Synthesis And Photocatalytic Activity Of TiO₂Nano-materials

TiO₂nano-material is one of the most widely investigated and used semiconductormaterials. Because of its low cost, simple preparation process, stable chemical properties,excellent biocompatibility and unique optical performance, TiO₂nano-material hasreceived a lot of scientific and technological attention, such as photocatalysis,dye-sensitized solar cell, photochromic devices and gas sensors.Mesocrystals are a new class of nano-structured materials, which are built ofcrystallographically oriented nanoparticles. TiO₂mesocrystals are likely to possess highphotocatalytic activity due to their high degree of crystallinity and large porosity. However,because of complexity of its formation and difficulty to control the reaction, most of thereporters employ bottom-up approaches to prepare the mesocrystals, during whichnanoparticles form the mesocrystals self-assembly. With the basis of this, we utilized anew two-steps strategy to synthesize TiO₂mesocrystals, and prepared polycrystals ascomparison with a similar method. The main work is summarized as follows:（1） Studies on synthesis of TiO₂polycrystals and their photocatalytic activity.Anatase TiO₂polycrystals were prepared with liquid phase deposition, then, were calcinedat different temperatures to get a series of sintered products. The results indicate that75°Csample possesses the highest photocatalytic activity in the samples synthesized inhydrolyzing ways. The photocatalytic activity of these samples increases first, anddecreases with continuous growth of water bath temperature. With the rising of calcinedtemperature, up to500°C photocatalytic activity of sintered samples increases first, butthe photocatalytic activity goes down when the calcined temperature is above500°C.Generally, the sintered TiO₂polycrystals posses better photocatalytic activity thanhydrolysis powders.（2） Studies on synthesis of TiO₂mesocrystals and their photocatalytic activity. We developed a general, facile and green approach to synthesize anatase TiO₂mesocrystalswith a large quantity of exposed {001} facets on the surfaces, utilizing the topotactictransformation reaction of NH₄TiOF₃to anatase TiO₂. The experiments indicate that thephotocatalytic activity of H₃BO₃hydrolysis products becomes higher with the rising ofhydrolyzing temperature, and95°C sample has the best photocatalytic activity in thisrange. In the series of sintered powders,700°C sample owns highest photocatalyticactivity, which is compatible with that of the commercially available TiO₂powder （P25,Degussa）. Highly reactive exposed {001} facets may play a very important role in thisprocess.