Vicia faba peel extracts bearing fatty acids moieties as a cost-effective and green corrosion inhibitor for mild steel in marine water: computational and electrochemical studies

Abstract

The goal of this research is to determine what chemicals are present in two different extracts (hexane and acetone) of Vicia faba (family Fabaceae, VF) peels and evaluate their effectiveness as a corrosion inhibitor on mild steel in a saline media containing 3.5% sodium chloride. Gas chromatography-mass spectrometry (GC/MS) was used to determine the composition of various extracts. It was determined that fourteen different chemicals were present in the hexane extract, the most prominent of which were octacosane, tetrasodium tetracontane, palmitic acid, and ethyl palmitate. Heptacosane, lauric acid, myristic acid, ethyl palmitate, and methyl stearate were some of the 13 chemicals found in the acetone extract. Using open circuit potential, potentiodynamic polarisation, and electrochemical impedance spectroscopic techniques, we can approximate the inhibitory effects of (VF) extracts on mild steel. The most effective inhibitory concentrations were found to be 200 ppm for both the hexane and acetone extracts (97.84% for the hexane extract and 88.67% for the acetone extract). Evaluation experiments were conducted at 298 K, with a 3.5% (wt/v) NaCl content and a flow velocity of about 250 rpm. Langmuir adsorption isotherm shows that the two extracts function as a mixed-type inhibitor in nature. Docking models were used to investigate the putative mechanism of corrosion inhibition, and GC/MS was used to identify the major and secondary components of the two extracts. Surface roughness values were calculated after analyzing the morphology of the metal's surface with and without (VF) using a scanning electron microscope (SEM). The results showed that throughout the surface of the mild steel, a thick adsorbate layer was formed. Quantum chemical calculations conducted on the two extracts as part of the theoretical research of quantum chemical calculation demonstrated a connection between the experimental analysis results and the theoretical study of the major chemical components.

Figure 1

GC chromatogram of hexane extract of Vicia faba peel.

Figure 2

GC chromatogram of acetone extract of Vicia faba peel.

Figure 3

Representative the plots of open circuit potential versus time for mild steel in 3.5% NaCl solution without and with different concentrations (50, 100, 150, and 200 ppm) of (VF) (a) Hexane extract and (b) Acetone extract at 298 K.

Figure 4

Representative the curves of potentiodynamic polarization for mild steel in 3.5% NaCl solution without and with different concentrations (50, 100, 150, and 200 ppm) of (VF) (a) Hexane extract and (b) Acetone extract included sweeping the potential between -200 and + 200 mV from OCP at a scan rate of 0.001 V/s at 298 K.

Figure 5

Electrochemical Impedance Spectroscopy (EIS diagrams); Nyquist plots for mild steel in 3.5% NaCl solution without and with different concentrations (50, 100, 150, and 200 ppm) of (a) Hexane extract and (b) Acetone extract at OCP and 298 K.

Figure 6

Electrochemical Impedance Spectroscopy (EIS diagrams); Bode plots for mild steel in 3.5% NaCl solution without and with different concentrations (50, 100, 150, and 200 ppm) of (VF) (a) Hexane extract and (b) Acetone extract at OCP and 298 K.

Figure 7

Electrochemical Impedance Spectroscopy (EIS diagrams); Phase plots for mild steel in 3.5% NaCl solution without and with different concentrations (50, 100, 150, and 200 ppm) of (a) Hexane extract and (b) Acetone extract at OCP and 298 K.

Figure 8

Equivalent circuit of fitting data of mild steel in 3.5% NaCl solution with (VF) (a) Hexane extract and (b) Acetone extract at OCP and 298 K.

Figure 9

SEM micrograph of mild steel surfaces before and after immersion for 24 h in 3.5% NaCl at 298 ± 1 K, (a) Polished mild steel sample, (b) In absence of inhibitor (blank), (c) in presence of 200 ppm from (VF) hexane extract (d) in presence of 200 ppm from (VF) acetone extract.

Figure 10

The effect of temperature on the inhibition efficiency of mild steel in 3.5% NaCl at the highest concentration (200 ppm) of (VF) extracts (a) Hexane extract and (b) Acetone extract.

Figure 11

The effect of concentration on the inhibition efficiency of mild steel in 3.5% NaCl at the highest concentration (200 ppm) of (VF) extracts (a) Hexane extract and (b) Acetone extract.

Figure 12

Representative the Langmuir isotherms for the adsorption of mild steel in 3.5% sodium chloride in the presence of (200 ppm) from (a) hexane and (b) acetone extracts.

Figure 13

Representative the Temkin isotherms for the adsorption of mild steel in 3.5% sodium chloride solution in the presence of (200 ppm) from the (a) hexane and (b) acetone extracts.

Figure 14

Arrhenius plots for the corrosion of mild steel in 3.5% NaCl solution with several concentrations of (VF) (a) hexane and (b) acetone extract.

Figure 15

Transition-state plots for mild steel corrosion in 3.5% NaCl solution with several concentrations of (VF) (a) hexane and (b) acetone extract.

Figure 16

Structure optimization and FMOs obtained by distributions of (HOMO) and (LUMO) at the major constituents of (VF) obtained by DFT/B3YLB/6-311G** for AO and HERA.

Figure 17

Representative the side view of molecular simulations for the most favorable modes of adsorption mode for the inhibitors on the Fe (100) surface.