Gas-sensing properties of organic sulfonic acid doped polyaniline

Through oxy-polymerization method, the polyaniline (PAn) was synthesized in acidic aqueous solution by using aniline as monomer and ammonium persulfate (APS) as oxidizer. With the help of FT-IR spectra and TG-DTA, the structural changes and the thermal stability of the polyanilines before and after doping were studied respectively. The results show that the dopants reduce the molecule chain decompose temperature of PAn, and the organic sulfonic acid doped PAn has better thermal stability than that of HCl doped PAn. The influence of the doped acid on the NH3 sensitivity of polyaniline was also investigated; the results reveal that the gas sensors based on organic sulfonic acid doped polyanilines have better gas sensitivity than that based on PAn-HCl; especially the sensitivity of PAn-SSA (PAn doped with 5-sulphosalicylic acid) to 1000 × 10-6 NH3 reaches 15.47, and its response time is less than 20 s, recovery time is less than 2 min. The long-term NH3 sensitivity of acid doped polyanilines were also investigated; combining with the analysis result of TG-DTA, it can be concluded that the organic acid doped polyanilines have better environmental stability than that of PAn-HCl.