Evaluation of the corrosion inhibitory effect of Napoleonaea Imperalis leaf extract on mild steel in a 1.3 M H2SO4 medium

Abstract

The study investigated the corrosion inhibitory effect of Napoleonaea imperalis leaf extracts (‘NI’) on Mild steel (M-steel) in 1.3 M H2SO4. Weight loss, potentiodynamic and electrochemical impedance spectroscopy (EIS) at 303 K–343 K were the investigative approaches adopted in the study. The resultant oxide from the study was characterized using Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM). Meanwhile, the experimental results were validated using theoretical calculations. The experimental findings showed that by increasing the inhibitor concentration (from 0.2 to 1.0 g/L) at a low operational temperature of 303 K, an increased inhibition efficiency (from 47.93 to 85.54%) was observed. The organic functional groups responsible for inhibition effect were identified in the FTIR result. Similarly, the SEM result showed the occurrence of significant transformation on the M-steel surface due to effective corrosion inhibition by ‘NI’. The range of values of the free energy of adsorption, ∆Gads (− 12.88 to − 5.83 kJ/kmol) and heat of adsorption, Qads, (− 24.10 to − 5.10 KJ/kmol) indicates the occurrence of physisorption process. The negative values obtained for the free energy of adsorption is an indication for a spontaneous and exothermic inhibition process. Tafel polarization curves depicted the inhibitor used in the study as a mixed-type. Similarly, the density functional theory (using molecular dynamic simulations) suggested a dependent adsorption process with coordinate bonds via metal/inhibitor interface. The study succinctly demonstrated an excellent inhibition performance of ‘NI’ in M-steel corrosion.