Citation: Li Yuhong, Wu Xin-Ping, Liu Cong, Wang Meng, Song Benteng, Yu Guiyun, Yang Gang, Hou Wenhua, Gong Xue-Qing, Peng Luming. NMR and EPR Studies of Partially Reduced TiO₂[J]. Acta Physico-Chimica Sinica, ;2020, 36(4): 190502. doi: 10.3866/PKU.WHXB201905021 shu

NMR and EPR Studies of Partially Reduced TiO₂

Li Yuhong ^1,2 ,
Wu Xin-Ping ³ ,
Liu Cong ¹ ,
Wang Meng ¹ ,
Song Benteng ² ,
Yu Guiyun ⁴ ,
Yang Gang ¹ ,
Hou Wenhua ² ,
Gong Xue-Qing ³ ,
Peng Luming ^2,,

1.
Suzhou Key Laboratory of Functional Ceramic Materials, School of Chemistry and Material Engineering, Changshu Institute of Technology, Changshu 215500, Jiangsu Province, P. R. China
2.
Key Laboratory of Mesoscopic Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, P. R. China
3.
Key Laboratory for Advanced Materials, Centre for Computational Chemistry, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P. R. China
4.
School of Chemical and Biological Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu Province, P. R. China

Corresponding author: Peng Luming, luming@nju.edu.cn
Received Date: 5 May 2019
Revised Date: 20 June 2019
Accepted Date: 21 June 2019
Available Online: 27 April 2019
Fund Project: the Natural Science Foundation of Jiangsu Province, China BK20170435the National Natural Science Foundation of China 21573103the National Natural Science Foundation of China 91745202The project was supported by the Natural Science Foundation of Jiangsu Province, China (BK20170435) and the National Natural Science Foundation of China (91745202, 21573103)

