The photocatalytic activity of a nanostrcutured rutile consisting of oriented nanoneedles was studied by comparing a reaction of a thiazin dye, methylene blue, with dispersed rutile nanoneedles and anatase nanoparticles. Demethylation of methylene blue occurred preferably through partial oxidation under UV irradiation with the bundled rutile nanoneedles having small clearance gaps. On the other hand, most of the dye molecules were directly decolorized through the initiation by a reductive pathway with the dispersed rutile nanorods and the anatase nanoparticles. The reductive sites on (110) of the rutile nanoneedles were dominantly located in the small gaps inside the bundled architecture. Because the diffusion of large-sized organic molecules to the reductive sites would be restricted, the oxidative route for the dye molecule was selectively induced with the rutile bundles under UV irradiation.
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