Biomass of Anthonotha macrophylla leaf extract as a mild steel acid corrosion inhibitor: Experimental and theoretical study

This study investigated weight loss and electrochemical impedance spectroscopy (EIS) to explore the inhibition potential of Anthonotha macrophylla leaf extract (AME) on mild steel corrosion in 0.5 M H₂SO₄ medium. The result shows that the highest inhibition efficiency of 90.47 % at 303 K and 80.02 % at 333 K were obtained. At temperatures of 303 K and 333 K, it was discovered that the corrosion rate decreased as the concentration of the AME inhibitor rose from 0.1 g/L $(7.73\times {10}^{-4}$gcm⁻²hr⁻¹) to 0.5 g/L $(2.27\times {10}^{-4}$ gcm⁻²hr⁻¹). The result of the EIS measurement is in consistent with that of the weight loss method. Adsorption isotherms portrayed that Tempkin and Freundlich's adsorption isotherms were obeyed. Calculated values of Ea, $∆H_{\mathrm{ads}}$ and $∆G_{\mathrm{ads}}$ suggested a physical adsorption mechanism. FTIR, SEM-EDX, and XRD measurements revealed that the AME inhibitor efficiently shields the mild steel surface from further corrosion attack by inducing the formation of passivated film on the mild steel surface. The calculated quantum parameters correlated with experimental results, thus, AME can be used as an alternative inhibitor for the protection of mild steel against corrosion.