Carbon Nanotube Sheet-Synthesis and Applications

Abstract

Decades of extensive research have matured the development of carbon nanotubes (CNTs). Still, the properties of macroscale assemblages, such as sheets of carbon nanotubes, are not good enough to satisfy many applications. This paper gives an overview of different approaches to synthesize CNTs and then focuses on the floating catalyst method to form CNT sheets. A method is also described in this paper to modify the properties of macroscale carbon nanotube sheets produced by the floating catalyst method. The CNT sheet is modified to form a carbon nanotube hybrid (CNTH) sheet by incorporating metal, ceramic, or other types of nanoparticles into the high-temperature synthesis process to improve and customize the properties of the traditional nanotube sheet. This paper also discusses manufacturing obstacles and the possible commercial applications of the CNT sheet and CNTH sheet. Manufacturing problems include the difficulty of injecting dry nanoparticles uniformly, increasing the output of the process to reduce cost, and safely handling the hydrogen gas generated in the process. Applications for CNT sheet include air and water filtering, energy storage applications, and compositing CNTH sheets to produce apparel with anti-microbial properties to protect the population from infectious diseases. The paper also provides an outlook towards large scale commercialization of CNT material.

Keywords: carbon nanotube; gas-phase pyrolysis; hybrid sheet; nanoparticles.

Figure 1

Schematic diagrams of carbon nanotube (CNT) sheet fabrication processes: (a) process of drawing forest-grown CNT into a sheet; (b) process of winding the floating catalyst chemical vapor deposition (FCCVD) CNT sock into a sheet.

Figure 2

The fabrication process for carbon nanotube hybrid sheet: (a) experimental setup for CNT material synthesis; (b) short reactor (24-inch ceramic tube); (c) fuel, syringe pump, and atomizer controller which comprise the fuel injector; (d,e) the CNT sock forms in about 1 s and is wound up on the drum; (f,g) CNT sheet is peeled off the drum.

Figure 3

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images. (a) Ag-coated Cu particle under SEM; (b) TEM image of multiwall CNT with a tip-growth model.

Figure 4

Carbon nanotube hybrid (CNTH) materials. (a) Pristine CNT (black sock) then particle injection turned on with Ag-Cu (grey sock); (b) metal particles “glue” bundles of CNTs together which increases thermal and electrical conductivity and possibly strength the CNT sheet; (c) CNT-Ag-Cu high-density nanoparticles (NPs); (d) CNT spiral bundles of CNT; (e) CNTH graphene cones.

Figure 5

Raman spectroscopy: (a) the Raman scan of a CNT sample; (b) the I_G/I_D ratio of the CNT samples. This testing shows that higher temperatures increase the crystallinity of the CNTs. Changing other process conditions, such as fuel injection rate, also affects the Raman spectra and can produce higher I_G/I_D ratios.

Figure 6

Tensile strength testing of CNT pristine sheet. (a) Tensile strength testing using an Instron tensile test machine with a paper frame to hold the sample. (b) Mean tensile strength of CNT sheets synthesized at different temperatures.

Figure 7

Electrical conductivity in two orthogonal in-plane directions of the 2D CNT sheet. The composite CNTH sheet has a small percentage of Cu NPs.

Figure 8

Electrical energy storage: (a) the basic supercapacitor design (above: stacking plane; below: interdigitated pattern); (b) schematic of ion movement during the process of charging and discharging—the lower figure shows higher efficiency for the ion diffusion. Reproduced from [46] with permission from the Royal Society of Chemistry, 2020.

Figure 9

Device design: (a,b) different schematic processes for the fabrication of flexible CNT supercapacitors, both methods use polyaniline (PANI) as the active material. (a) Reproduced from [49] with permission from the Royal Society of Chemistry, 2020; (b) reproduced from [50] with permission from Wiley-VCH GmbH, 2020.