence of aluminum caused a lower thermal stability of HBCD. However, the presence of aluminum also resulted in a significant increase of the char yield and caused the shift towards an exothermic decomposition process. The analysis of the decomposition products showed that the presence of aluminum triggers polycondensation reactions during HBCD thermal degradation.     

Predicting optimal doses of ozone in the process of disinfecting drinking water based on a mathematical model

Statistical methods of miltifactorial experiment design have been applied to studying the disinfection of drinking water with ozone. Based on the mathematical model obtained, the optimal doses of ozone that are necessary for the ozone treatment of water of a known qualitative composition can be determined, and the efficiency of a chosen mode of ozone treatment can be predicted. It is demonstrated with river craft that the model can be used in the practice of water supply.     

The influence of the environment on the thermal decomposition of oxysalts

The environment can influence the thermal decomposition of an oxysalt by;

1. causing a change in the course of chemical decomposition or
2. causing an alteration in the physical nature of the solid product or solid intermediates.

The environment can also effect the equilibrium condition or the course of the kinetics. The use of special techniques such as thermogravimetry, differential thermal analysis, or differential scanning calorimetry to study the decomposition means that a special environment is imposed on the oxysalt and this effects the thermal decomposition process. The influence of the environment in changing the course of a chemical reaction can be illustrated by reference to the decomposition of zinc oxalate and nickel oxalate. The DTA shows that the decompositions are endothermic in inert atmospheres but exothermic in air or oxygen. The reasons are different however in each case. Thus although the product of decomposition of zinc oxalate is zinc oxide the change in character of the decomposition from endothermic to exothermic is due to the catalytic oxidation of carbon monoxide to carbon dioxide in the presence of oxygen. The similar change in the character of nickel oxalate decomposition is however due to nickel formation in an inert atmosphere but nickel oxide in air or oxygen. The alteration in the physical nature of the solid products is illustrated by surface area measurements on solid residues from the decomposition of carbonates or oxalates. The kinetic and chemical equilibrium studies showing the influence of environment are illustrated by reference to dehydration studies, carbonate and oxalate decompositions.     

The thermal decomposition of water

The reflected shock tube technique with multipass absorption spectrometric detection of OH‐radicals at 308 nm, corresponding to a total path length of 1.749 m, has been used to study the reaction H₂O + M → H + OH + M between 2196 and 2792 K using 0.3, 0.5, and 1% H₂O, diluted in Kr. As a result of the increased sensitivity for OH‐radical detection, the existing database for this reaction could be extended downward by ～500 K. Combining the present work with that of Homer and Hurle, the composite rate expression for water dissociation in either Ar or Kr bath gas is k_{1,Ar(or Kr)} = (2.43 ± 0.57) × 10^?10 exp(?47117 ± 633 K/T) cm³ molecule^?1 s^?1 over the T‐range of 2196–3290 K. Applying the Troe factorization method to data for both forward and reverse reactions, the rate behavior could be expressed to within <±18% over the T‐range, 300–3400 K, by the three‐parameter expression k_1,Ar = 1.007 × 10⁴ T^?3.322 exp(?60782 K/T) cm³ molecule^?1 s^?1 A large enhancement due to H₂O with H₂O collisional activation has been noted previously, and both absolute and relative data have been considered allowing us to suggest k₁, H₂ O = 1.671 × 10² T^?2.440 exp(?60475 K/T) cm³ molecule^?1 s^?1 for the rate constants with H₂O bath gas over the T‐range, 300–3400 K. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 211–219, 2006     

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.     

