Catalytic Effect of 1,4-Dioxane on the Kinetics of the Oxidation of Iodide by Dicyanobis(bipyridine)iron(III) in Water

• Main Authors: Rozina Khattak, Muhammad Sufaid Khan, Zahoor Iqbal, Rizwan Ullah, Abbas Khan, Shazia Summer, Hamsa Noreen, Muhammad Zahoor, Salah M. El-Bahy, Gaber El-Saber Batiha
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: Catalysts
• Subjects: photosensitive; sensitizer; 1,4-dioxane-water; dicyanobis(bipyridine)iron(III); oxidation; iodide
• Online Access: https://www.mdpi.com/2073-4344/11/7/840

Dye-sensitized solar cells (DSSCs) are a technically and financially viable alternative to today’s photovoltaic systems using p-n junctions. The two functions are isolated here, which are unlike traditional systems where the semiconductor is thought to perform both light absorption and charge carrier transport. This article discusses the potential use of dicyanobis(bipyridine)iron(III) to oxidize iodide as a sensitizer in DSSCs. However, it is critical to understand the kinetics of this essential process in order to understand the mechanism of electron transport. The oxidation of iodide by dicyanobis(bipyridine)iron(III) in three reaction media was studied: water, 10% <i>v</i>/<i>v</i> 1,4-dioxane-water, and 20% <i>v</i>/<i>v</i> 1,4-dioxane-water. The reaction was carried out in a regular laboratory setting, with no special sensitive conditions or the use of expensive materials, making it a cost-effective and practical method. Dicyanobis(bipyridine)iron(III) oxidized iodide in selected media at 0.06 M ionic strength and constant temperature. The reaction was subjected to a spectrophotometric analysis. The data were acquired by measuring the rise in visible absorbance as a function of time after the formation of dicyanobis(bipyridine)iron(II). The reaction proceeded with an overall fractional (0.5), first order, and third order in water, 10% media, and 20% media, respectively. The presence of dicyanobis(bipyridine)iron(III) in either of the reaction media had no effect on the rate. The effect of protons (H⁺) on the rate constant indicated resistance in water and catalysis in dioxane-water media containing 10–20% dioxane. When the ionic strength was raised, there was no change in the rate constant in water, but there was a deceleration in both binary solvent media. In an aqueous medium, the thermodynamic parameters of activation were computed as E_a 46.23 kJ mol⁻¹, 24.62 M s⁻¹, ΔH^# 43.76 kJ mol⁻¹, ΔS^# −226.5 J mol⁻¹ K⁻¹, and ΔG^# 111.26 kJ mol⁻¹ (25 °C). By increasing the rate of the reaction to its maximum, this study discovered the binary solvent media with the highest catalytic efficiency, i.e., 20% <i>v</i>/<i>v</i> 1,4-dioxane-water, which may increase the efficiency of DSSCs without using any expensive material or unusual experimental conditions.