Abstract
Although solution-plasma processing enables room-temperature synthesis of nanocarbons, the underlying mechanisms are not well understood. We investigated the routes of solution-plasma-induced nanocarbon formation from hexane, hexadecane, cyclohexane, and benzene. The synthesis rate from benzene was the highest. However, the nanocarbons from linear molecules were more crystalline than those from ring molecules. Linear molecules decomposed into shorter olefins, whereas ring molecules were reconstructed in the plasma. In the saturated ring molecules, C–H dissociation proceeded, followed by conversion into unsaturated ring molecules. However, unsaturated ring molecules were directly polymerized through cation radicals, such as benzene radical cation, and were converted into two- and three-ring molecules at the plasma–solution interface. The nanocarbons from linear molecules were synthesized in plasma from small molecules such as C2 under heat; the obtained products were the same as those obtained via pyrolysis synthesis. Conversely, the nanocarbons obtained from ring molecules were directly synthesized through an intermediate, such as benzene radical cation, at the interface between plasma and solution, resulting in the same products as those obtained via polymerization. These two different reaction fields provide a reasonable explanation for the fastest synthesis rate observed in the case of benzene.
Highlights
Liquid-phase plasma[1,2,3,4,5] has attracted the attention of several researchers engaged in plasma science, especially for applications involving materials and water treatment[6,7,8,9,10]
The synthesis rates of nanocarbons obtained from linear molecules, i.e., hexane and hexadecane, were obviously lower than that of nanocarbons obtained from ring molecules, i.e., benzene
In comparison to nanocarbons obtained from the ring molecules, nanocarbons obtained from the linear molecules exhibited greater crystallinity
Summary
Liquid-phase plasma[1,2,3,4,5] has attracted the attention of several researchers engaged in plasma science, especially for applications involving materials and water treatment[6,7,8,9,10]. The activated particles, including ions, electrons, radicals, and photons, are quenched and deactivated Such species have sufficient energy to induce precise chemical reactions but not physical changes. We attempted to adapt the solution plasma system to organic solutions (see Supplementary video and Fig. 1S) In such systems, the plasma enables unique reactions such as C–H activation reactions at the interface between the solution and plasma, whereas conventional plasma induces random decomposition reactions. The second is the reaction route at the interface between the plasma and solution, where the ion temperature is as low as room temperature, but the electron temperature is still sufficient to advance the organic reaction. The intermediates involved in the conversion of the starting materials to nanocarbon products were estimated; the nanocarbon formation routes are discussed
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