Oxidation Behavior of Multiwalled Carbon Nanotubes Fluidized with Ozone

Abstract

Multiwalled carbon nanotubes (MWCNTs) were simultaneously fluidized and oxidized with gaseous ozone in a vertical reactor. Two different varieties of MWCNTs were compared to determine the versatility of the treatment and to elucidate the effect of defects on the oxidation behavior of MWCNTs. The extent of oxidation and nature of functional groups introduced on the nanotube surfaces were determined using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Boehm titration, and structural changes were monitored with Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). After only a few minutes of treatment, nongraphitic impurities were removed from the MWCNTs, and significant levels of oxidation (∼8 atom % O) were achieved with very little damage to the nanotube sidewalls. Short O3 exposure resulted in primarily hydroxyl functionalities, whereas longer exposure led to the formation of mainly carboxylic acid groups. Aliphatic defects present in the commercially produced MWCNTs were found to play an important role in the oxidation mechanism. Because of its ability to remove impurities and to evenly oxidize the sidewalls of nanotubes without the use of any solvents, the fluidized O3 reaction developed in this study was found to be an attractive option for industrial-scale MWCNT functionalization.

Decoration of Carbon Nanotubes by Semiconducting or Metallic Nanoparticles using Fluidized Bed Chemical Vapour Deposition

“…But as the density in defects is generally low, a surface activation in the form of functionalization or creation of defects at the carbon nanotube surface is essential to achieve a high coating density (Feng and Puddephatt, 2007;Bacsa and Serp, 2012). The most common method at the lab scale is the oxidative acid reflux that purifies and functionalizes the nanotubes in one step by grafting hydroxyl (C-OH), carbonyl (C = O) and carboxyl (O = C-OH) groups on the nanotube surface (Bacsa and Serp, 2012;Vennerberg et al, 2014). However, the liquid wastes generated by these wet oxidation methods are not suited to industrial use (Kim and Min, 2010).…”

“…Some works about gas-phase oxidation of CNTs using either air (Ajayan et al, 1993;Behler et al, 2006) or nitric acid vapours (Xia et al, 2009;Li et al, 2012;Rong et al, 2010) at high temperatures have led to mixed results: the CNTs were structurally damaged or far worse, even partially burnt. Gas-phase oxidation from ozone (O 3 ) is an environmentally friendly and low-cost route to form oxygen-containing groups on the CNT surface, even for mass production (Vennerberg et al, 2014). This route will be tested in the present work.…”

Fluidized bed chemical vapor deposition of copper nanoparticles on multi-walled carbon nanotubes

“…Indeed, the deposited weight of metal is higher and the NPs are smaller and better dispersed along the MWCNT walls [27][28][29][30][31]. The most common method at the lab-scale is to oxidize carbon nanotubes by exposure to concentrated acidic liquids, but the liquid wastes and the noxious gases generated by this wet oxidation method, as well as the necessity to repeatedly wash and dry the CNTs, are not suited for industrial use [32][33][34][35]. Gas phase oxidation is much cleaner, it only involves one step and can be operated at large scale using appropriate processes [35][36].…”

“…The most common method at the lab-scale is to oxidize carbon nanotubes by exposure to concentrated acidic liquids, but the liquid wastes and the noxious gases generated by this wet oxidation method, as well as the necessity to repeatedly wash and dry the CNTs, are not suited for industrial use [32][33][34][35]. Gas phase oxidation is much cleaner, it only involves one step and can be operated at large scale using appropriate processes [35][36]. We have developed an original pre-industrial oxidation process able to treat 100 g of MWCNTS per run, using a fluidized bed reactor fed with ozone-containing gas mixtures [37].…”

Iron deposition on multi‐walled carbon nanotubes by fluidized bed MOCVD for aeronautic applications

“…Oxidation of CNTs by exposure to concentrated acids, in particular nitric acid (HNO 3 ), is a popular functionalization method to increase their surface reactivity at the lab-scale [12]. Hydroxyl (C-OH), carbonyl (C=O) and/or carboxyl (O=C-OH) chemical groups can thus been formed, which additionally improves CNTs dispersion and interfacial behaviour with various polymer matrices [13].…”