PNNL

Abstract

The interaction of water and methanol with well defined (1x1) terminated surfaces of anatase-TiO2(101) were investigated with temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). For water, three desorption states were observed in the TPD spectra at 160 K, 190 K, and 250 K. The three desorption peaks were assigned to multilayer water, water adsorbed to 2-fold coordinated O, and water adsorbed to 5-fold coordinated Ti, respectively. The TPD spectra for methanol were more complicated. For methanol five desorption peaks were observed in the TPD spectra at 135 K, 170 K, 260 K, 410 K, and 610 K. The five desorption peaks were assigned to multilayer methanol, methanol adsorbed to 2-fold coordinated O, methanol adsorbed to 5-fold coordinated Ti, methoxy adsorbed to 5-fold coordinated Ti, and methoxy adsorbed to Ti at step edges, respectively. The XPS results indicated that the adsorbed water and methanol were predominantly bound to the surface in a molecular state, with no evidence for dissociation. Furthermore, the O 1s core-level binding energy for water and methanol were found to shift to ~0.75 eV lower binding energy, for coverages before multilayer desorption is observed in the TPD spectra. The O 1s core-level binding energy shift appears to be linear in this region, and corresponds to water and methanol bonding to Ti cation and O anion sites on the surface. The C 1s core-level binding energy for methanol was found to remain approximately constant in the same coverage regime.