Anthocyanin as sustainable and non-toxic corrosion inhibitor for mild steel in HCl media: Electrochemical, surface morphology and theoretical investigations

•Anthocyanin as a sustainable and non-toxic corrosion inhibitor or mild steel in 1 M HCl.•Polarization studies revealed the mixed type behavior for anthocyanin molecules.•SEM and SECM examinations showed that the anthocyanin molecules have a strong adhesion to the metal surface.•DFT supported the anthocyanin inhibitor was adsorbed on steel substrate through donor–acceptor interaction mechanism. A bio-friendly anthocyanin from cherries was estimated as a potential green inhibitor for mild steel in 1 M HCl using weight loss test, electrochemical methods and surface measurements. The results showed that the adsorption of anthocyanin over steel surface followed Langmuir isotherm, and the inhibition efficiency was still maintained 85.23% at 45 ℃. The obtained electrochemical analysis results indicated that anthocyanin was a mixed inhibitor with the maximum inhibition efficiency of 94.44% at 800 mg/L. Result of the EIS showed that polarization resistance increased from 54.8 Ω cm2 to 877.8 Ω cm2 after anthocyanin was added. The surface morphology by SEM and SECM further substantiated the inhibitive and adsorptive behavior of anthocyanin on mild steel surface. Quantum chemical calculations revealed that anthocyanin was related to a high electron density and active binding sites, and cyanidin-3-rutinoside has the smallest ΔE value (2.615 eV), which could play a significant role in the corrosion inhibition of mild steel.