In addition to above, there is another fibrous carbon nanostructure which is rolled by multi-layer graphene called carbon nanofibers. The chirality index of CNTs is directly related to the helicity and electrical properties of CNTs. This difference is due to the fact that in the case of single-walled CNTs, the graphene sheets can be curled at any angle and therefore have different chiral structures. Besides, SWCNTs can be classified into three types according to their structural characteristics (depending on graphene sheet in a rolled manner as shown in Figure 2): armchair form, zigzag form, and chiral form. SWCNTs were firstly discovered by Iijima and Ichihashi in 1993, CNTs formed by the coaxial crimping of two or more layers of graphene are called MWCNTs. Multi-walled CNTs have graphene layers ranging from 2 and more. Therefore, the application of single-walled CNTs in nanomaterials field is more promising. Because there is only one layer of graphene in SWCNTs, the diameter range of SWCNTs is smaller than that of MWCNTs, which is only 0.4–3 nm. There are two ways of hybridizing carbon atoms in CNTs, mainly SP 2 hybridization, and specific SP 3 bonds can also be formed between hexagonal carbon atoms.ĬNTs are classified as single-walled CNTs and multi-wall CNTs according to the layer number of graphene sheets. The spacing between the tube walls is about the size of graphite layer spacing. Reproduced with permission of Ref.ĬNTs are tubes that are rolled up by a layer or several layers of graphite, or that can be coaxially wrapped together by different diameters of microtubules, which have only a few nanometers in diameter. It should be pointed out that many growth factors can control the particle size distribution, composition, and structure of the catalysts, such as catalyst substrate, metal transition components added, calcination temperature, etc.ĬNTs firstly discovered by Iijima in 1991. Among them, the catalyst is the most influential factor for the morphology, structure, and properties of CNTs. In order to gain a comprehensive understanding of the controlling parameters about the formation of CNTs, this chapter reviews the latest progress in the preparation of CNTs by CVD from three of the most important influencing factors: carbon sources, catalysts, and substrates. Compared with other methods, chemical vapor deposition (CVD) is the most effective method that has broad prospects for large-scale control of CNTs in recent years due to its simple equipment, simple operation, and lower cost. There are many synthesis methods to produce CNTs. As a new carbon material in the twenty-first century, carbon nanotubes (CNTs) have excellent optical, electrical, magnetic, thermal, chemical, and mechanical properties.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |