Synthesis And Properties Of Micro/Nano-structured TiO₂ And Their Graphene-based Composite

Micro/nano-structured metal oxides with controlled morphologies have been received special attention due to their unique structure and interesting physicochemical properties. As an important wide band gap semieonductor material,TiO₂ with diverse morphology or crystal structures are the most atractive materials. It is found that the physicochemical properties of TiO₂ depend on the morphology,exposed special crystal faces and the controlled size, especially applying in photocatalysis, UV-shielding and electrochemistry areas. In this dissertation, we controlled synthesis of micro/nano-structured TiO₂ and their graphene-based nanocomposite, and the relationship bteween their morphology and crystal structures and their properties have been investigated. The main research contents are summarized as follows:1. Flower-like rutile hierarchical microsphere building with 1D TiO₂ nanorods were successfully synthesized by a facile hydrothermal process with the assitance of PVP. The concentration of PVP aqueous solution and hydrothermal reaction time played the pivotal role in controlling the final structure of our products, in which appropriate concentration of PVP resulted in uniform and monodisperse hierarchical flower-like structure, while the diameter of the microsphere could be controlled by adjusting the hydrothermal reaction time. More significantly, all the as synthesized flower-like TiO₂ with different diameters exhibited higher UV shielding capability compared with commercial P25 and anatase, and the UV shielding performance of our hierarchical TiO₂ microsphere is regularly enhanced with the increase of their diameters and the relative packing density of constituted nanorods on individual microsphere. The S-24h-C sample showed the highest UV shielding efficiency and could block the entire UV light with a good transmittance in the visible region, as well as poor photocatalytic activity, which can be served as a safe and promising candidate for UV-screen agent.2. A facile method was proposed for fabricating uniform three-dimensional?3D?flower-like TiO₂?FT? microsphere decorated graphene?GN? heterostructures by using titanium?IV? isopropoxide?TTIP? and graphene oxide?GO? as precoursor through one-step poly?vinylpyrrolidone??PVP?-assisted hydrothermal process. That is to say,the reduction of GO and the situ growth of TiO₂ microsphere on the surface of the GN occurred simultaneously. The effects of PVP and reaction temperature on themicrostructure of the composite were investigated, and a possible formation process and mechanism were proposed. The adsorption ability and photocatalytic activity of FT/GN composite were evaluated in adsorption and photocatalytic degradation of RhB in aqueous solution. The results showed that the prepared FT/GN composite exhibited superior performance in the removal of RhB under irradiation of UV light in comparison with the pure FT microsphere. The FT/8GN composite with the addition amount of 8wt% GO exhibited best removal rate for RhB, 96.9% RhB was removed after irradiated by UV light for 50 min. Importantly, the repeated photocatalytic tests of the sample showed that the removal rate of RhB was still up to 90.2% after four cycles, indicating its excellent recyclability and tremendous potential application in removal of organic dye from water. In prospect, this preparation method could provide a new insight into designing and synthesizing new GN-based hybrid composite with multi-dimensional structures for other fields.3. Biphasic TiO₂ microsphere/graphene?TiO₂/GN? composites were successfully fabricated through one-step PVP-assisted hydrothermal process via adjusting the concentration of HCl. It was found that the concentration of HCl had a decisive influence on the morphology and crystal structures of TiO₂ for the TiO₂/GN composite. As the concentration of HCl was 3 mol/L, the combination of high quality of GN and micro/nano-structured TiO₂ microsphere with biphasic could be observed.By several characterization methods such as X-ray diffraction, scanning electron microscopy and transmission electron microscopy, we demonstrated that uniform TiO₂ microsphere building with nanoparticles ranging from 2 to 5 nm have successfully anchored on the surface of graphene sheets, and TiO₂ contained both anatase and rutile phases. In addition, the photocatalytic activities under visible light of the synthesized composites were measured for the removal of RhB. The synthesized composite of biphasic TiO₂ with micro/nano-structure showed enhanced catalytic activity compared to blank TiO₂ microsphere and commercial photocatalyst P25. The exceptional photocatalytic activity of the synthesized composite can be elucidated on the account of the unique micro/nano-structure and biphasic composition of TiO₂ as well as the doping of graphene.