Abstract
In this study, Multiwalled carbon nanotubes (MWCNTs) were oxidized by a mixture of sulfuric acid and nitric acid (V:V = 3:1) at 70 °C for 1, 2, and 4 h, respectively. The oxidized MWCNTs were characterized by N2 adsorption, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), and Raman spectroscopy to determine the oxidation degree. The dispersion of the MWCNTs was investigated by UV-vis-NIR, SEM, and dynamic light scattering measurements. Results show that sulfonitric treatment increased the surface area and total pore volume and reduced the average pore diameter of MWCNTs. The treatment promoted the formation of oxidized species on the surface MWCNTs, as identified by FT-IR, TGA, and X-ray photoelectron spectroscopy measurements, and more oxygen-containing functional groups were generated when treatment time was extended. Moreover, a general relationship between oxidation degree and dispersibility of MWCNTs in water was established. UV-vis-NIR and dynamic light scattering measurements and SEM images revealed that MWCNTs with higher oxidation degree showed better dispersibility in water.
Highlights
Multiwalled carbon nanotubes (MWCNTs) have attracted a great deal of attention from research institutes and enterprises due to their excellent mechanical, electrical, thermodynamic, and chemical stability properties [1,2,3]
MWCNTs have been successfully used to prepare cementitious nanocomposites, energy storage materials, microelectronics, etc. [4,5] MWCNTs tend to agglomerate into bundles due to their large specific surface area and strong van der Waals forces, which would inhibit the nanoenhancement or modification effect [6,7]
It was found that the surface area, average pore diameter, and total pore volume of pristine MWCNTs (CNT-1) were 80.72 m2/g, 16.14 nm, and 0.32
Summary
Multiwalled carbon nanotubes (MWCNTs) have attracted a great deal of attention from research institutes and enterprises due to their excellent mechanical, electrical, thermodynamic, and chemical stability properties [1,2,3]. The homogeneous dispersion of carbon nanotubes has become a major challenge to fabricate MWCNT-composited cementitious materials. Oxidation treatment is an effective covalent functionalization approach to improve the physicochemical properties of carbon materials such as carbon fiber, activated carbon, and carbon nanotubes. Oxidization technology of carbon materials with sodium dichlororisocyanurate [11], nitric acid [12,13], or hydrogen peroxide [14] has been developed. Oxidation with nitric acid was shown to be more effective than hydrogen peroxide in functionalizing the carbon surface. Oxidized carbon nanotubes can be used directly to prepare
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