Investigating expired Esofag-D as an eco-friendly corrosion inhibitor for aluminium-6061 in sulfuric acid: experimental, theoretical, and optimization approaches

The inhibitive effect of expired esofag-d on aluminium-6061 corrosion in 1 M H2SO4 solution was investigated via experimental and theoretical methods, supplemented by optimization using response surface methodology (RSM). Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectrometry (GC–MS) were deployed to characterise the inhibitor. The inhibition efficiency (IE) of esofag-d increased with the rise in esofag’s concentration and decreased as temperature increased. The FTIR analysis results showed the existence of heteroatoms in the drug. GC–MS results indicated that the drug contains diethyl phthalate, pentadecane, tridecane, octadecane, nonadecane, tetradecanoic acid, sulfurous acid, 2-propyl tridecyl ester, n-hexadecanoic acid, dodecanoic acid, among other compounds that contain heteroatoms. The adsorption study performed shows that the Langmuir model gave the finest description of the experimental data. Potentiodynamic polarization results revealed that esofag-d is a mixed-type inhibitor. Nyquist plot from the electrochemical impedance spectroscopy study gave depressed semi-circles and corrosion inhibition efficiency of 95.92%. DFT parameters further confirm the inhibitive ability of the inhibitor. RSM was used to model the combined effect of the variables on the corrosion process. RSM modelling gave an optimum IE of 92.03%, which was further improved by artificial neural network (ANN) modelling. The results obtained show that esofag-d is a good inhibitor for aluminium-6061. Hence, this study has established the viability of expired pharmaceuticals such as expired esofag-d in the corrosion inhibition of Al-6061.