Electro-controlled angstrom-scale membrane channels and ion dehydration for tunable ion and molecule separations

Membranes with tunable, selective separation properties are promising candidates for complex water/wastewater treatment and sustainable resource recovery. However, conventional membranes with fixed structures lack pore/channel adjustability and separation adaptability, making it extremely challenging to achieve angstrom-scale tunable and selective separation. Here, we report an electro-controlled MXene@polyaniline-poly(styrenesulfonate) membrane that enables precise regulation of angstrom‑scale channels and ionic dehydration, thereby achieving selective separations of mono- and di-valent salts and organic molecules. Applying a negative bias (0 - 2.5 V, membrane cathode) induces Na⁺ to undergo dehydration and embed into the polyaniline network, causing polymer chain deformation and enabling tunable membrane channel size between 5.6 Å and 10.3 Å. This electro-regulation endows the membrane with permeation selectivities of 30.4 for NaCl/Na₂SO₄ and 216-904 for salt/dye and salt/antibiotic, while their retention selectivities reach 196-312, significantly outperforming previously reported membranes. Theoretical calculations and simulations reveal that NaCl/Na₂SO₄ separation arises primarily from the preferential dehydration and permeation of Cl^- over SO₄^2- at a pore size of 7.1 Å (1.5 V). In contrast, salt/molecule separation relies on molecular steric hindrance to retain large molecules and ionic dehydration to permit salt permeation at a larger pore size of 10.3 Å (2.5 V). This study provides new insights for the development of smart membranes for fine separation and resource-based water treatment.