Inhibition Performance of Selected Medicinal Plant Extracts on Mild Steel Q235: FTIR Characterization and Gravimetric Analysis

Abstract

Corrosion of mild steel in acidic and alkaline environments remains a practical concern because it reduces material durability and increases maintenance requirements. This study evaluated selected medicinal plant extracts as potential corrosion inhibitors for Q235 mild steel using Fourier transform infrared (FTIR) spectroscopy and gravimetric weight-loss analysis. Aqueous extracts were prepared from Calotropis procera, Euphorbia kamerunica, Camellia sinensis, Azadirachta indica and Cymbopogon citratus, and a 50:50 blend of Calotropis procera and Euphorbia kamerunica was also examined. The plant materials were collected from Shabu, Nasarawa State, Nigeria, authenticated, air-dried, pulverised and extracted by cold maceration. FTIR analysis indicated the presence of hydroxyl, carbonyl, ether, amine and related oxygen- and nitrogen-containing functional groups, which may contribute to adsorption on the steel surface. Gravimetric measurements conducted in 0.5 M HCl and 3.0 M NaOH showed that the plant extracts reduced corrosion rates compared with uninhibited media. Inhibition performance varied among the extracts, with Azadirachta indica showing the highest reported inhibition efficiency of about 99%, followed by the Calotropis procera–Euphorbia kamerunica blend at about 98%, Camellia sinensis at about 97% and Cymbopogon citratus at about 80%. The improved inhibition may be attributed to the adsorption of phytochemical constituents and the formation of a protective interfacial film on the mild steel surface. Overall, the results suggest that the investigated plant extracts have potential as environmentally benign corrosion inhibitors, although further quantitative, electrochemical and surface analytical studies are required to clarify the inhibition mechanism and confirm practical applicability.