The Low Temperature Synthesis, Characterization And Mechanism Of Carbon Nanomaterials

The morphologies and phase of the materials mean a lot in the application, but the way that used to prepare samples is crucial for the formation of morphologies and phase. The aim of this thesis is to explore new synthetic methods for nanomaterials, especially carbonaceous materials. On the basis of investigation and study of many literatures, we use a new reaction route--Grignard reagent route to prepare carbon nanotubes, hollow nanospheres and nanofibres. With the study of different kind of reaction conditions, appropriate solvents and the control of reaction temperature, distinct morphologies of the products have been synthesized successfully. Carbon nanotubes have the morphology of claw-like ends, which haven't been reported to the best of our knowledge. In the experiments, enlightened by the solvothermal reduce route. we, used alkali metals sodium and polytetrafluorethylene, at mild reaction condition, obtained carbon spheres. And we also got Tl₂E (E=S or Se) nanorods under this way, which was highly appreciated by many foreign scientists. Now let's summary as follows: 1. Carbon nanotubes with claw-like ends were synthesized at 200oC, using aluminun and hexachloroethane as reactants, aluminum chloride as catalyst and benzene as solvent. The products had low yield and were characterized with X-ray diffractometor, Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectrum. Many stack faults had been found, but this kind of morphologies may have applications in many fields, such as the tips in STM and field emission, nanotweezers. A possible growth mechanism was proposed. 2.Carbon hollow nanosphers were synthesized at 200oC, using magnesium and hexachloroethane as reactants, aluminum chloride as catalyst and benzene as solvent. The samples were characterized with many measurements. The products with uniform diameter, high yield, but not well crystallinity. When the reaction temperature was increased, large amount of irregular carbon spheres and some nanotubes could be observed, while the temperature conducted to 150 oC, many amorphous sheets of graphite could be found. Many control experiments were under taken to explore possible reaction mechanism and growth mechanism. When the solvent benzene was changed with ethylenediamine, kept other experimental invariables, carbon nanofibres were obtained. The reaction conditions were easy to be maintained and controlled. It might provide a new method to produce other carbonaceous materials. 3. Carbon spheres made of entangled fibers were prepared at 250 oC for 24 h using sodium and polytetrafluorethylene as reactants and benzene as solvent. A possible mechanism of the formation was proposed. The products were characterized with many measurements, such as XRD, TEM, HRTEM and Raman. It might have application in environment protection and lessen pollution with some kind of plastics. 4.Tl₂E (E=S or Se) nanorods were synthesized via solvothermal route with the addition of KI at the temperature of 150 ℃about 12h. The products were characterized with X-ray powder diffraction (XRD) patterns and transmission electron microscope (TEM) images. Their optical properties were studied by UV-vis transmittance and photoluminescence spectrum. The band gap of direct forbidden transitions was found larger than that of bulk materials, because of the blue shift caused by nanometer-scale crystalline particles due to quantum confinement effects. A possible growth mechanism was proposed. And the work was highly appreciated by many scientists.