Bismuth tungstate (Bi₂WO₆) as a kind of material with narrow band gap photocatalyst response to visible light and visible light catalytic activities. The band gap is only about 2.7eV, under visible light can be chloroform, acetaldehyde and other harmful substances mineralization, decomposed into harmless gas CO₂. Bismuth tungstate photocatalyst has the advantages of excellent UV and visible light response, stable photocatalytic performance and good thermal stability, and has low cost and friendly environment. It is an ideal photocatalytic material.

Bismuth based photocatalyst is a good visible light catalyst. However, bismuth based photocatalyst is easy to compounded due to its narrow gap width (1.76eV to 3.1eV), resulting in low photo activity.

In recent years, bismuth tungstate (Bi₂WO₆) and tungstate semiconductor material, nano structure and due to their unique physical and chemical properties, it has good application prospects, such as used in magnetic devices, scintillation materials, corrosion inhibitor and catalyst, has become a research hotspot in recent years. Polyvinylidene fluoride (PVDF) has high dielectric constant and has good physical and chemical properties, can work for a long time in the environment of high intensity, easy to make a flexible film with special response materials in large area, so the collection of bismuth tungstate (Bi₂WO₆) and polyvinylidene fluoride (PVDF) / advantages of bismuth tungstate the prepared PVDF composite material has great application prospects in the field of dielectric materials.

Some new non TiO2 photocatalysts have been developed, such as perovskite type, vanadium subgroup complex oxide and bismuth series photocatalyst, since TiO₂ has been found to be able to degrade water and degrade organic pollutants under ultraviolet radiation. The research of new photocatalytic Bi₂WO₆ has been developed in recent ten years. Only the pure phase Bi₂WO₆ has low quantum efficiency, and its low utilization rate of visible light (about 400nm), which limits its application in photocatalysis.

Liquid stripping method is a way to achieve industrial production, but also to produce two-dimensional tungsten oxide composite materials. Stripping the two-dimensional tungsten oxide from the two-dimensional tungsten oxide layer needs to overcome the van der Waals forces between layers, and the tungsten oxide dispersed in the liquid is a direct and effective way to reduce van der Waals forces. This makes the liquid phase separation method has the possibility of industrialization.

Tungsten oxide ultrathin nanosheets obtained by supercritical carbon dioxide. At the beginning of the stripping, smaller nanosheets 5-10 nm in diameter are randomly dispersed and have no significant orientation. Nanosheet lattice spacing 0.37 nm, corresponding to the (120) face of tungsten oxide.

The ultra-thin nanosheets Raman scattering spectra are very sensitive to the vibration and lattice defects of the W-O bond, which is a good way to characterize the samples. As can be seen from the figure, the prepared ultrathin nanosheets have two characteristic peaks: 645 and 943 cm. The peak at 943 cm corresponds to the stretching vibration of the W = O bond in the structural unit. The peak at 645 cm corresponds to the tensile vibration mode of the W-O bond.

Tungsten oxide thin nanosheets preparation principle is the use of supercritical carbon dioxide device assisted stripping tungstic acid. One supercritical carbon dioxide device is a two-cylinder piston pump, a high-pressure reactor, a heating jacket and a temperature controller.

The semiconductor material is used as a photocatalyst, due to the limitation of the photocatalytic mechanism, photogenerated electrons and holes can easily be recombined inside and on the surface of the material to affect the photocatalytic efficiency. Pure tungsten oxide nanomaterials also have this problem. By constructing semiconductor / semiconductor heterostructures with other semiconductors, the effective separation of photogenerated electrons and holes can be well promoted, and recombination of photogenerated electron-hole pairs can be avoided.

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