Preparation Of Titania And Titanate Nanostructured Materials And Applications In Catalysis And Lithium Ion Battery

Titanium-based oxides, as an important semiconductor material, offer the potential application for energy and environmental issues owing to their excellent photoelectrical properties, low cost and chemical inertness. In this thesis, Co doped Li4Ti5O12 nanofibers, Pd/CeO2-TiO2 nanofibrous membrane and N-TiO2/g-C3N4 composite were prepared using simple liquid method. Also, the corresponding physical and chemical properties were studied to illustrate the relationship between microstructure and properties.1. Preparation of Co-doped Li4Ti5O12 nanofibers with enhanced electrochemical properties for lithium-ion batteryLi4Ti5O12 and Co-doped Li4Ti5-xCoxO12 (x=0.01,0.05,0.10) nanofibers were prepared through the sol-gel method combined with electrospinning technique with tetrabutyl titanate, lithium acetate and cobalt acetate as starting materials, ethanol as solvent, polyethylene oxide as spinning aid. The dopant of Co does not alter the crystal structure of lithium titanate and inhibits the grain growth in the calcination process, leading to the reduction of the particle size from 230 nm to 140 nm. Electrochemical tests show that the introduction of cobalt improves the conductivity of Li4Ti5O12, and then rate charge-discharge performance can be enhanced. At the current density of 1C,2C,4C and 8C,5 mol% Co-Li4Ti5O12 shows the specific discharge capacity of 170,143,129 and 116 mAh/g in the first cycle, respectively. And corresponding capacity of pristine Li4Ti5O12 is 171,128,109 and 90 mhA/g, respectively. The capacity retention ratio of 68.2% for 5 mol% Co-Li4Ti5O12 is higher than that of pristine Li4Ti5O12(52.8%) when the current density increases to 8C from 1C. After circulation with 60 times at the current density of 1C, the attenuation of reversible capacity for Co-doped Li4Ti5O12 is rare. Co-doped Li4Ti5O12 shows excellent electrochemical performance due to its higher electronic conductivity and lithium ion diffusivity compared with pristine Li4Ti5O12.2. Flexible Pd/CeO2-TiO2 nanofibrous membrane with high efficient ultrafine particulate filtration and improved CO catalytic oxidationHigh tensile, self-support CeO2-TiO2 and Pd/CeO2-TiO2 nanofibrous membrane were achieved by controlling the parameters in sol-gel and electrospinning process with tetrabutyl titanate, cerium nitrate, palladium chloride and polyethylene oxide as raw materials. The content of CeO2 has a great influence on the flexibility and tensile strength of the fibrous membrane. The highest tensile-strength of the TiO2-CeO2 (1.38 MPa) was attained at the Ce and Ti molar ratio of 5:100, which was 3 times as high as that of pure TiO2. After loading Pd on the fibers, the strength of fibrous membrane (1.28 MPa) stays almost the same. The filtration efficiency of Pd/CeO2-TiO2 fibrous membrane with the basic weight of 16.84 g/m2 for 300-500 sodium chloride can reach 99.86% and corresponding pressure drop is 178 Pa. By adjusting the electrospinning time, the basic weight of the fiber membrane can increase to 20.76 g/cm3, and the corresponding filtration efficiency of 99.95% and the pressure drop of 352 Pa can be obtained. The results can satisfy the requirement of the high efficiency particle filtration. Moreover, the Pd/CeO2-TiO2 nanofibrous membrane exhibits excellent thermal stability against long time use and could still retain the strength up to 1.22 MPa after 400℃ for 20 h, which endows the nanofibrous membrane with the ability of the application under the high temperature condition. The fibrous membrane also exhibits good CO oxidation catalytic performance with a total conversion of CO to CO2 at 200℃ and no decrease of catalytic activity over 30 h. The high thermal stability, excellent filtration performance and high catalytic property towards the oxidation of CO of Pd/CeO2-TiO2 fibrous membrane make it potential application in high temperature flue gas treatment.3. Facile synthesis of sheet-like N-TiO2/g-C3N4 Composite with highly enhanced and stable visible-light photocatalytic activityN-TiO2 nanoparticles around 20nm were prepared by the combined method of co-precipitation and calcinations using TiCl4 and NH3·H2O as raw materials. G-C3N4 nanosheets with thickness about 8-15 nm, width of several microns were obtained by thermal polymerization of NH4SCN. Sheet-like N-TiO2/g-C3N4 composite with well-controlled structures as high-efficiency visible-light photocatalysts can be synthesized by direct co-calcination of preformed N-TiO2 nanoparticles and g-C3N4 nanosheets. The visible-light photocatalytic activity of the composite with different mass ratios of N-TiO2 and g-C3N4 was evaluated by photodegradation of rhodamine B dye. The highest photocatalytic activity was attained at a mass ratio of 1:3. The rate constant of a first-order kinetic model for N-TiO2/g-C3N4 (1:3) is 19 times as high as that of N- TiO2 nanoparticles,5.3 times of individual g-C3N4 nanosheets, and 35.1 times of P25, respectively. Moreover, the sheet-like N-TiO2/g-C3N4 photocatalyst exhibits excellent stability against repeated use and could still retain over 98.8% of the initial activity after seven cycles. Such prior visible-light photocatalytic performance is mainly due to the high specific surface area (>80 m2/g) of the product as well as efficient charge transfer at the interfaces. The mechanism of photocatalytic reaction is studied and the results show that ·O2- and h+ play an important role in the phtocatalytic process. This work presents a simple method for preparation of highly active photocatalysts. The prepared composite shows good application prospect in dealing with water pollutants.