Development of direct gas injection system for atmospheric-pressure in-solution discharge plasma for plasma degradation and material syntheses

Abstract

By applying a high pulsed voltage to a gap between two electrodes placed in a solution, an atmospheric-pressure in-solution glow (ASG) plasma is generated. The ASG plasma is applied in a new material processing method, called solution plasma processing (SPP). In order to accelerate the reaction and to add functions to the synthesized materials, it is important to alter the gas content in the ASG plasma. We developed a direct gas injection system for an ASG discharge cell. When O₂, CO₂, N₂ and Ar gases were injected into the ASG plasma, emission bands due to the derivatives of the injected gases were observed in the emission spectra from the ASG plasma. The electron number density in the ASG plasma was increased by the O₂, CO₂, and N₂ injections, probably due to the enhancements of the α and γ processes by the larger molecular weights than H₂O. In addition, the first dielectric breakdown of the solution and the formation of the gas bubble processes gradually disappeared due to the gas injection. When O₂ was injected, the amount of ·OH generation was increased. By the enhancement of the ·OH generation, the degradation speed of rhodamine B in the ASG plasma was increased by a factor of two. When Au nanoparticles were synthesized utilizing the ASG plasma, the zeta potential of the Au nanoparticles was increased by about 30% by the O₂ injection. The plasma parameters and the reactivity of the ASG plasma can be altered more widely by changing the kind of injected gas and the flow rate.