Bismuth Excess Type Bismuth Tungstate Photocatalyst

In recent years, photocatalytic degradation technology has been paid much attention to environmental pollution control. Photocatalytic treatment of pesticide wastewater is considered an ideal method for energy consumption and effect. The tungstate photocatalyst is widely praised by people for its advantages of energy saving, high efficiency, easy operation, wide range of application, thorough degradation of pollutants and no secondary pollution.

Bismuth tungstate is a star product in the field of photocatalyst. Because of its narrow gap width (about 2.7eV), bismuth tungstate can be excited by visible light and has high catalytic activity under visible light. Because of the variation of the parameters in the preparation process, Bi₂WO₆ has different graininess, such as globule, petal, flower, umbilicus and helix. The best photocatalytic activity is petal shape.

There are also many methods for the preparation of bismuth tungstate. Solid phase method, hydrothermal method, solvent heat method and microemulsion method are complete and Bi₂WO₆ also has good compatibility. Hydrothermal synthesis technology, weighed 0.4075 g (0.84 mmol) of Bi(NO₃)3·5H₂O Teflon liner in 25mL, add 7mL of distilled water and magnetic stirring, and then weighed 0.1319g (0.40mmol) Na₂WO₄·2H₂O and dissolved in 10 mL of water, and then dripped into the above precursor solution of Bi (NO₃)₃. After stirring for 30 min, the resulting white suspension was hydrothermally reacted at 160 °C for 12 h. After naturally cooling to room temperature, the product was centrifuged, washed and dried to obtain a light yellow photocatalyst powder having a Bi: W molar ratio of 2.1: 1.

In situ medium acidity precursor system, by adjusting the reaction of Bi (NO₃)₃ - 5H₂O and the initial molar ratio of Na₂WO₄ / 2H₂O for 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.5:1, 4.0:1, Bi series of prepared photocatalyst source excess.

The results show that Bi2WO6 system with the best photocatalytic Bi source can effectively suppress the recombination of photogenerated carriers and further improve the photocatalytic activity when the molar ratio of Bi (NO3)₃·5H₂O: Na₂WO₄·2H₂O is 2.3-2.8: 1 Photocatalytic activity, the photocatalytic reaction kinetic constant can be increased 2.47 times. On the one hand, the phenomenon is attributed to the generation of basic bismuth nitrate when Bi source is excessive, and the fluorescence intensity decreased, indicating that it has formed effective interfacial charge transfer with Bi₂WO₆. On the other hand, when the Bi source is excessive, the flower like superstructure has thinner lamellar structure and more abundant micropores. These factors are favorable for the enhancement of the specific surface area, and provide more active sites and ion transport channels for the photocatalytic process, thus improving the photocatalytic activity.

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