Photocatalytic degradation of low concentration formaldehyde and simultaneous elimination of ozone by-product using palladium modified TiO2 films under UV254+185nm irradiation

Simultaneous elimination of formaldehyde and O3 by-product was investigated in the UV254+185nm photocatalysis with a continuous flow mode using palladium modified TiO2 films (Pd-TiO2). Formaldehyde (HCHO) was introduced at a low concentration (ca. 450 ppbv), typical of polluted indoor environments. Pd nanoparticles, deposited via an electrostatic self-assembly method, had uniform distribution on TiO2 films with an average size of 3–4 nm. Under UV254+185nm irradiation, the steady state concentration of HCHO was reduced to 10–50 ppbv for a long irradiation period (>30 h), and catalyst deactivation was not observed. Modification of TiO2 with palladium could simultaneously increase the conversion of HCHO and O3, especially at the high RH level, showing the excellent moisture-resistant behaviors. At the Pd loading of 0.3–0.4 μg cm−2, the O3 conversion ratio increased over 3 times compared to pure TiO2. XPS analysis exhibited that PdO on the TiO2 was oxidized to mixture palladium oxides PdOx(x > 1) under UV254+185nm irradiation. Due to high electron affinity of formed PdO2, the photogenerated electrons could be trapped by PdOx, thus improving the separation of e−/h+ pairs. As the reduction of PdO2 and oxidation of PdO coexisted, the PdOx could be dynamically stabilized, thus increasing the photoactivity of Pd-TiO2. Under UV254+185nm irradiation, the ozone might be decomposed on the Pd-TiO2 via two different routes, i.e., photocatalytic reduction of O3 on exposed TiO2 and decomposition of O3 on PdOx particles involved with UV irradiation and trapped electrons.

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► Ultra-fine Pd nanoparticles are uniformly dispersed on TiO2 films.
► Formaldehyde can be rapidly degraded to a low level under UV254+185nm irradiation.
► Modification of TiO2 with palladium increases the removal rate of both formaldehyde and O3, with over 3 times improvement of O3 decomposition.
► The PdOx inhibit the recombination of e−/h+ pairs.
► Ozone can be decomposed on UV irradiated TiO2 and PdOx surfaces.