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The Influence of Surface Platinum Deposits on the Photocatalytic Activity of Anatase TiO₂ Nanocrystals

Pepin, Paul A., Lee, Jennifer D., Foucher, Alexandre C., Murray, Christopher B., Stach, Eric A., Vohs, John M.
Journal of physical chemistry 2019 v.123 no.16 pp. 10477-10486
X-ray photoelectron spectroscopy, acetaldehyde, condensation reactions, desorption, electrons, energy-dispersive X-ray analysis, nanocrystals, oxidation, oxygen, photocatalysis, photocatalysts, platinum, titanium dioxide, transmission electron microscopy
In this study, the impact of supported Pt particles on the thermal and photocatalytic activity of well-defined anatase TiO₂ (A-TiO₂) nanocrystals (NCs) was investigated. Pt-decorated NCs were characterized using scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The activity of the Pt-decorated NCs for the thermal and photocatalytic reactions of acetaldehyde was then studied using temperature-programmed desorption in ultrahigh vacuum. The bare TiO₂ NCs demonstrated thermal activity primarily for aldol condensation, partial oxidation, and reductive coupling pathways. For the Pt-decorated NCs, the Pt deposits were found to act mainly as a site blocker for the thermal aldol condensation and partial oxidation pathways, as well as acting as recombination centers for photogenerated electrons and holes at the surface, suppressing the photocatalytic activity of the NCs. Upon pretreating with O₂, however, the photocatalytic activity of the Pt-decorated NCs was restored, indicating that oxygen adsorbed at the Pt reacts with the photogenerated conduction band electrons captured by the Pt deposits, preventing their recombination with photogenerated holes at the surface. These results demonstrate how the dynamics of the photogenerated charge carriers may be influenced both by the presence of Pt deposits and adsorbates at the surface of a photocatalyst.