Design of polypyrrole layer enhanced MIL-88B(Fe) composite electrode material for electrosorption separation of copper ions

Abstract

Recycling copper ions from wastewater is critical for sustainable development of resources and the environment. Faraday materials present significant advantages for the capture and recycling of copper ions in an electric field; however, challenges such as severe self-aggregation of the electrode materials and the degradation of active substances due to the Jahn–Teller effect during charge–discharge cycles impede practical application. This study introduces an in situ polymerization technique for coating iron-based metal–organic framework (MOF) surfaces with a polypyrrole (PPy) layer to form the composite electrode material MIL@PPy. The optimized conductive PPy layer mitigates interfacial interactions between compound particles, reducing self-aggregation of the composite; and alleviates structural distortion during ion intercalation/deintercalation, significantly ameliorating iron dissolution in the material. The electron vacancy-rich conductive PPy molecular chains stably chelate with copper ions, locally creating DNA-like molecular strips for ion storage across the electrode surface, enhancing the copper ion adsorption capacity of MIL@PPy-1 (228 mg/g). Mixed ion tests demonstrated the good Cu adsorption affinity of MIL@PPy-1 (distribution coefficient K_d = 7440.29 mL/g). The mechanism of electrosorption process was explained by density functional theory calculations. This work harnesses the complementary strengths of MOFs and conductive polymers to design composite capacitive deionization materials for selective copper recovery from water.