Over-oxidation of multi-walled carbon nanotubes and formation of fluorescent carbon nanoparticles

• Multiwalled carbon nanotubes were over-oxidized using HNO3–H2SO4.
• Over-oxidation resulted in formation of florescent carbon nanoparticle (CNP).
• Crystallinity of CNPs was lowered and O, S and N groups were generated.
• Nanoparticles showed semiconductor behavior with energy band gap of 4.13 eV.
• Breakdown of walls and thereby collapsing of nanotubes formed nanoparticles.

Over-oxidation of multi-walled carbon nanotubes (MWCNTs) was studied after heating with HNO3–H2SO4 for 50 h. High resolution transmission electron microscopy (HRTEM) showed the formation of oval shaped carbon nanoparticles (CNPs) during the reaction. Graphitic structure of MWCNTs was reduced and oxygen, sulfur and nitrogen containing groups were generated on the CNPs. Contrary to the metallic MWCNTs, CNPs exhibited semiconductor behavior with the band gap of 4.13 eV and yellow–green color fluorescence during exposure to the ultraviolet (UV) radiations. A mechanism for the formation of CNPs during the over-oxidation of MWCNTs is proposed in the paper.

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