The synthesis of carbon nanotubes (CNTs) has been proved to be greatly promoted by vapor metal catalysts, but the fast reaction feature and the required high-temperature environment involved in CNT evolution usually make it difficult for an insight into the evolution mechanism. Here, we successfully freeze the synthetic reaction at intermediary stages and observe the detailed morphologies and structures of the obtained intermediates and various objects related to carbon nanotubes. It is unveiled that there is a kindred evolution linkage among carbon nanoparticles, nanowires, and nanotubes in the vapor catalyst-involved synthetic processes: tiny carbon nanoparticles first form from a condensation of gaseous carbon species and then self-assemble into nanowires driven by an anisotropic interaction, and the nanowires finally develop into nanotubes, as a consequence of particle coalescence and structural crystallization. The function of metals is to promote the anisotropic interactions between the nanoparticles and the structural crystallization. An annealing transformation of carbon nanoparticles into nanotubes is also achieved, which gives further evidence for the evolution mechanism.
The excellent physical and chemical properties of porous carbon materials allow them to be widely used in many fields. Their performance in a specific application is usually determined by structural features such as pore diameter, channel length, and architecture. In recent years, great efforts have been made to develop suitable carbon-based materials with short pores and/or hierarchical porous architectures, for use in transport or diffusion of guest objects by reducing pathways and resistance. In the present paper, we report on a novel carbon nanostructure constructed with a mesoporous core and a microporous shell. The mesopore walls are constructed of only a few graphene layers and can be controllably removed by a wetting oxidation reaction, which leaves behind hollow nanoparticles. These short-pore structures could facilitate the diffusion of molecules; they also show a very high and stable catalytic performance during the dehydrogenation of cyclohexane that is far superior to currently available long-pore materials, such as active carbon and carbon nanotubes.
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