Selective Transport Energy Barriers in Chitin-Assisted Polyamide Membranes for Efficient Cl^-/SO₄^2- Sieving

Nanofiltration (NF) technology is crucial in alleviating global water scarcity through desalination. Overcoming the permselectivity trade-off to improve both the permeance and rejection of polyamide (PA) nanofiltration (NF) membranes beyond the log-log upper bound remains a significant scientific challenge. Herein, we explored advanced ion-transport barriers by constructing a chitin-assisted PA NF membrane, incorporating a biomass-derived carboxylated chitin nanofiber (CO-ChNF) interlayer that simultaneously modulates the pore architecture and surface charge of the PA layer. CO-ChNFs, sustainably extracted from squid cartilage and featuring rich carboxyl and amino functionalities, effectively suppressed the diffusion kinetics of amine monomers during interfacial polymerization. The engineered CO-ChNF/PA membranes demonstrated a sharper pore size distribution and an enhanced charge density, providing an ideal platform to systematically investigate the mechanisms behind ion sieving at PA microinterfaces by exploring ion dehydration energy and electrostatic repulsion energy. Leveraging the enhanced transport barriers, the optimal CO-ChNF/PA membrane achieved impressive performances with a permeance of up to 31.4 L m^-2 h^-1 bar^-1 and a superior Cl^-/SO₄^2- selectivity of 91.3, surpassing most commercial and reported NF membranes. This work sheds light on the regulatory mechanism of the chitin-assisted interfacial polymerization reaction and introduces an innovative approach for efficient Cl^-/SO₄^2- sieving.