Synthesis and anti-corrosive potential of Schiff bases derived 4-nitrocinnamaldehyde for mild steel in HCl medium: Experimental and DFT studies

The following points are addressed in this submission.•Two Schiff bases derived from 4-nitrocinnamaldehyde have been synthesized and characterized using spectroscopic methods.•Corrosion inhibition potentials of the compounds were investigated via gravimetric and theoretical method.•Inhibition efficiencies increase with concentration and decrease with temperature rise.•Calculated parameters further establish the good inhibitory efficiencies of the two Schiff bases; 4-NPPABT and 4-NPPACH. The anti-corrosive potential of synthesized Schiff base derivatives comprising of 4-[(E)-[(2E)-3-(4-nitrophenyl)prop‑2-en-1-ylidene]amino]benzenethiol (4-NPPABT) and 4‐[(E)‐[(2E)‐3‐(4‐nitrophenyl)prop‐2‐en‐1‐ylidene]amino]cyclohexan‐1‐ol (4-NPPACH) on mild steel in 0.1 M HCl medium was investigated via gravimetric and theoretical method. The results revealed that the inhibition efficiency of the Schiff bases improved with increase in inhibitor concentration and decrease as temperature rises. 4-NPPABT showed inhibition efficiency of 64.9% at the highest concentration. Results obtained showed that 4-NPPABT with more pi bonds gave the best corrosion inhibition efficiency compared to 4-NPPACH. The Freundlich adsorption isotherm best describes the adsorption behaviour of the inhibitors on mild steel surface. The mechanism of adsorption of the inhibitors on mild steel occurs predominantly by physisorption. Scanning electron microscopy (SEM) micrographs revealed the availability of an adsorbed protective film on the surface of the mild steel. The compounds were optimized using density functional theory (DFT) with Becke three Lee Yang Parr (B3LYP) and 6–31G(d) basis set. The calculated electronic properties and global reactivity descriptors agree with experimental findings. The high dipole moment values and the electron-donating abilities (fraction of transferred electrons) of 4-NPPABT and 4-NPPACH further demonstrate good inhibitory efficiency.