Preparation And Characterization Of Polyaniline Composite Film Gas Sensors

Gas sensor is a kind of important chemical sensors, which is widely used in many fields such as aviation and spaceflight, petrolic and chemical industry, environment and foodstuff inspection. Gas-sensing materials are the center of gas sensor. Comparing with the conventional gas-sensing materials(TiO₂,SnO₂,ZnO and so on), macromolecular gas-sensing materials(polypyrrole, polythiophne, polyaniline and so on)expand the application range of gas sensors, due to their low cost, simple preparation and being used at room temperature. In comparision with other conjugate polymers, PANI is cheaper, which is easily polymerized, with high conductivity and a broad prospect for application. However, because of the rigid nature of its chain backbone, PANI is difficult to dissolve and melt. It is difficult to be put into practical application. The PANI composites are widely used in a lot of fields such as optic field, electronical field, magnetic field, sensitive field and so on, because it not only has small size effect, surface effect and quantum effect of the nano-particles, but also has advantage of macromoclecule. Aiming at solving the problem mentioned above, the thesis contained two sections as follows:First, PANI and PANI/TiO₂ thin films were prepared by in-situ chemical oxidation polymerization and electrostatic self-assembly combined technique. The films were characterized by scanning electron microcopy (SEM), UV-Vis absorption spectrum and FTIR. At the same time, the sensitivity of the PANI and PANI/TiO₂ film sensors to toxic gase NH₃ were tested. The results showed that the PANI/TiO₂ film sensor had a better charateristic than PANI film sensor in sensitivity and its response-recovery time was shorter than PANI film sensor. Then the effect of proton acid dopants on the PANI/TiO₂ composite thin films was studied. PANI/TiO_<sub>2 composite thin film doped by HCl and PTSA were prepared in the same method. SEM, UV-Vis absorption spectrum and the sensitive properties of sensors to NH₃ were studied. The results showed that the sensitivity, response and recovery characteristic of PANI/TiO₂ composite thin film doped by HCl were superior to that of PANI/TiO₂ composite thin film doped by PTSA, whereas both of the sensors were bad in stability. And the effect of various polymerization temperatures on the sensors was studied. As a result, it showed that the sensor made under 10℃had the best sensitivity and the shortest response and recovery time.Second, SnO₂ was chosen as the dopant. PANI/SnO₂ and PANI/SnO₂-TTAB gas sensors were made in the same method. SEM, UV-Vis absorption spectrum and FTIR were used to characterize the composite films. Through the analysis of the sensitivity to NH₃ and the response and recovery time, PANI/SnO₂-TTAB gas sensor had the higher sensitivity, and its response and recovery time improves a lot.