Spectroscopic investigation of vanadium speciation in vanadium-doped nanocrystalline anatase

Abstract

The speciation of vanadium doped into anatase particles of 50–90 Å diameter has been studied by a variety of techniques including solid state ⁵¹V NMR, EPR, XPS and Raman spectroscopy. EPR spectra of V-doped anatase are extremely complex showing up to five different V⁴⁺ centres (species A–E). Partial spin Hamiltonian parameters for these species have been determined and ascribed to interstitial (species A) and substitutional V⁴⁺ (species B–D), as well as surface V⁴⁺-rich clusters (species E). Solid state ⁵¹V NMR also shows the presence of several V⁵⁺ species that exhibit both tetrahedral and octahedral coordination and which are attributed to structural and residual surface V⁵⁺. It is shown by NMR, Raman spectroscopy and XPS that the dissolution of this residual surface vanadium component into the anatase structure becomes increasingly difficult as the vanadium concentration increases.

References

1. A. Fujishima and K. Honda, Nature (London), 1972, 238, 37.
2. K. E. Karakitsou and Z. E. Verykios, J. Phys. Chem., 1993, 97, 1184.
3. W. Choi, A. Termin and M. R. Hoffmann, Angew. Chem., Int. Ed. Engl., 1994, 33, 1091.
4. W. Choi, A. Termin and M. R. Hoffmann, J. Phys. Chem., 1994, 98, 13669.
5. S. T. Martin, C. L. Morrison and M. R. Hoffmann, J. Phys. Chem., 1994, 98, 13695.
6. N. Serpone, D. Lawless, J. Disdier and J.-M. Herrmann, Langmuir, 1994, 10, 643.
7. B. O'Regan, J. Moser, M. Anderson and M. Grätzel, J. Phys. Chem., 1990, 94, 8720.
8. V. Luca and D. J. MacLachan, SIMER—a program for the nonlinear least squares fitting of EPR spectra using second-order perturbation theory. Research School of Chemistry, The Australian National University, Canberra, Australia, 1994.
9. H. Eckert, G. Deo, I. E. Wachs and A. M. Hirt, J. Phys. Chem., 1990, 93, 6796.
10. J. Nogier, M. Delamar, P. Ruiz, B. Delmon, J. P. Bonnelle, M. Guelton, L. Gengembre, J. C. Vedrine, M. Brun, P. Albers, K. Seibold, M. Baerns, H. Papp, J. Stoch, L. T. Andersson, J. Kiwi, R. Thampi, M. Grätzel, G. C. Bond, N. Verma, J. C. Vickerman and R. H. West, Catal. Today, 1994, 20, 109.
11. A. Davidson and M. Che, J. Phys. Chem., 1992, 96, 9909.
12. H. Eckert and I. E. Wachs, J. Phys. Chem., 1989, 93, 6796.
13. O. B. Lapina, V. M. Mastikhin, A. A. Shubin, V. N. Krasilnikov and K. I. Zamaraev, Prog. NMR Spectrosc., 1992, 24, 457.
14. R. H. H. Smits, K. Seshan, J. R. H. Ross and A. P. M. Kentgens, J. Phys. Chem., 1995, 99, 9169.
15. G. T. Went, S. T. Oyama and A. T. Bell, J. Phys. Chem., 1990, 94, 4240.
16. J. Engweiler and A. Baiker, Appl. Catal., 1994, 120, 187.
17. R. Gallay, J. J. van der Klink and J. Moser, Phys. Rev. B: Condens. Matter, 1986, 34, 3060.
18. M. Grätzel and R. F. Howe, J. Phys. Chem., 1990, 94, 2566.
19. (a) R. K. Nurman and K. C. Giese, Inorg. Chem., 1978, 17, 1160; (b) C. F. Baes and R. E. Mesmer, The Hydrolysis of Cations, Wiley-Interscience, New York, 1976, p. 123.
20. H. J. Gerristen and H. Lewis, Phys. Rev., 1960, 119, 1010.
21. R. de Biasi, A. A. R. Fernandes, M. L. N. Grillo and R. J. Brazil, J. Phys. Chem. Solids, 1994, 55, 453.
22. F. C. Newman and L. G. Rowan, Phys. Rev. B: Solid State, 1972, 5, 4231.
23. F. Kubec and Z. Šroubek, J. Chem. Phys., 1972, 57, 1660.
24. S. Jansen, T. Yaping, M. J. Palmieri, M. Sanati and A. Andersson, J. Catal., 1992, 138, 79.
25. D. W. Murphy, R. J. Cava, S. M. Zahurak and A. Santoro, Solid State Ionics, 1983, 9&10, 413.