Application of the hard-soft acid–base principle in plasma-in-liquid processing

Plasma, owing to its reactivity and nonequilibrium properties, is a unique field commonly used in material processing. In recent years, plasma processing with a liquid phase has attracted considerable attention owing to its important advantages, such as high electron density and the availability of a wide variety of reactions in solutions. However, plasma-in-liquid material synthesis is occasionally difficult to control and guidelines are lacking. In this study, we investigated whether the hard-soft acid–base (HSAB) principle, which is often applied in material synthesis, is applicable to the plasma-in-liquid process and demonstrated that organic solvent-derived substances produced by plasma-in-liquid processing reacted with solutes according to the HSAB principle. These results suggest that the HSAB principle may apply to plasma-in-liquid processing.