Absorption and Quantum Chemical studies on some DYES as Corrosion Inhibitors on Mild Steel in Acidic Medium

Abstract

The corrosion inhibition of some selected dyes namely Sunset yellow (SS). Amaranth (AM). Allura red (AR). Tartrazine(TZ) and Fast green (FG) on mild steel in 0.5M HCI was studied at 30-60°C using weight loss, electrochernical and quantum chemical methods. Quantum calculation based on the density functional theory (DFT) was used to investigate the reactivities and selectivities of four (4) of the studied dyes. The effects of inhibitor concentration on the inhibition efficiency have been studied. Inhibition efficiency increased with increase in concentration of the all the studied dyes within the concentration range 25-50 pm. The results obtained showed that the experimental inhibition efficiency follows the order: Fast green (FU) > Allura red (AR) > Amaranth (AM) >Tartrazine (TZ). The potentiodynamic studies revealed that all the inhibitors are of mix-type. The adsorption of the studied dyes obeyed the Langrnuir adsorption isotherm. Some thermodynamic parameters such as the heat of adsorption, entropy of adsorption and free energy of adsorption have been calculated. Apparent activation energy has been calculated and discussed. Synergism parameter evaluated was found to be greater than unity for all the concentration of the dyes used suggesting that the increase in the inhibition efficiency of the dyes by the addition of KI is only due to the synergism. Density Functional Theory method was used utilized on the quantum chemical calculation performed both in vacuo and in solution using both the protonated and non-protonated species. The quantum chemical descriptors e.g. EHOMO, ELUMO and Fukui indices have been discussed and compared with the trend in experimental inhibition efficiencies.