Nano-titanium dioxide mainly has two crystal forms: Anatase and Rutile. Rutile titanium dioxide is more stable and dense than anatase titanium dioxide, has higher hardness, density, dielectric constant and refractive index, and its hiding power and tinting power are also higher. The anatase titanium dioxide has a higher reflectivity in the short-wave part of visible light than the rutile titanium dioxide, has a bluish hue, and has lower ultraviolet absorption capacity than the rutile type, and has a higher photocatalytic activity than the rutile type. Under certain conditions, anatase titanium dioxide can be converted into rutile titanium dioxide.

There are many methods for preparing nano-TiO2, which can basically be summarized as physical methods and chemical methods.

Physical method is also called mechanical crushing method, which requires high crushing equipment; chemical method can be divided into vapor phase method (CVD), liquid phase method and solid phase method. Physical vapor deposition (PVD) uses high-stability heat sources such as arc, high frequency or plasma to heat the raw materials to vaporize or form plasma, and then quench them to condense them into nanoparticles. Among them, the vacuum evaporation method is the most commonly used. The particle size and distribution of the particles can be controlled by changing the gas pressure and heating temperature. The method can also be used for the preparation of single oxides, composite oxides, carbides and metal powders. Chemical vapor deposition (CVD) uses the vapor of volatile metal compounds to generate the required compounds through chemical reactions. The nano TiO2 prepared by this method has fine particle size, high chemical activity, spherical particles, good monodispersity, and good visible light transmittance. Strong ability to absorb and shield ultraviolet rays. The process is easy to scale up and realize continuous production, but it has a large one-time investment and needs to solve the problem of powder collection and storage. CVD method can be divided into gas phase oxidation method, gas phase synthesis method, gas phase pyrolysis method and gas phase hydrogen flame method. The gas phase hydrogen flame method is obtained by burning titanium tetrachloride with hydrogen flame.

Nano-titanium dioxide has strong ability to absorb ultraviolet light, unique color reaction, good thermal stability, chemical stability and good optical, mechanical and electrical properties. Among them, anatase has higher catalytic efficiency and rutile type. The structure is stable and has relatively strong covering power, tinting power and UV absorption ability. Therefore, its catalyst carrier, ultraviolet absorber, high-efficiency photosensitive catalyst, skin care products, sunscreen, plastic film products, water treatment, fine ceramics and other fields have a wide range of applications.