Precise regulating the hierarchical structure of MCPMs for mono/multivalent ions separation

Surface modification is a promising strategy to prepare monovalent cation perm-selective membranes (MCPMs) that can offer improved perm-selectivity with a slight increase in membrane resistance. Herein, we have developed MCPMs by precisely regulating the hierarchical structure through the auto-mixing of two different polymers (chloromethylated polyethersulfone (CMPES) and sulfonated polyphenylsulfone (SPPSU)) and controlling the electrochemical properties of the top modified layer. In analogy to the penetrating glue, a semi-permeable selective functional layer can be drawn between the supporting membrane and the functional layer in terms of the spreading and solvent evaporation process. With further cross-linking and quaternization, the excess aldehyde groups (CHO) in the functional layer of the membrane can be transformed into -COO- groups in the presence of an alkaline medium. Thus, an electric-double structure was formed. The synergy of the semi-permeable and electric-double hierarchical structure in the MCPMs enables accurate mono/multivalent ion separation during ED-based separation processes.