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 ⁵¹ V NMR, EPR, XPS and Raman spectroscopy. EPR spectra of V-doped anatase are extremely complex showing up to five different V ⁴⁺ centres (species A–E). Partial spin Hamiltonian parameters for these species have been determined and ascribed to interstitial (species A) and substitutional V ⁴⁺ (species B–D), as well as surface V ⁴⁺ -rich clusters (species E). Solid state ⁵¹ V NMR also shows the presence of several V ⁵⁺ species that exhibit both tetrahedral and octahedral coordination and which are attributed to structural and residual surface V ⁵⁺ . 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.