Oxidation of Single-Walled Carbon Nanotubes under Controlled Chemical Conditions

Single-walled carbon nanotubes are oxidized in the presence of H2SO4/HNO3 mixtures containing distinct concentrations of the nitronium ion, [NO2+]. The spectroscopic analyses of the final samples suggest a higher structural disorder in the oxidized systems with increasing [NO2+]. This is due to a considerable oxygen amount on the tube surface, reaching up to 30%, depending on the reaction time and [NO2+]. Interestingly, if long reaction time is considered, the oxygen amount on the tube surface is maximum for low [NO2+] and reduces slightly for larger [NO2+]. On the other hand, the oxidation process occurs gradually at 4 h, allowing a fine control of the oxidation process. Therefore, if fine tuning of the oxidation degree is desirable, the reaction must be conducted during short time (4 h) using increasing [NO2+] as those obtained from 2:1, 2.5:1 and 3:1 H2SO4/HNO3 acid mixtures to produce increasing content of functionalization.

单壁碳纳米管（Single-walled carbon nanotubes）在含有不同浓度硝鎓离子（nitronium ion, [NO₂⁺]）的硫酸/硝酸（H₂SO₄/HNO₃）混合酸体系中被氧化。对最终样品的光谱分析结果显示，随着硝鎓离子浓度升高，氧化改性后的碳纳米管体系的结构无序度显著提升。这一现象源于碳纳米管表面负载的可观氧含量，其最高可达30%，具体数值取决于反应时长与硝鎓离子浓度。值得注意的是，当反应时长较长时，碳纳米管表面的氧含量会在硝鎓离子浓度较低时达到峰值，而随着硝鎓离子浓度进一步升高，氧含量会小幅下降。另一方面，在4小时的反应条件下，氧化过程会逐步进行，可实现对氧化进程的精准调控。因此，若需对氧化程度进行精细调谐，应在短时长（4小时）条件下开展反应，通过使用体积比分别为2:1、2.5:1与3:1的硫酸/硝酸混合酸体系获得逐步升高的硝鎓离子浓度，从而实现官能化含量的逐步提升。