Surface-enhanced Raman scattering (SERS) of benzotriazole derivative corrosion inhibitor prepared in aqueous media

The surface structure and inhibiting properties of a benzotriazole (BTAH) derivative, dibenzotriazole-1-yl-methyloctylamine (DBTO), on a copper surface in 1 M sodium acetate solution (pH 5.8) were investigated by cyclic voltammetry, impedance spectroscopy and Raman spectroscopy. Raman spectra of pure DBTO and BTAH, their complexes with Cu (I) ions and surface-enhanced Raman scattering (SERS) spectra of DBTO and BTAH molecules on a copper surface were measured and analysed. Almost identical SERS spectra of DBTO and BTAH on a copper surface, as well as very similar inhibiting properties and structure parameters of their surface films obtained by impedance measurements, pointed to identical chemical composition. It seems that, after having been adsorbed on a copper surface, DBTO molecules lost their aliphatic chain and reacted with copper(I) ions to form a surface layer. Both Raman and impedance spectra have shown a multilayer structure of the surface film: Cu/Cu2O/Cu(I) inhibitor. The results of impedance measurements indicated that the surface film was of a dielectric nature. Similarly to BTAH, its thickness and protection against corrosion increased with increasing inhibitor concentrations and/or ageing. At low inhibitor concentrations and shorter immersion time, DBTO molecules were chemically adsorbed on the electrode surface. The adsorptive behaviour followed a Frumkin adsorption isotherm with free energy of adsorption ΔG = −19.5 kJ mol−1.