Dispersive adsorption and anticorrosion properties of natural capsaicin on Q235 steel in mixed H2SO4 and NaCl environment: Characterization, experimental and theoretical studies

Abstract

Although traditional corrosion inhibitors have demonstrated immense relevance in metal protection for many years now, issues relating to their moderate to high toxicities, non-biodegradability, and cost-effectiveness have persisted. For these reasons, bio-based corrosion inhibitors are gathering significant research attention and have shown great potentials in the corrosion suppression of metals while being relatively cheap and eco-friendly. This study focuses on the anticorrosion and adsorption properties of natural capsaicin isolated from Capsicum annuum L. as a bio-based corrosion inhibitor for Q235 steel in a mixed acid and chloride system (0.25 M H2SO4 + 0.5 M NaCl). FTIR and NMR techniques afforded the characterization and identification of the phytocompound. Electrochemical and gravimetric measurements were employed for anticorrosion evaluations. 3D surface profilometer, SEM, and water contact angle examinations provided adsorption proof for capsaicin on steel surface. XPS provided insights into the corrosion suppression mechanism of capsaicin. Computational techniques allowed the description of the adsorption characteristics, molecular interactions, molecular orientations and binding energies of capsaicin on steel substrate. Having a maximum inhibition performance of 94.8% at 298 K, capsaicin was classified as a functional mixed-type corrosion inhibitor that is reliant on concentration and surrounding temperature for its effectiveness. While also validating the results from water contact angle measurements, 3D profiling, and SEM, XPS results disclosed that the interactions of capsaicin with steel surface leading to its adsorption and anticorrosion effect involved both physisorption and chemisorption processes, and this was in perfect correlation with the Langmuir monolayer adsorption model.