Lithographically Cut Multiwalled Carbon Nanotubes: Opening Caps, Controlling Length Distribution, and Functionalization

This work presents a microwave digestion heating method using a 40 ml mixture of potassium permanganate and sulfuric acid (3/1 mol) to cut, end-open, and functionalize as-prepared multiwalled carbon nanotubes (A-MWCNTs). Also, the ability of the microwave digestion method was studied at different reaction times (5, 10, 20, 30, and 40 minutes). To harness the extent of treatment, shortened multiwalled carbon nanotubes (S-MWCNTs) were fully characterized by UV-visible, Fourier transform infrared spectroscopy, and Raman spectroscopies, as well as, transmission electron microscopy and optical microscopy. The results showed that, with this mild treatment, the A-MWCNTs (>80 µm) were efficiently and significantly shortened to below 1 µm after 40 minutes. Also, heating the closed reaction vessel under microwave irradiation at 90°C for 20 minutes was very effective in the functionalization of MWNTs. At the same time, the S-MWCNTs formed the best state of dispersion in water without the help of surfactants that provided possibility for further functionalizations. For the first 10 minutes, crystallinity increased then decreased until 20 minutes, and after that improved slightly. Finally, the mechanism of this process is explained schematically. This method could be used as high-efficiency and damage-free process to the cut, end-open, and functionalization of CNTs that led to dispersion of CNTs and ultimately for such application.