The superiority of air oxidation over liquid-phase oxidative treatment in the purification of carbon nanotubes

The role of steam treatment on the structure, purity and length distribution of multi-walled carbon nanotubes

“…Purification studies on as-produced single-walled carbon nanotubes (SWCNTs) have revealed that air-oxidation can remove the associated impurities while inflicting considerably less damage than oxidising acid-treatment, and avoid the formation of oxidation debris [15]. Unlike liquid phase oxidation the gas phase process preferentially oxidizes SWCNTs without introducing sidewall defects [22].…”

“…Gas phase reactions not only reduce the amount of chemical waste but also present some advantages compared to liquid phase treatments [14,15]. Gas phase purification of MWCNTs commonly involve air [16] but steam [17], carbon dioxide [18], chlorine [19], hydrogen [20], and plasma-thermal purification [21] have also been explored.…”

Pre-treatment of multi-walled carbon nanotubes for polyetherimide mixed matrix hollow fiber membranes

“…In present study, in order to improve the quality of the MWCNTs, the MWCNTs were first subjected to dry phase air oxidation followed by washing with non-oxidizing acid HCl prior to the surfactant dispersion to remove amorphous carbon and metallic catalyst found in the as-grown nanotubes. Previous studies [14][15][16][17] on CNT purification have witnessed the advantages of air oxidation over conventionally used liquid-phase oxidative treatment, where air oxidation has been identified as an effective method to remove the associated impurities present in the as-grown CNTs without imparting severe damage to the CNT structure and also does not lead to the formation of debris on CNT surfaces. Previous results have evidenced the effectiveness of this method in eliminating the elemental carbon with irregular structures [18,19].…”

Large‐scale oxidation of multi‐walled carbon nanotubes in fluidized bed from ozone‐containing gas mixtures

“…It is worth noting that all these studies have treated very low weights of MWCNTs, generally of the milligram‐scale, and not higher than 2 g, by using lab‐scale homemade glass reactors in which the contact between the gas phase and the MWCNTs powder is not really controlled. Gas‐solid fluidized bed reactors consist of vertical cylindrical columns in which the powder is maintained at rest by a porous plate, and the gas flows vertically upward through the bed of powder . Within an appropriate range of bed dimensions and gas flow rates, the powder is put in suspension into the gas, and an intense gas‐solid mixing appears, increasing the interphase thermal and mass transfer rates.…”

“…Within an appropriate range of bed dimensions and gas flow rates, the powder is put in suspension into the gas, and an intense gas‐solid mixing appears, increasing the interphase thermal and mass transfer rates. This explains why fluidized bed reactors are well‐known to produce uniform powder treatments . As a consequence, they have been intensively used at the multi‐ton scale in the chemical and polymer industries for fifty years .…”