Electronic/atomic level fundamental theoretical evaluations combined with electrochemical/surface examinations of Tamarindus indiaca aqueous extract as a new green inhibitor for mild steel in acidic solution (HCl 1 M)

Abstract

Abstract Green/sustainable plant origin organic molecules with structures including polar functional groups, heteroatoms and aromatic rings play a vital role in the adsorption and inhibition effectiveness on metal substance in harsh acidic environments. The components like apigenin, eriodictyol, naringenin, taxifolin in Tamarindus indiaca extract can easily adsorb on the mild steel (MS) surface and sufficiently control its rate of corrosion in contact with aggressive acids. In this paper, the corrosion retardation potentiality of Tamarindus indiaca extract for MS in 1 M HCl was experimentally (EIS, potentiodynamic polarization, SEM, AFM and contact angle) and theoretically (basic atomic/electronic scale tools) explored. EIS outcomes proposed 93% numerical inhibition power for 800 ppm Tamarindus indiaca extract after 2.5 h steel immersion in aggressive media. Potentiodynamic polarization experiment results declared that Tamarindus indiaca extract operated as combined anodic/cathodic green inhibitor with cathodic inhibition prevalence. Final results demonstrated the icorr value reduction from 0.98 µA cm−2 (for bare sample) to 0.14 µA cm−2 (for 800 ppm inhibitor concentration), demonstrating 85% inhibition performance in acidic solution. Also, the weight loss measurements depicted 93% efficiency after 4 h steel exposure to 1 M HCl media (solution temperature = 25 °C). The temperature effect on the inhibitor properties was evaluated in the temperature range of 25 °C to 55 °C and outcomes showed endothermic reactions occurrence for protection. Based on the AFM micrographs it was shown that HCl solution combined with 800 ppm Tamarindus indiaca extract led to the most smoothened MS surface and the average roughness decreased to lower values (average roughness for uninhibited sample = 119 nm and for inhibited sample = 31 nm). Conclusions derived from different isotherms demonstrated that following Langmuir isotherm a mono inhibitive layer of Tamarindus indiaca extract molecules covered the iron substance. Molecular simulations strongly affirmed the preference of Tamarindus indiaca extract molecules for adsorption on the MS substrate. The DFT explorations highlighted that the aromatic rings and oxygen heteroatoms behaved as influential local sites for molecular adsorption.