Spectroscopic investigation of vanadium speciation in vanadium-doped nanocrystalline anatase

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.