The Kinetics of Complexed and Free Ho₂ Radical in the Reaction of Ce⁺⁴ and H₂O₂

Abstract

The intermediates formed in the reaction of Ce+4 with H2O2 in 0.5 M perchloric acid were studied, spectrophotometrically and through the quenching method, using a stopped‐flow system. The spectrum in the UV range and the kinetics of the generated radicals and their dependence on Ce+3 concentration were investigated. On adding Ce+3 to the mixture, a change in the spectrum as well as in the recombination rate constant was observed. This behaviour was attributed to the formation of a complex between the cerous ion and the HO2 radical. The values of the recombination rate constant of the complexed radical is 4.0 ± 0.4·106 F−1 sec−1 while that of the free HO2 radical is 0.9 ± 0.1·106 F−1 sec−1. The stabilization constant of the complex was found to be 60 ± 18 F−1.

Hydroperoxyl Radical Reactions. III. Pulse-Radiolytic Study of the Reaction of the Hydroperoxyl Radical with Some Metal Ions

“…In accordance with previous observation13 the decay rate was inversely proportional to [U022+]. This is attributed to the replacement of the relatively fast self-recombination, reaction 9, by the slower cross recombination, reaction 10, and the self-recombination (reaction 11), of the [m"*-ho2•] + H02• --Mn* + h2o2 + 02 (10) [ *-02•] + [ "*-02•] -* 2M"* H202 + 02 (11) complex. Since equilibrium la is achieved rapidly as compared to the slow decay of [U(VI)-H02•], the rate of the disappearance of the complex can be given by (12) The decay rate was measured and was found to be a superposition of pseudo first and second orders.…”

Decolorization and Mineralization of Rhodamine B in Aqueous Solution with a Triple System of Cerium(IV)/H2O2/Hydroxylamine

“…In this system, it can be assumed that Ce(IV) can react with HA to produce NH 2 O • free radicals through reactions 3 and 4, but can also consume NH 2 O • free radicals by reaction 6. In addition, excessive Ce(IV) can react with H 2 O 2 with a high rate constant following reactions 11(37) and 12, 38 whereas the HO • radical competes with the reduction product Ce(III) by reaction 14. 39 Increased degradation of RhB was observed with the increase in the initial HA concentration.…”