Few studies have been reported on materials processing in the solution plasma although this reaction field is promising. Recently, the synthesis of carbon nanotubes in the solution plasma has been the subject of vigorous investigation [3–7]. Nomura et al. demonstrated the synthesis of carbon-related materials with a microwave-generated plasma in a hydrocarbon liquid under evacuation [6]. The evacuation prevents the oxidation of products such as graphite, silicon carbide, diamond-like carbon, and carbon nanotubes. The most attractive feature of this process is that the liquid phase plays an important role as a plasma reactor. However, this method is limited to nonpolar solvents such as hydrocarbons, because polar solvents adsorb microwaves and prevent plasma formation.