Fig. 1. ¹³C CP-MAS spectra of TiO_2−xC_x samples: before thermal oxidation: (a) C-I, after partial thermal oxidation in air; (b) C-II, after thermal oxidation; (c) C-I at 400 °C; (d) C-II at 400 °C; (e) C-II at 425 °C (ω_rot=6 kHz).

Fig. 2. (a) ¹³C CP interrupted decoupled spectrum and (b) regular CP spectrum for C-I(4 2 5) (ω_rot=4 kHz).

Fig. 3. Variable contact (contact time indicated for each spectrum) CP spectra for sample C-II: (a) calcined at the indicated temperature and (b) calcined in air at 425 °C. (ω_rot=6 kHz).

Fig. 4. EPR spectra of TiO_2−xC_x samples after calcination in air: (a) C-I(5 0 0) and (b) C-II(4 5 0); C-III calcined in air at (c) 400 °C (20 min), (d) 450 °C (15 min) and (e) 400 °C (60 min). Spectra were acquired at 10 K (a), 140 K (b) and (e) and 298 K (c) and (d).

Fig. 5. XRD powder patterns of TiO_2−xC_x samples (a) C-I, product of hydrothermal reaction at 190 °C and after calcination in air at 400 and 500 °C; (b) C-II, purified product at 100 °C and calcined in air at 425 and 450 °C; (c) C-III, purified product at 100 °C and calcined in air at 400 and 450 °C.

Fig. 6. (Top) UV/vis diffuse reflectance spectra of C-I as-synthesized product (190 °C), and after calcination in air at 400, 450, and 500 °C. For comparison, commercial TiO₂ P25 is shown. (Bottom) Modified UV/vis diffuse reflectance plot used to determine the indirect optical band gap of TiO_2−xC_x samples after being calcined in air at 400 °C (a) and 475 °C (b) prepared by method C-II, and 400 °C (c), 450 °C (d) and 500 °C (e) prepared by method C-III, (f) TiO₂ Degussa (P-25).

Fig. 7. XPS high-resolution spectra for the C(1s), Ti(2p), and O(1s) core levels. The individual spectra correspond to (a) C-I(4 0 0), (b) C-I(5 0 0), and (c) C-II(4 5 0).

¹³C SSNMR peak assignments for the TiO_2−xC_x samples.

All values are given in ppm; nd: not detected.

Selected structural parameters for the TiO_2−xC_x samples.