Electrochemical, surface morphological and DFT calculations towards the corrosion inhibition of steel using seeds of Tribulus terrestris: an eco-friendly and sustainable approach

Abstract

This study describes a novel application of the Tribulus terrestris extract as a highly efficient corrosion inhibitor for steel in 1 M H₂SO₄ solution. The Tribulus terrestris extract contains considerable phytochemicals, notably Tribuloside, Kaempferol, and Kaempferol-3-glucoside that are basically for its anticorrosive behavior. Various studies including weight reduction analysis, electrochemical measurements (PDP and EIS), surface investigations, DFT calculations and simulation, etc. were performed to explore the Tribulus terrestris extract as a corrosion inhibitor. The highest inhibition efficiency of 96.25% was observed at 700 mg/L concentration of the Tribulus terrestris extract. The polarization curves obtained in the presence of the Tribulus terrestris extract indicate the extract behaved as a mixed type of inhibitor. In addition, the formation of a protective layer on the surface of steel was confirmed using the scanning electron microscope (SEM). The DFT analysis revealed a few electron-rich regions in the inhibitor's phytochemicals, which supported the high nucleophilicity. According to Frontier molecular orbital analysis, all three inhibitors contain electrons in their HOMO regions, which allow them to interact with vacant d-orbitals of iron on metal surfaces. Consequently, covalent bonds are formed between the metal surface and the corrosion inhibitor, which results in the inhibitor adsorption on the metal surface.

Graphical Abstract