Surface-enhanced Raman spectroscopy has been successfully extended to the study of corrosion inhibition of bare iron and nickel metals. The inhibition effects of benzotriazole (BTAH) for copper, iron, and nickel electrodes in 0.1 M KCl solution were investigated by using both polarization curves and in situ Raman techniques. The protective films formed on copper and iron surfaces, in the presence of BTAH, are characterized as [Cu I BTA]n and [Fe II (BTA)2]n, respectively. The formation of Fe-N coordinated bonds and the deprotonation of the triazole ring may occur while BTAH interacts with the iron surface. On the contrary, BTAH may interact with the nickel surface as neutral molecules in the whole potential range investigated resulting in a poor inhibition effect. The surface complex is characterized as [Ni-BTAH]. The potential dependence of the Raman spectra on copper and iron shows that the BTAion in the surface complex may rebind with H + at more negative potentials and accordingly the inhibition efficiency of benzotriazole decreases.

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The different initial interactions of benzotriazole (BTAH) with iron in both 0.5 M H2SO4 and simulated saline water (3.4% NaCl) have been investigated systematically by using a confocal microprobe Raman system, surface-enhanced Raman spectroscopy (SERS), and electrochemical potentiodynamic polarization curves. The SERS spectra of BTAH at the bare iron electrodes in both 0.5 M H2SO4 and simulated saline water have been obtained successfully for the first time. Electrochemical measurements show that the inhibition efficiency of BTAH is higher in saline water than that in acid solution, which is in accordance with the identification of the surface interaction on the basis of the SERS data. BTAH may be physisorbed onto the iron surface through its neutral molecule form or protonated BTAH2 + ions. While in saline water, the formation of the surface coordination compound characterized as Fe(II)-BTA may contribute to the outstanding spectral features. A cleavage of the NH bond is believed to occur while adsorption of BTAH onto iron proceeds. This more compact surface film results in a higher inhibition efficiency in comparison with that in an acid solution.

Surface-enhanced Raman scattering (SERS) spectrum of imidazole adsorbed at a silver electrode in nonaqueous acetonitrile solution has been investigated as a function of applied potential. The electrolyte is 0.1 M LiClO4. Results show that imidazole adsorbs on silver as a neutral molecule via the pyridine nitrogen atom. Coadsorption of perchlorate anion with imidazole, possibly by forming intermolecular hydrogen bonding, is also suggested by the enhancement of the ClO4 - band at 933 cm-1. An edge-on orientation of imidazole at more positive potentials is proposed by the observation of the increase in frequency of the ring breathing modes, along with the enhancement of most of the in-plane modes of imidazole. When the potential is made more negative, particularly near −0.5 V, the imidazole ring may change from vertical to be slightly inclined to the silver surface at an intermediate angle from the surface normal. At the same time, a slight rotation of the imidazole ring plane may occur, evidenced by the observation of the changes in relative intensity of ν(C2H) to asymmetric ν(HCCH) vibration. In addition, the decomposition reaction of the solvent acetonitrile at the silver surface is also assumed by the appearance of a characteristic band of cyanide ion at ca. 2110 cm-1. Competitive adsorption of imidazole at more positive potentials inhibits significantly the decomposition of acetonitrile.