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The Properties Of Microemulsion Template And Its Applications To Preparation Of Nanomaterials

Posted on:2010-10-22Degree:DoctorType:Dissertation
Country:ChinaCandidate:X C LiFull Text:PDF
GTID:1101360275958565Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Precise control on the morphology and the function are the main objectives for preparation of nanomaterials.Surfactant molecule self-assembly soft template has attracted considerable interests due to its promising applications in preparation of nanomaterials.The study on the inducing and controlling effect of the template interface and the microstructure on crystal growth is crucial to the synthesis of nanomaterials with different structures, photoelectric and catalytic properties.It was proved by the conductivity property that there were clusters/aggregates or dispersed droplets in the microemulsion system.The state of the microemulsion droplets can be used to study the dispersity of the as-synthesized particles.Furthermore,the parametrs such as water core and hydrodynamic diameter of the droplets were calculated.The synergistic controlling mechnism of microemulsion interface and PEG400 on the growth of ZnO crystal have been proposed and discussed in detail.The monodispersed ZnO nanocolumns with 50-80nm in diameter and 80-100nm in length were prepared with 12.5%or 25.0%of PEG400 in Zn(NO3)2 solution,and this was due to the controlling effect on(0001) direction of ZnO crystal.ZnO nanostructures with band gap energy of 3.06eV,3.02eV, 2.95eV and 2.85eV were obtained with 0.0%,12.5%,25.0%and 50.0%of PEG400 in Zn(NO3)2 solution respectively,which are lower than that of bulk ZnO(3.37eV).The result demonstrates ZnO nanostructures with low band gap energy and different morphologies can be prepared by controlling the microemulsion interface strength.TiO2 nanoparticles with 6-10nm in diameter were prepared in W/O,bicontinuous and O/W microemulsion zones respectively.TiO2 nanostructures with different shapes and photocatalytic activities were obtained in a microemulsion system with different interface strength resulting from increasing the hydrothermal temperature.The increase of fluctuation and the decrease of strength of microemulsion interface with the increase of hydrothermal temperature result in the reduction of restrictions on the crystal growth.Accordingly,TiO2 nanoparticles were synthesized at temperature of 120-200℃and TiO2 nanorods and cubes were obtained at 200-350℃.The photocatalytic constants increase to 0.86-0.966cm-1 at 200-350℃,which is comparable or higher than that of P-25.The higher photoactivity of TiO2 samples can be assigned to their higher crystallinity and lower surface defects. In order to further control the structure and the morphology of TiO2 material,the bisurfactant AOT/Lecithin template with high interface strength instead of TritonX-100 microemulsion system were used to prepare porous TiO2 nanostructure.The rapid hydrolysis of titanium isopropoxide(TIP) at the interface of water channels and oil phase resulted in the formation of porous titania material,leaving the integrity of the water channels in the template.The water channels in AOT/Lecithin template exhibit highly order upon shearing alignment.The patterned porous TiO2 materials were prepared using the sheared soft template. The photocatalytic activity of the sheared samples increase by 36.0%compared with the unsheared TiO2 samples at W=70.The enhancement of the activities of the sheared samples can be attributed to their open-end channels and higher photoenergy absorption efficiency. The average diameters of the pores in the sheared and unsheared materials increased from 100nm to 200nm with adjusting the water content from W=70 to W=200 respectively. Furthermore,the photocatalytic activities for degradation of Rhodamine B increased with the increase of pore diameters(0.0378-0.0417min-1 for sheared samples;0.0278-0.0335min-1 for unsheared materials).
Keywords/Search Tags:Soft-template, Microemulsion, Zinc Oxide (ZnO), Titania (TiO2), Photocatalytic activity
PDF Full Text Request
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