Novel eco-friendly green inhibitor of corrosion based on Acerola (Malpighia glabra) waste aqueous extract for mild steel in 1 mol L–1 HCl solution

In this study, the effectiveness of a sustainable corrosion inhibitor derived from acerola peels and seeds (an industrial waste) applied to a mild steel substrate (acerola aqueous extract - AAE) was studied. The corrosion inhibitory action was evaluated by surface analysis, gravimetric, and electrochemical tests. Results demonstrate that the acerola waste aqueous extract shows a good inhibition efficiency acting through chemical adsorption onto mild steel. The aqueous extract demonstrated a maximum inhibition efficiency of 92.0% at 8000 ppm after 2 hours of immersion and around 96% from 1000 ppm in the period from 6 to 96 hours of immersion. High and low molecular mass fractions (HMMF and LMMF) obtained from the acerola waste aqueous extract (cutoff 3kDa) were evaluated and compared to the crude extract. After 2 h immersion at a concentration of 1000 ppm, the crude extract showed 82.5% inhibition efficiency, while HMMF and LMMF showed 88.0% and 77.6%, respectively, suggesting that components from both fractions participate in the inhibition process showing that in the studied extract several molecules may be responsible for the inhibitory efficiency of the extract. XPS analysis and biochemical characterization of the crude extract showed that the proteins are strong candidates to play a role in the inhibition process, through the N-Fe chemical bond, corroborating the activation energy studies. These results show an excellent alternative for using acerola peel and seed as corrosion inhibitors.