Simultaneous elimination of formaldehyde and 03 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 O-3, especially at the high RH level, showing the excellent moisture-resistant behaviors. At the Pd loading of 0.3-0.4 mu g cm(-2), the O-3 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-hO(2). Under UV254+185nm irradiation, the ozone might be decomposed on the Pd-TiO2 via two different routes, i.e., photocatalytic reduction of O-3 on exposed TiO2 and decomposition of O-3 on PdOx particles involved with UV irradiation and trapped electrons. (C) 2011 Elsevier B.V. All rights reserved.