(678g) Increasing Oxygen Reduction On TiO2 Via Non-Precious-Metal Surface Doping

The photocatalytic activity of TiO₂ is limited by its high band gap, ~3.2 eV which limits photoabsorption to the small percentage of UV light in the solar spectrum and slow oxidation reduction reaction rates. This is particularly true in photocatalytic degradation of aqueous organic pollutants (OP). Traditionally Pt is deposited on TiO₂ to increase the photocatalytic OP degradation. Recently this was shown to increase the TiO₂ photocatalytic activity because Pt acts as an excellent catalyst for O₂ reduction reaction, the OP degradation rate limiting step. Pt provides high energy electrons that simultainusly reduce O₂ and allow for the formation of O-surface bonds. However, Pt is expensive and if too much Pt is deposited on the TiO2 surface the photocatalytic activity is worse than if there was no surface Pt because Pt clusters completely bridges the TiO2 band-gap and therefore acts as an electron/hole pair. We have utilized density functional theory (DFT) to investigate the use of non-Pt surface dopants to increase the O₂ reduction reaction.   Among the non-metals investigated, B improves O₂ reduction the best, enabling O₂ reduction independent of dopant location, followed by C, which enables O₂ reduction only at interstitial dopant sites, while N doping does not allow for increased O₂ reduction. V, Nb, and Mo act to increase O₂ adsorption while Cr is not as effective. These results are consistent with the hypthosysis that filled bands sitting high in TiO₂'s band gap are needed for O2 adsorption and therefore reduction.