Adsorption and inhibitive properties of Apigenin derivatives as eco-friendly corrosion inhibitors for brass in nitric acid solution

Six apigenin derivatives were synthesized through Mannich reaction by using apigenin isolated from Hypericum perforatum as raw material. The inhibition performance of these apigenin derivatives were investigated as eco-friendly corrosion inhibitors for brass in 1.0 M HNO3 solution by means of weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. The obtained results show that the as-synthesized apigenin derivatives act as efficient inhibitors for brass in 1.0 M HNO3. The inhibition efficiency increased with the increase in inhibitor concentration but decreased with a rise in temperature. The inhibition efficiency higher than 90% for these compounds was found even at a low concentration of 30 mg L-1, which is superior to the commonly used synthetic organic corrosion inhibitors for brass in acidic media. Electrochemical studies indicate that the inhibitors are of mixed type but predominantly cathodic in HNO3 solution. The inhibitor performance depends on the adsorption of the molecules on the metal surface. The thermodynamic parameters for inhibiting process were calculated according to the statistical model. The calculated thermodynamic parameters revealed that the adsorption of these inhibitors on brass surface was spontaneous, controlled by physiochemical processes. The adsorption behaviour of these apigenin derivatives on the surface of brass was analyzed utilizing SEM, AFM, XPS, and Raman spectroscopy measurements. The results confirmed that the apigenin derivatives prevented corrosion of brass by forming protective layer on its surface.