抄録
Solution plasma processing, a reaction field available for chemical engineering, has high chemical activity because of its high electron temperature in the liquid, but low gas temperature. Consequently, it supplies activated species from plasma to liquid phases. Therefore, solution plasma has been anticipated for application to chemical processes such as synthesis of metal nanoparticles, and as a water treatment for sterilization and waste. We sought to synthesize silica by solution plasma, and to examine the effects of pH in the solution on the morphology and the chemical bonding state. Aqueous solutions containing tetraethoxysilane (TEOS) and ethanol were used as starting solutions. Then HCl or DEA (2.2'-iminodiethanol) was added to the solution to adjust the pH. The obtained materials were evaluated using scanning electron spectroscopy (SEM) and nuclear magnetic resonance (NMR). The morphology changes were observed as a two-dimensional tabular structure in an acid state, three-dimensional spherical structure in a base state, and two-dimensional and three-dimensional mixed structures in a neutral state. These structures originate mainly from the chemical bonding state of Si(OR)3(OSi), Si(OR)2(OSi)2 in an acid state, Si(OR)1(OSi)3, Si(OSi)4 in a base state, and Si(OR)2(OSi)2 and Si(OR)(OSi)3 in a neutral state.
