A self-assembled flavin protective coating enhances the oxidative thermal stability of multi-walled carbon nanotubes

Multi-walled carbon nanotube (MWNT) has many commercial applications. However, its broad use is limited by the surface-bound oxygen lowering its thermal stability. Here, we developed a facile method to enhance the oxidative thermal resistance of MWNTs that involves molecular coating promoted surface passivation. In the approach, ball milling is employed to self assemble flavin mononucleotide (FMN) helically around MWNTs through non-covalent interactions with no increased defects in MWNT. Upon high temperature oxidation, the ribityl phosphate side chain of FMN in the nanoconstruct undergoes partial decomposition to generate a corresponding isoalloxazine derivative on the surface of the MWNTs. Transmission electron microscopy reveals that the oxidatively annealed material is comprised of a tight isoalloxazine coating stacked on the sidewalls of the MWNT. The results of thermal gravimetric analysis studies show that the coating further elevates long-term stability and the energy barrier for oxidation of the MWNT by 28 kJ/mol from 113 kJ/mol for the bare MWNT. The role of the isoalloxazine coating is proposed to be surface passivation from molecular oxygen. As a consequence of the passivation, the maximum oxidative temperature of the MWNT is raised to 938 K as compared to that of 843 K for bare MWNT.