(Nanowerk Spotlight) A standard microwave oven sits on a laboratory bench. Inside, a small sample of carbon nanotubes (CNTs) erupts into brilliant yellow-white plasma, reaching temperatures over 800 °C. This intense plasma forms spontaneously within seconds and maintains itself until the power switches off. Unlike conventional plasma generation methods that rely on vacuum chambers, electrodes, or controlled gas mixtures, this process requires only carbon nanotubes and a standard microwave.
These nanotubes behave unlike any others tested. Commercial carbon nanotubes fail to produce plasma under the same conditions, likely due to differences in purity, conductivity, and structural properties. The difference lies in their unique molecular architecture – a direct result of their creation through molten carbonate electrolysis of CO2.
Video shows a sustained plasma from microwaving CO2-derived carbon nanotubes at 3200 W.
Many plasma applications require specialized equipment. Semiconductor manufacturers often use vacuum chambers and high-voltage systems, while other methods rely on controlled gas environments or microwave-driven plasmas. Medical sterilization units use radio frequency generators. Materials processors require precise gas mixtures and controlled environments. These complex requirements have restricted plasma applications to specialized facilities, despite its vast potential in manufacturing, medicine, and materials science.
The molten carbonate synthesis process creates nanotubes with distinctive properties absent in conventional materials. As CO2 splits into carbon and oxygen, transition metals integrate into the growing nanotubes. These CNTs interact with microwaves differently due to their unique structure and composition. The molten carbonate electrolysis process incorporates transition metals, enhancing their electrical conductivity and magnetic properties. This allows them to absorb microwave energy more efficiently, generating the intense, self-sustaining plasma observed in the experiments.
Stuart Licht, a professor of Chemistry at George Washington University, led this work and documented the results in Nanoscale (“Intense, self-induced sustainable microwave plasma using carbon nanotubes made from CO2“). The investigation reveals that within seconds of microwave exposure, these specialized nanotubes generate plasma that maintains stability throughout the irradiation period. The plasma reaches precise temperatures between 820 °C and 925 °C – hot enough to soften borosilicate glass but cool enough to avoid oxidizing stainless steel.
Carbon Nanotubes, made from the greenhouse gas CO2, create a hotspot on the substrate, which initiates the observed sustained microwave plasma. (Image: Reprinted from DOI:10.1039/d4nr04097j, CC BY 3.0)
The research team conducted extensive comparisons with other carbon materials. Commercial carbon nanotubes, graphene, and carbon black all failed to produce sustained plasma under identical conditions. Detailed analysis identified crucial characteristics unique to the CO2-derived nanotubes: superior thermal conductivity, enhanced electron transport, and specific magnetic properties resulting from their molten carbonate synthesis.
This discovery demonstrates immediate practical value. The team used the plasma to purify carbon nanotube samples, achieving in one minute what conventional plasma cleaning requires an hour to accomplish. Their method consumed just one-tenth of the power while producing higher purity materials. The plasma confines itself to a specific region and adapts its shape to maximize microwave energy absorption, enabling precise control without complex containment systems.
“Our research establishes fundamental advances in both plasma generation and carbon dioxide utilization,” Licht explains to Nanowerk. “Beyond simplifying existing applications, our method could enable plasma technologies in settings where traditional systems prove impractical or cost-prohibitive. The process simultaneously addresses environmental challenges by providing productive use for captured carbon dioxide.”
The researchers’ current investigations focus on mapping the detailed plasma characteristics and exploring additional applications. The plasma’s precise temperature control suits it for materials processing, surface treatment, and chemical synthesis. Its formation in open air, using standard microwave frequencies, suggests possibilities for portable plasma systems.
The discovery also advances carbon dioxide conversion technology. The molten carbonate electrolysis process transforms a greenhouse gas into functional nanomaterials with unique electromagnetic properties. This creates value from carbon dioxide while enabling simpler approaches to industrial processes that typically require complex infrastructure.
This research not only simplifies plasma generation but also advances carbon dioxide utilization. By transforming CO2 into functional nanomaterials with unique electromagnetic properties, this method offers both environmental and technological benefits. According to Licht, future studies will explore additional applications, including materials processing and chemical synthesis, expanding the potential of this unexpected discovery.
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