Fabrication of Poly(p-Phenylene)/Zeolite Composites and Their Responses Towards Ammonia

Abstract: Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl₃. The electrical conductivity response of the doped PPP (dPPP) towards CO, H₂ and NH₃ is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H₂), but it shows a definite negative response towards NH₃. The electrical conductivity sensitivity of dPPP increases linearly with increasing NH₃ concentration. To improve the sensitivity of the sensor towards NH₃, ZSM-5 zeolite is added into the conductive polymer matrix. The electrical sensitivity of the sensor increases with increasing zeolite content up to 30%. The effect of the type of cation in the zeolite pores is investigated: namely, Na⁺, K⁺, NH₄⁺ and H⁺. The electrical conductivity sensitivity of the composites with different cations in the zeolite can be arranged in this order: K⁺ < no zeolite < Na⁺ < NH₄⁺ < H⁺. The variation in electrical sensitivity with cation type can be described in terms of the acid-base interaction, the zeolite pore size and surface area. The PPP/Zeolite composite with H⁺ possesses the highest electrical sensitivity of −0.36 since H⁺ has the highest acidity, the highest pore volume and surface area, which combine to induce a more favorable NH₃ adsorption and interaction with the conductive polymer.