Experimental investigation of the interaction of water and methanol with anatase-TiO2(101)

The interaction of water and methanol with well-defined (1 x 1) 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, 190, 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, 170, 260, 410, 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 energies for water and methanol were found to shift to an similar to0.75 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.