Electrical conductivity response of poly(p-phenylene)/ZSM-5 composite

Poly(p-phenylene) (PPP) was chemically synthesized via the oxidative polymerization of benzene and doped with FeCl₃. Electrical conductivity response of doped PPP (dPPP) towards CO, H₂ and NH₃ was investigated. dPPP shows no response towards CO and H₂, but it shows a definite negative response to NH₃. The electrical conductivity sensitivity of dPPP increases with increasing NH₃ concentration. In order to improve sensitivity of the sensor, ZSM-5 zeolite is added into the conductive polymer matrix. The sensitivity of the sensor increases with increasing zeolite content up to 30%. Moreover, the effect of cation type residing in the zeolite pore is investigated: including Na⁺, K⁺, NH₄ ⁺ and H⁺. The electrical conductivity sensitivity of the composites with different cations in the zeolite can be arranged in this order; 50:1 dPPP(90)/KZ23 <50:1 dPPP<50:1 dPPP(90)/NaZ23<50:1 dPPP(90)/NH₄Z23<50:1 dPPP(90)/HZ23. The variation in sensitivity with cation type can be described in term of the acid-base interaction. The 50:1 dPPP(90)/HZ23 possesses the highest sensitivity of -0.36 since H⁺ has the highest acidity which induces more favorable NH₃ adsorption and interaction with the conductive polymer.