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 C₂under 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.

Proposed mechanisms for the bubble formation on the graphite electrodes discharged in distilled water.

Herein, we report an autonomous viscosity oscillation of polymer solutions coupled with the metal–ligand association/dissociation between Ru and terpyridine (tpy), driven by the Belousov–Zhabotinsky (BZ) reaction. The tpy ligand for the Ru catalyst was attached to the terminals of poly(ethylene glycol) (PEG) with different numbers of branches (linear-, tetra-, and octa-PEG). It is well known that mono-tpy coordination is stable when Ru is oxidized (Ru(tpy)³⁺), whereas bis-tpy coordination is stable when the Ru centre is reduced (Ru(tpy)₂ ²⁺). In the oxidized state, the three different polymers existed as solutions. In contrast, when the Ru centre was reduced, gels were obtained for the tetra- and octa-PEG owing to the formation of a three-dimensional polymer network through Ru–tpy coordination. Rheological measurements confirmed that the sol–gel transition occurred much more quickly in the octa-PEG system than in the tetra-PEG system, because of the requirement of fewer crosslinking points. The polymer solutions exhibited self-oscillation of absorbance and viscosity when BZ substrates were added to the solutions of Ru²⁺–tpy-modified tetra-/octa-PEG. This indicated that the Ru(tpy)₂ ²⁺ attached to the polymer ends could work as a metal catalyst for the BZ reaction. By increasing the number of branches from 4 to 8, the amount of crosslinking changed more remarkably during the oscillation, with a maximum value closer to that necessary for gelation. Thus, viscosity oscillation with a larger amplitude in the region of higher viscosity was achieved by using octa-PEG.

Autonomous viscosity oscillation by the reversible complex formation of terpyridine-terminated PEG and/or terpyridine-terminated TetraPEG in the BZ reaction was achieved. The BZ reaction induces the periodical binding/dissociation of the Ru–terpyridine complex and causes periodical molecular changes to result in viscosity changes.

An extraordinary high-speed synthesis of gold nanoparticles (AuNPs) was discovered by synthesizing the AuNPs in ethanol–water mixtures using a solution plasma process (SPP). The influence of the ethanol mole fraction (χ_ethanol) in the ethanol–water mixtures on the reduction rate of gold chloride ions to AuNPs under the SPP system was studied. The results indicated that the reaction rate of the AuNPs synthesis exhibited a maximum value (i.e. 35.2 times faster than in a pure water system) at the significant point where the partial molar volumes of ethanol and water changed drastically.