IN-LIQUID PLASMA USING MICROWAVE POWER FOR APPLICATIONS
Authors: Horikoshi Satoshi 
Published: October 2019

More than 30 years have passed since Clements, et. al. succeeded in generating plasma in liquid (in-Liquid plasma: LP). Meanwhile, then plasma generation experiments using AC and DC power sources have been performed in electrolyte solutions. On the other hand, in 2000, by Nomura, et. al., they succeeded in generating plasma in aqueous solution by using microwave as a power source. When the microwave is used as a power source, there is a problem that the electrode is deteriorated and melted by the heat of plasma, and there is a problem that the device cannot be used continuously. We solved this problem using a semiconductor (solid-state) microwave generator. In order to investigate the possibility of using this new plasma, we have applied to wastewater treatment (e.g. degradation of 1,4-dioxane, rhodamine B dye and hypochlorous) and gel synthesis (polyvinylpyrrolidone (PVP) gel and silicone hydrogel gel). The photograph of the LP apparatus is illustrated in Figures 1. The MW generator was constructed using an Ampleon M2A-R semiconductor generator (2.45-GHz; maximal power, 1300 W) coupled to an isolator (air cooling device), a power monitor, a three-stub tuner and a short-circuit plunger. Microwaves continuously irradiated the liquid through the tungsten antenna (dia.: 10 mm; length: 200 mm). The tungsten antenna was isolated from the reactor and the waveguide using a ceramic spacer to irradiate MW in the solution. In the application of LP for wastewater treatment, the model wastewater of rhodamine B dye (RhB) were decomposed by LP irradiation, and degradation efficency of LP method was compared with conventional methods (UV photodegradation, NaClO chemical treatment, UV/NaClO chemical/photodegradation and the UV/TiO2 photocatalytic degradation method). The degradationon rate of LP method was remarkably fastest to conventional methods (Figure 2). In the application of LP for gel-synthesis, synthesizing the polymer-gel (PVP-gel and HySi-gel) was tried by the LP method. This feature of the method can significantly reduce (or eliminate) the initiator and crosslinking agent needed for conventional synthesis. Because these chemicals are very toxic, the LP approach is effective in green chemistry. In addition, it will further extend the application of these gels to the medical field.More than 30 years have passed since Clements, et. al. succeeded in generating plasma in liquid (in-Liquid plasma: LP) [1]. Meanwhile, then plasma generation experiments using AC and DC power sources have been performed in electrolyte solutions. On the other hand, in 2000, by Nomura, et. al., [1], they succeeded in generating plasma in aqueous solution by using microwave as a power source. When the microwave is used as a power source, there is a problem that the electrode is deteriorated and melted by the heat of plasma, and there is a problem that the device cannot be used continuously. We solved this problem using a semiconductor (solid-state) microwave generator [2]. In order to investigate the possibility of using this new plasma, we have applied to wastewater treatment (e.g. degradation of 1,4-dioxane, rhodamine B dye and hypochlorous) and gel synthesis (polyvinylpyrrolidone (PVP) gel and silicone hydrogel gel).More than 30 years have passed since Clements, et. al. succeeded in generating plasma in liquid (in-Liquid plasma: LP) [1]. Meanwhile, then plasma generation experiments using AC and DC power sources have been performed in electrolyte solutions. On the other hand, in 2000, by Nomura, et. al., [1], they succeeded in generating plasma in aqueous solution by using microwave as a power source. When the microwave is used as a power source, there is a problem that the electrode is deteriorated and melted by the heat of plasma, and there is a problem that the device cannot be used continuously. We solved this problem using a semiconductor (solid-state) microwave generator [2]. In order to investigate the possibility of using this new plasma, we have applied to wastewater treatment (e.g. degradation of 1,4-dioxane, rhodamine B dye and hypochlorous) and gel synthesis (polyvinylpyrrolidone (PVP) gel and silicone hydrogel gel).