Polypyrrole ion exchange capacity and its potential application in water purification

摘要

The redox processes of conductive polymers, e.g. polypyrrole (PPy), are accompanied by the exchange of ions (absorption or desorption). This ion exchange ability was used to develop an electrochemically switched ion exchange resins for water treatment and purification. Compared with traditional ion exchange resin, ion exchange property of PPy is advantageous in that there is no secondary pollution caused by consumption of acids or basic solutions. The ion exchange process can be accurately controlled. This can be used for recovering heavy metal or noble metal from aqueous solutions, and for water purification and/or softening. Polypyrrole films doped with dodecylbenzenesulfonate (PPy/DBS) as doping anion were electrochemically prepared from aqueous solution on Pt electrode and active carbon fibre (ACF), respectively. PPy/DBS film prepared on ACF is thick, has larger mass quantity and bigger surface area, that effectively enhances ion exchange capacity of PPy/DBS. The morphology of ACF/PPy/DBS film was characterized using scanning electron microscope (SEM). The ion exchange behaviour and capacity were studied using cyclic voltammetry (CV) and atomic adsorption spectroscopy (AAS). It was found that, for various cations, the order of exchange ability is K + > Na + > Ca 2+ > Mg 2+ for PPy/DBS film formed on Pt electrode. The ion exchange capacity of the PPy/DBS film formed on ACF was calculated to be 1.16 mmol/g and 0.41 mmol/g for Na + and Ca 2+ , respectively. Absorption capacity of cation increased with the decrease of the cathodic polarization potential, but when cathodic polarization potential was less than -0.8V, absorption capacity of cation increased slowly. Desorption capacity of cation was not influenced by the anodic polarization potential.