The photocatalytic activity of TiO2 is limited by its high band gap, ~3.2 eV, and the small percentage of UV light in the solar spectrum and slow reduction reactions. This is particularly true in photocatlatic degradation of aqueous organic pollutants (OP). Traditionally Pt is deposited on TiO2 to increase the photocatalytic OP degradation. At low Pt loadings Pt increases the photodegredation rate, but the photoactivity decreases at higher Pt loadings. We have used periodic boundary condition density functional theory (DFT) to develop an understanding of the processes that cause the initial increase and subsequent decrease in photoactivity as the Pt coverage increases. Pt allows O2 to interact with the TiO2 surface by providing adsorption sites, which are rare on pure TiO2 surfaces. However, Pt clusters always act as electron hole recombination centers. The initial rise and subsequent fall in TiO2’s photoactivity with Pt loading results from the competition between enhanced electron scavenging due to increased O2 adsorption and increased electron-hole recombination. Therefore we also investigate using near surface B, C and N interstitial and O substitutional dopants to increase the O2 reduction reaction by providing electron density to enable Ti-O2 bond formation. Sites that create unoccupied band gap states with energies below that of the O2 πz* orbital reduce TiO2’s reduction ability as these states result in photoexcited electrons with insufficient reduction potential to reduce O2. Dopants for enhancing the photocatalytic reduction of O2 in order of predicted effectiveness are interstitial B, relaxed substitutional B, and interstitial C. In contrast, substitutional C, and interstitial and substitutional N hinder O2 reduction despite increasing visible light absorption.

Investigations of the role of surface metal catalysis and near surface nonmetal dopants in the photocatalytic activity of TiO2

249th National Meeting (2015)

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