Study Of Gas Sensitivity Of Doped Polyaniline And Its Composite Materials

Gas sensor is a kind of important chemical sensors, which is widely used in many fields such as avigation and spaceflight, petrolic chemical industry, environment and foodstuff inspection. Gas-sensing materials are the center of gas sensor, but conventional gas-sensing materials(SnO₂,ZnO,Fe₂O₃ and so on)have some problems, such as bad selectivity, high work temperature and discontented stability, which have restricted the development and application of gas sensor. Compared with inorganic semiconductor materials, macromolecule gas-sensing materials(polypyrrole, polythiophene, polyaniline and so on)expand gas sensors'applied range ,as a result of their low cost, simple preparation and being used at room temperature ,which is the most important. The synthesis, gas-sensing properties, gas-sensing mechanism and some related matters of polyaniline had been researched in this thesis. The main contents were listed below:Aniline was oxidized by ammonium persulfate(APS) in acidic aqueous solutions for the synthesis of polyaniline by chemical oxidation polymerization. And then, the effect between different synthetical conditions and products' gas-sensing properties was researched, as a result, the polyaniline doped by acid had fine sensitivity to NH₃ at room temperature;The structure changes of polyaniline fore-and-aft doped by HCl acid were analysed by FT-IR and UV-Vis. At the same time, the thermal stability of polyaniline doped by different kinds of acid were tested by TG-DTA. The effect on gas-sensing properties of polyaniline doped by different kinds of acid was researched. As a result, compared with the polyaniline doped by HCl acid, the polyaniline doped by big molecule organic sulphonic acid had better environment stability, meanwhile, the sensitivity hightened with different degree, in which the polyaniline doped by sulfosalicylic acid(SSA)had the best effect as its sensitivity to 1000ppm NH₃ at room temperature is 16.By mechanical mixing method, the SSA-PAN/SnO₂ and SSA-PAN/In₂O₃ composite materials were prepared, and the processability of polyaniline was improved. The gas-sensing properties of composite materials were researched, and the result indicated that, for the SSA-PAN/SnO₂, the sensitivity heightened along with the increase content of SnO₂, moreover, when the content of SnO₂ was 50%, the material's sensitivity to 1000ppm NH₃ at room temperature was the highest as to25; for the SSA-PAN/In₂O₃, the sensitivity reduced along with the increase content of In₂O₃. Compared with the simplex polyaniline doped by SSA, the composite materials had better processability and environment stability.