Agricultural Waste of Sunflower Stalk Extract as a Novel Green Inhibitor on Aluminium Corrosion in Hcl Solution

Abstract

Utilization of agricultural waste sunflower stalks to develop green and efficient corrosion inhibitors can be "turn waste into treasure". In this work, sunflower (Helianthus annuus L.) stalks extract (HASE) was prepared for the first time by ultrasonic extraction method. To investigate the effectiveness and mechanism of HASE's aluminium corrosion prevention in HCl media, a variety of experimental techniques and theoretical modelling were utilized. The findings show that in HCl solution at 20 ℃, 500 mg L-1 HASE has an inhibitory effectiveness of up to 93.3%. HASE adsorption adheres to Langmuir adsorption isotherm model, which includes both chemisorption and physisorption in its adsorption behaviour on aluminium surface. As a mixed-type inhibitor, HASE mainly slows down cathodic hydrogen precipitation process. HASE greatly lowers the double layer capacitance and dramatically raising charge transfer resistance. The inhibitory action of HASE on aluminium in HCl medium is confirmed by corrosive solution testing and metal surface characterisation, which also provides evidence of inhibitor molecule adsorption. The active adsorption sites for the primary effective organic compounds in HASE are the oxygen atoms and benzene rings. At the molecular level, inhibitor molecules can parallel adsorb on Al (111) substrate according to molecular dynamics (MD) simulation.

Keywords: Sunflower stalk extract, Aluminium, Hydrochloric acid, Corrosion inhibition, adsorption