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A research group led by Prof. Tetsu Yonezawa of the Graduate School of Engineering in conjunction with Arios, Inc. and Suga Co., Ltd. developed a microwave in-liquid plasma generator that allows continuous underwater plasma production which enables quick and simple submerged synthesis of various metal nanoparticles. Until this method was developed, metal nanoparticles were produced by vaporizing and coagulating metals in a vacuum or by adding a chemical reducing agent to a metal salt solution. With the microwave in-liquid plasma technique, microwaves are concentrated through the waveguide to the tip of a coaxially arranged electrode projected under water in order to generate plasma below the water's surface. Submerged plasma generation using microwaves previously required evacuation equipment. However, this technique renders such equipment unnecessary, and plasma can be generated at atmospheric pressure. Previously methods used to produce a high-voltage direct-current pulse to generate plasma under water required voltages as high as several kilovolts and necessitated a large-scale, expensive power source. In contrast to this, the microwave source used in this study was at the 1.5-kW level - approximately twice the voltage of a household microwave oven. Therefore, the cost of applying this technique is expected to be only a third to a fifth of the high-voltage direct-current pulse technique. The new approach also enables the synthesis of metal-supported catalysts when used in conjunction with supports; and catalytic application for fuel cells and various organic reactions is also feasible. The research group plans to work on the synthesis of nanoparticle materials for biosensing by constructing continuously operable systems. Contact information:
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