Prepareing Carbon Nanotubes By Chemical Vapor Deposition Method

In this thesis, the effect between catalyst and carbon nanotubes (CNT) grown in Chemical Vapor Deposition (CVD) method were studied and how to prepare chemically modified electrode based on carbon nanotubes grown in situ were carried out by CVD method.1. A series of La-Ni-0 compounds were synthesized with modifying the mol ratio of La and Ni by citric acid complexometry and used as the catalyst precursors to prepare CNT by CVD method. At the same time, H₂, N₂ and C₂H₂ were used as the reduction gas, protection gas and carbon source gas, respectively. The structures of the catalyst precursors before and after reducing by H₂ were characterized by XRD and the patterns of the CNT obtained from the catalyst precursors were characterized by TEM. The results showed that there were only chemical compounds LaNiO₃ and La₂NiO₄ in the series La-Ni-O catalyst precursors. However, the yield of CNT from the catalyst precursor LaNiO₃ was greatly higher than that from the catalyst precursor La₂NiO₄. And the reason was that the content of nano-meter metal Ni (111) crystal face in the productions from LaNiO₃ after being reduced was higher than that from La₂NiO₄. That is to say, higher the content of nano-meter metal Ni(111) crystal face; higher yield of CNT, and larger the size of the metal Ni(111) crystal face; larger inner diameter of CNT.2. Carbon nanotubes were prepared by CVD method using the catalyst, which was prepared by citric acid complexometry. The effect of the dosage of citric acid on the CNT yield and morphology was studied. The transmission microscopy was used to characterize CNT morphology. CNT yield is about 1345.8%(1h) at a 2 : 1 mol ration of citric acid and metal ion, CNT diameter is relatively narrow distributed and CNT wall is slick. But when mol ration of citric acid and metal ion is 3 : 1, CNT yield is about 407.2% (1h), and the obtained CNT diameter is relatively wide distributed. Analyzing the X-ray diffraction images of the product of catalyst precursor after being reduced, the product maybe the main reason to affect the CNT yield. One is the content of metal Ni (111) crystal face; the other is the different structure of La₂O₃.3. Carbon nanotubes in situ chemically modified electrodes (CNT-CME) were prepared by CVD method. Carbon nanotubes grew on the graphite substratum, which was impregnated in catalyst solution. In order to prepare different CNT-CMEs, we changed the catalyst content in graphite substratum by changing impregnating time and numbers. They showed different electrochemical character. Surface morphology of CNT-CME was characterized by SEM, the patterns of obtained from CNT-CME were measured by TEM. With cyclic voltammetry of Na₂SO₄ solution and [Fe(CN)₆]^3-/[Fe(CN)₆]^4- redox couple solution, CNT-CME (5/10-S), which was prepared on graphite substratum impregnated 5 numbers per 10 minute in catalyst solution indicated better electrochemical character. Anodic peak currents depended linearly on the square root of the scan rate over the range of 5～100mV? s^-1. From this, we know the chemically modified electrode is a quasi-reversible cyclic voltammetric electrode. Thus it not only expands rang of carbon nanotubes application, but also abounds the content and the technique of electrochemical analysis. There is future for the applications of carbon nanotubes chemically modified electrode in electroanalysis.