Partially reduced TiO₂ nanomaterials have attracted significant interest because of their visible-light activity for catalysis and photodegradation. Herein, we prepared a partially reduced anatase TiO₂ (Re-A-TiO₂) 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 H₂¹⁷O (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 TiO₂ (A-TiO₂). The EPR results showed that the concentrations of paramagnetic species (i.e., oxygen vacancies (OV) and Ti³⁺) in Re-A-TiO₂ were much higher than that in A-TiO₂, while the former was associated with a higher OV/Ti³⁺ 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-TiO₂ appeared at larger chemical shifts, denoting the increased acidity of the sample, and these ¹H species on Re-A-TiO₂ were more difficult to remove than those on A-TiO₂. 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 TiO₂(101) surface on A-TiO₂, but a more complex surface environment for Re-A-TiO₂. Furthermore, a larger amount of hydroxyl groups (OH) were observed on Re-A-TiO₂ compared to that on A-TiO₂, indicating a larger proportion of exposed (001) facets on Re-A-TiO₂. However, the μ₂-O signals broadened and became similar when the drying temperature was increased to 100 ℃, indicating a non-faceted anatase TiO₂ 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 TiO₂ materials by combining EPR along with ¹H and ¹⁷O solid-state NMR spectroscopy. The differences in the surface structures of Re-A-TiO₂ and A-TiO₂ should be closely related to their different properties toward the photodegradation of methyl orange.
- Partially reduced TiO₂,
- Solid-state NMR,
- ¹⁷O NMR spectrum,
- ¹H NMR spectrum,
- EPR,
- Hydroxyl group,
- Hydrogen bond,
- Visible light degradation
1. [1]
  Liu, L.; Chen, X. B. Chem. Rev. 2014, 114, 9890. doi: 10.1021/cr400624r doi: 10.1021/cr400624r
2. [2]
  Zuo, F.; Wang, L.; Wu, T.; Zhang, Z. Y.; Borchardt, D.; Feng, P. Y. J. Am. Chem. Soc. 2010, 132, 11856. doi: 10.1021/ja103843d doi: 10.1021/ja103843d
3. [3]
  Chen, X. B.; Liu, L.; Yu, P. Y.; Mao, S. S. Science 2011, 331, 746. doi: 10.1126/science.1200448 doi: 10.1126/science.1200448
4. [4]
  Wang, Z.; Yang, C. Y.; Lin, T. Q.; Yin, H.; Chen, P.; Wan, D. Y.; Xu, F. F.; Huang, F. Q.; Lin, J. H.; Xie, X. M.; et al. Adv. Funct. Mater. 2013, 23, 5444. doi: 10.1002/adfm.201300486 doi: 10.1002/adfm.201300486
5. [5]
  Liu, H.; Ma, H. T.; Li, X. Z.; Li, W. Z.; Wu, M.; Bao, X. H. Chemosphere 2003, 50, 39. doi: 10.1016/S0045-6535[02]00486-1 doi: 10.1016/S0045-6535[02]00486-1
6. [6]
  Wang, G. M.; Wang, H. Y.; Ling, Y. C.; Tang, Y. C.; Yang, X. Y.; Fitzmorris, R. C.; Wang, C. C.; Zhang, J. Z.; Li, Y. Nano Lett. 2011, 11, 3026. doi: 10.1021/nl201766h doi: 10.1021/nl201766h
7. [7]
  Hoang, S.; Berglund, S. P.; Hahn, N. T.; Bard, A. J.; Mullins, C. B. J. Am. Chem. Soc. 2012, 134, 3659. doi: 10.1021/ja211369s doi: 10.1021/ja211369s
8. [8]
  Nakamura, I.; Negishi, N.; Kutsuna, S.; Ihara, T.; Sugihara, S.; Takeuchi, K. J. Mol. Catal. A-Chem. 2000, 161, 205. doi: 10.1016/S1381-1169[00]00362-9 doi: 10.1016/S1381-1169[00]00362-9
9. [9]
