Sageretia theezans extract as an eco-friendly corrosion inhibitor for mild steel in acidic medium: experimental studies and first-principles calculations.

Severe corrosion of mild steel constitutes a critical challenge in acidic environments, and the incorporation of corrosion inhibitors serves as a feasible strategy to alleviate this issue. Herein, electrochemical tests, surface analyses together with DFT-based first-principles calculations were adopted to assess the anticorrosion performance of Sageretia theezans extract (STE), an eco-friendly corrosion inhibitor, toward mild steel in HCl medium. Electrochemical measurements demonstrate that the inhibition efficiency of STE is concentration-dependent, with a maximum value of 99.2% at 100 mg L-1. First-principles calculations demonstrate that the main active constituents of STE, in both protonated and unprotonated states, can bind to mild steel substrates via Fe-O and Fe-C chemical bonds, verifying the occurrence of chemisorption at the molecular level.