Potential-induced reversible uptake/release of perchlorate from wastewater by polypyrrole@CoNi-layered double hydroxide modified electrode with proton-ligand effect.

In this study, CoNi-layered double hydroxide (CoNi-LDH) nanosheets coated conducting polypyrrole (PPy) nanowire was controllably fabricated on Pt plate or carbon cloth by using unipolar pulse electrodeposition (UPED) method and served as a novel electrochemically switched ion exchange (ESIX) hybrid film with proton-ligand effect for the removal of perchlorate anions (ClO4-). It is expected that the space among CoNi-LDH nanosheets of the shell could act as the reservoir for the anions while the PPy core serve as the potential-induced element for proton-ligand. The effects of pulse potential during film deposition and initial pH of the wastewater on the ClO4- removal performance of this core-shell hybrid film were investigated. It is found that ClO4- adsorption onto PPy@CoNi-LDH followed pseudo-second-order model, and the film fabricated with -1.5 V pulse potential showed an excellent performance for the rapid removal of ClO4- with a high selectivity, and the ClO4- adsorption quantity reached as high as 302 mg g-1. In a wide pH range (3-10), the hybrid film removed ClO4- efficiently. The proton-ligand effect in PPy@CoNi-LDH was proved by using XPS analysis and density functional theory. Such a PPy@CoNi-LDH hybrid core-shell film should be a potential electroactive material for the separation of ClO4- and other anions from wastewater.