Rapid production of carbon nanotubes: a review on advancement in growth control and morphology manipulations of flame synthesis

Abstract

Carbon nanotube synthesis using flame has enormous potential for large scale carbon nanotubes production. Carbon-rich and autothermal conditions within the flame environment allow for a rapid and continuous single-step carbon nanotube synthesis process, which is highly energy efficient and cost-effective compared to the conventional carbon vapour deposition method. Despite its significant potential, controlling the synthesis of carbon nanotubes in flame remains a great challenge due to combustion physics that does not allow independent control of the flame temperature and gas phase composition. In the present review, systematic analysis of the optimization method of carbon nanotubes catalytic growth in flames using various combinations of flame configurations, catalytic materials, and fuel types is highlighted. Catalytic materials are added into the flame as aerosols or substrate-based, which has direct effects on the carbon nanotubes growth, yield and morphology. The effects of additional parameters such as residence time and inert gas dilution are also presented. The recent developments in the application of additives in flame synthesis to significantly enhance growth control and nanotube quality are highlighted. Furthermore, current progress on the advanced control mechanism over the flame synthesis process through application of electrical or magnetic force fields and novel nanotemplates is presented. These control mechanisms enable manipulation of the synthesized carbon nanotubes' physical characteristics, which is crucial for application in nano-mechanical and electrical instruments.