| Recently, with the need of sources exploitation, aviation and spaceflight, petrochemistry, security, the detection of combustible and noxious gases has become more and more important. Especially, the gas sensors with high sensitivity, excellent selectivity and stability, short response time and long usage life, are the main research subject in the future. Therefore, it is a hotspot to develop a new kind of gas-sensing material for practical application.In recent years, the conductive polymers such as polythiophene(PTP), polypyrrole and polyaniline have received much attention. They have a variety of potential applications including chemical and biological sensors, electronic devices, as well as efficient and low cost solar cells due to their remarkable mechanical and electrical properties such as low operating temperature, low cost, flexibility and easy processability and so on. However, they also have some disadvantages such as low chemical stability and mechanical strength that are unfavorable for the applications in sensors and electronic devices. Now the widely used gas sensing materials are semiconductive metal oxides. Those materials have some shortcomings such as poor selectivity and high operation temperature. The inorganic-organic (metal oxide/conducting polymer) hybrid materials are currently of great interest for the employment to explore enhanced sensor characteristics, owing to their synergetic or complementary behaviors that are not available for their single component.In the paper, we have put forward the studies of the gas sensors based on organic-inorganic hybrid materials. The typical organic and inorganic materials (SnO2/PTP and WO3/PTP) were selected. The in situ oxidative polymerization method was used to prepare many kinds of organic-inorganic hybrid materials. The gas-sensing properties of the hybrid materials were studied at low operation temperate (< 100℃) and compared to those of the pure organic and inorganic materials. The sensing-mechanism of the hybrid materials was also explored. Meanwhile, some work has been done to improve the gas sensing properties including to increase the sensitivity and selectivity as well as lower the working temperature by doping noble metal Pt in the WO3 materials. The main work can be summarized as follows:1. WO3/PTP hybrid materials with different PTP mass percent (1%,10%,20%30% and 40%) were prepared by an in situ oxidative polymerization method. The results of sensing tests indicated that WO3/PTP hybrid materials had less or no gas response to methanol, ethanol, acetone and H2S, but good selectivity to NO2, and could alleviate the irreversibility to some extent of the single PTP to NO2。The sensitivity of this kinds of hybrid materials was changed with the different PTP content. When the PTP content was 10%, the hybrids showed the maximum sensitivity at the working temperature of 70℃. The mechanism of the WO3/PTP hybrids to gas NO2 was suggested to be formation of p-n hereojunction.2. The Pt-WO3 nanocrystalline powders were prepared by the colloidal-coprecipitation method (Pt:x wt%:0.25,0.5,1.0,2.0 respectively), and calcined at 600℃for 2 h. The test result of the gas sensing properties showed that the sensitivity of the sensor became to the highest when the Pt content was 0.5wt% and the optimum working temperature was 120℃which was 20℃lower than the pure WO3. The gas sensing properties of the Pt-doped WO3 sensors were superior to that of the undoped one, especially to H2S. After 4 months, the sensor based on the 0.5wt% Pt-WO3 showed better response to 20 ppm H2S, much higher than the pure WO3, but lower than itself before. The reason for the sensitivity decreases of the sensor is not clear. Also, further study is underway.3. The hs-SnO2/PTP hybrid materials were prepared by an in situ oxidative polymerization method and characterized by XRD, FT-IR, TGA and TEM. The gas sensitivities of the materials were studied at the operation temperatures below 100℃. By gas-sensing properties measurement, it was found that, take the hs-SnO2/(20%)PTP hybrids for example, the PTP/SnO2 hybrids not only had better selectivity and lower working temperature than the SnO2 but also could alleviate the irreversibility to some extent of the single PTP to NO2. The sensitivity of this kinds of hybrid materials was changed with the change of PTP content. When the PTP content was 40%, at the working temperature of 70℃, the hybrids showed the best sensitivity. The mechanism of the hs-SnO2/PTP hybrids to NO2 is probably the formation of p-n hereojunction. |
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