Synthesis of Nitrogen-Doped Titanium Oxide Nanostructures Via a Surfactant-Free Hydrothermal Route

Nitrogen-doped titanium oxides nanostructures were synthesized by a new method proposed here from titanium oxysulfate precursor in a NH₄OH solution under hydrothermal conditions without any extra templates as structure driving agents. The material synthesized with NH₄OH was an ammonium titanate and showed curled nanosheets, nanofibers or nanorods morphologies depending on the molar ratio of NH₄OH to titanium precursor and the hydrothermal temperature. The nanofibrous titanates had a high surface area over 500 m² g⁻¹ and a pore volume of 0.72 cm³ g⁻¹. The calcination of as-synthesized material at 673 K produced a titanium oxynitride TiO_2−xN_x with anatase phase, which absorbed visible light. Ion exchange of ammonium ion of the titanate with sodium Na₂Ti₃O_7−xN_x enhanced the thermal stability of the titanate phase.