fig8
![Solid-state NMR of active sites in TiO<sub>2</sub> photocatalysis: a critical review](https://image.oaes.cc/aee4ec06-4c22-4959-90f1-d08b90ca3a45/cs4012.fig.8.jpg)
Figure 8. (A) 17O MAS NMR spectra recorded at 14.1T on 17O enriched TiO2; (B) 17O MAS NMR spectrum recorded at 35.2 T on a TiO2 phase enriched in 17O; (C) 17O DNP NMR spectrum of a TiO2 phase enriched in 17O; (D) 17O DNP CPMAS NMR spectra in comparison to the DFS-enhanced echo spectrum. Reproduced with permission from[130]. Copyright 2020, American Chemical Society. MAS: Magic angle spinning; NMR: nuclear magnetic resonance; DNP: dynamic nuclear polarization; CPMAS: cross-polarization magic angle spinning; DFS: double-frequency sweep.