Dissolution of poly(vinyl alcohol)-modified carbon nanotubes in a buffer solution

Multiwalled carbon nanotubes (MWCNTs) were modified with a water-soluble poly(vinyl alcohol) (PVA) polymer (MWCNTs-PVA). The dissolution of the MWCNTs-PVA in Tris-HCl buffer solution was carried out in a shaking water bath by a soaking method. The microstructural changes of the MWCNTs-PVA during soaking was investigated using Fourier transform-infrared spectroscopy, differential scanning calorimetry, transmission electron microscopy, and X-ray diffraction. It is found that part of the MWCNTs-PVA was dissociated into amorphous carbonaceous debris, but most of tubular structures were retained after 21 days of soaking. The dissolution process revealed that the C-C bonds of the MWCNTs-PVA were broken-down with the generation of carbonaceous debris and residual carbon nanotube layers, and the latter can be further dissociated into amorphous carbonaceous debris. A possible dissolution mechanism of the MWCNTs-PVA in the buffer solution was proposed and discussed. The surface modified MWCNTs have many defects and open C-C bonds on the surfaces of the CNTs. The dissolution of the PVA in the buffer solution leads to a release of carbon atoms on the outer surface of the MWCNTs. It results in a further rupture of the C-C bonds and destroys the tubular structure .