Preparation And Ammonia-sensitive Properties Study Of Polyaniline And Its Composite Materials

Polyaniline was used widely in gas sensor owing to its exceptional properties as a conducting polymer. The purpose of this work was that preparing excellent capability of polyaniline and its composite materials. Synthetising technological parameters and gas-sensitive characteristic were studied in the interview of deeply understanding of current circumstances at home and abroad.Through Chemical oxidative polymerization method, doped polyaniline was synthetised in different acidic aqueous solution by using aniline as monomer and ammonium persulfate as oxidizer. Eigenstated polyaniline was prepared by anti-doping process. Polyaniline presoma method in Sol-Gel process was employed to prepare polyaniline/nano-SnO₂ composite materials. Finally, their thin film elements were obtained by dip-coating technique.Structure of polyaniline and its composite materials was characterised using XRD, Raman, FT-IR and so on. SEM was applied to illustrate surface appearance of polyaniline and its composite materials. Their thermal properties was analysed by TG-DSC.Sensing character of thin film elements to ammonia was detected using static distribution method at room temperature. The effect of synthetising technological parameters and molar ratio of tin oxide and aniline on sensing character of thin film elements were investigated. The text have also studied variation of gas sensitivity of different thin film elements with the improving of ammonia concentration and long-time stability of sensor.The results show that eigenstated polyaniline present formLess state and particle distribution is loose, but doped polyaniline has the orientation order and certain crystallinity, particles piling up appear"rock". The main parts are doped with quinoid formula nitrogen atoms, instead of benzene nitrogen atoms. Polyaniline possessing preferably gas sensitivity is got on condition that the concentration of aninline is 0.2 mol/L, acid concentration is 0.3 mol/L, molar ratio of ammonium persulfate and aniline is 1, and keep 5 hours reaction. Sensitivity of organic acid doped polyaniline higher than inorganic acid doped polyaniline, and environmental stability is also better. With regard to composite materials, diffraction peak of polyaniline gradually lower with the increasing of molar ratio of tin oxide and aniline, and reunions of composite materials lighten. Gas sensitivity of composite materials appear decrease-increase-decrease with the improving of molar ratio of tin oxide and aniline. The best sensitivity gets 16.0 when molar ratio of tin oxide and aniline is 0.8. The sensitivities of composite thin films increase with improving of ammonia concentration, and it also have preferably sensitivity to low concentration.