Intense Plasma Effect Induced by Microwave Irradiation of CO2 -Derived Carbon Nanotubes

A powerful and unexpected plasma effect has been observed when CO2-derived Carbon NanoTubes (CNTs) synthesized by molten carbonate electrolysis (C2CNT), are exposed to microwave irradiation in air. The electrochemical splitting of CO2 in molten carbonate and concurrent growth of CNTs at the cathode has been termed the C2CNT process and is being scaled upwards. It is hypothesized that unique features of the electrochemical CO2-made CNT, such as transition-metal-based nucleation during growth, enhance electrical and magnetic characteristics in a way that is critical to enabling the plasma effect. CNTs’ intrinsic structures are characterized by their high aspect ratio and concentric graphene cylinder arrangement, which is known to promote strong electron field emission. However, in this case, the plasma initiated by microwave exposure is remarkably intense and spatially localized. Several potential applications stemming from this discovery, including hybrid microwave heating, are considered. One application is explored in detail: the use of this plasma effect for rapid purification of CNTs. Compared to standard plasma cleaning in dedicated chambers, this method demonstrates significantly improved performance, achieving over a 100-fold reduction in treatment time, and less than one tenth the energy to yield CNTs with improved purity and enhanced resistance to oxidation and combustion.