Study On Photocatalysis Of TiO₂ And Preparation Of Nanocomposites

Titania has been widely used as gas sensors, solar-energy conversion and a promising photocatalyst for water and air purification because of its high oxidative power, chemical stability, low cost and nontoxicity. Unfortunately, one severe disadvantage of the titania semiconductor material is the large band gap of 3.0 or 3.2 eV in the rutile or anatase crystalline phase respectively and only absorbs the UV light which accounts for merely-5% of the solar spectrum.Therefore, there have been many efforts to extend activity of titania into the visible region to improve utilize efficiency of titania. Titania materials with different morphology and structure have applications in different fields. For their distinctive geometries, novel physical and chemical properties and potential applications in nanodevices, drug delivery, nanosensors and microelectronics,one-dimensional(1D)chemical nanostructures such as nanorods, nanowires, nanotubes, and nanobelts have attracted a great attention. Titania nanofibers and nanotubes had been successfully prepared by the electrospinning technique because it is a relatively simple and versatile method for fabricating ultrafine fibers. Herein, we used a convenient controlled nonhydrolytic sol-gel method to prepare alkoxide-bonded titania nanoparticles. The whole reaction procedure between TiCl4 and ethanol is simple without using any additional peptizing agent. Anatase titania hydrosol, anatase titania DMF sol and carbon-doped titania nanoparticles were prepared using the as-synthesized alkoxide-bonded titania nanoparticles. Then the PMMA/titania hybrid materials were prepared by the photocatalytic polymerization of the anatase titania hydrosol under the Xe light. The PMMA/titania hybrid nanofibers were prepared via the electrospinning method using the PMMA solution containing an anatase titania nonaqueous sol.After the calcination, the carbon-doped anatase titania nanofibers responded to the visible light were obtained. The PMMA polymer was also synthesized by the photocatalytic polymerization of the carbon-doped titania nanoparticles under visible light illumination. The main research content and results are as follows.(1)The anatase titania nanoparticles prepared by a facile nonhydrolytic sol-gel reaction. Then the anatase titania nanoparticles were dispersed into water to form stale hydrosol.The titania DMF sol were also obtained by dispersing the anatase titania nanoparticles into DMF solvent. The two kinds of titania sols were stale and kept good transparency when the concentration of titania was low. The XRD patterns showed that the crystals of the titania in titania sols still retained the anatase phase and high crystalline. The DLS results exhibited the size of titania nanoparticles in the two kind sols gradually became large with increasing titania concentration.(2) The surface modification of the titania nanoparticles was achieved by the formation of the bidentate coordination between titania and methacrylic acid molecules. The photocatalytic polymerization of methyl methacrylate was initiated by surface modified anatase titania nanoparticles under Xe lamp irradiation. The transparency of PMMA hybrid films was maintained because the modified titania nanoparticles were well dispersed in the polymer matrix.The glass transition temperatures and the thermal stabilities of PMMA nanocomposites prepared via photocatalytic polymerization were greatly improved compared with pure polymer.(3) The PMMA/anatase titania hybrid nanofibers were prepared via electrospinning technique using the PMMA solution containing an anatase titania DMF sol. The carbon-doped titania nanofibers were also obtained by calcining the hybrid nanofibers. The XRD results showed that the anatase phase in the PMMA/titania hybrid nanofibers was preserved during the spinning. The XPS results demonstrated that the carbon doping into titania nanofibers was achieved via the calcination at 400℃. Compared with hybrid nanofibers, the carbon-doped titania nanofibers had higher photocatalytic activities toward the degradation of methylene blue under visible light irradiation. Therefore, the carbon-doped titania nanofibers showed promising applications in water cleaning and air purification. (4) Carbon-doped titania nanoparticles in a pure anatase phase colored dark brown were successfully prepared using a convenient controlled nonhydrolytic sol-gel method followed by annealing at 400℃. The XPS indicated that substitutional and interstitial carbon atoms coexist in the lattice of titania. The UV-Vis spectrum showed that these carbon-doped titania nanoparticles exhibit significant photo response from UV to near infrared region in excess of 950 nm. The PMMA polymer was prepared by photocatalytic polymerization of the carbon-doped titania nanoparticles under the visible light illumination. The Mn of the purified PMMA was～1.28×106 g/mol and its polydispersity was 3.0. The glass transition temperature of obtained PMMA was about 127℃. This carbon-doped titania would be benefit to allow the more efficient use of sunlight in photocatalysis and photochemistry.