Crispy Dry Chili Extract as an Eco‑Friendly Corrosion Inhibitor for Mild Steel in Chloride Solutions: Experimental and Theoretical Studies

Abstract

The development of eco-friendly corrosion inhibitors is an area under several investigations; especially, natural plant extract. Such as crispy dry capsicum chili extracts (containing capsaicinoids as the active ingredient), the plant extract is an inexpensive and renewable material. Surface properties were studied such as fourier transforms infrared spectroscopy, contact angle measurements (θ), and scanning electron microscope. The inhibitive effects of the extract on mild steel in chloride solutions were experimentally evaluated by electrochemical methods such as potentiodynamic polarization, and electrochemical impedance spectroscopy. The results illustrated that the maximum inhibition efficiency of the coating was 97.1, 94.7, and 85.2%, for mild steel in 3.5% NaCl, 2.0, and 1.0 M HCl, respectively. The protective hydrophobic film attributed high protection to the homogeneous distribution. The significance of quantum chemical descriptors to the performance of the extract as a corrosion inhibitor was determined using the density functional theory. Quantum parameters were evaluated and discussed, such as the highest and lowest occupied orbital energy, the energy gap, hardness, and other quantum descriptors.