Description
The global demand for high-quality graphene continues to drive the search for sustainable, scalable, and cost-effective synthesis methods. Among the most promising emerging technologies, microwave-induced plasmas generated by the TIAGO torch (Torche à Injection Axiale sur Guide d’Ondes) offer a streamlined, catalyst-free, and environmentally friendly approach to producing few-layered graphene nanosheets through ethanol decomposition at atmospheric pressure. While this technology represents a significant leap forward in green nanomaterial manufacturing, unlocking its full industrial potential requires a deeper understanding of the fundamental physics governing its energy transport mechanisms.
Using optical emission spectroscopy techniques, the fundamental characteristics of the TIAGO torch have been investigated, revealing that it behaves as a surface wave discharge (SWD), where electromagnetic wave sustaining it propagates along the plasma-dielectric (air) interface. More importantly, a distinct "radiation zone" located near the nozzle exit has been identified for the first time at atmospheric pressure, highlighting a critical inefficiency: nearly 43% of the input microwave energy can be dissipated as non-guided radiation. This fundamental insight serves as the cornerstone for technological optimization of graphene synthesis.
By implementing a custom-designed metallic electromagnetic shielding around the reaction chamber it is possible to suppress these radiation losses. This strategic modification results in a significant volumetric expansion of the plasma and a more efficient decomposition of carbon precursors. Quantitative analysis demonstrates a remarkable 22.8% increase in graphene production alongside a 21% improvement in overall energy yield.
Critically, this boost in productivity does not come at the expense of material integrity. Extensive multi-technique characterization, including Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and High-Resolution Transmission Electron Microscopy (HRTEM), confirms that the synthesized powder maintains its high-quality, few-layered structure with low defect density and high sp2 hybridization. Ultimately, the bridge between fundamental plasma diagnostics and industrial optimization proves that understanding basic energy loss mechanisms is the key to achieving the energy efficiency and scalability required for the next generation of sustainable nanostructure manufacturing.
Acknowledgements: This work was supported by project PID2023-147436OA-I00 funded by MICIU/AEI /10.13039/501100011033 and by FEDER, UE. The predoctoral contract of F.J. Morales-Calero was granted by MOD-2.2 from Plan Propio de la Universidad de Córdoba (2020).