Development of an Advanced Catalyst for Carbon Nanotube Synthesis
Whilst research into carbon nanotube (CNT) synthesis via chemical vapour deposition (CVD) has advanced tremendously in recent years, much of the focus has been on the development of catalysts supported on insoluble alumina and silica substrates. Thus, the large-scale production of high quality nanotubes via CVD is restricted by the requirement to separate the nanotubes from the catalyst and substrate. Most commonly, catalyst substrates are removed using harsh conditions, e.g. refluxing in concentrated mineral acids or alkalis for several hours and has been shown to have a detrimental effect on the quality of the nanotubes. More recently, researchers have revived the idea of using soluble catalyst support materials, e.g. CaCO3, thereby negating the need for complicated and expensive purification processes. The results of preliminary studies suggest that using a soluble substrate is not detrimental to the CNT quality.
In this work, we demonstrate for the first time, the synthesis of carbon nanotubes on a transition metal catalyst supported on a soluble calcium carbonate substrate, contained within a fluidised bed. The reaction products were analysed using thermogravimetric analysis coupled with a mass spectrometer (TGA-MS) and several different electron microscopy techniques (TEM, HRTEM, SEM). The carbon yield obtained was consistently greater than 10 times the weight of the catalyst metal loading. Thermogravimetric analysis of the reaction products showed only a single peak centred on 575ºC, with no peaks below 400ºC, indicating that very little amorphous carbon was present. TEM images verified that the products contained a large proportion of CNTs.