Recent Progress on the Growth Mechanism of Carbon Nanotubes: A Review

Abstract

Tremendous progress has been achieved during the past 20 years on not only improving the yields of carbon nanotubes and move progressively towards their mass production, but also on gaining a profound fundamental understanding of the nucleation and the growth processes. Parameters that influence the yield but also the quality (e.g., microstructure, homogeneity within a batch) are better understood. The influence of the carbon precursor, the reaction conditions, the presence of a catalyst, the chemical and physical status of the latter, and other factors have been extensively studied. The purpose of the present Review is not to list all the experiments reported in the literature, but rather to identify trends and provide a comprehensive summary on the role of selected parameters. The role of the catalyst occupies a central place in this Review as a careful control of the metal particle size, particle dispersion on the support, the metastable phase formed under reaction conditions, its possible reconstruction, and faceting strongly influence the diameter of the carbon nanotubes, their structure (number of walls, graphene sheet orientation, chirality), their alignment, and the yield. The identified trends will be compared with recent observations on the growth of graphene. Recent results on metal-free catalysts will be analyzed from a different perspective.

Control of steam input to the pyrolysis-gasification of waste plastics for improved production of hydrogen or carbon nanotubes

“…CNTs are thought to be formed by a modified version of the vapour-liquid-solid mechanism proposed by Baker et al [21,22]. A vapoursolid-solid mechanism has been proposed where carbon dissociates on the surface of a catalyst particle, diffuses across its surface and finally precipitates in the form of CNTs [23].…”

Data-driven understanding of collective carbon nanotube growth by in situ characterization and nanoscale metrology

“…Although, there are different schools of thought with respect to the exact atomic scale physicochemical processes underlying catalytic activation and nucleation of CNTs, 48 the process generally proceeds by the arrangement of carbon atoms on the surface of the catalyst nanoparticles, leading to cap formation and liftoff. A major challenge is identifying which phase is the catalytically active phase and which pathways leads to the most active CNT growth (faster growth kinetics and higher density of CNTs).…”

Structure in nascent carbon nanotubes revealed by spatially resolved Raman spectroscopy

“…Their development, in order to extend their potentialities, is strongly related to the precise control of carbon nanotube (CNT) growth which is a direct result of the understanding of their growth mechanisms. This is one of the motivations for the study of nanotube formation which has been widely investigated by researchers all over the world [13]. Ex-situ physico-chemical analyses of samples synthesized under precise conditions are focused on the size and shape of catalyst particles as well as on their physical state and their chemical composition and structure [11,[14][15][16].…”