Search

Oxidation of the iodide ion is an important facet of the solar cells such as perovskite solar cells and dye‐sensitized solar cells. The rate of reaction undoubtedly depends upon several factors. Such parameters include reaction media, electrolyte, and the nature of solvents, and electrolyte. If these factors are optimized then the rate of the reaction can be controlled and could be used to get the maximum benefit out of it such as economically and industrially cost‐effective uses of the reaction and globally environmentally benign. We studied the kinetics of the oxidation of the iodide ion in the binary solvent system that consisted of 10% (v/v) tertiary butyl alcohol and water. The transition metal complex such as dicyanobis(phenanthroline)iron(III) oxidizes the iodide ion spontaneously without any external triggering with a fast rate at 293 ± 1 K. The reaction was probed under the pseudo–first‐order condition with an excess concentration of the iodide ion over dicyanobis(phenanthroline)iron(III) at 0.06 M ionic strength. The reaction was observed independent of the concentration of dicyanobis(phenanthroline)iron(III), that is, the zero order and third order with respect to the iodide ion in the selected solvent system. An overall third‐order was observed for the redox reaction. The value of the multiplication product of the molar absorptivity (ɛ), path length of the cuvette (b), and overall rate constant (k) was deduced to be 1.59 × 106 M−3 s−1. The observed zero‐order rate constant of the reaction was increased by the fractional (1.5) power of the concentration of protons in the excess concentration of acid 1 mM to 0.1 M. The multiplication product of ɛ⋅b to the fractional order rate constant (k′) was found 0.773 M−1.5 s−1 that confirms protonation of triiodide in acidic‐10% (v/v) tertiary butyl alcohol‐water. The effect of ionic strength showed a similar impact in different compositions of solvents such as 5, 10, and 20% (v/v) tertiary butyl alcohol‐water. The observed zero‐order rate constant was decreased upon increasing the ionic strength in each medium consisting of the binary solvent system. [ABSTRACT FROM AUTHOR]

The kinetics of the oxidation of tris (2,2'-bipyridine)iron(II) ([Fe(bipy)3]2+) by bromate ion (BrO3-) in aqueous medium have been investigated. The reaction was probed spectrophotometrically in the pH range 3.5-5.0, and from 0.01 to 0.1 mol/dm³ ionic strength. The kinetic runs were pursued to more than two half lives of the reaction. The pseudo first order rate constant was found independent of the concentration of tris (2, 2'-bipyridine) iron (II), and increases with increasing concentration of bromate ion in the reaction mixture. Protonation of BrO3- in the acidic medium yields monoprotonated (HbrO3) and diprotonated (H2BrO3+) species. The rising figure of the rate constant upon lowering the pH refers to the involvement of protonated species in the rate-determining step. A rise in the value of the rate constant with increasing ionic strength implies, however, the diprotonated species, H2BrO3+, as the reactive species among the two competing. Involvement of the other Br(V) species results in a complex reaction pathway, consequently. The rate law is suggested as follows: Rate = k1 [Fe ((2,2'-bipy)32+][HBrO 3] + k2 Kip [Fe ((2,2'-bipy )32+] [H 2BrO 33+]/ (1 + K ip [ H 2BrO 3+] [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the catalytic effect of Cu2+ ions and hydrogen ion concentration on the kinetics of [Fe (bipy)3]2+ oxidation in aqueous medium. It notes that the kinetics of iron (II) oxidation by iodine indicate that the redox reaction proceeds by analogous mechanism. The study reveals the stability of transition metal complexes in the 3.0-4.5 pH range for several days after its formation.