Highly Efficient Baobab (Adansonia digitata) Fruit Seeds and Pulp Extracts as Potential Green Corrosion Inhibitors for Mild Steel in 0.5M HCl Solution

Abstract

The methanolic extracts of adansonia digitata (baobab) fruit pulp (ADPE) and seeds (ADSE) for mild steel corrosion inhibition in 0.5M HCl solution was studied by gravimetric, potentiodynamic polarisation, electrochemical impedance spectroscopic (EIS) and SEM methods. The results revealed that both ADSE and ADPE act as efficient mixed-type corrosion inhibitors. The weight loss and polarisation studies reveal that the corrosion inhibition efficiency increases with increase in the concentrations of inhibitors ADSE and ADPE in acidic medium. ADSE exhibited high corrosion inhibitor efficiency (91.12%) for mild steel. Tafel plots show that baobab fruit extracts act as efficient mixed-type corrosion inhibitors. The double layer capacitance (C_dl) and charge transfer resistance (R_ct) values derived from Nyquist plots proved the anticorrosive nature of extracts. The inhibition of corrosion is possibly due to adsorption of the extracts on mild steel surface. The adsorption obeys Langmuir adsorption isotherm. The low free energy of adsorption (∆G_ads) values for both the extracts confirmed physisorption on mild steel surface. The SEM images confirmed severe surface deterioration of mild steel exposed to HCl solution in the absence of inhibitors. The ADSE exhibited high efficiency as green and eco-friendly corrosion inhibitor for mild steel in acidic medium due to specific interaction between functional groups containing heteroatoms like nitrogen, sulfur, oxygen having free lone pair of electrons, and the metal surface.