Catalytically Active Coatings on the Basis of Titanium Dioxide for Ozone Destruction
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Catalytically Active Coatings on the Basis of Titanium Dioxide for Ozone Destruction Sergey M. Karabanov, Andrey S. Karabanov, Dmitriy V. Suvorov, Gennadiy P. Gololobov, EvgeniyV. Slivkin, Mariya A. Klyagina, Dmitriy Y. Tarabrin Ryazan State Radio Engineering University, 59/1 Gagarina St., Ryazan 390005, Russia INTRODUCTION Ozone destruction problem Creation of high efficiency and safe air cleaning systems is an important task because of their wide usage in accommodations, health care organizations, industries and agriculture [1]. The most effective and environmentally safe cleaning systems are the systems based on ozone (О3) formed in barrier or corona discharges. Ozone is a strong oxidizer, it decomposes molecules of pollutants in the air and sterilizes from microorganisms. One of the most common solutions is a plasma air cleaning based on the usage of a corona discharge. Despite of the high efficiency of these systems, their main disadvantage is an emission of considerably concentrated ozone together with the cleaned air. The maximum permissible concentration of ozone according to the World Health Organization data is less than 6 ppm, besides it is also a carcinogen even in small amounts. There are a few methods of the ozone destruction: photochemical, thermal and catalytic [2]. The catalytic ozone destruction is more preferable in most cases because it is a more energysaving, «service-free» and inexpensive method providing simplicity of the air cleaning system technical implementation. Catalytic coatings, problem of the catalytic activity calculation Currently there are a lot of materials used as a catalyst of the ozone decomposition - MnO2, Al2O3, Mn3O4, NiO, MgO, TiO2, carbon, etc. and compositions on their basis [1, 3, 8]. Usage of a titanium oxide TiO2 as a catalytic coating on collecting plates of a plasma filter is a promising technique [4]. It is caused by its high catalytic activity towards both volatile organic compounds (VOCs) and high activity in relation to ozone. The method of electrochemical anodizing allows obtaining TiO2 coatings with the ordered porous structure. Changes of anode oxidation terms in the electrolyte containing fluoride electrolyte control the coating structure in wide ranges: changes of the diameter of coating pores within 20-200 nm and depth up to 200 μm [5]. Catalytic activity of TiO2 coatings depends on their structure. Dynamics of the ozone decomposition within heterophase catalytic reactions inside the porous coating is rather complicated. It is described not only by constants of the ozone decomposition reaction on the catalyst surface but also by the ozone transfer process deep into the coating. The effective area increases when the coating thickness (pore depth) increases and the pore diameter decreases but transfer of the ozone deep into the coating becomes worse. On the contrary the transport becomes better when the pore diameter increases, but the area decreases. Physics of the transfer process under simultaneous influence of the heterophase reaction of ozone decompositi
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