Induced interaction between polypyrrole and SO2 via molecular sieve 13X

Electrical conductivity sensitivity and interaction mechanisms between polypyrrole (Ppy)/molecular sieve 13X composites and CO2, CO, and SO2 were investigated. Polypyrrole was synthesized and composites were fabricated by dispersing zeolite particles into the Ppy matrix, followed by compression into a pellet form. Effects of zeolite concentration, cation type, and cation concentration were investigated. The electrical conductivity in air of Ppy doped with naphthalene-2-sulfonic acid (β) sodium salt increases monotonically with the doping level. There are negligible negative electrical conductivity responses of Ppy and its composites when exposed to CO2, and CO in contrast to definite positive responses towards SO2 in which the interaction is irreversible. Undoped Ppy and doped Ppy composites at 10% (v/v) of zeolite 13X content possess the highest sensitivity to SO2; beyond this volume fraction the sensitivity is reduced with increasing molecular sieve 13X content. The composites of unmodified 13X, with Na+ fully present within its cavity, give the highest electrical conductivity sensitivity towards SO2. The sensitivity of Ppy/13X composite to SO2 diminishes as the cation Na+ is exchanged to other alkali cations in this decreasing order: Cs+, K+, and Li+, in the opposite order to the binding energy between the gas and the cations. The sensitivity and interaction are also reduced with increasing amount of Li+ present.