LAUSR

A titanium metal surface was heated with an alkali metal chloride in order to produce a phase transition from amorphous titania to crystalline titania on the surface. The crystalline phase was identified by XRD and Raman spectroscopic analyses. The anatase-type titania phase was formed by heating the surface with KCl or CsCl at 500–550 °C for 3 h. The heating at a higher temperature caused a transition to the rutile-type titania. The amorphous titania layer on the surface of the titanium metal was reduced with assistance of the alkali metal chloride and re-oxidized to transform into the metastable anatase-type titania phase under certain conditions. The surface layer having the anatase titania phase exhibited the faster photocatalytic degradation of acetaldehyde, which was demonstrated by gas chromatography and FTIR spectroscopic measurement. Furthermore, the titanium metal coated with KCl and subsequent titanium alkoxide sol was heated in order to form a thicker titania film. The structural characterization of the film surface was conducted by XRD, Raman spectroscopy, and XPS analyses. Larger anatase-type titania crystallites were clearly formed on the titanium metal surface, to which they strongly adhered by heating at 500–550 °C for 30 min. The deposited KCl promoted the crystallization of the original amorphous titania and coated titania gel layers. The particle size of the titania film was also confirmed by SEM and TEM observations. The surface layer having the thicker anatase titania phase exhibited the faster photocatalytic degradation of acetaldehyde.