Preparation And Selective Separation Of Zn²⁺and Cl^- By Electroactive Composite Films Based On Ion Imprinted And Aperture Effect

Electrochemically switched ion exchange（ESIX）technique switches the uptake/release of ions in solution by adjusting the oxidation/reduction state of the electroactive ion exchange materials（EIXMs）.Although EIXMs has been used to separate ions from wastewater,the selectivity of target ions needs to be further improved.Therefore,the development of new electroactive materials with selectivity is the focus of our current research field.In this paper,selective electroactive materials are prepared by ion imprinted method and the selectivity of target ions is improved by using aperture effect of nanometer materials.Based on the two points,selective hybrid composite films are prepared for the electrochemical separation of zinc ions and chloride ions in wastewater.Although zinc ions are essential trace elements in human body,they are toxic and carcinogenic in excess of standard limits.For the separation of zinc ions in wastewater,the zinc ion imprinted 8-hydroxyquinoline/polypyrrole（8-HQ/PPy）composite film is successfully prepared by using the unipolar pulse electropolymerization（UPEP）method on the carbon cloth substrate.Based on ESIX method,the ion imprinted film is used to selectively separate zinc ions in the aqueous solution.The zinc ion adsorption kinetics is studied in a batch experiment due to the specific recognition of ion imprinted composite film toward zinc ion.The kinetics data of zinc ions adsorption by the imprinted composite film fits well with the pseudo-first-order kinetic model.As a result,when the adsorption potential and initial concentration are-1.2 V and 25 ppm respectively,the ion exchange capacity of the imprinted composite film for zinc ions reaches at 145.6 mg g^-1.In addition,the separation factors（α）are 2.6 and2.3 of the imprinted composite film for the Zn²⁺comparing with Co²⁺and Ni²⁺,which is attributed to the specific recognition ability of the imprinted composite film for zinc ions.It is expected that the imprinted composite film prepared by the described method can be used for the separation target metal ions.Wastewater containing high chloride ions is discharged without control,which makes ecosystem and human health threaten.For the removal of chloride ions,the nanometer electroactive materials（UIO-66^PPy-Cl）with PPy-Cl and UIO-66 are prepared by soaking method,and are used as film electrode to investigate the electrochemical activity,ion exchange performance and the adsorption performance of halogen chloride ions in aqueous solution.It shows that UIO-66^PPy-Cl film electrode has a good ion exchange behavior for chlorine ions based on its pore characteristics and the interaction between metal sites and negatively charged chlorine ions.The removal rate of chlorine ions at the initial concentrations of 50 ppm and 100 ppm by UIO-66^PPy-Cl composite film can reach over 90%under a certain current,indicating that the film electrode has a good removal effect on chlorine ions.Meanwhile,in the mixed solution containing chloride ion and iodide ion,UIO-66^PPy-Cl composite film has a good selectivity to chloride ions,and its distribution coefficients are 4.6 L g^-1 and 1.0 L g^-1,respectively.Therefore,the composite film is expected to be widely used in the removal of chloride ions.