Influences of the Pd doping on the visible light photocatalytic activities of InVO4–TiO2 thin films

Novel Pd/InVO4–TiO2 thin films with visible light photo activity were synthesized via a sol–gel method from the Pd and InVO2 co-doped TiO2 sol. The photocatalytic activities of Pd/InVO4–TiO2 thin films were investigated based on the oxidation decomposition of methyl orange in aqueous solution. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV–vis absorption spectroscopy (UV–vis). The results indicate that the Pd/InVO4–TiO2 thin films are compact, uniform and consist of sphere nanoparticles with diameters about 80–100 nm. The UV–vis spectra show that the Pd/InVO4–TiO2 thin films extend the light absorption spectrum toward the visible region. XPS result reveal that doped Pd exist in the form of metallic palladium. The photocatalytic experiments demonstrate that Pd doping can effectively enhance the photo activities of InVO4–TiO2 thin films in decomposition of aqueous methyl orange under visible light irradiation. It has been confirmed that Pd/InVO4–TiO2 thin films could be excited by visible light (E < 3.2 eV) due to the existence of the Pd and InVO4 doped in the films. The photocatalytic mechanism of Pd/InVO4–TiO2 thin films is investigated in this paper.