Photo-oxidation activities on Pd-doped TiO2 nanoparticles: critical PdO formation effect

The catalytic activities of three distinct Pd-doped TiO2 (PdTiO2) nanoparticle samples, post-annealed (at 700, 800, and 900 degrees C) after fabrication on silicon substrates, were analyzed with respect to the photo-oxidation of aniline and 2-thiophenecarboxaldehyde. Through a combination of Raman spectroscopy and high-resolution photoemission spectroscopy (HRPES), we demonstrated that the photocatalytic oxidation occurred only when the PdTiO2 nanoparticles were annealed at temperatures above 800 degrees C, that is, when PdO and Ti3+ had partially formed on the PdTiO2 nanoparticles, which indicates that the presence of PdO and Ti3+ is critical for the photocatalytic oxidation. Additionally, we determined the decrease in the band gaps to visible region with PdTiO2 nanoparticles annealed above 800 degrees C from their valence-band spectra, which resulted in photocatalytic activities even under visible light, lambda = 540 nm. (C) 2014 Elsevier B.V. All rights reserved.