Investigation of the inhibition effect of newly synthesized pyrazoline derivative on mild steel in hydrochloric acid medium by experimental and theoretical approach

Abstract

• Synthesized pyrazoline derivative 5-[5-(4-bromophenyl)1-1(pyridine-2-yl)-4-5-dihydro-14-pyrazol-3-yl]-2-methoxy pyridine (BPPM) and characterized by IR and NMR spectroscopy. • The electrochemical studies were carried out using electrochemical impedance spectroscopy and potentiodynamic polarization studies. • Surface characteristics of mild steel sample was performed with the use of scanning electron microscopy (SEM) and Energy Dispersive X-ray analysis (EDX). • The quantum chemical calculations were performed with the help of the DFT/B3LYP level using Gaussian 16 software for the neutral and protonated form of BPPM. • The UV-Visible spectroscopic study has been employed to confirm the formation of metal-inhibitor complex. The novel pyrazoline derivative 5-[5-(4-bromophenyl)1-1(pyridine-2-yl)-4-5-dihydro-14-pyrazol-3-yl]-2-methoxy pyridine (BPPM) was synthesized the spectral analysis has been carried out using 1 HNMR, 13 CNMR, and FT-IR spectra. The evaluation of the inhibition effect of BPPM on the corrosion of mild steel in 0.5M HCl solution has been carried out by Tafel polarization and electrochemical impedance spectroscopy techniques with the variation of its concentration from 10ppm to 40ppm at the temperature range from 303K to 323K. The inhibitor exhibited maximum corrosion inhibition efficiency of 97.5% in Tafel studies and 96.5% in electrochemical impedance studies at 303K for 40 ppm concentration. The change in the free energy of the adsorption process was found to be approximately 40kJ/mol which shows a mixed type of adsorption process. The theoretical analysis of the inhibition effect was performed with quantum chemical calculations using density functional theory (DFT) which proved the ability of protonated form of BPPM to interact with the vacant d-orbital of iron to arrest the rate of corrosion. The scanning electron microscopy with EDX studies and UV-Visible spectroscopy study confirmed the formation of the metal-BPPM complex. The experimental and theoretical data proved BPPM as a potent corrosion inhibitor at a considerably low concentration exceeding not more than 40ppm. Optimised geometry of BPPM in (a) Neutral form ( b) Protonated form.