Anatase titanium(IV) oxide (TiO 2 ) particles with specific exposed crystal faces were prepared by hydrothermal treatment of peroxo titanic acid (PTA) solution with polyvinyl alcohol as a shape-control reagent. Crystal phase, shape, and size of TiO 2 particles were found to be greatly dependent on pH value of PTA solution and time of hydrothermal treatment. TiO 2 particles prepared from PTA solution of pH 7 had {101} and {001} exposed crystal faces, and the shape of TiO 2 particles changed with the time of hydrothermal treatment. The prepared TiO 2 particles with specific exposed crystal faces showed higher photocatalytic activity for acetaldehyde decomposition than commercial spherical TiO 2 particles. This result implies that back reaction was prevented by spatial separation of redox sites in the particles because of selective migration of electrons and positive holes to specific exposed crystal faces and/or different reactivity of electrons and positive holes on the specific exposed crystal face. Furthermore, the shape evolution of TiO 2 particles showed a relationship with photocatalytic activity, and a stacked structure of octahedral anatase showed the highest photocatalytic activity due to both oxidation and reduction sites with large surface area.
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Murakami et al. (2009) studied this question.
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