Catalytic growth of single wall carbon nanotubes in metal incorporated MCM-41 and their applications.

摘要

This thesis focuses on how to manipulate one nanometer scale material (MCM-41 "Mobil Composition of Matter 41" a mesoporous molecular sieve) to control the structure of another nanostructure (SWNT "Single Wall carbon Nano Tubes"). It is demonstrated that MCM-41 with Co incorporated in the framework can be used for the growth of ordered SWNT by CO disproportionation with a narrow distribution of diameters (+/- 0.35A) at 8 A and very good selectivity to SWNT.; SWNT characterization by thermogravimetric analysis, nitrogen physisorption, multi-excitation Raman, fluorescence, near infrared and ultraviolet-visible spectroscopy, scanning electron microscopy, and high resolution transmission electron microscopy combined with ex-situ and in-situ X-ray absorption near edge structure and extended X-ray fine structure spectroscopic characterization of catalysts suggests that uniformity of SWNT diameter results from the uniformity of the metallic clusters formed in the MCM-41 template. Pre-reduction in hydrogen facilitates the removal of hydroxyl groups and creates Co1+ intermediate species in MCM-41; subsequent exposure to CO causes the cobalt atoms to become more mobile at the surface, allowing them to nucleate into larger clusters capable of CO dissociation and initiates the growth of SWNT. SWNT diameters are controlled by the tunable subnanometer metallic clusters formed during CO reaction. The diameter distribution and quality of SWNT can be engineered by controlling cobalt cluster size through controlling the reducibility of Co in MCM-41 (cobalt concentration in MCM-41, pore size of MCM-41, pH and silica source used) and SWNT synthesis conditions (the catalyst pretreatment temperature, nanotube synthesis temperature, CO pressure and reaction time). Comparison studies between Co and Ni indicate that Co clusters are better controlled than Ni in MCM-41 under CO disproportionation.; The advantage of using Co-MCM-41 in SWNT production is that it not only provides a narrow diameter distribution, but also helps to simplify the purification procedure and produce SWNT with fewer defects. Amorphous silica of MCM-41 and cobalt clusters are removed by a four step purification process using NaOH reflux, HCl acid wash and dilute oxidation by molecular oxygen. Purified SWNT is further separated by a DNA-assisted method at DuPont, demonstrated as field effect transistors at IBM, and incorporated into an organic polymer monolith stationary phase for high performance liquid chromatography and capillary electrochromatography.