Adsorption characteristics and inhibition effect of two Schiff base compounds on corrosion of mild steel in 0.5 M HCl solution: experimental, DFT studies, and Monte Carlo simulation

Abstract

In this work, we report the synthesis of two Schiff bases of substituted gallic acid derivatives via amidation reaction and their characterization using ¹H-NMR spectroscopy to study their inhibition performance on the aggressive attack of HCl on mild steel (MS). The inhibitive performance was examined using chemical (weight loss) and electrochemical (Tafel and EIS) test methods. The results indicate that these derivatives significantly suppress the dissolution rate of mild steel via adsorption phenomena, which correlates to the Langmuir adsorption model. Tafel data display the mixed-type properties of these compounds and EIS results show that increasing Schiff base concentration not only leads to delaying the charge transfer (R_ct) of iron from 26.4 ohm cm⁻² to 227.7 ohm cm⁻² but also decreases the capacitance of the adsorbed double layer (C_dl) from 8.58 (F cm⁻²) × 10⁻⁵ to 2.55 (F cm⁻²) × 10⁻⁵. The inhibition efficiency percentage reaches the peak (90%) at optimum concentration of 250 ppm. The Monte Carlo simulations confirm the adsorption ability of the as-prepared compounds on the Fe (1 1 0) crystal. The SEM/EDX results revealed the presence of a protective film on the mild steel sample.