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.

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