TFC membrane with in-situ crosslinked ultrathin chitosan layer for efficient water/ethanol separation enabled by multiple supramolecular interactions

Abstract

Chitosan (CS) membranes have been widely applied in water/ethanol separation via membrane-based pervaporation, but a bottleneck in the practical application always exists due to their severe swelling behavior in aqueous solution and consequently low permeation flux due to the large membrane thickness. Here, thin film composite (TFC) hollow fiber (HF) membrane with an in-situ-crosslinked ultrathin CS selective layer is developed via multiple supramolecular interaction-crosslinking strategy for efficient water/ethanol separation via pervaporation. With Fe³⁺-phytic acid (PhA) complex pre-deposited on the substrate, the subsequently introduced CS selective layer is in-situ crosslinked via multiple supramolecular interactions, including coordination, electrostatic, and hydrogen bonding interactions. By varying the cycle number of Fe³⁺/PhA assembly and the species of employed organophosphorus acid, the anti-swelling properties of the resultant TFC CS membrane is enhanced and the separation performance is maximized. The optimal TFC-CS-Fe₂PhA₂ membrane with two cycles of Fe³⁺/PhA assembly has a selective layer thickness of 60 ​nm and a corresponding ultrahigh flux of 2.87 ​kg/m² h, coupled with a permeate water concentration of 99.5 ​wt% and good long-term stability for the dehydration of 85 ​wt% ethanol aqueous solution at 50 ​°C. The supramolecular interaction-crosslinking presented in this work provides an efficient and promising strategy for the construction of TFC CS membrane with excellent anti-swelling property and superior separation performance.