Specific and high-affinity adsorption of volatile organic compounds on titanium dioxide surface

The interaction between metal oxides and volatile organic compounds (VOCs) from the ambient atmosphere plays an important role in environmental and catalytic applications. Previous scanning probe microscopy and x-ray spectroscopy studies revealed surprisingly that the TiO2 [rutile (110)] surface selectively adsorbed atmospheric carboxylic acids, which typically exist in only parts-per-billion concentrations. In this work, we used in situ sum-frequency vibrational spectroscopy to study the interaction between rutile (110) and typical VOC molecules, including formic acid, acetic acid, and formaldehyde. Spectra from all three adsorbed molecules on rutile (110) were similar to the rutile surface spectrum in the ambient atmosphere, showing a broad resonance near 2950 cm-1 that can be attributed to the bridging bidentate adsorption of corresponding compounds. In contrast, on a fused silica surface, a molecular monodentate adsorption configuration was observed for all the molecules, with aliphatic carbons appearing to be the dominant adventitious species.