Titania from nanoclusters to nanowires and nanoforks

Abstract.

A novel method - inverse microemulsion has been developed not only for synthesizing low cost TiO₂ nanoclusters but also for the first time preparing titania nanowires and nanoforks with rutile structure of single crystal. With two microemulsion systems, spherical TiO₂ nanoclusters of 5 nm in average diameter are produced. These nanoclusters are amorphous and turned into anatase at an annealing temperature lower than 750 ^°C, and changed into rutile when annealed at higher temperature. When three microemulsions with TiCl₄, ammonia and NaCl as aqueous phase, are used, the precursor powder containing Ti(OH)₄/NaCl with molar ratio of 1000 are annealed at 750 ^°C and then TiO₂ rutile nanowires with 22 nm in thickness and 4 μm in length are formed. At the same time two kinds of nanoforks with defined boundary structures are constructed: one is a bent wire composed of two straight whiskers related by twinning on a (101) plane with the angle of 114^° between the two legs, and the other by twinning on a (301) planes with the angle of 55^° between the legs. Screw dislocations and a periodic structure are found in (301) twin boundary, while edge dislocations are observed in (101) twin boundaries.The experiments demonstrate that the titania rutile nanowires are formed through solid state phase transformation and sodium chloride play an important role in the process.