Fig. 4: The simultaneous fractionation and enantioseparation performance in a model protein hydrolysate system.

a Schematic of the cascade membrane process for enriching D-threonine from a model of protein hydrolysis system containing threonine, leucine, tyrosine and phenylalanine. Stage 1 separates amino acids with larger molecular dimensions and L-form, while Stage 2 enriches D-threonine. Figure 4a was created using BioRender.com. b The composition percentages of the model protein hydrolysis system used as feed solution. Separation performance of the D-TAH COF membranes for the model feed with Stage 1 (c) and Stage 2 (d). Error bars represent the SDs based on three independent tests.