Abstract: (Ni-Mo)/TiO₂ composite thin films were prepared by composite electroplating at a constant current. The surface morphology, phase structure, and optical characteristics of the thin films were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectrum, and ultravioletvisible diffuse reflectance spectroscopy (UV-Vis DRS), respectively. The photocatalytic properties of the (Ni-Mo)/TiO₂ composite thin films were evaluated with Congo red as a model compound. The effects of pH of the Congo red aqueous solution on the photocatalytic activity of the (Ni-Mo)/TiO₂ thin films were investigated. Using cyclic voltammetry technique and a method of adding active species scavengers to the solution, the mechanisms of photocatalytic degradation of the films were explored. The results show that the (Ni-Mo)/TiO₂ films consist of crystalline grains of TiO₂ in the size range of 50-100 nm and nanocrystalline grains of Ni-Mo in solid solution. The (Ni-Mo)/TiO₂ films are photocatalytically more active than a TiO₂/ITO (indium tin oxide) reference film. Under halogen light irradiation, the photocatalytic degradation rate of the (Ni-Mo)/TiO₂ films is 2.43 times as much as that of a porous TiO₂ (Degussa P25)/ ITO film. The improvement in photocatalytic activity for the composite films could be mainly attributed to the heterojunction of (Ni-Mo)/TiO₂, the electronic passageway of Ni-Mo in the composite films, and the catalysis of Ni-Mo in the composite film for the reaction of excited electrons with dissolved oxygen. The photocatalytic reaction mechanisms of the (Ni-Mo)/TiO₂ films evaluated with Congo red are given under visible and UV light irradiation, respectively.

Key words: Photocatalysis, (Ni-Mo)/TiO₂ nanofilm, Composite electroplating, Cogon red, Reaction mechanism