Growth and morphology manipulation of carbon nanostructures on porous supports

Structural polymorphism of carbon grown on porous supports by chemical vapor deposition (CVD) is demonstrated. Combining three different supports (activated carbon, macroporous polymeric beads, and microporous aluminophosphate molecular sieves), with two catalysts (Ni and Fe), yielded a variety of carbon nanostructures ranging from coils and belts to fibers and tubes, without changing CVD temperature, time, and precursor composition and flow rate. Ion exchange between ammonium-impregnated supports and the metals was necessary in order to achieve a fine dispersion of the catalyst over the support surface. Metal-support interactions and the balance between ammonium and metal concentrations were investigated and found to considerably affect catalyst dispersion, shape, and crystallographic orientation, which in turn determined the morphological and structural characteristics, and yield of the carbon product. The catalyst-loaded supports and the resulting carbon materials were characterized by scanning and transmission electron microscopy, thermogravimetic analysis, X-ray diffraction, and Raman spectroscopy, while nitrogen and mercury porosimetry were used to characterize the supports and evaluate the degree of support pore blocking by the carbon deposits.