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, TiOxNy fibers (a = 4.1930 angstrom) during 4 h at 600 degrees C in ammonia atmosphere. The obtained material is convertible back into TiO2 fibers by heat treatment in air at 500 degrees C. The TiO2 fibers, which were reformed in this way, contain anatase as the main phase. Their follow-up reaction with NH3 at 600 degrees C/2 h leads to a less crystalline oxynitride material with a approximate to 4.173 angstrom, 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 angstrom) containing only 0.2 wt % O, was prepared from TiOxNy fibers in NH3 at temperatures up to 1000 degrees C. This TiN material maintains the morphology of fibers and is composed of nanocrystals of a similar size as those of the precursor.