(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.