| Electroactive ion exchange materials(EIXMs), such as inorganic metal hexacyanoferrates and organic conducting polymers, have attracted increasing interests owing to their unique properties. The charge and discharge of the EIXMs can be electrochemically controlled by external electric field or by redox agent while the charge balance can be compensated via the ion exchange with electrolyte solution. Based on this unique electrochemically switched ion exchange property and electrocatalytic activity, the EIXMs have been wildly used in energy storage devices, toxic ion separation recovery, environmental/biomedical sensors and other fields. Recently, in order to address the energy crisis and environment issue, considerable attentions have been given to develop the novel EIXMs for energy storage, environmental testing and wastewater treatment.Polypyrrole(PPy) film was fabricated on platinum substrate by a facile unipolar pulse electropolymerization(UPEP) method. Mechansim for the formation of highly stable PPy was proposed based on the chronoamperogram obtained during the polymerizaition process. Structure, surface morphology and hydrophilic property of the PPy film prepared using either UPEP method or potentiostatic method(PM) were characterized by Fourier transfer infrared spectroscopy(FT-IR), scanning electron microscopy(SEM) and contact angle goniometer, respectively. Electrochemical performances of PPy films prepared by UPEP and PM were compared using cyclic voltammetry(CV), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy(EIS) in 1.0 M of KCl solution. It is found that the PPy film prepared by UPEP method under the conditions of ultra short on-time pulse(10 ms) and low temperature(10.0 oC) showed an ordered structure with reduced chain defects and exhibited high specific capacitance and excellent cycling stability in neutral solution. The capacitance of such a PPy film electrode retained 93.6% of its initial value even after 50000 charge/discharge cycles. The specific capacitance of the UPEP PPy film reached 406.0 F/g at a scan rate of 5 mV/s when temperature, pulse potential, pulse time ratio(ton/toff) and pulse cycles were 10.0 oC, 0.7 V, 10 ms/100 ms and 12000, respectively.A facile UPEP technique is successfully applied for the preparation of ion-imprinted composite film composed of ferricyanide-embedded conductive polypyrrole(FCN/PPy) for the selective electrochemical removal of heavy metal ions in the wastewater. The imprinted heavy metal ions are found to be easily in-situ removed from the growing film only by tactfully applying potential oscillation due to the unstable coordination reaction of FCN to the imprinted ions. The obtained Ni2+ ion-imprinted FCN/PPy composite film shows fast uptake/release ability for the removal of Ni2+ ions from aqueous solution and the adsorption equilibrium time is less than 50 s. The ion exchange capacity reaches 1.298 mM/g and retains 93.5% of its initial value even after 1000 uptake/release cycles. The separation factors of 6.3, 5.6 and 6.2 for Ni2+/Ca2+, Ni2+/K+ and Ni2+/Na+ respectively are obtained. These characteristics are attributed to the high identification capability of ion-imprinted composite film for the target ions and the dual driving forces resulted from both PPy and FCN during the redox process. It is expected that the present method can be used for simple preparation of other ion-imprinted composite films for the separation and recovery of the target heavy metal ions as well.A novel electroactive trivalent yttrium ions imprinted polymer film composed of FCN/PPy is fabricated by using a facile UPEP method. The imprinted Y3+ ions can be removed in situ from the growing film by tactfully inducing potential oscillation on the film electrode based on the electric repulsion. CV measurements combined with Electrochemical Quartz Crystal Microbalance(EQCM) are applied to characterize quantitatively the electrochemical uptake/release process of Y3+ ions in various electroactive ions imprinted polymer films(E-IIPs), including non-ion, divalent nickel ion and trivalent yttrium ion imprinted FCN/PPy composite films. It is found that the reversible uptake/release of Y3+ ions can be realized by simply regulating the operating potential applied to the Y3+ ions imprinted composite film electrode in aqueous solution of 0.1 mol/L Y(NO3)3 due to the unique Y3+ ion identification capability of ion imprinted cavity and the dual driving forces resulting from both PPy and FCN. From the electrode mass change of different E-IIPs, one can speculate that parts of bound water molecules around the hydrated Y3+ ions could move into the E-IIPs with the ions adsorption process. Two distinct stages, the adsorption of Y3+ ions at the surface layer of E-IIPs and the transport of adsorbed ions to inner layer of E-IIPs, should be involved in the adsorption process of Y3+ ions into the E-IIPs. For hydrated Y3+ ions adsorbed electrochemically into the surface layer of Ni2+-imprinted and Y3+-imprinted FCN/PPy composite films, the numbers of bound water molecules with Y3+ ions are estimated to be 1 and 4.6, respectively. It suggests that the Y3+ ion exchange performance in E-IIPs significantly depends on the size of ion cavity and the stereochemistry of binding sites.In view of the rapid expansion of worldwide lithium battery market, the research for Li recovery has attracted wide attention. An electroactive hybrid film composed of the spinel manganese oxide, polypyrrole and polystyrenesulfonate(HMn2O4/PPy/PSS) was successfully fabricated by using a facile one-step unipolar pulse electrodeposition technique. This film was used for recovery of Li+ ions from seawater via an electrochemically switched ion exchange(ESIX) technique. The ion exchange capacity and selectivity of hybrid film for Li+, K+, Na+, Mg+, and Ca+ ions were characterized by using the electrochemical quartz crystal microbalance(EQCM). The obtained HMn2O4/PPy/PSS hybrid film shows higher electrochemical adsorption capacity and selectivity for Li+ ions than other metal ions. |
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