A visible light photocatalyst: effects of vanadium substitution on ETS-10

Abstract

Hybrid density functional theory/molecular mechanics (DFT/MM) methods have been used to investigate the effects of vanadium substitution in ETS-10. Models have been developed to contain varying concentrations of V(IV) and V(V) within the O-M-O (M = Ti, V) chain. Most of the V-substituted models have a localized mid-gap state. The occupation of this localized state depends upon the dopant oxidation state, leading to the addition of multiple low energy transitions. A linear correlation has been identified between band gap energies estimated using ground state orbital energies and those calculated using the more accurate and computationally demanding time-dependent DFT (TDDFT) method for a variety of transition metal substituted models of ETS-10. Consistent with experimental data for V substitution, our models predict a decrease in the optical band gap with increasing [V], due to a lowering of the delocalized d-orbital states at the bottom of the conduction band with increasing V d-orbital character. This effect is more pronounced in the case of V(V) substitution than V(IV). Excitation energies for the V-doped models, calculated with TDDFT methods correlate well with experimental data, allowing for the assignment of specific optical transitions to experimental UV-Vis spectra. The electronic structure of V-substituted ETS-10 at high V concentration demonstrates band gap energies within the visible range of the spectrum. Additionally, at high [V] the band gap energy and presence of low energy electron traps can be controlled by the relative concentration of V(IV) and V(V) along the O-M-O chain, establishing V-substituted ETS-10 as a promising visible light photocatalyst.