| Many promising applications of SWNT are being developed in electronics, biomedicine, composite materials, and energy production, but the limited yield and quality have been key roadblocks.;Research has shown that different applications require SWNT of different diameters. SWNT can be grown from supported cobalt catalyst where the cobalt particles template the diameter of the SWNT. Using cobalt incorporated MCM-41 catalyst, in which the cobalt is initially atomically dispersed in the pore wall, the SWNT diameter was successfully tuned from 0.6 to 2.0 run (covering most of its applications) by controlling the size of the cobalt particles. A series of characterization techniques revealed that the combination of occlusion by silica comprising the support and the spatial confinement of MCM-41 pore structure are key factors for cobalt particle size control.;Another barrier to SWNT's application is its price which nowadays is still higher than gold and platinum. The strategy of this dissertation is to increase SWNT yield from a low cost catalyst -- the impregnated cobalt/silica catalyst. It has been suggested that cobalt (or cobalt oxide) particles in this system are generally large (∼10 nm or larger). Large particles in general lead to inefficient utilization of active metal and undesired coke formation. In this specific case, large particles are not active in catalyzing SWNT production. It has been found that by introducing appropriate cobalt precursors, the metal-support interaction could be enhanced through the formation of surface cobalt silicate, which resulted in very small cobalt particles (∼1 nm) after hydrogen reduction. The catalysts with a larger proportion of small particles have much higher yield of SWNT (up to 75 wt %, 10 times higher than the yield from a commercial catalyst). The process in this study is simple and scalable, and provides direction for future design of SWNT- synthesis catalyst through a surface phase formation.;SWNT produced in the study has extremely high surface area (1800 m 2/g). The products are of high quality and easy to purify, and the catalyst can be easily removed, which suggests many promising applications in various fields. The SWNT produced in this dissertation have been used in a number of applications: 1) SWNT as antibody stimuli in biomedical application; 2) SWNT as a catalyst support in hydrogen production; 3) SWNT/polymer composite as an antimicrobial biomaterial; 4) fabrication of superconductivity materials. |
