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

• Enhanced photocatalytic oxidation activity of PdTiO2 nanoparticles with existence of PdO.
• PdO formation in PdTiO2 nanoparticles by thermal annealing above 800 °C.
• Capability for photo-oxidation of aniline and 2-thiophenecarboxaldehyde under visible light.
• Decrease of PdTiO2 band gap to visible region (1.92 eV) by thermal annealing at 900 °C.

The catalytic activities of three distinct Pd-doped TiO2 (PdTiO2) nanoparticle samples, post-annealed (at 700, 800, and 900 °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 °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 °C from their valence-band spectra, which resulted in photocatalytic activities even under visible light, λ = 540 nm.

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