Effective control of nanodefects in multiwalled carbon nanotubes by acid treatment

• Published in: Carbon (New York) Vol. 78; pp. 121 - 129
• Main Authors: WEIWEI ZHOU, SASAKI, Shun, KAWASAKI, Akira
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 01.11.2014
• Subjects: Chemistry; Cross-disciplinary physics: materials science; rheology; Defects; Evolution; Exact sciences and technology; Formations; Fullerenes and related materials; diamonds, graphite; General and physical chemistry; Graphene; Materials science; Multi wall carbon nanotubes; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Nanotubes; Oxidation; Physics; Specific materials; Surface physical chemistry; Walls; Multiwalled nanotube; Oxidizing environment; Carbon nanotubes; Reaction rates; Oxidation; Nanostructured materials; Nitric acid; Sulfuric acid; Low temperature; Defects
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2014.06.055

The defect-type evolution and gradual increase in nanodefects in the outer walls of multiwalled carbon nanotubes (MWCNTs) in a chemically oxidizing environment were thoroughly investigated using a mixture of sulfuric acid (H sub(2)SO sub(4)) and nitric acid (HNO sub(3)). A fairly low temperature of 323 K was employed for the acid treatment, and this limited the reaction rate to provide a mild acidic environment for gradual chemical oxidation compared to commonly used treatment conditions. High-resolution transmission electron microscopy (HRTEM) observations clearly demonstrated the formation of groove-type defects in the outer walls of MWCNTs in the early period around 0.5-3 h, followed by a morphological change into circumference-type defects and further into unzipped graphene nanoribbons. A unique parabolic variation in the intensity ratio of D and G bands (I sub(D)/I sub(G)) was observed. This observation supports the gradual oxidation of graphitic walls with increasing acid treatment time and corresponds well with the formation and evolution of nanodefects. Herein, the appropriate acid treatment time that would result in an effective number of nanodefects via suitable carboxyl functionalization, providing preferential nanocarbide sites for interfacial improvement as well as uniform dispersibility of MWCNTs, has been discussed.