Shape Evolution of Highly Crystalline Anatase TiO2 Nanobipyramids

Introduced by sodium fluoride, we employed fluorine ions as novel morphology control agents and synthesized highly crystalline TiO2 truncated tetragonal nanobipyramids enclosed by {001} and {101} facets via a facile microemulsion method. By investigating the influence of halogens ions such as fluorine, chloride, and bromine on the morphology of TiO2 nanocrystals, we demonstrate that the rate of crystal growth could be promoted by fluorine and that the selective absorption of fluorine onto the surface of nanoparticles would alter the relative surface free energies of {001} and {101}, eventually controlling the ration of {001} facets to total surface area. Additionally, chainlike 1-D TiO2 nanostructures aligned from nanobipyramids were generated via the mechanism of oriented attachment at a relatively high temperature. The driving force for shape evolution is reducing the high surface free energy. The photocatalytic properties were performance by the photodegradation of methylene blue. This greener and versatile synthetic strategy may provide an attractive and effective route for shape-controlling of inorganic nanoparticles.