Available online 8 May 2008.
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The nanometer potassium niobate powders with tungsten bronze (TB)-type structure were synthesized by a wet chemical method and characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). X-ray photoelectron spectroscopy (XPS) analysis confirmed the niobium with mixed valence states exists in the crystal structure of the photocatalyst, which may be advantage for increasing the photocatalytic activity. The band gap of K6Nb10.8O30 powders was estimated to be about 2.92 eV and shows a markedly blue-shift as compared to that of the sample obtained by the solid-state reaction. The photocatalytic activity of the samples was evaluated by degradation of acid red G under UV irradiation and the photocatalytic reaction follows first-order kinetics. The photocatalytic activity of the as-prepared sample is much higher than that of sample synthesized by solid-state reaction, and slightly higher than that of P25-TiO2.
The K6Nb10.8O30 powders with TB-type structure were synthesized by a wet chemical method at lower temperature. The particle size of the as-prepared powders is much smaller than that of the sample by obtained solid-state method and its photocatalytic activity is much higher than that of the latter and slightly higher than that of P25-TiO2.
Keywords: K6Nb10.8O30; Niobate; Tungsten bronze structure; Wet chemical synthesis; Photocatalytic activity; Acid red G
Fig. 1. Flowchart for the synthesis of K6Nb10.8O30.
Fig. 2. Powder XRD patterns of K6Nb10.8O30 (a) prepared by the wet chemical method calcined at 800 °C and (b) obtained by the solid-state method.
Fig. 3. SEM images of the as-prepared K6Nb10.8O30 powders by the wet chemical method calcined at 800 °C ((a) low magnification view image and (b) high magnification view image) and by the solid-state reaction ((c) low magnification view image and (d) high magnification view image).
Fig. 4. High-resolution XPS spectra of the Nb3d region of the catalyst.
Fig. 5. XPS survey spectrum of the Nb3d region of the catalyst.
Fig. 6. Diffuse reflectance spectrum of the as-prepared catalyst (a) by the wet chemical method and (b) by the solid-state reaction.
Fig. 7. UV–Vis absorption spectra changes of acid red G solution during the photocatalytic process by K6Nb10.8O30 at different irradiation time.
Fig. 8. FT-IR spectra of samples (a) before degradation and (b) after degradation.
Fig. 9. The reaction rate constants of the catalyst (A) prepared using the wet chemical method; (B) synthesized by the solid-state reaction; (C) P25-TiO2.
Results of curve-fitting of the high-resolution XPS spectra of the Nb3d region