Adsorption and Orientation of Isomeric Phthalic Acids on Alumina Surface Observed by Inelastic Electron Tunneling Spectroscopy

Abstract

Abstract The vibrational spectra of phthalic, isophthalic and terephthalic acid adsorbed onto the alumina surface have been measured by using inelastic electron tunneling spectroscopy. The tunneling spectra of these acids were obtained by liquid-phase doping with water or various alcohol solutions. The detailed assignments for these spectra are given, together with a comparison of their infrared and Raman spectra. It has been found that both phthalic and isophthalic acid are adsorbed onto the alumina surface mainly as the dicarboxylate ions. However, a comparison between the tunneling spectra of terephthalic and p-acetylbenzoic acid shows that terephthalic acid is adsorbed predominantly as the monocarboxylate ion onto the surface when doped with alcohol solutions. Hydrogen bonding is observed among the adsorbed hydrogen terephthalate ions. These results show a difference in their orientation and different probabilities of chemical interaction between the alumina surface and the carboxyl groups of the adsorbed isomeric phthalic acids.