Effect of Surface Deposited Pt on the Photoactivity of TiO2

The roles of deposited Pt clusters and adsorbed O 2 in the photoactivity of anatase TiO 2 (101) surfaces have been studied using density functional theory. O 2 only adsorbs to TiO 2 surfaces when excess negative charge is available to form O–Ti bonds, which can be provided by a photoexcited electron or subsurface oxygen vacancy, in which cases the adsorption energies are −0.94 and −2.52 eV, respectively. When O 2 adsorbs near a subsurface defect, it scavenges extra electron density and creates a hole that can annihilate excited electrons. In aqueous solutions, O 2 interactions with the TiO 2 surface are rare because water preferentially adsorbs at the surface. Pt clusters on TiO 2 significantly enhance O 2 adsorption providing many adsorption sites with adsorption energies up to −1.69 eV, stronger than the −0.52 eV adsorption energy of H 2 O on the Pt cluster. Consequently, Pt increases the rate of electron scavenging by O 2 relative to that of undoped TiO 2 leading to enhanced photocatalytic performance. Pt states completely bridge the band gap and act as electron–hole recombination centers, which are deleterious to the photoactivity of TiO 2 . The initial rise and subsequent fall in TiO 2 ’s photoactivity with Pt loading results from the competition between enhanced electron scavenging due to increased O 2 adsorption and increased electron–hole recombination.