Fluorine Effect On Morphology And Light Catalytic Properties Of Titanium Dioxide

Among various metal oxide（s） photocatalysts, TiO₂has been proven to be the mostsuitable material for its strong oxidizing power, nontoxicity and long-term stabilityagainst photo and chemical corrosion and cost effectiveness. Now titanium dioxidesphotocatalyst is widely used in various fields such as deodorization, antibacterial, airand water purification as well. Although TiO₂is an efficient photocatalyst, itsphotocatalytic activity needs to be further improved from the viewpoint of commercialapplication. In this thesis, effects of fluoride ions on the morphology and photocatalyticactivity of anatase TiO₂were systematically studied. The thesis consists of two sectionsas follows:In chapter one, TiO₂nanocrystals with exposed high-energy （001） facets weretailored by hydrothermal reaction of tetrabutyl titanate （50g） and HF solution at200Cfor24h. It shows that, with increase in the amount of HF, the shape of TiO₂nanocrystalevolves from octahedral bipyramid to nanosheet and the percentage of exposedhigh-energy （001） facets increases. The photocatalytic activity of the preparedhigh-energy anatase nanocrystals is positively related to the percentage of exposed （001）facets. When the amount of HF is more than12mL, the photocatalytic activity ofanatase TiO₂nanosheets is high than that of P25. The high photocatalytic activity of thehigh-energy anatase TiO₂nanocrystals is ascribed to the synergetic effect of exposedhigh reactive （001） facets and surface fluorination. However, high concentrated HF （20mL） results in the formation of cubic TiOF2, which shows very poor photocatalyticactivity.Chapter two deals with the effect of residual fluoride ions on the photocatalyticactivity of TiO₂hollow microspheres prepared by fluoride induced self-transformation（FIST）. Photocatalytic activity of TiO₂is known to be enhanced by surface fluorinationdue to the enhanced production of free.OH radicals in solution. Recently, hollow TiO₂microspheres with enhanced photocatalytic activity was developed through FIST, andthe enhanced photocatalytic activity has been attributed to the fluoride-inducedenhanced crystallization of TiO₂hollow microspheres without taking into account theeffect of surface fluorination. This section aims to re-evaluate the effects offluoride-induced crystallization and surface fluorination on the photocatalytic activity ofhollow TiO₂microspheres prepared by FIST. It was found that the presence of fluoridepromoted the crystallization of TiO₂nanoparticles and enhanced the hollowing process.However, it was also shown that surface fluorination, resulted from the residual fluorideions, played a more important role than its crystallization on the enhancement of the photocatalytic activity.