Amphoteric metal–organic framework subnanochannels with pH-tuneable cation and anion sieving properties

The construction of ion-selective channels and membranes has attracted substantial interest owing to their wide potential in metal ion recovery, energy conversion, wastewater treatment and sensing. Here, amphoteric metal–organic framework (MOF) subnanochannels (SNCs) were reported to achieve dual cation and anion sieving properties. The amphoteric MOFSNCs with both amino and carboxylic groups were synthesized by interfacial growth of mixed-ligand MOF crystals into polymer nanochannels. The amphoteric UiO-66-NH₂/COOH–SNCs exhibited excellent anion sieving properties (e.g., Br⁻/SO₄²⁻ selectivity of 40) under acidic conditions and cation sieving properties (e.g., K⁺/Mg²⁺ selectivity up to 100) under alkaline conditions. The anion/cation sieving properties varied depending on the pH of the solution. This work provides a new approach to manipulate the selectivity of ion channels and guide the choice of MOFs for different application scenarios.