Effects of Vanadium Substitution on the Structure and Photocatalytic Behavior of ETS-10

A combination of experimental and computational methods has been used to investigate the effects of vanadium doping in ETS-10. Near edge X-ray absorption fine structure (NEXAFS) spectra reveal octahedrally coordinated VIV and VV species within V-doped ETS-10 materials, confirming substitution for TiIV sites only. Computational models, using hybrid density functional theory/molecular mechanics (DFT/MM) methods, have been developed that contain varying concentrations of VIV and VV within the O−M−O (M = Ti, V) chain. Geometry optimizations indicate that VV substitution leads to larger changes in the local chain geometry than VIV substitution. Substitution energetics for VIV and VV in different sites have been calculated to determine preferred locations of the two species, suggesting that long chains of VV are not stable and demonstrating the need for both VV and VIV within V-substituted materials. Wavefunctions for systems with an electron added or removed are used to identify electron and hole trapping sites associated with the VV and VIV doping centers respectively. An increase in photocatalytic activity is predicted at low [V] due to improved charge separation. However photocatalytic activity is expected to decrease at high [V] due to increased carrier recombination. These results are consistent with recent experimental data.