Electrochromic refers to the phenomenon that the optical properties (such as reflectivity, transmittance, absorption rate, etc.) of tungsten oxide nanosheets undergo a stable and reversible color change under the action of an applied electric field. In appearance, it shows the reversible change of color and transparency of tungsten oxide nanosheet. Materials with electrochromic properties are called electrochromic materials and devices made with electrochromic materials are called electrochromic devices.

In recent years, tungsten oxide materials containing oxygen defects have attracted the attention of researchers. Tungsten oxide lattice can withstand a considerable amount of oxygen vacancies, the performance of the unique non-stoichiometric. Oxygen vacancy in tungsten oxide can improve the conductivity and electrode activity of the material, and even a key factor in the electrode reaction. Oxygen vacancies in tungsten oxide as a shallow donor can improve its photocatalytic activity and electrochemical performance. Tungsten oxide exhibits better thermodynamic stability than other non-stoichiometric metal oxides, and oxygen vacancies can only occur in air at temperatures above 300 ° C.

The heterojunction of titanium dioxide nanosheets and tungsten oxide composites with different mass ratios of 90:10 to 95: 5 have different photochemical catalytic activities. The heterojunction current density of 2.6μA at a mass ratio of 90:10 is well below the heterojunction mass ratio of 95: 5. In other words, the content of tungsten oxide in the titanium dioxide/tungsten oxide heterojunction is not as high as possible.

As a typical n-type semiconductor, tungsten oxide and titanium dioxide can be used as a photocatalyst. Due to the large specific surface area and heterostructure, it is foreseeable that the titanium dioxide/tungsten oxide heterojunction should have excellent photocatalytic properties.

Nano thin films have large surface area of one-dimensional nanosheets, and provide direct and smooth transmission paths for photoelectrons and holes. It can effectively promote the electron transport to the material interface. The preparation of a thin film of bismuth tungstate photocatalyst needs the following process:

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.