Preparation Of Large-area Three-dimensionally Ordered Macroporous TiO₂ Films By Sol-gel Method

Sol-gel method is abroad applied to prepare three-dimensionally orderedmacroporous materials, because it is flexible and simple. There are two kindsof templates used commonly: polystyrene and silica colloidal photoniccrystals. The former require low heat-treatment temperature and are easilyremoved. Therefore, polystyrene colloidal photonic crystals are used astemplates in this thesis, large-area three-dimensionally ordered macroporousTiO₂ films are prepared by sol-gel technique.Monodisperse polystyrene microspheres were prepared by emulsionpolymerization. The standard deviation of microspheres diameter was lessthan 2%. Some factors effecting on growth of microspheres were investigated.The several phenomena during the synthesis process of monodispersepolystyrene microspheres were explained.For the vertical deposition method, the conditions of preparinghigh-quality polystyrene colloidal crystals were explored. The results indicatethat the essential factors are the concentration of microspheres in theemulsion, temperature of the crystal growth and liquid surface dropping ratesof the emulsion. The preferable conditions of the crystals growth are asfollows. For particles of 262nm in diameter, temperature of the crystalgrowth, the weight fraction of microspheres in the emulsion and the liquidsurface dropping rate were 55℃, 0.3% and 3mm/day, respectively;forparticles of 309nm in diameter, temperature of the crystal growth, the weightfraction of microspheres in the emulsion and the liquid surface dropping ratewere 55℃, 0.2% and 1.6mm/day.Finally, with unimproved and improved sol, the macroporous TiO₂ filmsof different quality were prepared through a sol-gel process using polystyrenecolloidal crystals as templates, and the films were compared. The resultsindicate that the quality of the films obtained using improved sol, such as theorder, structural integrity, framework compactness and area, are better thanthe ones using unimproved sol. The thickness of TiO2 films on the surface ofthe inverse opals is moderate and the ordered holes of the films are clearlyseen. Furthermore, the immersion time and dipping times are only 1min and2 times, respectively. It can be avoided the long immersion time andsuperabundant dipping times to destroy the templates. Comparing with thepreviously reports, the process is more simple, rapid, inexpensive andeffective. Additionally, the shrinkage of polystyrene template was about 18%,lower than the previously reports. The results of the electron diffraction andX-ray diffraction show that the porous framework consists of nanocrystallitesof anatase.