Degradation of Methyl Red Azo Dye by Hexacyanoferrate(III) Ions from Water using Ultrafine Ir–Cu Bimetallic Nanoparticles: a Kinetic Approach

Abstract

In this study, the kinetics of catalytic degradation of methyl red, an anionic azo dye, by hexacyanoferrate(III) ions in the presence of ultrafine Ir–Cu bimetallic nanoparticles has been investigated. The effect of various parameters, including the concentration of dye, oxidant, Ir–Cu bimetallic nanoparticles (BMNPs), and solution pH on the reaction rate was investigated by measuring the light absorption at a wavelength of 425 nm, corresponding to the maximum absorption of the dye. The results reveal that the reaction follows first-order kinetics with respect to the concentration of hexacyanoferrate(III), methyl red, and Ir–Cu BMNPs at an optimum pH of 8.0 and a constant temperature of 40 ± 0.1°C. In order to determine how electrolytes interact with the reaction rate, the impact of ionic strength on the degradation rate was also examined. The high catalytic activity of Ir–Cu BMNPs was demonstrated by a three to four-fold rise in the reaction rate with increasing concentration of Ir–Cu BMNPs (particle size ca. 0.98nm). Thermodynamic parameters including activation energy (E_a), enthalpy of activation (ΔH^#), entropy of activation (ΔS^#), and free energy of formation (ΔF^#) of the reaction were calculated by analyzing the reaction rate at four different temperatures within the 40 to 55°C range. The low value of activation energy also suggests a high degradation rate. A reaction mechanism through complex formation was proposed based on the experimental findings which were supported by the analysis of the products formed. The formation of simpler and less hazardous products (1,5-pentanediol and benzoic acid) was verified by UV–Vis spectroscopy and liquid chromatography and mass spectroscopy (LC–MS). The assessment of turnover frequencies for each catalytic cycle also proved the stability and reusability of the catalyst. As a result, the discovery offers an innovative and highly cost-effective solution for environmental safety against dye contamination, with the potential for expansion to additional toxins.