Preparation By Pyrolyzation Of Metallic Organic Frameworks And Gas-sensing Properties Of SnO₂-based Composites

Metal oxide semiconductor(MOS)is one of the widely studied gas sensitive materials at present.The single MOS material has many shortcomings,such as low sensitivity,high working temperature and poor selectivity.How to strengthen the gas-sensing properties of MOS and reduce the working temperature of gas sensitive materials has become a key problem urgently to be solved by researchers.In this paper,n-type semiconductor SnO₂ as the research object,SnO₂ based composites were prepared by pyrolyzation of metallic organic frameworks(MOFs).The effects of precious metals doping,transiton metal oxide combining and photoactivation method on the gas-sensing properties of the composite were investigated.The main work is as follows:(1)SnO₂ was prepared by pyrolyzation of metallic organic framework and Ag-SnO₂ composites were fabricated with AgNO₃ reduction by NaBH₄.The effects of Ag dopping on the material structure and gas-sensing properties were explored and the gas-sensing strengthening mechanism was analyzed.The results show that the response value of the composite to 10 ppm ethanol reaches 157 when the mass fraction of Ag is 7%and the operating temperature is 250?,which is 10 times higher than that of pure SnO₂.It showes good selectivity and stability.Such excellent performance is contributed to the increase of the gas adsorption capacity,catalytic active site and oxygen vacancy of the composites caused by the doping of Ag.(2)The SnO₂/Co₃O₄ composites were prepared by pyrolyzation of bimetallic organic framework.The effects of different pyrolysis temperatures and the ratio of Sn to Co on the structure and gas-sensing properties of the composites were studied.And the gas-sensing strengthening mechanism of the composites were investigated.The results show that the SnO₂/Co₃O₄ composites with the molar ratio of Sn/Co 2:1 obtained after pyrolysis temperature of 400?has excellent gas-sensing properties to 50 ppm acetone at 275?.The response value to 50 ppm acetone reaches 498,which is 5 times of that of pure SnO₂.The enhancement of gas-sensing reponse value is caused by the formation of p-n heterojunction at the interface of SnO₂/Co₃O₄ composites and the catalytic properties of Co³⁺.(3)Photoactivation of SnO₂/Co₃O₄ composites was used to reduce its operating temperature.The effects of light of different wavelengths and environmental humidity on the sensing performance of the SnO₂/Co₃O₄ composites and the gas-sensing strengthening mechanism were discussed.The results show that the working temperature of SnO₂/Co₃O₄ can be reduced to 80?under the light of370-375 nm and the SnO₂/Co₃O₄ has good gas-sensing properties to 50 ppm acetone.The response value is 14.5,which is 7 times higher than that without photoactivation.The SnO₂/Co₃O₄ composite has the characteristics of fast response and good stability.In addition,the response value of SnO₂/Co₃O₄composite to 50 ppm acetone decreases with the increase of relative humidity,showing a cross sensitivity.