Partially reduced TiO
2 nanomaterials have attracted significant interest because of their visible-light activity for catalysis and photodegradation. Herein, we prepared a partially reduced anatase TiO
2 (Re-A-TiO
2) nanoparticle material using a fast combustion method, demonstrating good activity toward decomposing methyl orange under visible light irradiation. The surface structure of the prepared material, after being surface-selectively
17O-labeled with H
217O (
17O-enriched water), was studied
via 17O and
1H solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, and the obtained results were compared to those of non-reduced anatase TiO
2 (A-TiO
2). The EPR results showed that the concentrations of paramagnetic species (i.e., oxygen vacancies (OV) and Ti
3+) in Re-A-TiO
2 were much higher than that in A-TiO
2, while the former was associated with a higher OV/Ti
3+ ratio. The intensities of the EPR signals were significantly affected by the adsorbed water, and this phenomenon was explored in combination with
1H NMR spectroscopy. The
1H species on Re-A-TiO
2 appeared at larger chemical shifts, denoting the increased acidity of the sample, and these
1H species on Re-A-TiO
2 were more difficult to remove than those on A-TiO
2. On the other hand, different features were observed for the signals arising from the two-coordinated oxygen atoms (
μ2-O) in
17O NMR, suggesting a typical anatase TiO
2(101) surface on A-TiO
2, but a more complex surface environment for Re-A-TiO
2. Furthermore, a larger amount of hydroxyl groups (OH) were observed on Re-A-TiO
2 compared to that on A-TiO
2, indicating a larger proportion of exposed (001) facets on Re-A-TiO
2. However, the
μ2-O signals broadened and became similar when the drying temperature was increased to 100 ℃, indicating a non-faceted anatase TiO
2 surface in such conditions. Based on the EPR and NMR results, a significant fraction of the OH species is believed to be formed from the reaction of the paramagnetic centers and adsorbed water molecules. The
1H→
17O cross polarization (CP) MAS and two-dimensional heteronuclear correlation (2D HETCOR) NMR spectra were used to verify the spatial proximity of the hydrogen and oxygen species, confirming the spectral assignments of a strongly adsorbed water and one type of surface OH species. In particular, the
1H NMR signals at approximately 11 ppm were ascribed to the hydrogen species in the intramolecular hydrogen bond. In summary, this study investigated the paramagnetic species and surface structure of anatase TiO
2 materials by combining EPR along with
1H and
17O solid-state NMR spectroscopy. The differences in the surface structures of Re-A-TiO
2 and A-TiO
2 should be closely related to their different properties toward the photodegradation of methyl orange.
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