Ultramicroporous Tröger's Base Framework Membranes With Ionized Sub-nanochannels for Efficient Acid/Alkali Recovery

Abstract

Membrane technology holds significant potential for the recovery of acids and alkalis from industrial wastewater systems, with ion exchange membranes (IEMs) playing a crucial role in these applications. However, conventional IEMs are limited to separating only monovalent cations or anions, presenting a significant challenge in achieving concomitant H⁺/OH⁻ permselectivity for simultaneous acid and alkali recovery. To address this issue, the charged microporous polymer framework membranes are developed, featuring rigid Tröger's Base network chains constructed through a facile sol-gel process. The intrinsic ultramicropore confinement and quaternary ammonium-charged functional groups provide ultrahigh size-sieving capability and enhanced Donnan exclusion for H⁺/OH⁻ selectivity; meanwhile, the internal protoplasmic channels of the polymer frameworks serve as highways for rapid ion transfer. The resulting membrane achieves high H⁺/Fe²⁺ and OH⁻/WO₄²⁻ selectivities of 694.4 and 181.0, respectively, for concurrent acid and alkali separation in diffusion dialysis and electrodialysis processes over extended operational periods (exceeding 1600 and 600 h, respectively), while maintaining remarkable transport rates. These results outperform most literature-reported and nearly all commercially available membranes. This study validates the novel applicability of polymer framework materials with ionized angstrom-scale channels and versatile functionalities in high-performance IEMs for acid/alkali resource recovery.