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

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 C˭S. 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.