In this study, the refinement of Multiwalled Carbon Nanotubes (MWCNTs) derived from chemical vapor decomposition is investigated. An ultrasonic pretreatment method is employed to disentangle carbon and metal impurities intertwined with MWCNTs. The pretreated MWCNTs exhibit a marginal decrease in C–O/C = O content from 8.9 to 8.8%, accompanied by a 2.5% increase in sp3 carbon content, indicating a mildly destructive pretreatment approach. Subsequently, selective oxidation by CO2 and hydrochloric acid etching are utilized to selectively remove carbon impurities and residual metal, respectively. The resulting yield of intact MWCNTs is approximately 85.65 wt.%, signifying a 19.91% enhancement in the one-way yield of pristine MWCNTs. Notably, the residual metal content experiences a substantial reduction from 9.95 ± 2.42 wt.% to 1.34 ± 0.06 wt.%, representing a 15.68% increase in the removal rate. These compelling findings highlight the potential of employing a mild purification process for MWCNTs production, demonstrating promising application prospects.

Mild purification of multiwalled carbon nanotubes with increased selectivity for carbon impurity and residual metal removal
    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Ultrasonic dispersion
        2.3 Etching and oxidation
        2.4 Mild cascade purification process
        2.5 Characterization
    3 Results and discussion
        3.1 Entanglement of AP-MWCNTs
        3.2 Dispersion of AP-MWCNTs
        3.3 Selectivity of gas oxidation and liquid etching
        3.4 Mild purification process
    4 Conclusion
    Acknowledgements 
    References

• Erdong Chen(Low‑Carbon Technology and Chemical Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, People’s Republic of China)
• Qiang Liu(Low‑Carbon Technology and Chemical Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, People’s Republic of China, Research Institute of Tianfu New Energy, Chengdu 610065, People’s Republic of China)
• Pan Wu(Low‑Carbon Technology and Chemical Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, People’s Republic of China)
• Jian He(Low‑Carbon Technology and Chemical Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, People’s Republic of China)
• Changjun Liu(Low‑Carbon Technology and Chemical Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, People’s Republic of China)
• Wei Jiang(Low‑Carbon Technology and Chemical Reaction Engineering Laboratory, School of Chemical Engineering, Sichuan University, Chengdu 610065, People’s Republic of China) Corresponding author