activity of pure TiO2 is limited to ultraviolet
(UV) light due to the wide bandgap of anatase and rutile phases. The
bandgap of high-pressure phases of TiO2 can theoretically
coincide with visible light, but these phases are unstable at ambient
pressure. In this work, the high-pressure TiO2-II (columbite)
phase with large fractions of oxygen vacancies was stabilized by inducing
plastic strain to anatase under 6 GPa. The material could absorb visible
light as a consequence of bandgap narrowing by ∼0.7 eV. Formation
of nanosized TiO2-II enhanced the hydrogen generation efficiency
under visible light, and the efficiency improved after removing the
oxygen vacancies by annealing.
Wettability and the adhesion force between two silica particles were measured as a function of relative humidity. The wettability of silica particles was controlled by rehydroxylation and modification by hexamethyldisilazane and evaluated by a preferential dispersion test, heat of immersion, and water adsorption. The adhesion force between two particles was measured by atomic force microscopy using a "colloidal technique". The wettability varied from hydrophilic to hydrophobic at trimethylsilyl density ) 1.0 nm -2 as modified groups shielded the residual silanol groups and hindered the formation of a capillary bridge between the two particles. This "hindrance effect" is thought to result in the absence of a critical increase in adhesion force at high relative humidity and also the reduction of surface energy at low humidity where hydrogen bonding dominated the adhesion force.
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