Abstract:

A PW₁₁Cr/TiO₂ nano film photocatalyst was prepared on the surface of a glass slide via the sol-gel dipping pulling method using tetrabutyl titanate Ti(OC₄H₉)₄ as the precursor of TiO₂ and the Keggin type chromium substituted heteropolyanion(PW₁₁Cr) as the visible light active component. Then the light absorption properties, chemical composition, crystal phase and surface morphology of the as-prepared catalyst were characterized using solid ultraviolet-visible diffuse reflection spectroscopy, infrared spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The interaction between PW₁₁Cr and TiO₂ in the film was discussed. Visible photocatalytic activity of the catalyst was assessed using photocatalytic degradation of RhB as a probe. Meanwhile, a photocatalysis mechanism was suggested and compared with that of TiO₂. Influences of the calcination temperature, the PW₁₁Cr dosage and the solution pH on the catalyst activity were also examined. In the end, a recycle test of the catalyst for RhB degradation was employed to evaluate the stability of the catalyst. The PW₁₁Cr/TiO₂ photocatalyst has a good absorption of visible light. The film obtained at low calcination temperature(100 ℃) is amorphous but crystal at high calcination temperature(500 ℃). The former has higher photocatalytic activity, and is employed to degrade RhB with a concentration of 10 μmol/L under the irradiation of 200 W metal halide lamp. The degradation ratio is 95% at 120 min and the COD removal is 72% at 4 h. The hydroxyl radicals are the main reactive oxygen species leading to RhB degradation. Low processing temperature, high PW₁₁Cr dosage and high solution acidity are favorable to enhance the photocatalytic activity of the PW₁₁Cr/TiO₂ film. After recycles of 10 times for RhB degradaion, the photocatalytic activity of the PW₁₁Cr/TiO₂ film lose insignificantly.

Key words: Keggin-type Cr-substituted phosphotungstates, titanium dioxide, visible photocatalyst, sol-gel method, rhodamine B