Synthesis of Crystal-Controlled TiO2 Nanorods by a Hydrothermal Method: Rutile and Brookite as Highly Active Photocatalysts

Rutile, anatase, and brookite TiO 2 nanorods (TNs) with specific exposed crystal facets have been obtained by a hydrothermal method using peroxide titanic acid (PTA) solution of different pH values. Below pH PTA 10, the condensing complex is uncharged Ti 2 O 5 (OH) 2 (H 2 O) 4 or cations Ti 2 O 5 (H 2 O) 6 2+, and the corner-shared bonding easily occurs to form rutile phase. Above pH PTA 10, the condensing species is anions Ti 2 O 5 (OH) 4 (H 2 O) 2 2–, resulting in the larger probability of edge-shared bonding which favor the formation of anatase TiO 2 . Brookite whose structure contains both corner-shared and edge-shared bonding can be formed when pH PTA equals to 10. Rutile TN synthesized from PTA solution at pH 4 showed the optimal photocatalytic oxidation activity for MB degradation; Brookite TN exhibited the highest photocatalytic activity for reduction of Cr (VI) despite that it does not exhibit the largest surface area. The presence of a spatial separation of redox sites in faceted rutile TiO 2 nanorod determined the photocatalytic activity of MB decomposition. Compared with rutile and anatase phase, the optimal photocatalytic reduction activity of brookite TN might be resulting from a cathodic shift of the conduction band.