Functionalized carbon nanotube-quantum dot thin film nanocomposite membrane for separation of β-substituted-α-amino acid enantiomers

This work introduces a novel thin-film nanocomposite membrane, designed for highly efficient chiral separation, utilizing functionalized Multi-walled Carbon Nantubes (COOH-MWCNTs) and carbon quantum dots (CQDs). Fabricated via interfacial polymerization on a polysulfone support embedded with COOH-MWCNTs, the membrane was evaluated for its ability to separate racemic mixtures of 3,4-dihydroxyphenylalanine, tryptophan, threonine, tyrosine, and 1-methyltryptophan. The optimized membrane composition was found to be 3 % COOH-MWCNTs and 2 % CQDs in 4 bar operating pressure, feed concentrations at 10 mmol·L⁻¹, and temperature at 35 °C, under which an enantiomeric excess (%ee) was achieved as 99 % for L-tryptophan in the permeate side, the highest among the five tested racemic mixtures. This enhanced separation performance is driven by the synergistic role of COOH-MWCNTs in the support layer and the precise interactions between CQDs and D-tryptophan in the active layer. Additionally, the membrane exhibited excellent long-term stability and antifouling properties, ensuring sustained performance over ten permeation cycles. The membrane's outstanding enantioselectivity, mechanical robustness, and durability represent a significant breakthrough in chiral separation technologies.