Polypyrrole Modified with Macrocyclesfor the Detection of Aqueous Pollutantsand Carbon Membranes for theSeparation of Gases

The development of environmental technologies and their applications in aqueous and gaseous systems are essential in combating pollution. The formation and detailed characterisation of a polypyrrole (PPy) film modified with anionic macrocycles of either sulfonated-bcyclodextrin (sul-bCD) or sulfonated-calix[4]arene (sul-calix[4]) were carried out. These composite modified electrodes were used as electrochemical sensors for the detection of the harmful herbicide, paraquat. These polymer films were highly conducting and due to the immobilisation of the large anionic dopants within the PPy matrix they exhibited cation exchange behaviour on reduction. Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and constant potential amperometry (CPA) were the techniques employed to evaluate the sensitivity of PPy/sul-bCD and PPy/sul-calix[4] towards the redox states of MV2+, MV+ and MV0 of paraquat. A limit of detection of 1.28 ´ 10-5 mol dm-3 and 3.48 ´ 10-6 mol dm-3 for the reduction of MV2+ was evaluated using CPA for PPy/sul-bCD and PPy/sul-calix[4], respectively. Additional studies were carried out to probe the nature of the complex interaction between the macrocyclic structures of sul-bCD and sul-calix[4] and the analytes, paraquat and diquat. Electrochemical and spectroscopic techniques were used to quantify the association constant, Ka. The data obtained from these techniques was consistent with electrostatic interactions as the major driving force in complex formation. In the case of the sul-calix[4] system the magnitude of Ka was influenced by ionic strength. The Ka values decreased from 106 to 103 mol-1 dm3 for the complex of diquat and sul-calix[4] in the absence and presence of 0.1 mol dm-3 Na2SO4, respectively. Carbon molecular sieve membranes (CMSMs) were employed for the separation of gases. CMSMs displayed selective permeation of CO2 over N2 by a factor of 24.7:1.0. Reduction in the permeability of the membrane was observed with aging. This was restored using an electro-regeneration procedure.