Abstract:

Photocatalytic degradation of gaseous formaldehyde for 35 h was performed using Pt-TiO₂ film in the following irradiation systems: UV_{254 nm}, O₃+UV_{254 nm}, and UV_{254+185 nm}. Concurrent improvements in formaldehyde degradation and O₃ removal were achieved by modifying TiO₂ with Pt nanoparticles, resulting in a 3.1-3.4-fold O₃ elimination increase. X-ray photoelectron spectroscopy (XPS) of the Pt-TiO₂ film was carried out to assess the electronic states of the Pt nanoparticles and accumulated organic species. The deconvoluted C 1s and O 1s XPS spectra revealed that the content of carbonyl and carboxyl groups on Pt-TiO₂ and degree of catalyst deactivation in the systems studied decreased in the following order: UV_{254 nm} > O₃+UV_{254 nm} > UV_{254+185 nm}. Metallic Pt⁰ was oxidized to a mixture of PtO_ads and Pt⁴⁺ species under O₃+UV_{254 nm} and UV_{254+185 nm} irradiation owing to the presence of O₃ and hydroxyl radicals, but remained stable under UV_{254 nm} irradiation. Pt species at higher oxidation states can act as electron trapping centers, and improve the photocatalytic activity of Pt-TiO₂ and provide reactive sites for O₃ decomposition under UV irradiation, resulting in a faster O₃ removal rate than that displayed by TiO₂. The XPS studies provided valuable information to elucidate the beneficial role of Pt species and the reduction of catalyst deactivation under UV_{254+185 nm} irradiation.

Key words: Platinum nanoparticle, Vacuum ultraviolet, Photocatalysis, Ozone decomposition, Catalyst deactivation