Effect of voltage polarity and supply frequency on the properties of plasma contacting liquid electrodes and gold nanoparticle synthesis

Plasma contacting with liquid (PCL) provides many charged particles and reactive species into the liquid. The difficulty in controlling or selecting each specific species has significantly limited its applications in industry. Here, we present a study on using voltage polarity to regulate the type of charged particles absorbing from the plasma into the liquid. A detailed understanding of the processes at the plasma-liquid interface and electrolysis due to switching in voltage polarity was determined via a visual pH observation, measuring the concentration of H2O2 and solvated electrons. The results indicated that changes in voltage polarity strongly affect the plasma properties, chemical properties and electrolysis process in liquid, and also in the types of reducing species for gold nanoparticle (GNP) synthesis. The results also showed that using a suitable frequency could improve the efficiency of absorption of H2O2 from plasma into the bulk liquid as well as the yield in the production of GNPs. The results provide a way to select desired species from the plasma to be transferred into the liquid for a distinct purpose and to accompany other properties in the system of PCL.