The influence of carbon source and catalyst nanoparticles on CVD synthesis of CNT aerogel

Abstract

The floating catalyst chemical vapour deposition (FC-CVD) method is unique in providing the capability for continuous carbon nanotube (CNT) synthesis at an industrial scale from a one-step continuous gas-phase process. Controlling the formation of the iron-based catalyst nanoparticles is widely recognized as a primary parameter in optimizing both CNT product properties and production rate. Herein the combined influences of pyrolytic carbon species and catalytic nanoparticles are both shown to influence CNT aerogel formation. This work studies the source of carbon in the formed CNTs, the location of aerogel formation, the in-situ behaviour of catalyst nanoparticles and the correlated morphology of the resultant CNTs.Axial measurements using isotopically-labelled methane (CH 4 ) demonstrate that carbon within all CNTs is primarily derived from CH 4 rather than some of the early-forming CNTs being predominantly supplied with carbon via thermal decomposition of catalytic precursor components. Quantification of CNT production along the axis of the reactor definitively 2 dispels the notion that injection parameters influence CNT formation and instead shows that bulk CNT formation occurs near the reactor exit regardless of the carbon source (CH 4 , toluene or ethanol). Supply of carbon to different reactor locations indicates that CNT aerogel formation will occur even when carbon is delivered near the exit of the reactor so long as the carbon source reaches a sufficient temperature (>1000 °C) to induce pyrolysis. These results give an indication of how future large-scale CNT reactors may be optimized and controlled by modifying downstream catalyst and carbon delivery.

Agglomeration Dynamics of 1D Materials: Gas‐Phase Collision Rates of Nanotubes and Nanorods

“…An application of the collision kernel for rigid 1D materials is the process of self-assembled aerogel formation within a CNT reactor, which is of significant academic and industrial interest. [18,19,42,43] Despite the large number of studies on the nanotube aerogel process, [60] the lack of known collision rates between the nanotubes has hindered quantitative understanding of the bundle formation process, a precursor to aerogel formation. Figure 5a shows the production of nanotubes and resulting self-assembled aerogel formation within a continuous gas-phase chemical vapor deposition reactor.…”

“…Quantifying the range of collision kernels β ij in gas‐phase systems consisting of 1D materials gives new insights into the spontaneous formation of aerogels from 1D materials. These results are broadly applicable to all natural and anthropogenic 1D materials of similar geometries undergoing gas‐phase collisions . As such, we employ the term nanotube generally to represent 1D materials that may consist of nanorods, nanotubes, or chain‐like agglomerates with an axial length to diameter ratio > 10:1.…”

“…These results are broadly applicable to all natural and anthropogenic 1D materials of similar geometries undergoing gas-phase collisions. [19,42,43] As such, we employ the term nanotube generally to represent 1D materials that may consist of nanorods, nanotubes, or chain-like agglomerates with an axial length to diameter ratio > 10:1.…”

Synthesis and mechanism perspectives of a carbon nanotube aerogel via a floating catalyst chemical vapour deposition method

“…It offers a controlled approach to directly spray a range of carbonaceous liquids into the deposition chamber, eliminating the need for an intermediate stage to prepare the catalyst, and simultaneously ensuring that there is a continuous growth for CNTs. These benefits show great promise for scale-up production regarding CNTs at prices that are commercially viable [12,76,77].…”

Carbon aerogel evolution: Allotrope, graphene-inspired, and 3D-printed aerogels

“…In general, CNT aerogel synthesis begins with a dispersion of CNTs. Although there are a few examples where CNTs are grown within an aerogel matrix, [35][36][37][38] they are the exception. Pristine CNTs, being hydrophobic, require a surfactant if dispersal in aqueous media is required.…”