Preparation Of Carbon Nanotubes And Other Fullerenes Material Spectroscopic Properties Of Single-walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) have been an area of intense research since their discovery in 1993, because of their extraordinary mechanical and unique electronic properties. The preparation of SWCNTs is a key part of research about SWCNTs, and the preparation of SWCNTs with good quality is precondition and foundation of characterizing structure, testing properties and further study in application. The SWCNTs growth by CCVD is strongly affected by catalysts, growth time and synthesis temperature and so on. The formation mechanism is still not well established and the understanding of the catalytic growth of SWCNTs lags behind. Hence it is of great significance to study the growth mechanism of SWCNTs.With narrow bands, Raman spectroscopy has advantages for probing molecular structures, and has been proved to be a useful tool to analyze the structure of SWCNTs. However, the information it provided is limited by its low sensitivity. Surface-enhanced Raman Scattering (SERS) has high sensitivity and resolution, which has been used as a powerful technique for providing high-quality spectra exhibiting fine structural details of molecules. Using SERS for studying CNTs, high quality spectra have been observed and more structural details of CNTs have been obtained.In this paper, the Mo-Co-MgO and W-Co-MgO catalysts were first prepared by the "citric add" method. SWCNTs were synthesized by decomposing CH₄ in Ar over the Mo-Co-MgO and W-Co-MgO catalysts at 1123K. The effects of composition of the catalysts on the synthesis of SWCNTs were studied by Raman spectroscopy and Transmission Electron Microscope (TEM). The results show that molar ratio of Mo:Co:MgO=1:10:100 in Mo-Co-MgO catalyst may be the optimal composition, and molar ratio of W:Co:MgO=l:5:100 in W-Co-MgO catalyst may be the optimal composition. Dependence of diameter distribution of SWCNTs on the composition of catalysts is small. There were some differences in the inner structure of SWCNTs synthesized over different catalysts. The carbon yield rates of products were increased by the addition of W and Mo in the catalysts. Comparing with the addition of W, the addition of W may be more effective for the increase of carbon yield rate.The growth time plays an important role in the course of preparing SWCNTs and influence the quality and amount of SWCNTs. The influence of growth time on synthesizing SWCNTs over Mo-Fe-MgO catalyst by decomposing CH₄ in Ar was studied this paper. Results show that The SWCNTs were longer and the graphitization degree was higher for the synthesis time prolonged. At 30min, the long bundles of SWCNTs with lower defect level were obtained, and the growth of most SWCNTs had taken place within 30min. After 30min, nearly no SWCNTs were generated without the presence of the active catalytic sites, but amorphous graphite was still deposited due to the continuous decomposition of CH₄. The growth mechanism of SWCNTs over Mo-Fe-MgO catalyst was proposed according to the experimental results and the "Solid -liquid - solid" growth mechanism proposed by A.Gorbunov.The growth time also plays an important role in the course of preparing SWCNTs. By using Mo-Co-MgO bimetallic catalyst, generation of SWCNTs even at 940K was demonstrated. The optimum temperature of synthesizing SWCNTs over Mo-Co-MgO bimetallic catalyst may be about 1123K. The content of SWCNTs is increased with the increase of temperature below 1123K and the carbon yield rate is also increased with the increase of synthesis temperature. Therefore, the amount of SWCNTs increases with the increase of temperature below 1123K. However, above 1123K, the content of SWCNTs is decreased with the increase of temperature; therefore, it is not effective to increase the amount of SWCNTs through increasing synthesis temperature above 1123K.In this paper, SERS spectra of SWCNTs on the metal-coated filter paper were reported for the first time. The SERS spectrum not only exhibits that all Raman bands of SWCNTs in normal Raman scattering have been generally enhanced, but also many new bands appear, such as a series of bands within 1100-1500 cm^-1 and RBM peaks at 119, 239 and 308cm^-1. Our SERS system could provide more signals with fine structures related to defects of SWCNTs and carbon particles in nano-size on SWCNTs. Moreover, this can be used as a probe technique for monitoring the synthesis quality of SWCNTs with significant higher sensitivity than other methods, which has promising potentiality of being a new technique for practically monitoring synthesis quality of SWCNTs.A SERS spectrum of very good quality of "silver nano-particles/C60/silver film" system was reported for the first time by using the pyridine as a intermediate to connect and nest the C60 molecules to the gap of silver nano-particles and silver film. Experiment results show that the ternary system of "silver nano-particles/C60/silver film" is very effective and active. Not only was the number of vibrational modes greatly increased, especially some modes that were forbidden in Raman spectrum, but also were the significant Raman bands splitted as well as frequencies up and down shifted, respectively, arising from symmetry lowering and selection rule relaxing of C60 induced by the silver surface. In addition, the SERS mechanism of this system was study. In this paper, SERS of C60 on different substrates was also studied. The results show that conglomeration of nano-particles plays an important role in SERS of C60.