Plasma electrolysis using atmospheric dc glow discharge in contact with liquid for synthesis of metal nano-particles

For the synthesis of metal nanoparticles in aqueous solution, we propose dual plasma electrolysis, which consists of Hoffman electrolysis apparatus with two atmospheric glow discharge plasmas as electrodes instead of conventional metal electrodes immersed in a liquid. The plasma anode irradiates positive ions to the solution surface while the plasma cathode irradiates electrons to the solution surface. The dual plasma electrolysis system enables us simultaneously to investigate the influence of electron and positive ion irradiation to a solution surface on metal nanoparticle generation at the same current. We used aqueous solutions of AgNO$_{3}$, HAuCl$_{4}$ and their mixture. In dual plasma electrolysis with AgNO$_{3}$, Ag nanoparticles were only synthesized on the plasma cathode side. This means that Ag nanoparticles are generated via the reduction of Ag$^{+}$ by electrons. With HAuCl$_{4}$ solution, Au nanoparticles were synthesized on both the plasma anode and plasma cathode sides. Ion irradiation with the plasma anode is more effective than electron irradiation for Au nanoparticle synthesis. This finding suggests that positive ions from the plasma trigger the dissociative reaction of AuCl$_{4}^{-}$ at the plasma-liquid interface.