Preparation Of Mesoporous Single Crystal TiO 2 And Its Photocatalytic Activity By Spray Drying

With the booming of world’s population, the ecological environment protection has become a global problem. Scientists have tried to eliminate the pollution of the environment using various methods, but the result is not so satisfactory. Photocatalysis is a kind of advanced oxidation treatment method, characterized by high activity, nontoxic, simple and moderate reaction conditions. Owing to the promising future, photocatalysis plays a special role in the treatment of environment pollution and undoubtedly becomes the hot research topics. Titanium dioxide（TiO₂） can create electron/hole（e-/h+） pairs when it is exposed to light with the special wavelength. The strong oxidation capability of h+ can oxidize most organic and make part toxic- matter convert into nontoxic. So, TiO₂ is very important in environment pollution treatment.Then, the nanocrystals are self-assembled in an oriented fashion into mesocrystals owing to the preferential adsorption of the additives onto specific surfaces of the nanocrystals and the oriented attachment of the nanocrystals. Later on, the mesocrystal concept was extended from the classical mesocrystals formed via a mesoscale transformation to all the solid materials constructed by crystallographically oriented nanocrystals without regard to the mechanism of formation. To date, mesocrystals of a wide range of materials including CaCO3, BaSO4, metal oxides, metal tungstates and chromates, NH4TiOF3,（NH4）3PW12O40, LiFePO4, metal chalcogenides, noble metals, and organic ma terials have been successfully synthesized. Titanium dioxide（TiO₂） is among the most widely investigated materials by virtue of its unique physicochemical properties and many promising applications in environmental and energy areas ranging from photocatalysis and sensing to solar cells and lithium ion batteries. TiO₂ mesocrystals have the potential to improve material performance due to their unique properties such as high crystallinity, high porosity, and subunit alignment. O’Brien’s group for the first time synthesized the mesocrystals of NH4TiOF3 and their remarkable topotaxial conversion by washing H3BO3 or annealing to TiO₂ mesocrystals in 2008. In particular, mesocrystals, which are assemblies of crystallographically oriented nanocrystals, which have attracted much attention in recent years. Up to now, There are many structures or morphologies have been reported about TiO₂ mesocrystals and they are used different synthesis techniques such as sol–gel, microwave-assisted hydrothermal routes, etc. However, all these methods have their own shortcomings. For exemple, used hydrothermal/solvothermal method to synthesis material is very complex and time-consuming process, and other way like one-step direct annealing approach can only get less samples. And pure TiO₂ in life and industrial application is still limited, because it can’t absorb visible light, and the quantum efficiency is low. So, through a series of modified approach makes TiO₂ has visible performance appear urgent and important.To solve the above problems, three parts work in this paper done as following:（1） We developed the ultrasonic aerosol-spray approach to synthesize anatase TiO₂ mesocrystals. TiO₂ mesocrystal nanosheets could be self-assembled into hollow hierarchical spheres due to the effect of the template of the spray droplets. The performance of hollow TiO₂ mesocrystals spheres were displayed enhanced photocatalytic activity. This method represents a simple and continued way for the synthesis of TiO₂ mesocrystals. It will be great significance for the development and application of the TiO₂ mesocrystals.（2） We developed the ultrasonic aerosol-spray approach to synthesize Au doped anatase TiO₂ mesocrystals,both Au and TiO₂ have good crystallinty. In the samples, Au nanoparticles for electron capture trap, make photocatalytic generated electrons and holes is easy to be separated, used for ultraviolet photocatalytic hydrogen production, greatly improve the photocatalytic performance of the samples.（3） We developed the ultrasonic aerosol-spray approach to synthesize CuO/TiO₂ mesocrystals composite photocatalyst. Through controlling the proportion of Cu and Ti source, realize the compound of C uO and TiO₂ photocatalyst proportional control. Photocatalytic degradation results show that the composite photocatalyst in the visible region has stronger light absorption ability, and excellent photocatalytic activity. The photocatalytic activity of the composite increase is mainly due to two different types of semiconductor constitutes the p-n junction, greatly promote the separation of the photo- generate electrons and holes.