Novel cost-effective and high-performance green inhibitor based on aqueous Peganum harmala seed extract for mild steel corrosion in HCl solution: Detailed experimental and electronic/atomic level computational explorations

Traditional corrosion inhibitors have been frequently used for metal protection against strong acids. However, most of them are hazardous/toxic compounds with high cost. Therefore, due to the strict environmentally friendly regulation the green and low-cost compounds from renewable sources like plant extracts have gained high consideration in recent applications. In the present study, the aqueous Peganum harmala seed extract, commonly called Esfand, a cost-effective and green source of amine-rich molecules like harmaline, harmalol, harmane, harmol, vasicine and vasicinone, was selected to inhibit mild steel corrosion in 1 mol·L−1 HCl media. The Peganum harmala seed extract composition was investigated by FT-IR and UV–Visible analysis. The Peganum harmala seed extract corrosion inhibition behavior on mild steel in HCl solution was examined through electrochemical methods (EIS and polarization), surface analyses (AFM, SEM and contact angle) and theoretical studies (MD, DFT and MC). The presence of many electron donor atoms based on nitrogen and oxygen in the molecules of Peganum harmala seed extract is responsible for its effective adsorption behavior on metal surface through chelation with iron atoms. Experimental exploration declared that with the increase in Peganum harmala seed extract concentration and time of immersion the inhibition power increased and reached the high value of 95%. Peganum harmala seed extract behaved as a mixed type inhibitor and properly obeyed an adsorption isotherm of Freundlich. Results of AFM and SEM analyses clearly proved that Peganum harmala molecules adsorption on the metallic surface considerably reduced its dissolution rate and resulted in clean and smooth surface. The use of water instead of ethanol for extraction of major organic compounds of Peganum harmala seed, being non-toxic and cost-effective and exhibiting inhibition efficiency much greater than other green inhibitors (which are almost in the range of 80–90%), propose the Peganum harmala seed as a unique green corrosion inhibitor. Furthermore, the detailed theoretical observations elucidated from molecular simulations and density functional theory affirmed the Peganum harmala compounds adhesion via reactive sites.