Advances in synthesizing and preparing carbon nanotubes from different carbon sources

Carbon nanotubes (CNTs) can be obtained using different conversion processes with different carbon sources, such as high carbon-containing materials (e.g. graphite, coal or carbon black), organic compound (e.g. methane, ethene or benzene), inorganic carbon-containing compounds (e.g. CO or SiC). In this review, recently developed preparation processes for CNTs, depending on the carbon source used, combined with the latest advances in modifications to conventional methods, such as arc discharge, laser ablation and chemical vapour deposition, are discussed and compared with each other to clarify the advantages and disadvantages of the different methods. Also, a novel idea for the CNT bottom-up synthesis, namely, the stepwise cycloaromatization route starting from small aromatic molecules, is briefly introduced. In conclusion, the advances in commercial scale-up production of CNTs and commercial sources for providing CNTs are briefly outlined.