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 V IV and V V species within V-doped ETS-10 materials, confirming substitution for Ti IV sites only. Computational models, using hybrid density functional theory/molecular mechanics (DFT/MM) methods, have been developed that contain varying concentrations of V IV and V V within the O−M−O (M = Ti, V) chain. Geometry optimizations indicate that V V substitution leads to larger changes in the local chain geometry than V IV substitution. Substitution energetics for V IV and V V in different sites have been calculated to determine preferred locations of the two species, suggesting that long chains of V V are not stable and demonstrating the need for both V V and V IV 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 V V and V IV 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.