Moleculer Recognition and Decomposition by Functional Ceramics

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Selective gas sensing of poisonous gases such as NOx or CO by a simple device is thought to be important technique for the view point of safe environment, control of productivity and control of reaction process and development of decomposition process pf NOx or other atmospheric pollution gases are one of the most important subjects especially for safe environment.Heterocontact is one of the electric devices, of which electrica resistance is changed by the introduction of water vapor, oxidizing gases (NOx , Cl2) or reducing gases (CO,H2). The authors have been studied on the electric properites of hetercontact of ceramics and its application to chemical sensors. When we used CuO (p-type semiconductor) and ZnO(n-type semiconductor) sintered compacts for hueterocontact, the electric current thorough CuO-ZnO interface increased by the introduction of reducing gases and its gas sensitivity varied as a function of applied voltage. The effect of additives on CO gas sensing characteristics of … More CuO or Cuo/ZnO heterocontact is discussed. Some additives affect the CO gas sensing properties of CuO powder compact and CO sensitive surface is constructed by sodium or ther alkali metal addition. Variation in surface properties of CuO by the alkali metal addition would be reflected to gas sensing characteristics of CuO/ZnO heterocontact and Na^+ added CuO/ZnO heterocontact shows selective CO gas sensing characteristics. The result gives us a useful information for the material design of CO sensor based on CuO ceramics or CuO based heterocontact.The nitrogen oxide (No_x) sensing mechanism of SiC/ZnO heterocontact is investigated by thermogravimetric analysis and temperature-programd desorption of surface product on ZnO.A pronounced decrease in electric current was observed only when a SiC/ZnO heterocontact specimen was suffiently exposed to NOx with wet air. From these results, formation of zinc nitrite on the ZnO surface is suggested and it would affect the electron transfer process at the ZnO-SiC interface.CuO/ZnO heterocontct is fabricated by the stacking of 6 layrs of declined composition of CuO-ZnO system and the exhaust gas passing through CuO/ZnO interface is analyzed by gas chromatography with flowing system. The variation of turnover number from CO to CO_2 as a function of applied electric field is observed and electric field controlled CO oxidative reaction at p-n semiconductor interface is performed at CuO-ZnO interface. Less