The heterogeneous decomposition of ozone on atmospheric mineral dust surrogates at ambient temperature

The rate of uptake of ozone on various mineral dust surrogates, expressed as uptake coefficient γ, has been studied employing a Knudsen flow reactor. Experiments were performed at T = 298 ± 2 K on substrates of kaolinite, CaCO₃, natural limestone, Saharan dust, and Arizona test dust. Initially, the uptake coefficients have been calculated on the basis of the geometric surface area of the powder samples. Both initial and steady‐state uptake coefficients γ₀ and γ_ss were found very similar for all the examined substrates. In addition, additional uptake experiments on marble sample have shown that γ₀ and γ_ss may be overestimated between a factor of 50 and 100, respectively. Based on these considerations, we proposed initial and steady‐state uptake values of the order of 10^?4 and 10^?5, respectively. On kaolinite, the uptake coefficient decreased with increasing O₃ residence time τ_g thus indicating a complex mechanism. In contrast, γ decreased and became independent of τ_g at long residence time after long exposure to O₃. For all uptake experiments the disappearance of O₃ was accompanied by the formation of O₂. The different mineral dust surrogates may be more accurately distinguished by their time‐dependent O₂ yield r(t) rather than the magnitude of γ. The heterogeneous reaction of O₃ on mineral dust has been found to be noncatalytic and of limited importance in the atmosphere. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 407–419, 2006     

Design of a combined ozone/electron beam process for waste water and economic feasibility of the process

A design of a combined ozone/electron beam irradiation process for treating a 50 m³/h waste water stream from a molasses processing is discussed. Moreover, a cost evaluation of such a process in comparison to a conventional ozonation/biology treatment process has been performed to assess the potential of the irradiation process for technical use. Although the result of this comparison is not bad for the irradiation process an implementation into a full scale plant would not seem to be the thing to do in the present case.     

Synthesis of thiophosphoramidates in water: click chemistry for phosphates

An aqueous method for the preparation of N,S-dialkyl thiophosphoramidates is reported. Thiophosphorylation of alkylamines was performed using SPCl(3) in aqueous reaction media, and the resulting thiophosphoramidate-S-anions were S-alkylated with soft electrophiles. Ranges of amines and electrophiles were explored.     

The influence of chemical modification on structure and sorption properties of titanium phosphates

Physical and chemical methods of analysis were used to study the effect of chemical modification of titanium phosphates on their sorption properties, depending on the chemical composition of a composite and nature of a modifier. The dependence of exchange capacity of the materials on the degree of their crystallinity was determined.     

The role of added water in the ionothermal synthesis of microporous aluminium phosphates

Water plays an important role in ionothermal synthesis and it has been suggested that it can influence phase selection. We have carried out an extensive study to determine the phases produced at various ratios of water to ionic liquid in the microwave assisted ionothermal synthesis of fluorinated aluminium phosphate frameworks using 1-ethyl-3-methylimidazolium bromide and 1-ethylpyridinium bromide. Aluminophosphate chabazite is the main product under ionothermal conditions while at increased levels of water the ionic liquids appear to be poor templates with dense phases predominating. The low synthesis pressure in ionothermal reactions is demonstrated and the role of template breakdown in phase selection is also discussed.     

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.     

A kinetic study of ozone decomposition on illuminated oxide surfaces

The heterogeneous chemistry and photochemistry of ozone on oxide components of mineral dust aerosol, including α-Fe(2)O(3), TiO(2), and α-Al(2)O(3), at different relative humidities have been investigated using an environmental aerosol chamber. The rate and extent of ozone decomposition on these oxide surfaces are found to be a function of the nature of the surface as well as the presence of light and relative humidity. Under dark and dry conditions, only α-Fe(2)O(3) exhibits catalytic decomposition toward ozone, whereas the reactivity of TiO(2) and α-Al(2)O(3) is rapidly quenched upon ozone exposure. However, upon irradiation, TiO(2) is active toward O(3) decomposition and α-Al(2)O(3) remains inactive. In the presence of relative humidity, ozone decay on α-Fe(2)O(3) subject to irradiation or under dark conditions is found to decrease. In contrast, ozone decomposition is enhanced for irradiated TiO(2) as relative humidity initially increases but then begins to decrease at higher relative humidity levels. A kinetic model was used to obtain heterogeneous reaction rates for different homogeneous and heterogeneous reaction pathways taking place in the environmental aerosol chamber. The atmospheric implications of these results are discussed.