Sol–gel preparation and characterization of black titanium oxides Ti2O3 and Ti3O5

Sub-micron black titanium oxides powders Ti2O3 and Ti3O5 were synthesized via a facile and economical sol–gel method in this paper. Relatively pure Ti3O5 and Ti2O3 can be obtained by annealing the as-prepared PEG600-based gel with a heating rate of 10 °C min−1 and maintaining the temperature at 1,000 and 1,200 °C, respectively, under high pure (99.999 %) argon atmosphere for 4 h. The FESEM images reveal that the morphologies of the as-prepared Ti3O5 and Ti2O3 are sphere-like and plate-like mixed type structures. The particle size of Ti3O5 sample is in the range of 50–200 nm. However, the appearance of Ti2O3 is 200–500 nm irregular flake structures covered with 20–50 nm spherical particles. This PEG600-based sol–gel approach has a low reaction temperature of 1,000 °C herein for the preparation of Ti3O5, which is ascribed to that, the molecular PEG-600 was distributed well in the homogeneous gel through secondary cross-linking of the organic molecules, and with the increasing of heating temperature, molecular PEG-600 was carbonized. These nanoscaled and homogeneous mixtures of carbon and TiO2 made the carbon thermal reduction reaction occur subsequently at 1,000 °C. The Raman vibrational wavenumbers of as-prepared Ti3O5 and Ti2O3 are perfectly coincident with those of calculated results of pure Ti3O5 and Ti2O3. Besides, the Fourier transform infrared spectra of Ti3O5 and Ti2O3 were also investigated in this article. Finally, the powder electrical resistivity of Ti3O5 and Ti2O3 is 4.7 × 10−3 and 2.5 × 10−3 Ω m, respectively.