Adsorption configuration of sodium 2-quinoxalinecarboxylate on iron substrate: Investigation by in situ SERS, XPS and theoretical calculation

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2016-03, Vol.156, p.123-130
• Main Authors: Huo, Sheng-Juan, He, Jin-Mei, Chen, Li-Hong, Fang, Jian-Hui
• Format: Article
• Language: English
• Subjects: Iron; Sodium 2-quinoxalinecarboxylate; Surface-enhanced Raman scattering spectroscopy; Theoretical calculation; X-ray photoelectron spectroscopy
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2015.11.033

The adsorption geometry of sodium 2-quinoxalinecarboxylate (2-QC) on iron surface was investigated by in situ surface-enhanced Raman scattering spectroscopy (SERS) and X-ray photoelectron spectroscopy (XPS) measurements. The density functional theory (DFT) calculations predicted that 2-QC ion was a highly efficient inhibitor and N as well as O atoms were the possible adsorption centers, and theoretically offered the Raman-active band position and intensity. Potential-dependent SERS results suggested that the 2-QC strongly bonded to the iron surface via the lone pair electrons of the two O atoms of the carboxylate group in a bidentate configuration with a vertical orientation at more positive potentials; However, at −1.0V, only one O atom of the carboxylate and the neighboring N1 atom (or very close to surface) adsorbed on the iron surface forming an unidentate configuration with a titled orientation. The ions did not remain on the iron surface at more negative potentials. [Display omitted] •NBO, HOMO–LUMO energy, dipole moment, Raman-active bands and assignments of sodium 2-QC have been carried out.•XPS measurements evidenced that 2-QC adsorbed on iron via two equivalent O atoms in carboxylate group.•Interesting potential induced structural changes were observed by EC-SERS.•Experimental results were in accordance with DFT prediction.