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

Although traditional corrosion inhibitors have demonstrated immense relevance in metal protec-tion 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 in-hibitors are gathering significant research attention and have shown great potentials in the corro-sion 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 identifica-tion 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, cap-saicin was classified as a functional mixed-type corrosion inhibitor that is reliant on concentra-tion and surrounding temperature for its effectiveness. While also validating the results from wa-ter contact angle measurements, 3D profiling, and SEM, XPS results disclosed that the interac-tions 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.

Automated summary

While traditional corrosion inhibitors have drawbacks such as toxicity and non-biodegradability, bio-based corrosion inhibitors, such as natural capsaicin, show great potential in metal protection due to their low cost and eco-friendliness. This study investigates the anticorrosion and adsorption properties of capsaicin on Q235 steel, revealing its effectiveness as a corrosion inhibitor through both physical and chemical adsorption processes.