Insights into ion imprinted membrane with a delayed permeation mechanism for enhancing Cd2+ selective separation

Highlights: • IIM possesses specific host-guest sites and recognized more Cd²⁺ than NIM. • The Cd²⁺ bind ability is ascribed to the coordination of functional monomer. • Structure predetermination of Cd²⁺ plays a vital role in forming sites. • Delayed permeation of IIM can selective separate Cd²⁺ from other ions. • DFT calculation expound the delayed permeation mechanism from molecular level. Ion imprinted polymers exhibit great potential in ion separation from wastewater. However, the difficulty of ion separation by membrane is proverbial, which severely restricts the application of membrane in metal resource recovery from industrial wastewater. Herein, a rational molecular-level design approaches for membrane fabrication was developed to modify a layer of ion imprinted polymer onto the PVDF membrane. Batch rebind and permeation experiments suggest that specific host-guest binding sites had been fabricated along the membrane pore in ion imprinted membranes (IIM). A higher monomer dose leads to a higher rejection of Cd²⁺, and the more bind sites in IIM. The binding of IIM to Cd²⁺ was 1.84 times that of non-ion imprinted membranes (NIM). Permselectivity factors (γ) of IIM are larger than 5.39 in mixture ions solutions. Chemical characterization and density functional theory (DFT) calculation reveal that the Cd²⁺ recognition sites of functional groups are C−S and CS. Cd²⁺ mass transport in IIM suggest that the imprint effects provide a binding force that would delay Cd²⁺ to permeate through IIM, so as to selectively separate Cd²⁺ with other ions. The imprint effects may enlighten a novel molecular-level design approaches for membrane fabrication to enhance the selectivity of ion-ion.