Low-temperature Synthesis Of InVO₄ Sol And Photocatalytic Activities Of InVO₄-TiO₂ Composite Thin Films

InVO₄-TiO₂ composite materials are found to be a visible light responding photocatalyst because the conduction band potential level of novel semiconductor InVO₄ with narrow band gap is more negative than that of TiO₂. The precursor precipitation of InVO₄ was synthesized by co-precipitation using indium trichloride (InCl3), ammonium metavanadate (NH₄VO₃) and ammonia (NH3·H2O) as raw materials. The milk white InVO₄ sols with orthorhombic phase were obtained by low-temperature hydrothermal treatment, which reveals the synthetic temperature of InVO₄ is effectively reduced. InVO₄ doped RS sol had been prepared through blending InVO₄ sol into RS sol under continual magnetic stirring. Novel InVO₄-TiO₂ thin films on glass slides were synthesized via a sol-gel dipping method from the as-synthesized composite sol. The influences of technological parameters on the phase of InVO₄ sol, optical absorption and photocatalytic performance of InVO₄-TiO₂ composite thin films were investigated in detail.The results of samples reveal that the pH value of the reaction mixture and reaction temperature play important roles to the target phase. It is shown that the particle size and grain size distribution increase according to the increase of the reaction temperature, time and compactedness. The morphology changes drastically when increasing reaction temperature and extending time. A lot of the particles take on cubic-like morphology. According to the in-situ Transformation, the forming process of the InVO₄ sol under hydrothermal conditions and the phenomenon of coalescence are investigated in this paper based on the hydrothermal crystallography. The whole process can be formulated that VO₃- incorporate into the In(OH)3 particles and replace OH- to yield InVO₄ nuclei. The forming reason of cubic-like morphology can be explained by the relation between InVO₄ crystalline morphology and InVO₄ grow unit.In this study, the UV and visible-light activity of TiO₂ thin films and InVO₄-TiO₂ composite thin films are compared. The photocatalytic results by degradation of methyl orange indicate that the InVO₄-TiO₂ composite thin films show excellent photocatalytic activities under UV light irradiation; the films with 3.0wt% InVO₄ content without heat treatment exhibits the highest visible light photocatalytic activity, the decoloration rate of methyl orange solution reaches 80.1% after irradiated for 15 h. The films with 500oC heat treatment reach 25.1% under the same conditions. It is due to outer-shell electrons of InVO₄ can absorb the energy of light and the electrons in the InVO₄ valence band can be excited into conduction band by visible light, and the excited electrons inject into the conduction of the TiO₂, and making photogenerated electrons and holes separation more efficient, thereby visible light photocatalytic activity are enhanced.