Oxidation of CNTs

The major drawbacks to standard sol-gel synthesis include slow growth rate and the typically amorphous product, rather than defined crystals, which requires crystallization and post annealing steps. Growth rate and crystallization of the fabricated hybrid can be improved via solvothermal, reflux [224], sonication, and microwave [225] treatment. However, the air oxidation of CNTs (600 °C) and graphene (450 °C) may still be lower than MO crystallization temperature. Moreover, it has been shown that the MO coatings on CNTs can drastically affect their thermal oxidation, particularly with easily reducible metal oxides (e.g. TiOz = 520 °C, Bi203 = 330 °C) [180]. It appears that metal oxides can catalyze the oxidation of CNTs via a Mars van Krevelen mechanism, limiting the maximum temperature of their synthesis as well as applications (i.e. catalysis, fuel cells). 

Oxidation of CNTs - Oxidative Purification 1.3.2.1 Carboxylation of CNTs... 

One of the purification procedures involves air-oxidation followed by washing with HCl to remove metals. Metal nanoparticles that are covered with carbon coating are difficult to dissolve in an acid treatment. In order to break-up the carbon coating, air-oxidation is usually done at an optimal temperature for a specific duration. The presence of metal impurities enhances the oxidization of CNTs at higher temperatures and, hence, the oxidation is done by a step-by-step manner. In this procedure, the sample is heated first in air at a moderate temperature (Ti 225-300°C) for a certain duration (tj)... 

The oxidation of CNTs has been done using microwave (2.5 GHz, 150 W) treatment at 500 Irradiation by... 

Oxidation provides a great potential for the purification and functionalization of carbon nanomaterials. In situ Raman spectroscopy during oxidation of CNTs enables a time-resolved investigation of the oxidation process and can identify changes in material structure and composition in real time, allowing for an accurate determination of the optimal oxidation conditions. 

Work with the toxin should be performed in a contained space and all the materials contaminated with CNTs should be autoclaved or washed at the end of the experiment with dilute sodium hypochloride, due to the extreme sensitivity to oxidants of CNTs (see Chapter 20). 

The oxidation of cnt-kaurene is inhibited by the plant-growth regulator ancymidol at 10 mol 1 the drug blocks the formation of ent-kaurenol and at 10 mol it stops the conversion of MVA into ent-kaurene. These effects are completely reversed by the addition of gibberellic acid. Isosteviol (84) and steviol acetate (85) are effectively metabolized by cultures of mycelia of a G. fujikuroi... 

Mechanisms of liquid-phase oxidation of CNTs have been studied in much less detail. Kanai et al. [149] reported on first-principles calculation of NO3-SWCNT interactions and provided an atomistic model for the oxidation process. 

Oxidation of CNTs by 8 M nitric acid with sonication... 

Oxidation of CNTs using 2.6 M nitric acid by reflux... 

Scheme 2 Oxidation of CNT to generate carboxylic group capped CNTs (Reproduced with permission from [12])...

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