Synthesis of gaseous hydrogen and nanoparticles of silicon and silicon oxide by pyrolysis of tetraethoxysilane in an electric discharge under the action of ultrasound

Abstract

In this work, we studied the process of synthesis of gaseous hydrogen, as well as silicon and silica nanoparticles under the action of intensive ultrasonic cavitation in a plasma discharge in a tetraethoxysilane medium.It is shown that a new form of plasma discharge arising in a liquid in an intensive ultrasonic field above the cavitation threshold, characterized by a volumetric glow in the entire space between the electrodes and falling volt-ampere characteristics, can be effectively used to initiate various physical and chemical processes. It was shown that ultrasonic action in combination with an electric discharge is capable to decompose tetraethoxysilane molecules with the formation of hydrogen, carbon oxides, and also solid-phase products - silicon and silica nanoparticles.Experiments on the production of hydrogen and nanoparticles were carried out on a special experimental setup for the implementation of a plasma discharge in liquid-phase media. The setup consists of an ultrasonic generator, a piezoceramic transducer, a discharge power source, a reaction chamber, and discharge electrodes.The results of the analysis of gaseous reaction products by gas chromatography show that during the pyrolysis of liquid tetraethoxysilane, hydrogen with a content of about 90% and carbon oxides are formed. The synthesized silicon and silica nanoparticles were isolated and studied using the methods of physicochemical analysis - infrared spectroscopy, X-ray phase analysis and transmission electron microscopy to determine the composition, shape and size of nanoparticles.The study of nanoparticles by electron microscopy showed that particles of a corner shape are obtained during the synthesis. The size of the synthesized nanoparticles is 50–100 nm. It was also shown by electron microscopy that, upon aggregation, the particles do not become larger in size, but form composite associates. It is also important to note that the advantage of this method for the synthesis of nanoparticles is their activated surface, which has a high reactivity as a result of exposure to intense ultrasound.The resulting nanoparticles and their agglomerates can also be used as functional materials, fillers, and components of composite materials.