Controllable Synthesis Of Micro/Nano-structure TiO₂, SnO₂and Research On Their Performances

TiO2and SnO2have been widely used in photocatalysis, gas sensor, paint, lithium ion battery, solarcell, drug delivery and medical imaging. With a deeper research by scientist, people realized that theproperties of materials are not only determined by the chemical compositions, but also determined bymorphology. TiO2and SnO2with different morphology synthetized by different methods can improve theperformance. However, the morphology is influenced by the synthesis method. Herein, the research onrelations among synthesis method, morphology and performance is great significant to improve theproperties of TiO2and SnO2.This work was supported by the Innovation Scientists and Technicians Troop Construction Projects ofHenan Province (Grant No.114200510004) and Henan Normal University Innovation Funds forPostgraduate (No.YL201202). This work was focused on the morphology of the TiO2, and studied theirelectrochemical performance. In addition, controllable synthesis of solid and hollow SnO2microspheresand their gas-sensing properties have also been studied. The several major works of this thesis are asfollows:(1) The reaction system by using tetrabutyl titanate as titanium source, oxalic acid dehydrate asadditive, and ethanol as solvent has been applied to research the controllable formation mechanism of TiO2yolk-shell hierarchical microspheres composed of small nanoparticles as building blocks by controlling thereaction time. This kind of yolk-shell TiO2is first used in LIBs. TiO2HYSHMs exhibit a high initialdischarge capacity of267.6mAhg-1at0.25C and retain191mAhg-1even after40cycles, indicating goodelectrochemical performance.(2) The TiO2submicrospheres have been fabricated through reflux in oil bath followed by calcinationsby using tetrabutyl titanate as titanium source, oxalic acid dehydrate as additive, and ethanol as solvent.Cycle performance has been researched. The initial discharge capacity is189.5mAhg-1at0.25C and retains188.9mAhg-1after40cycles, indicating excellent cycle performance.(3) The factors of tetrabutyl titanate, oxalic acid dehydrate and solvent have been applied to researchthe controllable formation mechanism of TiO2hollow microspheres composed of small nanoparticles asbuilding blocks by controlling the reaction time. When the concentration of titanium source is at certain amount, concentration of additive affects the morphology of products obviously. When applied theannealed products in LIBs, concentration of titanium source affects electrochemical performance obviouslyat fixed concentration of additive. The length of carbon chain of solvent can also affect the dimension ofTiO2hollow spheres and then affects the electrochemical performance. The dosage of titanium source,oadditive, and the length of solvent have great effect on the morphology and electrochemical performanceof products.(4) The reaction system by using SnCl2·2H2O as tin source, polyvinylpyrrolidone (PVP) as softtemplate, assisted with tartaric acid (C4H6O6) and distilled water as solvent has been applied to research thecontrollable formation mechanism of SnO2hollow microspheres composed of small nanoparticles asbuilding blocks by controlling the reaction time. Solid and hollow SnO2microspheres with differentspecific surface and pore size can be achieved at different reaction times. Moreover, the relationshipbetween specific surface and pore size is on the opposite side. With reaction time increasing, the specificsurface of sample increases, but the pore size decreases. It was firstly founded that the gas sensitiveproperties of SnO2microspheres were not only affected by the specific surface, but also affected by poresize in the real gas sensing test. From the experimental result, it founded that the gas sensitive properties ofSnO2microspheres were controlled by the surface chemical reaction kinetics shifting gradually to gasdiffusion kinetics when the operation voltage (opertaion temperature) increases. These new findingsprovide the experimental and theoretical basis for further studying the sensing mechanism and highperformance of gas sensors.