Review on porphyrins, phthalocyanines and their derivatives as corrosion inhibitors

Abstract

The use of porphyrins, phthalocyanines and their derivatives as corrosion inhibitors (CI) is considered in the work. These macromolecules contain four pyrrole rings linked into a flat cycle by four –CH= groups in the case of porphyrins, and in the case of phthalocyanines, by four – N= atoms. Four pyrrole nitrogen atoms form an inner square that can be occupied by a metal cation. The high inhibitory effect of these macromolecules is explained by their strong chemisorption on the surface of metals. Such adsorption is determined by the planarity of the molecule and a multi-loop conjugated system with lone pair electrons of nitrogen atoms. The π-electrons of the 16-membered ring can make a large contribution to the π-interaction. The results of gravimetric measurements, electrochemical studies by the methods of potentiodynamic polarization curves, as well as electrochemical impedance, the main mechanisms of the formation of these thin-layer organic inhibitors of ultrathin (nanoscale) protective layers on the surfaces of different metals in various media, mainly acidic, are discussed. In the given studies, the qualitative composition and structure of the surface adsorption layers were studied using X-ray photoelectron and vibrational spectroscopy, and the surface morphology was studied using a scanning electron microscope. Adsorption in solution in situ was studied by reflective ellipsometry with determination of the free energy of adsorption. Attempts to correlate the inhibition efficiency of macrocyclic corrosion inhibitors with the results of quantum chemical calculations were made in a number of studies.