Facile Conversion of Electrospun TiO₂ into Titanium Nitride/Oxynitride Fibers

Nanocrystalline fibrous TiO₂ (anatase) was prepared by electrostatic spinning from ethanolic solution of Ti(IV) butoxide, acetylacetone, and poly(vinylpyrrolidone) employing the Nanospider industrial process. These titania fibers were smoothly converted into cubic titanium oxynitride, TiO_xN_y fibers (a = 4.1930 Å) during 4 h at 600 °C in ammonia atmosphere. The obtained material is convertible back into TiO₂ fibers by heat treatment in air at 500 °C. The TiO₂ fibers, which were reformed in this way, contain anatase as the main phase. Their follow-up reaction with NH₃ at 600 °C/2 h leads to a less crystalline oxynitride material with a ≈ 4.173 Å, which is close to that of cubic TiO. Three subsequent cycles of this transformation were demonstrated. The described conversions are specific for electrospun anatase fibers only. At the same experimental conditions, other forms of nanocrystalline anatase do not react with ammonia yielding cubic phases. An almost perfectly stoichiometric titanium nitride, TiN (a = 4.2290 Å) containing only 0.2 wt % O, was prepared from TiO_xN_y fibers in NH₃ at temperatures up to 1000 °C. This TiN material maintains the morphology of fibers and is composed of nanocrystals of a similar size as those of the precursor.