Electrochemical, thermodynamic and DFT studies of Fomitopsis pinicola as green corrosion inhibitor for carbon steel in sulfuric acid

In this work, the methanolic extract of Fomitopsis pinicola has been evaluated as a green corrosion inhibitor for the dissolution of 1018 carbon steel in 0.5 M sulfuric acid. For this, gravimetric tests and electrochemical methods such as potentiodynamic polarization curves, linear polarization resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) techniques were used. These tests were aided with Infrared and GC-MS analytical techniques. In addition to this, theoretical calculation with the use of the density functional theory (DFT) technique has been used to correlate the electronic extract properties and its inhibitory capacity. Weight loss results have shown an inhibitor efficiency of 85 % with the addition of 400 ppm. Thermodynamic parameters have shown that Fomitopsis pinicola extract is physically adsorbed onto the steel following a Langmuir adsorption isotherm. Potentiodynamic polarization curves showed that the extract behaves as a mixed type of corrosion inhibitor inducing the formation of a protective film onto the steel surface. In the presence of the Fomitopsis pinicola extract, a more resistive film obtained the highest polarization resistance value when 400 ppm of extract was used. In addition to this, as the concentration of the extract increased the charge transfer resistance and the double electrochemical layer capacitance decreased. GC-MS results indicated that main compounds contained in the Fomitopsis pinicola extract were Dehydrergosterol, Hydrazino-acetic acid ethyl ester, and Phthalic acid, di (2-propylpentyl) ester, whereas theoretical calculations showed that the highest E-HOMO and lowest E-LUMO values correspond to Dehydrergosterol and the Phthalic acid, which are the responsible for the extract inhibitory properties.