Preparation And Modification Of Carbon Nanotubes And The Prelimilary Application In Glucose Biosensor

Many potential applications have been proposed for carbon nanotubes, including field emission displays, modified electrodes, nanometer-sized semiconductor devices, probes, high-strength composites, energy storage and energy conversion devices and catalysts support, based on their good thermal conductivity similar to diamond, the special mechanical property, the high aspect ratio and hollow structure with nano-scale of carbon nanotubes. At present, three methods to synthesize carbon nanotubes are widely used: arc discharge, laser blazing and chemical vapor deposition (CVD). Among them, CVD pyrolysis of hydrocarbons over transition metal catalysts has been the method of choice for CNTs synthesis. It has the advantage to allow large-scale production, as well as control over reaction temperature, feeding gas and selection of catalysts, parameters that govern the growth of CNTs. Large-scale synthesis of CNTs has been developed in recent years. However, catalysts as Fe, Co, Ni and their alloys supported by SiO₂, Al₂O₃ or MgO are not yet sufficiently effective. Since mass production of high quality CNTs has not been achieved at low cost so far, we are interested in developing new catalysts and studying the growth mechanism of the new catalysts for the synthesis of CNTs by CVD. Moreover, we have further done some researches on application of the prepared carbon nanotubes.We first prepared MgMoO₄ as a single-phase catalyst by sol-gel method. Our experiments reveal that the prepared catalysts have high activity and high efficiency. After react for 2 h, the yield of synthesized MWNTs is closed to 30 times of the pristine catalysts. Especially, the newly formed Ni/Mo/MgO has better activity for carbon nanotubes synthesis after proper amount of element Ni was added in MgMoO₄ After reacted for 2 h, the maximum yield of synthesized MWNTs is over 80 times of the Ni/Mo/MgO pristine catalysts. With a simple enlarged process, a single furnace can produce over 40 g MWNTs from 1 g Ni/Mo/MgO catalyst in 30 min.Our research shows that the formed MgMoO₄ single-phase catalyst is a good catalyst for nanotubes growth for its moderate acidity. There are phase transformations happened in the MWNTs synthesis process. Upon our TEM observations and analyses, the mechanism of theMWNTs bundles is proposed. The absorption of hydrogen makes the molybdenum nanoparticleoh broken from inside to outside of the catalyst, forming multiplayers molybdenum nanaoparticles oid the surface of the support, which is the main cause to form nanotubes bundles. The effect of thiui ratio of CH4/H2 or CH4/N2 was also studied on Ni/Mo/MgO catalysts. The results show that that ratio of CH4/H2 or CH4/N2 actually plays a key role in the synthesis process. The synergism of nickel-molybdenum causes the carbon atoms rapidly dissolved in the nickel-molybdenur nanoparticles, which should be responsible for the high yield and quality of MWNTs. Based of our observations and analyses, and on the phase transformation showing by the XRD, the formation mechanism of the MWNT bundles on Ni/Mo/MgO catalyst is presented.High quality SWNTs were synthesized by catalytic decomposition of CH4 at 1000°C CH4 Fe-Mo/MgO catalyst. The best calcination temperature is 550°C for the catalyst. The pronce acidity-basicity for CNT growth can explain the high performance of the catalyst. The very moei thing is that we find mainly adjusting the Fe-Mo, the activity composition in the catalysts, cata control the diameters of the as-prepared SWNTs. The best reaction atmosphere in the grow experiments is CH4 /H2 = 75/300 v/v or CH4 /N2 = 50/300 v/v for the catalyst. Different act oxidation methods were systematically carried out to purify the SWNTs synthesized. The resu show that the best purification process can reach purity higher than 98% for the resulted sin:g wall carbon nanotubes within 2 h. In this process, it is found by Raman characterization that thi amount of nanotubes with small diameters do not diminish within 3 h.The synthesized MWNTs by an enlarged furnace were annealed at 1000°C. Our results she: that the tips of many nanotubes are open when the anneal time extended. Raman results show he: the structure of the surface layers of the tubes is improved. TGA results show that both the initiid and end-combustion temperature confirmed above results, and the purity of the nanotubes increased from 96.1% to 99.5%.Two carboxylation processes were carried out to modify multi-walled carbon nanotube bund (m-MWNTs). The results showed that both of the m-MWNTs could be highly dispersed in wfs or hydrophilic reagents without obvious deposition or conglomeration for more than 6 monit The nanotube structure would be damaged a lot after modification treatments in mixed acids or24 h. Two functioning methods of nanotubes were carried out in the experiments for attaching long alkyl chains to the nanotubes via amide linkage. The results show that the nanotubes attached with long alkyl chains are more soluble in organic solvent than that of nanotubes attached with conjugated groups.Above m-MWNTs aqueous suspensions were successfully used as a filler of thermoplastic PVA composite to enhance its electrical conductivity. The results show that the addition of m-MWNTs greatly increased the conductivity to 8 orders of the magnitude and the threshold of mass fraction is about 5wt%. With the increase of the applied voltage, the nanotubes conductivity also increases.The m-MWNTs were successfully used to modify glucose biosensor. The results show that carbon nanotubes can accelerate the redox speed of Fe[(CN)6]3" /Fe[(CN)6]4' and thus enhance the response current level. The linearity and resolution of glucose biosensor based on the nanotubes are so good that the detecting sensitivity, detecting range and responding speed of the biosensor are greatly improved. An explanation of the mechanism of the glucose biosensor electrodes modified by carbon nanotubes is also proposed.