Dependence of Photocatalytic Activity on Aspect Ratio of Shape-Controlled Rutile Titanium(IV) Oxide Nanorods

Shape-controlled rutile titanium(IV) oxide (TiO2) nanorods with various aspect ratios were prepared by two-step synthesis in the presence of two kinds of inorganic anions. The first synthesis step from titanium(III) chloride solution induced the formation of aggregated needlelike rutile TiO2, the shape of which largely depended on the inorganic anion used. Moreover, shape-controlled rutile TiO2 rods with {110} side crystal faces and {111} and/or {001} edge crystal faces were obtained by hydrothermal treatment of the needlelike rutile TiO2. Their aspect ratios were largely influenced by the starting material used in the hydrothermal treatment. The photocatalytic activity for decomposition of acetaldehyde increased with decreasing aspect ratio because the surface area ratio of {111} and/or {001} to {110} exposed crystal faces, which are attributed to oxidation and reduction sites respectively, became more optimal.