Functionalization of multi-walled carbon nanotubes via surface unpaired electrons.

The unpaired electrons on multi-walled carbon nanotubes (MWNTs) treated by nitric-sulfuric mixed acid were detected and characterized by electron spin resonance (ESR). Through reacting with these unpaired electrons, highly soluble acrylamide-grafted MWNTs were successfully prepared and characterized by ESR, FT-IR, UV-vis and atomic force microscopy (AFM), etc. The results indicate that MWNTs could generate more unpaired electrons with longer mixed-acid treatment time and could be well functionalized by acrylamide. By AFM analysis, a 'net' structure was formed on MWNTs after grafting with acrylamide. This new method has some obvious advantages of mild reaction conditions and convenient operation, etc. Furthermore, the grafting of MWNTs may have great potential for biomedical applications in drug delivery and regenerative medicine owing to their excellent networks.