Preparation And Photocatalytic Properties Of Nanometer TiO₂ Composite Films

Nano-TiO₂ crystal has many advantages, such as good photochemical stability,innocuity, lower prices and high activities, and is widely used in cleaning waste water,cleaning air, self-cleaning, sterilization, and many other aspects. TiO₂ films, asphotocatalyst, with excellence of easier recovery and reuse has been one hotspot in theresearch field of nano-TiO₂ crystal. However, the poor heat-resistance of TiO₂nanocrystal in films leads to low calcination temperature(≤600℃) of TiO₂ films, sothe adhesive power to matrix is very poor, which reduces remarkably the service life ofnano-TiO₂ films and restricts its application in many fileds.This paper is emphasized on improving the heat-resistance and adhesive power ofnano-TiO₂ films. Nano-TiO₂ composite films on glazed ceramic plates are prepared bysol-gel method using nanocomposite method and La₂O₃, SiO₂, Al₂O₃-SiO₂ ascomposite agent. Grain growth, phase transition of TiO₂ nano-crystal in films and thephotocatalytic activities, adhesive power of TiO₂ films are studied in detail.For avoiding matrix effect on photocatalytic activity of nanometer TiO₂ in films,nanometer SiO₂ films and nanometer Al₂O₃ films are chosen to use as understratumfilms, respectively. Results show that TiO₂ films with SiO₂ films as understratumbecome varicolored. However, TiO₂ films with Al₂O₃ films as understratum have novariedness, and are smooth. Therefore, Al₂O₃ films are used as understratum in thepaper. TiO₂ nanocrystal after compounded by La₂O₃ in films is mixed crystallinestructure in which anatase(75.92%-87.18%) is dominant after calcination at 800℃.With compound quantity increasing, it is a rule that the particle size of anatase isreduced and anatase content is increased first, then reduced, after calcination at 800℃.When La₂O₃/TiO₂ mol ratio is 0.5%, anatase content is highest after calcination at800℃. The film with 4 layer Al₂O₃ films as understratum and 3 layer La₂O₃/TiO₂ filmsis more compact, without microcrack, the adhesive power is better after calcination at850℃, and has preferable photocatalytic activity with methylene blue solutiondegradation rate of about 95.72%.TiO₂ nanocrystal after compounded by SiO₂ in films is mixed crystalline structurein which anatase(73.8%～97.8%) is dominant after calcination at 1000℃, and theparticle size is about 30nm. When SiO₂/TiO₂ mole ratio is 0.1, anatase content with97.8% in mass is highest after calcination at 1000℃. The phase transition temperaturefrom anatase to rutile is enhanced and particle growth of TiO₂ nanocrystal is preventedafter compounded by SiO₂, ie, the heat-resistance of TiO₂ films has been improvedremarkably. The films with 2 layer SiO₂/TiO₂ films (SiO₂/TiO₂ mol ratio is 0.1) and 4layer Al₂O₃ films as understratum have the best photocatalytic activity and adhesivepower to glazed ceramic plate after calcination at 1000℃.TiO₂ nanocrystal after compounded with Al:Si:Ti mole ratio of 0.5:1:10 in filmsis only anatase with the particle size of about 28.77nm after calcination at 1050℃, andit is mixed crystalline structure with average particle size of about 32.8nm, in whichanatase is about 87.1% in mass, after calcination at 1150℃. The phase transition fromanatase to rutile and particle growth are restrained further. But, after calcinationbetween 1050℃and 1150℃, a fraction of TiO₂ films melts into the glaze on ceramicplate, which leads to low photocatalytic activity of TiO₂ composite films.