title: Structures and charging of alpha-alumina (0001)/water interfaces studied by sum-frequency vibrational spectroscopy.
abstract: Sum-frequency vibrational spectroscopy in the OH stretch region was employed to study structures of water/alpha-Al2O3 (0001) interfaces at different pH values. Observed spectra indicate that protonation and deprotonation of the alumina surface dominate at low and high pH, respectively, with the interface positively and negatively charged accordingly. The point of zero charge (pzc) appears at pH approximately = 6.3, which is close to the values obtained from streaming potential and second-harmonic generation studies. It is significantly lower than the pzc of alumina powder. The result can be understood from the pK values of protonation and deprotonation at the water/alpha-Al2O3 (0001) interface. The pzc of amorphous alumina was found to be similar to that of powder alumina.
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: Luning
authors.initials: L
authors.lastname: Zhang
authors.forename: Chuanshan
authors.initials: C
authors.lastname: Tian
authors.forename: Glenn A
authors.initials: GA
authors.lastname: Waychunas
authors.forename: Y Ron
authors.initials: YR
authors.lastname: Shen