Polyol-Mediated Synthesis of Ultrafine TiO2 Nanocrystals and Tailored Physiochemical Properties by Ni Doping

A polyol-mediated synthetic method has been developed to prepare ultrafine anatase TiO2 nanocrystals of about 2-5 nm in size, which, when connected, form a network with porous structure. The physiochemical properties of these nanocrystals are tuned by doping with Ni. High-resolution X-ray photoelectron spectroscopy analysis revealed that Ni incorporates into the TiO2 framework to form a Ti-O-Ni chain. Nitrogen adsorption measurements further showed that Ni doping can greatly enhance the surface area of these anatase TiO2 nanocrystals from 143 to 266 m(2)/g. Using UV-vis diffuse reflectance spectroscopy analysis, we found that the Ni doping reduced the band gap from 3.08 to 2.73 eV and permitted these TiO2 nanocrystals to successfully absorb light in the visible region. First principles band structure calculations were carried out to study the electronic origin of the nickel-induced optical absorption. The photocatalytic activities of the samples were tested through degradation of NO under typical indoor air flow and simulated solar light environment. Ni-doped TiO2 was found to exhibit much higher photocatalytic activity than its undoped counterpart and P25. The enhancement of photocatalytic activity of Ni-doped TiO2 is attributed to the larger surface area and the band gap narrowing tuned by nickel doping.