The essential role of redox potential/equilibrium constant in the ability of non-equilibrium plasma for nano-synthesis in liquids

In this study, we investigated the role of redox potential in the ability of nano-synthesis by plasma–liquid interactions. From redox potential, a parameter featured the standard Gibbs free energy, and the equilibrium constant of a reduction reaction can be determined. Our calculation showed that the reactions of AuCl 4 − / Au 0 with a redox potential of 1.0 V and Cu 2 + / Cu 0 of 0.34 V have equilibrium constants of approximately 10 50 and 10 11, respectively. The results are significant to explain the failure in the copper nanoparticle synthesis in the process of nucleation through the Lamer theory. To compare these results to experimental data, the nanoparticles synthesized in a mixed solution of AuCl 4 − and Cu 2 + by AC glow discharge were characterized. The experimental results showed that there were only gold nanoparticles synthesized even though the concentration of gold ions is 200 times smaller. Other results of silver and platinum nanoparticles were also agreeable to the theory. Our findings provide a prediction to explain the ability in the nano-synthesis by plasma in contact with liquid for any noble metals.