| Photocatalysis has attracted more and more attention as an ideal technology for the treatment of environmental pollution and clean energy production in recent years. TiO2is considered to be the preferred photocatalyst due to its high chemical stability, non-toxic, inexpensive and high activity. However, its wide application is limited since TiO2has a large band-gap and only be excited by ultraviolet or near ultroviolet and its quantum efficiency is very low. Therefore, it is highly desirable to develop photocatalysts with high activities under visible-light irradiation. Great efforts have been devoted on the developing of visible-light driven photocatalysts. Recently, the bismuthate oxides have attached much attention due to its special band structure. The formed second level above the valence band will make the energy gap of bismuthate oxides small and the absorption light shift to the visible light region.In this paper, we prepared three photocatalysts, calcium bismuth, strontium bismuth and CaBiO compound. Their photocatalytic activities were evaluated by the degradation of methylene blue under visible light irradiation. X ray powder diffraction (XRD), N2physical adsorption (BET), UV-vis diffuse reflectance spectra(UV-vis DRS), Raman (Raman), thermogravimetry (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), terephthalic acid photoluminescence (TA-PL) and inductively coupled plasma (ICP) are applied to investigate the structure, morphology, properties and photocatalytic activities of these catalysts.Pure phase of flower-like CaBi6O10catalyst was prepared by impregnation method at650℃, using Bi2O3and Ca(NO3)2·4H2O as precursors. The synthesized CaBi6O10catalyst has strong absorption in the visible light region. The band absorption edge is determined to be554nm, corresponding to the band gap energy2.24eV. The catalytic testing results indicate that CaBi6O10catalyst presents higher activity than Bi2O3and N-TiO2in the methylene blue degradation under visible light irradiation. That is because CaBi6O10has a special band structure which can extend the carrier lifetime, thereby improving catalyst’s activity.CaBiO compound was synthesized by precipitation method using Bi(NO3)3·5H2O and Ca(NO3)2-4H2O as precursors. The solutions of Bi(NO3)3and Ca(NO3)2were mixed first to obtain a deposit. After aging at room temperature for2h, the deposit was filtered, washed, and dried to remove water completely. Finally, the precursor material was calcined at500～700℃for12h to obtain the target catalyst. The synthesized CaBiO catalyst is in good response to visible light, and can absorb visible light with wavelength less than580nm. Their specific surface area is improved compared with the sample prepared by impregnation method. The photocatalytic activity of methylene blue degradation is very good under visible light irradiation. The active species-OH in catalytic reaction is detected by terephthalic acid photoluminescence (TA-PL) probe technique. In addition, the photocatalytic performance of the CaBiO catalyst is stable, and the catalyst can be recycled.Pure phase of Sr0.25Bi0.75O1.36catalyst was also prepared by impregnation method at800℃, using Bi2O3and Sr(NO3)2as precursors. Sr0.25Bi0.75O1.36catalyst has strong absorption in the visible light region, and the band absorption edge of it is determined to be510nm, corresponding to the band gap energy2.43eV. Although the specific surface area of Sr0.25Bi0.75O1.36is very small (only1.0m2·g-1), its photocatalytic activity is higher than that of CaBi6O10, Bi2O3and N-TiO2catalysts under visible light irradiation, which maybe attributed to its suitable band. |
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