  Bastow, T. J.; Gibson, M. A.; Forwood, C. T. Solid State Nucl. Magn. Reson. 1998, 12, 201. doi: 10.1016/S0926-2040[98]00066-6 doi: 10.1016/S0926-2040[98]00066-6
10. [10]
  Bastow, T. J.; Whitfield, H. J. Chem. Mater. 1999, 11, 3518. doi: 10.1021/cm990248r doi: 10.1021/cm990248r
11. [11]
  Larsen, F. H.; Farnan, I.; Lipton, A. S. J. Magn. Reson. 2006, 178, 228. doi: 10.1016/j.jmr.2005.10.003 doi: 10.1016/j.jmr.2005.10.003
12. [12]
  Chary, K. V. R.; Vijayakumar, V.; Rao, P. K.; Nosov, A. V.; Mastikhin, V. M. J. Mol. Catal. A-Chem. 1995, 96, L5. doi: 10.1016/1381-1169[94]00029-8 doi: 10.1016/1381-1169[94]00029-8
13. [13]
  Crocker, M.; Herold, R. H. M.; Wilson, A. E.; Mackay, M.; Emeis, C. A.; Hoogendoorn, A. M. J. Chem. Soc.-Faraday Trans. 1996, 92, 2791. doi: 10.1039/Ft9969202791 doi: 10.1039/Ft9969202791
14. [14]
  Soria, J.; Sanz, J.; Sobrados, I.; Coronado, J. M.; Maira, A. J.; Hernández-Alonso, M. D.; Fresno, F. J. Phys. Chem. C 2007, 111, 10590. doi: 10.1021/jp071440g doi: 10.1021/jp071440g
15. [15]
  Nosaka, A. Y.; Fujiwara, T.; Yagi, H.; Akutsu, H.; Nosaka, Y. J. Phys.Chem. B 2004, 108, 9121. doi: 10.1021/jp037297i doi: 10.1021/jp037297i
16. [16]
  Zhu, L. L.; Gu, Q.; Sun, P. C.; Chen, W.; Wang, X. L.; Xue, G. ACS Appl. Mater. Interfaces 2013, 5, 10352. doi: 10.1021/am403449j doi: 10.1021/am403449j
17. [17]
  Soria, J.; Sanz, J.; Sobrados, I.; Coronado, J. M.; Hernández-Alonso, M. D.; Fresno, F. J. Phys. Chem. C 2010, 114, 16534. doi: 10.1021/jp105131w doi: 10.1021/jp105131w
18. [18]
  Scolan, E.; Magnenet, C.; Massiot, D.; Sanchez, C. J. Mater. Chem. 1999, 9, 2467. doi: 10.1039/A903714d doi: 10.1039/A903714d
19. [19]
  Blanchard, J.; Bonhomme, C.; Maquet, J.; Sanchez, C. J. Mater. Chem. 1998, 8, 985. doi: 10.1039/A800118i doi: 10.1039/A800118i
20. [20]
  Sun, X. M.; Dyballa, M.; Yan, J. Q.; Li, L. D.; Guan, N. J.; Hunger, M. Chem. Phys. Lett. 2014, 594, 34. doi: 10.1016/j.cplett.2014.01.014 doi: 10.1016/j.cplett.2014.01.014
21. [21]
  Li, Y. H.; Wu, X. P.; Jiang, N. X.; Lin, M.; Shen, L.; Sun, H. C.; Wang, Y. Z.; Wang, M.; Ke, X. K.; Yu, Z. W.; et al. Nat. Commun. 2017, 8, 581. doi: 10.1038/s41467-017-00603-7 doi: 10.1038/s41467-017-00603-7
22. [22]
  Shen, L.; Peng, L. M. Chin. J. Catal. 2015, 36, 1494. doi: 10.1016/S1872-2067[15]60931-7 doi: 10.1016/S1872-2067[15]60931-7
23. [23]
  Wang, M.; Wu, X. -P.; Zheng, S. J.; Zhao, L.; Li, L.; Shen, L.; Gao, Y. X.; Xue, N. H.; Guo, X. F.; Huang, W. X.; et al. Sci. Adv. 2015, 1, e1400133. doi: 10.1126/sciadv.1400133 doi: 10.1126/sciadv.1400133
24. [24]
  Du, J.-H.; Peng, L. M. Chin. Chem. Lett. 2018, 29, 747. doi: 10.1016/j.cclet.2018.02.012 doi: 10.1016/j.cclet.2018.02.012
25. [25]
  Shen, L.; Wu, X. P.; Wang, Y.; Wang, M.; Chen, J. C.; Li, Y. H.; Huo, H.; Hou, W. H.; Ding, W. P.; Gong, X. Q.; et al. J. Phys. Chem. C 2019, 123, 4158. doi: 10.1021/acs.jpcc.8b11091 doi: 10.1021/acs.jpcc.8b11091
26. [26]
  Hou, W. H. Acta Phys. -Chim. Sin. 2018, 34, 329. doi: 10.3866/PKU.WHXB201709251
27. [27]
  Chen, C. C.; Hu, S. H.; Fu, Y. P. J. Alloys Compd. 2015, 632, 326. doi: 10.1016/j.jallcom.2015.01.206 doi: 10.1016/j.jallcom.2015.01.206
