SERS, SEIRA, TPD, and DFT Study of Cyanobenzoic Acid Isomer Film Growth on Silver Nanostructured Films and Powder

A combination of surface-enhanced infrared absorption (SEIRA), surface-enhanced Raman spectroscopy (SERS), temperature programmed desorption (TPD), and density functional theory (DFT) calculations were used to explore the adsorption of the cyanobenzoic acid (CBA) isomers on evaporated silver films and a silver powder. All substrates exhibited the nanoscale roughness appropriate for SERS and SEIRA enhancement. SERS and DFT demonstrated that each of the CBA isomers adsorbed to a silver film as a carboxylate ion. The impact of resonance effects in SERS spectra among the different CBA isomers was discussed. For 2-cyanobenzoic acid (2CBA), the DFT calculated dipole moment was 5.87 D, for 3-cyanobenzoic acid (3CBA), the dipole moment was 5.31 D, and for 4-cyanobenzoic acid (4CBA), the dipole moment was 3.57 D. It was shown with SEIRA that 3CBA and 2CBA underwent significant ionization in the multilayer when deposition occurred using an alkane solvent with nonpolar bonds. 4CBA adsorption was not impacted by the polar properties of the deposition solvent because 4CBA had a smaller dipole moment than 2CBA and 3CBA which induced less attraction to the underlying silver nanostructures. A comparison of the SEIRA results on silver films versus silver powder highlighted the importance of the nanoscale nature of the silver substrate on film growth during deposition of the CBA isomers. Details of the TPD spectra of each of the CBA isomers on the silver powder were also outlined. It is anticipated that this work will have a significant impact in areas of nanotechnology, applied physics, biochemistry, and organic synthesis where benzonitrile chemistry is important.