Low Temperature Preparation Of Nona-TiO₂ Coated Fibers And Their Photocatalytical And Bactericidal Properties

In this paper, technichques relating to modification of TiO₂2 based photocatalysts in recent years such as metal cation doping, metalloid anion doping, ion implantation, photosensitization, fixed technology and so on were reviewed based on the brief introduction of the degradation mechanisms of semiconductor photocatalysts. The recent developments in the preparation of the photocatalytical titania nanoparticles and thin films at low temperature were reviewed with comparation for the different preparation methods, such as hydrothermal methods, sol-gel methods, precipitation process at low temperatures , liquid phase deposition, and so on. The research direction in the near future has also been previewed.Thin film coatings of titania nanocrystals based on cotton fibers (TiO₂/Cotton), polyacrylonitrile fibers (TiO₂/PAN) and polyvinyl alcohol fibers (TiO₂/PVA) were prepared successfully at low temperature by different methods such as microwave assisted liquid phase deposition (MW-LPD) process, sol-gel process with hot water treatment, dissolution-reprecipitition process and so on. The thin films were anatase crystalline and annealing post-treatment at high temperature was avoided.(1) Compared with the conventional LPD processes, the MW-LPD technique could provide quickly high yield and crystallinity in a diluted precursor solution at a low temperature because the high-frequency microwaves penetrated into the bulk of the material and the volumetric interaction of the electromagnetic fields with the material results in dielectric (volumetric) heating. This leaded to higher heating efficiency with faster processing and not only the deposition rate but also the crystalinity of the products were improved remarkably by MV irradiation. The microwave irradiation is benefit for the formation of higher crystallinity of titania and continuous layers of titania on fibers.(2) Titania thin film was deposited successfully on fiber by the sol-gel process with the assistance of tetraethyl silicate (TEOS) at low temperature. It was found that the densification and crystallization of the film was resulted from the post-treatment in boiling water because of the hydrolysis of the Si-O-Ti bonds and dissolution of thesilica component formed in the film. For the silica coatings on which anatase nanocrystals were precipitated superficially, the residual silica under-layer acted as a protective coating against the photocatalytic degradeation of the fiber substrates.(3) For the preparation of nanocrystalline anatase thin films deposited on fibers by sol-gel dip-coating method, the TiO2 sol were prepared by a low temperature dissolution-reprecipitition process in a liquid media using cheaper TiCLj as precursor, and the crystallization of amorphous precursor was proceeded by peptizing with acid and then refiuxing for a periodic time. The TiO2 sol was prepared firstly and the crystallization of titania could be controlled easily.The fibers with anatase coatings showed high photocatalytic property and better repetition on the photodegradation of MB. The quantitative examination of antibacterial activity indicated that the fibers as-prepared had higher bactericidal activities towards E. coli, P. aeruginosa, and S. aureus. The titania coated fibers are expected to be applied as novel photocatalysts for the antibacterial action, air clean-up indoor, deodoring and antifouling.In order to improve the repeating circles of the semiconductor titania photocatalyst and broaden its applications, TiO2 photocatalysts immobilized on suitable supports such as PDVB microspheres (PDVB@TiC>2), cheaper adsorbent attapulgite (TiO2-ATP) and carbon (TiCVC) were developed. The hybrid photocatalysts developed were characterized by scaning electron microscopy (SEM), transmitsion electron microscopy(TEM), X-ray diffraction (XRD), elemental analysis, Brunauer-Emmett-Teller (BET), and UV-vis adsorption spectroscopy.(4) The core/shell anatase TiC>2 encapsulated poly(divinylbenzene) (PDVB@TiO2) hybrid microspheres were prepared by the two steps: (D the copolymer particles (PDVB) were prepared by the radical precipitation copolymerization of divinylbenzene (DVB) and y-methacryloxypropyltrimethoxy silane (KH-570);(2) tetrabutyl titanate (TBOT) was co-hydrolyzed with the trimethoxy silane groups on the surfaces of the PDVB cores and then the amorphous TiO2 shell obtained was phase transformed to anatase Ti(>2 by acid peptization. The polymer supported TiC>2 photocatalysts prepared at low temperature, had better repetition because of thecoupled action of KH-570 between the PDVB core and TiCh shell. Furthermore, it could be easily separated from the solution by simple sedimentation.(5) A new route for preparation of TiCVC hybrid photocatalysts were developed by calcining the core/shell (PDVB@TiO2) hybrids at temperatures of 400, 450 or 500 °C in a furnace under air for certain time. The TiCVC hybrids obtained at higher calcination temperature had higher surface area because of more eliminateion of polymer core. The present catalysts show high adsorptivity and high photoactivity for the degradation of MB and can be very easily separated from the solution by sedimentation or simple filtration and it can be used repeatedly for MB removal with preservation of its photoactivity.(6) Fine particles of photoactive anatase-type TiC>2, prepared by hydrolysis of TBOT with hydrolysis control agent tetrabutylammonium hydroxide (TBA)OH and crystallized under microwave (MV) irradiation, were loaded on adsorbent support attapulgite (ATP). The substrates of target were adsorbed on the adsorbent support, and then a high concentration environments of the substrate was formed around the loaded TiC>2, resulting in an increase in the photodestruction rate. One of the most interesting features of the resulting catalysts with low titania contain (<30 %) is their fast decantability in comparison with that of TiC>2. This way one of the most important drawbacks of photocatalysis, the catalysts separation from the solution, was overcome by simple sedimentation and decantation.In particular, the typicall features of the photocatalysts prepared in this dissertation would make them very suitable for configurations and efficient photoreactor for purification of polluted water.