Cr3+-Doped Anatase-Phase TiO2 Nanocrystals with (101) and (004) Dominant Facets: Synthesis and Characterization

Anatase-phase rod-shaped TiO2 nanocrystals are prepared by the solvothermal method, the surface is metalated, and doped nanocrystals are achieved by thermal diffusion of surface metal ions. Incorporation of dopant ions into TiO2 lattice enhances the visible light absorption of the material and in some cases can increase the rate of photocatalysis. Even though there are overflowing studies on the preparation of doped TiO2 materials, there are no methods that enable the precise control of dopant concentration in TiO2 nanocrystals. We have developed a method to load the surface of oleic acid stabilized anatase-phase rod-shaped TiO2 nanocrystals (approx. 3 +/- 1 nm diameter and 40 +/- 10 nm long) with transition metal ions followed by ion diffusion to prepare metal-doped nanocrystals with exact control of the dopant concentration. Specifically, in this work, Cr3+ adsorbs TiO2 nanorods to yield a green colloid, followed by ion diffusion at elevated temperature. After removal of any remaining surface Cr3+, tan-colored chromium-doped TiO2 nanorods can be obtained. Electron microscopy and powder X-ray diffraction indicate no change in nanocrystal size and morphology throughout the process. The TiO2 nanorods play an important role in photocatalysis owing to their excellent chemical and physical properties. Titanium dioxide is a low-cost, non-toxic, highly stable, chemically robust material. Doped TiO2 materials have found application in photocatalysis (oxidative degradation of organic molecules, hydrogen evolution), photovoltaics, solar cells, lithium-ion batteries, supercapacitors, and sensors. TiO2 photocatalysis is also the basis for clean energy technologies, such as dye-sensitized solar cells and photoelectrochemical cells. In photocatalysis applications, nanocrystalline TiO2 presents advantages of a high surface area, ability to control the surface facet, and minimized bulk recombination.