A homochiral covalent organic framework membrane for the enantioseparation and fractionation of amino acids

The separation of amino acids from complex mixtures remains an essential yet multi-step, energy-intensive process. Membrane separation technology offers a more energy-efficient alternative, but its effectiveness relies on achieving highly precise molecular recognition. Here, we report a homochiral covalent organic framework (COF) membrane with ordered ultra-microporous pore structures for targeted extraction of specific enantiomer from amino acid mixtures. Benefiting from its high crystallinity and ultra-microporous chiral channels, the membrane exhibits both excellent permeability and enantioselectivity. A combination of experimental results, density functional theory calculations, and molecular dynamics simulations reveal a retarded transport mechanism, wherein stronger interactions between L-enantiomers and the homochiral pores hinder their transmembrane diffusion. We further demonstrate a two-stage cascade membrane process to simultaneously fractionate and enantioseparate amino acid mixtures, achieving near pure (99.5%) D-threonine from an eight-component protein hydrolysis complex. This study offers a promising and sustainable membrane-based solution for efficient amino acid purification.