28. [28]
  Niu, F.; Jiang, Y.; Song, W. G. Nano Res. 2010, 3, 757. doi: 10.1007/s12274-010-0043-3 doi: 10.1007/s12274-010-0043-3
29. [29]
  Wang, J. J.; Liu, X. N.; Li, R. H.; Qiao, P. S.; Xiao, L. P.; Fan, J. Catal. Commun. 2012, 19, 96. doi: 10.1016/j.catcom.2011.12.028 doi: 10.1016/j.catcom.2011.12.028
30. [30]
  Munuera, G. J. Catal. 1970, 18, 19. doi: 10.1016/0021-9517[70]90306-4 doi: 10.1016/0021-9517[70]90306-4
31. [31]
  Primet, M.; Pichat, P.; Mathieu, M. V. J. Phys. Chem. 1971, 75, 1221. doi: 10.1021/j100679a008 doi: 10.1021/j100679a008
32. [32]
  Chary, K. V. R.; Bhaskar, T.; Seela, K. K.; Lakshmi, K. S.; Reddy, K. R. Appl. Catal. A-Gen. 2001, 208, 291. doi: 10.1016/S0926-860x[00]00724-9 doi: 10.1016/S0926-860x[00]00724-9
33. [33]
  Bakhmutov, V. I. Chem. Rev. 2011, 111, 530. doi: 10.1021/Cr100144r doi: 10.1021/Cr100144r
34. [34]
  Namai, Y.; Matsuoka, O. J. Phys. Chem. B 2005, 109, 23948. doi: 10.1021/Jp058210r doi: 10.1021/Jp058210r
35. [35]
  Conesa, J. C.; Soria, J. J. Phys. Chem. 1982, 86, 1392. doi: 10.1021/J100397a035 doi: 10.1021/J100397a035
36. [36]
  Zhang, H. L.; Yu, H. G.; Zheng, A. M.; Li, S. H.; Shen, W. L.; Deng, F. Environ. Sci. Technol. 2008, 42, 5316. doi: 10.1021/es800917e doi: 10.1021/es800917e
37. [37]
  Wang, N.; Ru, G. Y.; Wang, L. Y.; Feng, J. W. Langmuir 2009, 25, 5898. doi: 10.1021/La8038363 doi: 10.1021/La8038363
38. [38]
  Gong, X. Q.; Selloni, A. J. Phys. Chem. B 2005, 109, 19560. doi: 10.1021/jp055311g doi: 10.1021/jp055311g
39. [39]
  He, Y. B.; Tilocca, A.; Dulub, O.; Selloni, A.; Diebold, U. Nat. Mater. 2009, 8, 585. doi: 10.1038/NMAT2466 doi: 10.1038/NMAT2466
40. [40]
  Tilocca, A.; Selloni, A. J. Phys. Chem. B 2004, 108, 4743. doi: 10.1021/jp037685k doi: 10.1021/jp037685k
41. [41]
  Bastow, T. J.; Moodie, A. F.; Smith, M. E.; Whitfield, H. J. J. Mater. Chem. 1993, 3, 697. doi: 10.1039/jm9930300697 doi: 10.1039/jm9930300697
42. [42]
  Day, V. W.; Eberspacher, T. A.; Klemperer, W. G.; Park, C. W.; Rosenberg, F. S. J. Am. Chem. Soc. 1991, 113, 8190. doi: 10.1021/Ja00021a068 doi: 10.1021/Ja00021a068
43. [43]
  Zhao, L.; Qi, Z.; Blanc, F.; Yu, G. Y.; Wang, M.; Xue, N. H.; Ke, X. K.; Guo, X. F.; Ding, W. P.; Grey, C. P.; et al. Adv. Funct. Mater. 2014, 24, 1696. doi: 10.1002/adfm.201301157 doi: 10.1002/adfm.201301157
44. [44]
  Harris, T. K.; Zhao, Q.; Mildvan, A. S. J. Mol. Struct. 2000, 552, 97. doi: 10.1016/S0022-2860[00]00469-5 doi: 10.1016/S0022-2860[00]00469-5
45. [45]
  Eckert, H.; Yesinowski, J. P.; Silver, L. A.; Stolper, E. M. J.Phys. Chem. 1988, 92, 2055. doi: 10.1021/J100318a070 doi: 10.1021/J100318a070
46. [46]
  Bertolasi, V.; Gilli, P.; Ferretti, V.; Gilli, G. J. Chem. Soc.-Perkin Trans. 1997, 2, 945. doi: 10.1039/A606862f doi: 10.1039/A606862f
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沈阳化工大学材料科学与工程学院沈阳 110142

NMR and EPR Studies of Partially Reduced TiO2

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通讯作者: 陈斌, bchen63@163.com

NMR and EPR Studies of Partially Reduced TiO₂