The Investigation On CO Sensors Fabricated From SnO₂-based Porous Nanosolids

With the development of economy and industry, our living situation has been improved at the expense of environmental pollution and health deterioration. Many kinds of toxic and harmful gases exist in our circumstance. Among them, CO is a kind of inflammable, explosive and poisonous gas, which may do serious harm to human body. CO is very difficult to detect due to its colorless and odorless characteristic, so poisoning and explosion incidents often take place. In recent years, metal oxide semiconductor CO sensors attract more attentions due to their advantages in thermal stability, corrosion resistance, low cost etc. However, almost all the sensing materials are prepared in lab scale, and the harsh preparation conditions limit their applications to a large extent. Here we focused on the developing a new facile route to prepare new sensing materials with excellent sensing performances, and investigating the sensing mechanisms of these new materials.SnO2 and Sn02-MOx (M=CuO、Co3O4、ZrO2、CeO2、TiO2) porous nanosolids were prepared by a solvothermal hot-press (SHP) method using SnO2 nanoparticle as raw materials. Subsequently, we fabricated SnO2 and Sn02-MOx thick film CO sensors from SnO2 and Sn02-MOx porous nanosolids following a conventional process. In order to further improve the gas-sensing performances of CO sensors, we fabricated dual-functional highly responsive CO sensors by directly using SnO2 porous nanosolid as the gas-sensing elements. Furthermore, CO sensors based on Pt-loaded SnO2 porous nanosolids were prepared using a pressure-driven exchange route. Because of the catalytic effect of Pt, a CO sensor that can be used to detect low level CO at room temperature was prepared.(1) The gas-sensing performances of two thick film sensors fabricated from SnO2 nanoparticles and SnO2 porous nanosolid were compared, and the results show that the latter possesses lower resistance and higher sensor response due to its porous nature. In addition, all the parameters during fabricating thick film CO sensors, including the solvent volume, hot-pressing temperature, sintering temperature etc., influence the gas-sensing properties of the sensor. It is proved that by varying these parameters, all the pore diameter distribution, pore volume and specific surface area of SnO2 porous nanosolid are changed. The results demonstrate that optimum values for the solvent volume, hot-pressing temperature, pressure and sintering temperature are 10 ml,200℃,60 MPa and 700℃, respectively.(2) For enhancing the gas-sensing performances of CO sensors, a series of metal oxides were doped into SnO2 nanoparticles and thick film CO sensors based on SnO2-MOx (M=metal atom) porous nanosolids were fabricated. The results show that, the sensor responses of SnO2 to CO are all improved to a certain extent by doping. When p-type metal oxide semiconductors CuO and Co3O4 are doped into n-type SnO2, the electronic interactions between CuO/Co3O4 and SnO2 is the major reason for the improvement of sensing performances. However, when CeO2、ZrO2 and TiO2 are added into SnO2, the pore diameter distributions of SnO2 porous nonsolid are changed, this phenomenon may be responsible for the improvement of the sensor responses. The thick film CO sensor doping with 10wt.% TiO2 has the largest sensor response.(3) In order to explore new routes for improving gas-sensing performances of CO sensors, the novel CO sensors were fabricated by directly using SnO2 porous nanosolids as sensitive elements. The results reveal that the novel CO sensor based on SnO2 porous nanosolid possesses lower intrinsic resistivity and higher sensor response by comparing with that fabricated from SnO2 nanoparticles. Furthermore, the SnO2 porous nanosolid sensor also has much lower working temperature, and it can be used as a dual functional gas sensor, i.e., as CO sensor at 300℃and as CH4 sensor at 400℃, respectively.(4) For further increase the sensor response while decrease the operation temperature of CO sensors, CO sensors were fabricated by using Pt-loaded SnO2 porous nanosolids, which were prepared by a pressure-driven exchange method. With the help of catalytic effect of Pt, the sensors exhibit rather high sensor response to 50 ppm CO at room temperature. Besides, the sintering temperature and the humidity have influences on the sensor response. When the sintering temperature and humidity increase, the sensor response of the sensors deteriorates to some extent. After being sintered at above 700℃, the sensors have no response to CO at all.