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Preparation method of nano titanium dioxide---sol-gel method
The sol-gel method is a very important method. It is generally prepared by using titanium alkoxide and anhydrous hexane as raw materials, adding a small amount of water and different acid or organic polymerization additives, and stirring and aging to form a stable coating film. Sol. Reuse TiO 2 sol deposited on various carriers. The sol-gel method is characterized in that the TiO 2 film is firmly bonded to the carrier and is not easily detached; the TiO 2 film of the desired crystal form can be obtained by controlling the burning temperature; the thickness of the film can be controlled. At present, TiO 2 film with controlled film thickness can be prepared by sol-gel method, and it is proved that the photocatalytic activity of acetaldehyde is higher than that of P-25 powder, and the catalytic activity increases with the increase of film thickness. .
The colloidal chemical method is also a sol-gel method in which Ti(OH) 4 precipitate is formed by using titanyl sulfate and alkali (Na 2 CO 3 ), and then dissolved with hydrochloric acid to form a positively charged sol, and then an organic surface treatment agent is used. The treatment is carried out to impart new oiliness to the particles, followed by phase inversion in an organic solvent, and calcination of the hydrated TiO 2 after removal of the organic solvent to obtain nano TiO 2 . The key to this process is the concentration and temperature control during acid dissolution.
The titanium alkoxide hydrolysis method is also a sol-gel method in which a sol is obtained by hydrolysis and polycondensation using titanium alkoxide as a raw material. Further condensation is carried out to obtain a gel. The gel is dried and calcined to obtain nano TiO 2 . Its reaction formula is as follows.
Hydrolysis Ti(OR) 4 +nH 2 O===Ti(OR) 4-n (OH) n +nROH
Polycondensation 2Ti(OR) 4-n (OH) n ===[Ti(OR) 4-n (OH) n-1 ] 2 O+H 2 O
The purity of the raw material of the process is high, and impurity ions are not introduced in the whole process. The nano-TiO 2 powder with high purity, small particle size and narrow particle size distribution can be obtained by strictly controlling the process conditions, and the product quality is stable. The disadvantage is that the raw material cost is high, and the gel shrinkage is large when drying and calcining, and it is easy to cause agglomeration between the nano TiO 2 particles.