Electronic Structure, Optical and Magnetic Properties of Oxygen-Deficient Gray TiO2–δ(B)

The gray-colored oxygen-deficient TiO2–δ(B) nanobelts have been synthesized through a combination of the hydrothermal method followed by an ion exchange process and vacuum annealing. Electron paramagnetic resonance reveals an existence of F-centers in the form of electron-trapped oxygen vacancies within the anionic sublattice of the gray bronze TiO2 that induces its colouration. The diffuse reflectance spectroscopy showed that the formation of oxygen vacancies into TiO2(B) significantly increases its absorption intensity in both visible and near infrared ranges. The band gap of TiO2(B) with anionic defects is equal to 3.03 eV (against 3.24 eV for white TiO2(B) treated in air). Room temperature ferromagnetism associated with the defects was detected in gray TiO2–δ(B), thus indicating it belongs it to the class of dilute magnetic oxide semiconductors. It was found that in the low-temperature range (4 K), the magnetic properties of vacuum annealed TiO2(B) do not differ from those for TiO2(B) treated in air. We hope that the findings are defined here make a contribution to further progress in fabrication and manufacturing of defective TiO2-based nanomaterials for catalysis, magnetic applications, batteries, etc.