Electrically Switched Ion Exchange Based on Carbon-Polypyrrole Composite Smart Materials for the Removal of ReO₄^– from Aqueous Solutions

A simple and rapid process of ReO4- (as a surrogate of TcO4-) removal from aqueous solutions based on the electrically switched ion exchange (ESIX) method has been demonstrated in this work. Activated carbon-Polypyrrole (AC-PPy) was synthesized from activated carbon and pyrrole by electrodeposition method which was served as an electrically switched ion exchanger for ReO4- removal. The characterization results show that the AC-PPy composite exhibited an excellent loading capacity and a high stability for ions uptake and release. Chronoamperometric studies show that the ESIX treatment could be completed within 60 s, demonstrating the rapid uptake and release of ions. Uptake and release of ReO4- was verified by electrochemical quartz crystal microbalance with dissipation shift (EQCMD) studies. By modulating the electrochemical potential of the AC-PPy, the uptake and release of ReO4- ions can be controlled. Similar trends of uptake and release of ReO4- were observed in cyclic voltammetry (-0.4 to 0.8 V) for five cycles with the EQCMD. X-ray photoelectron spectroscopy (XPS) confirmed the process of ReO4- removal in the AC-PPy composite. Conclusively, the smart material shows excellent efficiency and selectivity for the removal of ReO4- from aqueous solutions.