Table 3.
Oxidation steps for CNTs.
| step number | reference | ||
| [55,57] | [119] | [120] | |
| 1 | treating with sulfuric/nitric acid mixture (3:1) to remove impurities | treatment with nitric acid to remove amorphous carbon and to insert carboxyl groups (100 mg MWNT in 20 mL concentrated nitric acid) | bath sonication of CNT in acetone for 20 min |
| 2 | sonication in water bath for 3 h at 40 °C | heating for 2 h under reflux | filtration |
| 3 | dilution with distilled water (1:5 by volume) | washing with water | drying in a vacuum oven |
| 4 | filtration through polycarbonate membrane filter (0.8 µm pore size) | multiple filtrations through poly(tetrafluoroethylene) membranes | oxidation in a UV/O3 chamber for 1 h |
| 5 | washing with water | dispersion in water and freeze drying | further functionalization with triethylenetetramine (TETA) |
| 6 | drying in a vacuum oven for 24 h | bath sonication of CNT with TETA in excess amount (60 °C, 30 min) | |
| 7 | results in –COOH groups attached to the CNT surfaces | filtration | |
| 8 | removal of untreated amine by washing with acetone | ||