Kinetics of the oxidation of iodide by dicyanobis(phenanthroline)iron(III) in a binary solvent system

• Published in: International journal of chemical kinetics 2021-02, Vol.53 (2), p.230-241
• Main Authors: Khattak, Rozina, Khan, Muhammad Sufaid, Summer, Shazia, Ullah, Rizwan, Afridi, Humaira, Rehman, Zainab, Masood, Summyia, Noreen, Hamsa, Qazi, Raina Aman, Begum, Bushra
• Format: Article
• Language: English
• Subjects: Absorptivity; Alcohol; binary solvent; Butanol; Coordination compounds; dicyanobis(phenanthroline)iron(III); Dye-sensitized solar cells; Electrolytes; Electrolytic cells; iodide; Iron; Kinetics; Multiplication; Oxidation; Perovskites; Photovoltaic cells; Protonation; Reaction kinetics; Redox reactions; Solvents; Transition metal compounds
• ISSN: 0538-8066; 1097-4601
• DOI: 10.1002/kin.21436

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.