Fabrication And Electrical/Magnetic Properties Of Functional Carbon Nanotubes Composites

Carbon nanotubes(CNTs) have unique structure and novel physic-chemistry properties,which have been attained considerable attention.CNTs are good templates due to their hollow structure.Assembling CNTs with functional materials could impart the special properties of optical,electrical and magnetic on CNTs.The CNTs have weak magnetic properties.Combining CNTs with nanosize magnetic materials will prouce functional CNTs with good magnetic properties.The composites have important potential applications in many fields such as electric devices,absorbing materials,magnetically guided drug and synthesized by magnetic record.In this thesis, novel CNTs nanocomposites were synthesized by wet chemical methods.The as-synthesized composites were characterized systemically,especially the electrical magnetic properties were investigation deeply.Linear polyethyleneimine(PEI) was used as a noncovalent functionalizing agent to modify multi-walled carbon nanotubes(MWCNTs).Fe₃O₄ nanoparticles were then formed along the sidewalls of the as-modified MWCNTs through a simple solvothermal method.X-ray diffraction analysis(XRD),transmission electron microscopy(TEM),fourier transform spectroscopy(FTIR),vibrating sample magnetometer(VSM) were used to characterize the MWCNT/Fe₃O₄ nanocomposites. Results indicated that Fe₃O₄ nanoparticles with diameters ranging from 50～200 nm were attached to the surface of the MWCNTs by electrostatic interaction.The magnetic saturation value of the as-prepared nanocomposite was 61.8 emu g^-1.The coercive force is 83 Oe at 25℃.On the other hand,the unique structure of MWCNTs was reserved.PEI was found to improve the electrical conductivity of the Fe₃O₄/MWCNT nanocomposites.Mn_xZn_1-xFe₂O₄ nanospheres were self-assembled alongside MWCNTs via a facile solvothermal method.The shape,structure,and size of the as-synthesized sample were characterized by XRD,TEM,HRTEM,SAED,SEM,VSM.The results showed that a large number of the high purity Mn_xZn_1-xFe₂O₄ nanocrystallites were decorated on the sidewalls of the MWCNTs,and these nanocrystallites aggregated around the MWCNTs templates formed spherical aggregation.The magnetic saturation value of the magnetic nanocomposites was 55.6 emu.g^-1.The probable formation mechanism of the nanocomposites was also investigated based on the experimental results.Nanocrystals of indium tin oxide(ITO) polymorphs(rhombohedral and cubic) were deposited on the sidewalls of the MWCNTs by a simple co-precipitation process. XRD,TEM,HRTEM,SAED,energy-dispersive X-ray(EDX) spectroscopy were used to characterize the as-prepared samples.The results indicated that tuning of the ITO phase in the nanocomposites can be selectively achieved via controlling the pH value of the co-precipitation process and the temperature of the subsequent calcination.The formation mechanism of the ITO/MWCNTs nanocomposites was also investigated.Electrical conductivity measurements on the samples pressed into pellets showed that the maximum conductivities attained were 0.52±0.05 and 0.65±0.04 S cm^-1 for the rhombohedral and cubic ITO/MWCNTs nanocomposites at a dopant concentration of 12.5 wt%.The electrical conductivity of the nanocomposites was significantly enhanced compared to the pristine MWCNTs.