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

Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl(3). The electrical conductivity response of the doped PPP (dPPP) towards CO, H(2) and NH(3) is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H(2)), but it shows a definite negative response towards NH(3). The electrical conductivity sensitivity of dPPP increases linearly with increasing NH(3) concentration. To improve the sensitivity of the sensor towards NH(3), 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(+), NH(4) (+) 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(+) < NH(4) (+) < 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 NH(3) adsorption and interaction with the conductive polymer.