Adsorption Studies of p-Aminobenzoic Acid on the Anatase TiO₂(101) Surface

Abstract

The adsorption of p-aminobenzoic acid (pABA) on the anatase TiO2(101) surface has been investigated using synchrotron radiation photoelectron spectroscopy, near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT). Photoelectron spectroscopy indicates that the molecule is adsorbed in a bidentate mode through the carboxyl group following deprotonation. NEXAFS spectroscopy and DFT calculations of the adsorption structures indicate the ordering of a monolayer of the amino acid on the surface with the plane of the ring in an almost upright orientation. The adsorption of pABA on nanoparticulate TiO2 leads to a red shift of the optical absorption relative to bare TiO2 nanoparticles. DFT and valence band photoelectron spectroscopy suggest that the shift is attributed to the presence of the highest occupied molecular orbitals in the TiO2 band gap region and the presence of new molecularly derived states near the foot of the TiO2 conduction band.

Inner-shell excitation spectroscopy of peroxides

“…There is also a broad band from 290 to 310 eV in the experimental spectrum, in which there are three discernible maxima located at 293.2, 299.5 and 303.2 eV. The C 1s spectra of benzoic acid [38] and aminobenzoic acid [39] adsorbed to TiO 2 (1 1 0) both exhibit the two strong features seen in the gas phase spectrum of benzoic acid at the same energies. Fig.…”

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“…Electronic excitation is represented as dashed red arrows; this scheme does not necessarily represent the physical location where events take place. Energy levels were taken from the literature 39 – 43 . …”