Fig. 1

¹⁷O NMR spectra of faceted anatase titania nanocrystals compared to the non-faceted sample. Anatase TiO₂ nanosheets with dominant exposed (001) facets (NS001-TiO₂), and nano-octahedra preferentially exposing (101) facets (NO101-TiO₂) were surface-selectively ¹⁷O-labeled and vacuum dried for 2 and 12 h, respectively. The other sample, NF1-TiO₂, was nonselectively ¹⁷O-labeled. All data were obtained at 9.4 T under a MAS frequency of 14 kHz. A rotor synchronized Hahn-echo sequence (π/6−τ−π/3−τ—acquisition) and optimized recycle delays (0.5 s for NS001-TiO₂ and NO101-TiO₂, and 50 s for NF1-TiO₂, see Supplementary Fig. 8), with ¹H decoupling, were used to obtain the NMR data. 120,000, 110,000, and 1200 scans were collected for NS001-TiO₂, NO101-TiO₂, and NF1-TiO₂, respectively. The spectra are normalized according to the sample mass and the number of scans (Supplementary Table 4). Asterisks denote sidebands. The dependence of the ¹⁷O MAS NMR spectra of the two faceted samples on the vacuum-drying time is shown in Supplementary Figs. 9 and 10, and discussed in the Supplementary Notes 2 and 3. Comparison of the ¹⁷O NMR spectra of the two faceted nanocrystalline samples to a surface-selectively labeled, non-faceted anatase TiO₂ nanoparticle sample with comparable surface area (denoted as NF2-TiO₂ and the TEM image of the sample is shown in Supplementary Fig. 11) can be found in Supplementary Fig. 12 and Supplementary Note 4