Microporous membrane with ionized sub-nanochannels enabling highly selective monovalent and divalent anion separation.

Membranes tailored for selective ion transport represent a promising avenue toward enhancing sustainability across various fields including water treatment, resource recovery, and energy conversion and storage. While nanochannels formed by polymers of intrinsic microporosity (PIM) offer a compelling solution with their uniform and durable nanometer-sized pores, their effectiveness is hindered by limited interactions between ions and nanochannel. Herein, we introduce the randomly twisted V-shaped structure of Tröger's Base unit and quaternary ammonium groups to construct ionized sub-nanochannel with a window size of 5.89-6.54 Å between anion hydration and Stokes diameter, which enhanced the dehydrated monovalent ion transport. Combining the size sieving and electrostatic interaction effects, sub-nanochannel membranes achieved exceptional ion selectivity of 106 for Cl-/CO32- and 82 for Cl-/SO42-, significantly surpassing the state-of-the-art membranes. This work provides an efficient template for creating functionalized sub-nanometer channels in PIM membranes, and paves the way for the development of precise ion separation applications.

Removing miscellaneous heavy metals by all-in-one ion exchange-nanofiltration membrane.

The composition of wastewater containing heavy metal mixtures is often complex and poses a serious threat to human and environmental health. Effective removal of a variety of heavy metal ions with a single technology is challenging, and the conventional split integrated technologies require multi-step processing and a massive footprint. For the first time, we achieve hierarchically integrating ion exchange and nanofiltration into all-in-one "iNF" membranes. The iNF membrane has a hierarchical structure with an interfacial polymerization layer and an ion exchange layer, which can achieve highly efficient indiscriminate heavy metal ion removal, overcoming the defect that traditional nanofiltration membranes can only remove single metal cations or oxyanions. The ion exchange layer can remove heavy metal ions through sulfonic acid groups and quaternary amine groups. In addition, the ion exchange layer can be regenerated by electro-deionization, which is meaningful for sustainable membrane usage. This facile, scalable, and compact integrated process shows outstanding potential and universal applicability in complex wastewater treatment.