Growing single-walled carbon nanotubes from alumina sheet supported catalyst and investigating carrier effects on chirality distribution

Abstract

Both the structure and type of support material significantly influence the performances of supported metal catalyst in synthesizing single-walled carbon nanotubes (SWNTs) through chemical vapor deposition. In this work, thin porous boehmite sheets prepared by hydrothermal method are applied as the precursor carriers for developing a supported iron catalyst. Upon high temperature calcination, the resulting alumina (α-Al₂O₃) and Fe₂O₃ form a solid solution, which catalyzes the growth of SWNTs at a low temperature of 700 °C. Detailed optical characterizations reveal that mainly subnanometer SWNTs with a narrow chirality distribution are synthesized. To explore the roles of catalyst support in catalysis, a magnesia (MgO) supported Fe catalyst is also designed. The MgO supported catalyst achieves an even narrower chirality distribution compared to the alumina-supported counterpart. By combining experimental catalyst characterizations with theoretical calculations, the SWNT chirality distribution is revealed to be highly sensitive to the surface basicity of the support materials. The strong basicity of the MgO facilitates electron transfer to the supported Fe nanoparticles, enhancing the adsorption and dissociation of the carbon precursor. This interaction ultimately promotes the nucleation of SWNTs by a perpendicular model.