Synthesis of baicalin derivatives as eco-friendly green corrosion inhibitors for aluminum in hydrochloric acid solution

Three baicalin derivatives named methyl ester of baicalin (BM), ethyl ester of baicalin (BE), and n-propyl ester of baicalin (BP) were synthesized in the laboratory using the traditional Chinese medicinal herb Scutellaria baicalensis Georgi as raw material. The inhibition effect of the as-synthesized baicalin derivatives was investigated as eco-friendly green inhibitors on the corrosion of aluminum in 1.0 M HCl solution by weight loss and various electrochemical techniques. Results show that the baicalin derivatives exhibit excellent performance as inhibitors for aluminum corrosion. The synthesized baicalin derivatives suppress both the anodic and cathodic process and the compounds behave as mixed-type corrosion inhibitors for aluminum in HCl solution. Also, results obtained indicate that compound BM is the best inhibitor and the effectiveness of these inhibitors decreases in the order of BM > BE > BP. The maximum inhibition efficiency obtained at 25 degrees C using BM = 0.9 g/l was similar to 95%. The interpretation of the inhibition due to adsorption of the compounds on the aluminum surface is according to Langmuir adsorption isotherm. The free energy of adsorption for inhibition process was determined on the basis of Langmuir adsorption isotherm. Surface analyses were performed to establish the mechanism of corrosion inhibition of aluminum in acidic solution. The formation of the adsorbed baicalin-Al3+ complex on the metal surface led to slow down the corrosion rate of aluminum and improvement of the inhibition process.