The effect of chemical treatment on the crystallinity of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were chemically treated using nitric acid solution for different time. Quantitative analysis of the crystallinity of the MWCNTs was performed by wide-angle X-ray diffraction (WAXD). The WAXD patterns were deconvoluted into the crystalline diffraction peaks and the amorphous scattering peaks. The introduction of a correction factor for the integrated peak intensity can enhance the computational accuracy of the crystallinity. With increasing the chemical treatment time, the crystallinity of MWCNTs first increases, and then decreases. When the chemical treatment time is equal to 2 h, the crystallinity of MWCNTs reaches the maximum of 85.9%. Moreover, the degree of order in the structures of chemically treated MWCNTs was further studied by thermogravimetric analysis (TGA) and high-resolution transmission electron microscopy (HRTEM). It was found that the external walls of chemically treated MWCNTs with high crystallinity consist of a series of perfectly continuous and straight graphite layers.