DFT and electrochemical studies: N, N′, N″, N′″-tetrakis(2-methylpyridyl)-1,4,8,11-tetraazacyclotetradecane (TMPC) as an efficient corrosion inhibitor for carbon steel surfaces in an acid medium

The corrosion inhibition of N, N′, N″, N′″--tetrakis(2-methylpyridyl)-1,4,8,11-tetraazacyclotetradecane (TMPC) was analyzed by electrochemical and theoretical methods. Electrochemical data show that TMPC forms an adsorption layer over an iron surface that obeys the Langmuir isotherm (δG°ads of -32.96 kJ mol_-1). Furthermore, the value is higher than -20 kJ mol_-1 but less than -40 kJ mol_-1, thus it is classified as a conversion stage of physical adsorption to chemical adsorption or a comprehensive adsorption. Furthermore, the fractal dimension of the electrode surface, estimated by an impedance depression angle of a semicircle, shows that the surface is homogeneously covered by the formation of an inhibitor film. The DFT results show that TMPC possesses corrosion inhibition properties that give up its p orbital electron density through its HOMO orbital to the metal LUMO to form an adsorption layer.