Triazine-Tröger's Base framework membranes enabling ultra-fast H+ selectivity for acid recovery processes

Designing Ion-selective membranes (ISMs) with ultrafast H⁺ selectivity is highly challenging for efficiently recovering high-purity acids under harsh conditions. This challenge arises primarily because the channels of existing ISMs suitable for acid recovery tend to swell under high charged densities, resulting in reduced selectivity, despite high charge density being critical for achieving high acid flux. To address this, we developed a robust acid-recovery membrane based on a fully rigid skeletal framework of charged Tröger's Base (TB) polymer bearing triazine moieties. This TB polymer framework provides abundant rigid micropores, enabling efficient H⁺ recovery from mixed metal ion systems through confinement-dimensional sieving effects. Incorporation of triazine rings further regulates the chemical environment of the rigid channels, facilitating ultrafast proton transport. The resulting TB framework membrane exhibits exceptional acid-recovery performance, achieving an H⁺ dialysis coefficient of 22.80 × 10⁻³ m h⁻¹ and a selectivity of 7238, surpassing the commercial membrane DF-120 by 2.7-fold and 391.2-fold, respectively. The membrane also demonstrates outstanding durability under high-concentration acid (10 mol L⁻¹) and high-temperature (70 °C) conditions, making it highly suitable for practical applications. The membrane design strategy presented here may be further extended to develop advanced membrane materials for applications in electrochemical devices requiring precise ion selectivity.