Kinetics and Mechanism of the Carbonate Ion Inhibited Aqueous Ozone Decomposition

Abstract

The carbonate ion inhibited aqueous decomposition of ozone was studied by the stopped-flow method at 25.0 ± 0.1 °C in 0.5 M NaClO4. It was shown that the rate of decomposition sharply decreases and reaches a limiting value by increasing the carbonate ion concentration. A detailed kinetic model was developed for the interpretation of the results. The corresponding set of rate constants was calculated by simultaneously fitting kinetic traces obtained at the absorption maxima of O3 (260 nm), O3 - (430 nm), and CO3 - (600 nm). It was confirmed that the inhibition is mainly due to the removal of two dominant chain carrier radicals, OH and O3 -, via the following reaction steps: CO3 2- + OH → CO3 - + OH-, k = (1.0 ± 0.1) × 108 M-1 s-1, and CO3 - + O3 - → CO3 2- + O3, k = (5.5 ± 0.5) × 107 M-1 s-1. The kinetically less significant reactions of other transient species are also discussed in detail. The mechanism gives proper description of ozone decay, the formation and subsequent disappearance of ozonide ion and carbonate ion radicals, as well as the concentration change of other intermediates over the pH range 10.7−12.8. The model predicts that ozone decomposition occurs in a simple first-order process at high CO3 2- concentration, in agreement with the experimental data.

Mono- and Bimetallic Complexes of Mn(II), Co(II), Cu(II), and Zn(II) with Schiff Bases Immobilized on Nanosilica as Catalysts in Ozone Decomposition Reaction

“…The results of analyzing kinetic (τ 1/2 , k 1/2 ) and stoichiometric (Q exp , n) parameters for all nanocomposites under study are summarized in Table 3. Based on the classic conceptions concerning the mechanism of ozone decomposition [2][3][4] and our studies of kinetics of ozone decomposition by 3d metal complexes with Schiff bases immobilized on nanosilica [1,[14][15][16][17], it can be deduced that metal ions taking part in the chain propagation reaction increase the time of ozone halfconversion attainment (k 1/2 decreases) and the amount of ozone entering the reaction over the whole period of its proceeding (Q exp ). In this case, the higher the τ 1/2 and Q exp the more actively complex decomposes ozone.…”

“…As a result, the specific antiozonante activity of monometallic compositions immobilized on nanosilica exceeds by two orders the activity of complexes on porous matrix МL 2 /SiO 2 (L = NO ). In the presence of mentioned complexes, similarly to the reaction in solutions [2][3][4], the ozone decomposition proceeds by the radical chain mechanism, the kinetic proof of which can be the difference between the values of first-order reaction rate constant at the beginning of the reaction and at the ozone half-conversion time. Consequently, metal complex 1 Odesa I.I.…”

Selectivity of Nanocrystalline IrO2-Based Catalysts in Parallel Chlorine and Oxygen Evolution

“…Hydroperoxyl may, however, also recombine to ozone [25], the thermodynamic potential for the electrochemical formation of which is 1.51 V [25,35]. In an alkaline solution ozone decomposition is triggered by a direct reaction between O3 and OH - [36]. are not present in the solution, we expect ozone to be more stable [37].…”

Numerical simulation of the kinetics of ozone decomposition in an aqueous solution

“…The curves of the absorbance changes in time calculated for two variants of the initiation reaction do not virtually differ and agree similarly well with the experimental data. 4 However, the results of quantum mechanical simula tion 15 indicate that reaction (3) is energetically more fa vorable. Therefore, we ignore the above presented reaction.…”