Preparation of ultrathin, robust membranes through reactive layer-by-layer (LbL) assembly for pervaporation dehydration

Fabricating ultrathin membranes with high separation performance and stability remains a great challenge. Tannic acid (TA) is a bio-based polyphenol and can form multifunctional coatings through catechol chemistry. In this study, polyethyleneimine (PEI) and TA were alternatively deposited on hydrolyzed polyacrylonitrile (HPAN) porous membrane via layer-by-layer (LbL) assembly driven by covalent interaction between the amine groups of PEI and polyphenols of TA. The LbL assembly process was verified by the step-wise change of water contact angles. The formation of covalent bond was confirmed by X-ray photoelectron spectroscopy (XPS). The free volume property of the membranes was revealed by the Doppler broadening energy spectra. The resultant membranes possessed ultrathin active layers with thicknesses ranging from 118 to 220 nm. When utilized for pervaporation dehydration of 90 wt% ethanol aqueous solution, the membrane exhibited high separation performance with permeation flux of 1343 g/m(2) h and separation factor of 1012 with 5.5 bilayers and pH 8 at 349 K, arising from the increased hydrophilicity and favorable free volume property. Moreover, the membrane showed favorable long-term stability due to the strong interfacial interactions.