Effect of catalyst oxidation on the growth of carbon nanotubes by thermal chemical vapor deposition

Abstract

We report a heat treatment of catalyst in air that drastically enhances a growth of carbon nanotubes (CNTs) by means of thermal chemical vapor deposition (CVD). An Fe catalyst film deposited on a Si substrate was heat treated at 700°C in air before the acetylene CVD. The growth rate of the CNTs grown with the heat treatment was more than seven times higher than that of growth without the heat treatment. A scanning electron microscopy observation showed that the heat treatment in air promotes a granulation of the Fe catalyst. X-ray photoelectron spectroscopy and reflection high energy electron diffraction analyses showed that the heat treatment in air promotes an oxidation of the catalyst film and formation of Fe2O3 nanoparticles, suggesting that the heat treatment of Fe catalyst in air prevented the formation of Fe silicide that would deactivate the catalyst effect of Fe. The Fe2O3 nanoparticles do not agglomerate and can keep their original particles size. Thus the catalyst can maintain a catalyst activity during CNTs growth and, as a result, gives a growth enhancement of CNTs.

Evolution of iron nanoparticles by controlling oxidation states for carbon nanotubes growth

“…7(b) and (c) are exactly same, it is reasonable that this layer is not an oxygen layer but an iron oxide layer with a thickness of about 3 nm. After annealing, the Fe film can react with oxygen to form oxidized iron particles, especially Fe 2 O 3 [29]. This oxygen might be originated from native oxides on the Fe film after deposition on the substrate and/or from residual natural oxides on the silicon surface.…”

The Influence of Catalyst's Oxidation Degree on Carbon Nanotube Growth as a Substrate-Independent Parameter

“…6,7 However, a controversial point in these cases is that the chemical analysis is performed ex situ with the consequent modification of the original composition due to exposure to air, which makes interpretation of the data difficult.…”

Flame Synthesis of Carbon Nanotube through a Diesel Engine Using Normal Dodecane/Ethanol Mixing Fuel as a Feedstock

“…Of course, it can also be considered that other feedstock or precursors for CNT formation such as acetylene (Liu et al, 2005;Sato et al, 2006;Zhong et al, 2009) and ethylene (Pirard et al, 2007;Shukla et al, 2009;Inoue et al, 2014) may contribute to CNT formation in a diesel engine because oxidation reactions of normal dodecane (Vasu et al, 2009;Narayanaswamy et al, 2014) and ethanol (Ogura et al, 2007;Saxena and Williams, 2007) produce acetylene and ethylene during combustion. However, it is now underway in our laboratory and will be revealed elsewhere.…”