Adsorption of acetic and trifluoroacetic acid on the TiO2(110) surface

A. S. Foster, R. M. Nieminen
2004 Journal of Chemical Physics  
Infrared spectroscopy study of adsorption and photodecomposition of formic acid on reduced and defective rutile TiO 2 (110) surfaces. Articles you may be interested in The adsorption of α-cyanoacrylic acid on anatase TiO2 (101) and (001) surfaces: A density functional theory study Adsorption and thermal decomposition of acetic acid on Si ( 111 ) 7 × 7 studied by vibrational electron energy loss spectroscopy Adsorption and photodecomposition of formic acid on rutile TiO 2 (110) have been
more » ... ated with infrared reflection-absorption spectroscopy (IRRAS) employing p-and s-polarized light along the [001] and [1 10] crystal directions. The single crystal surfaces were prepared either by sputtering and annealing in ultrahigh vacuum (UHV) to obtain a reduced surface (r-TiO 2 ), or by sputtering without annealing to create a rough, highly defective surface (sp-TiO 2 ). Results are compared with corresponding measurements on rutile nanocrystals performed in synthetic air. IRRAS spectra obtained on r-TiO 2 and rutile nanocrystals are very similar, and show that in both cases formic acid dissociates and is predominately adsorbed as a bridging bidentate formate species, and that the formate adsorption structure on the nanocrystals is dominated by interactions with majority (110) surfaces. In contrast, the IRRAS spectra on sp-TiO 2 are different, with only minor spectral features associated with (110) surfaces and lost azimuthal symmetry, both of which imply changed adsorption geometry due to bonding to low-coordinated Ti atoms with lower valences. The UV-induced rate of formate photodecomposition is about 30 times higher on rutile nanocrystals in synthetic air compared with sp-TiO 2 under UHV conditions, and even larger than on r-TiO 2 . These differences are explained by the lack of oxygen and limited hydroxyl coverage under UHV conditions. The difference in reactivity between the r-TiO 2 and sp-TiO 2 surfaces is attributed to a high concentration of strongly bonded bridging bidentate formate species on the (110) surface, which lowers its reactivity. The results point to a pressure gap where the availability of molecular oxygen and the hydroxyl concentration limit the photoreactivity in UHV leading to an almost 20-fold decrease of the formate degradation rate in UHV. In contrast, the structure represented by the single crystal (110) surface is shown to capture the essential structural properties, which dictates the formic acid adsorption and adsorption structure of rutile nanocrystals.
doi:10.1063/1.1802652 pmid:15527369 fatcat:xxi4gypslffv5oaeirsjdadhtm