Morphology-controlled Synthesis And Photocatalytic Activity Of Nanosized Titanium Dioxide

To solve the increasingly serious problems of environmental pollution, variouscatalytic techniques are being applied in the fields of environmental protection. Oxidesemiconductor photocatalysis is one technique that has great potential to controlaqueous organic contaminates or air pollutants. Among various oxide semiconductors,TiO₂has been proved to be the most suitable photocatalyst for its strong oxidizingpower, nontoxicity and long-term stability against photo and chemical corrosion. Inrecent years, many attempts, such as finding new preparation methods and usingmodifications, have been made to improve the photocatalytic activity of TiO₂.However, the preparation of photocatalyst with highly photocatalytic activity, theimmobilization of powder photocatalyst, and the improvement of photocatalystperformance are priorities to be considered. Herein, valuable explorations have beencarried out on the synthesis of highly active TiO₂photocatalysts. The main pointscould be summarized as follows:Highly photoactive nano-sized TiO₂powder photocatalyst was prepared bycalcination post-treatment method using P25as the precursor. We investigated theinfluence of calcination temperature on the phase composition, microstructure andmorphology of titania. The results showed that the calcination temperature of thesolutions obviously influenced the microstructures and photocatalytic activity of theas-prepared TiO₂powders. The photocatalytic activity of TiO₂powders calcinationtemperature at400to600oC exceeded that of Degussa P-25by a factor of more than1.5times. This might be ascribed to the enhancement of anatase crystallization andthe optimal mass ratio （ca.1:2） of rutile to anatase.WO₃/TiO₂hollow spheres photocatalysts were synthesized by a hydrothermalmethod using （NH₄）₂TiF₆,Na₂WO₄as precursor at a variety of doping concentration.The synthesized products were characterized by XRD, XPS, N₂adsorption-desorptionmeasurement, SEM, HRTEM and FTIR. The results showed that dopingconcentration greatly affected the microstructures and photocatalytic activity of theas-prepared samples. With increasing doping concentration, the average pore sizes of WO₃/TiO₂hollow sphere increased enhanced, while the specific surface area,crystalline size and pore volume decreased. The improved photocatalytic activity ofthe composite hollow sphere is attributed to the increased surface acidity and bettercharge separation due to the coupling of WO₃species and TiO₂within the compositenanoparticles.F-doped titania were hytrothermally prepared at180oC using TiF4as precursorwithout the addition of templates and additives. The results revealed that hollowstructures of F-doped titania could spontaneously form by Ostwald ripening in acidwater solution. Hydrothermal time had a strong effect on the structures, crystallinesize and photocatalytic activity of the as-prepared titania. At12h, the sample showedthe highest photocatalytic activity. This is may be fluoride anions of starting reagentsare adsorbed on the surface sites of oxygen. The resultant anion overlayer maycontribute to stabilization of surface and creation of repulsive interaction among thefreestanding nanospheres. At24h, the photocatalytic activity slightly decreased.When the hydrothermal time was higher than12h, the photocatalytic activity greatlydecreased due to the increase in crystallite size and drastic decrease of specific surfaceareas of F-doped titania.