Transition Metal Catalyst Aided Growth of Novel Carbon Nanostructures
Final Report Abstract
Motivated by promising results previously achieved for Cu based catalysts, the goal of this study was to evaluate the potential of nanostructured catalysts based on transition metals such as Fe, Co, and Ni in the context of NF synthesis at low process temperature (250 - 350 °C) by means of a thermal CVD process. The catalyst particles for each of the three transition metals mentioned above were prepared by five different strategies: a precipitation route, a sol-gel route, thermal decomposition, a bulk route, and a nanopowder route, respectively. Distinct differences could be observed between the suitability of the various catalysts. In general Ni based catalysts showed the highest activity in the contexts of NF grovrth, whereas the Fe based ones featured the lowest activity of the three candidates in this study. Nevertheless, for all three transition metals it was possible to observe a surface diffusion based fiber growth for all types of catalysts with the exception of the ones prepared by the predpitation route. The latter appeared to require temperatures higher than 350 °C to initiate NF growth. The as-grown NFs featured a polymeric character, which was changed to a carbonized one by means of an appropriate heat treatment. In case of all three metals the nanopowder based catalysts particles represented the most efficient way in preparing multiform nanostructures. Here, size and morphology of the catalyst particles determined the growth mode as well as the morphology of the resulting structures, respectively. The smallest particles were typically found to Initiate NF growth by a tip growth mode, while larger ones feature a surface diffusion based growth mode leading to helical or straight symmetric fibers, respectively, depending on the actual size of the catalysts. An analysis of growth kinetics in the context of Ni nanopowders allowed a distinction between a nucleation and a growth phase of the nanostructures. Additionally, the important role of free radical oxygen in the process, with respect to growth rate or rather mass increase was demonstrated.
Publications
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"Catalyst facet selective growth of multi-branches carbon nanostructures", Nanofair 2012, Dresden
Xin Jiang
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Metal Catalyst Aided Growth of Novel Carbon Nanostructures", 0Z12-5th German-Japanese Symposium on Nanostructures 2012, Wenden
Xin Jiang
