Deprotonated tannic acid regulating pyrrole polymerization to enhance nanofiltration performance for molecular separations under both aqueous and organic solvent environments

Nanofiltration with precise separation ability demonstrates the increasing importance in water treatment and high-value substance recycling compared with traditional energy-intensive separation technologies. Nevertheless, nanofiltration membranes still suffer from the permeance-selectivity "trade-off" issue. Herein, we designed the de novo nanofiltration membrane with enhanced separation performance by adopting deprotonated tannic acid (TA) as intermediate layer to tune pyrrole polymerizaiton for forming the polypyrrole selective layer. TA were coated followed by in-situ polymerization of pyrrole and they assembled based on the strong electrostatic and hydrogen bonding interaction. The deprotonation of phenolic hydroxyl groups in TA effectively regulated the polymerization process of pyrrole to obtain the synthesized nanofiltration membrane with the average pore diameter of 0.45 nm. The optimized nanofiltration membrane exhibited a 3.7-fold increase in permeance and almost complete rejection for various dyes with different molecular weights and charges, which breaks the permance-selectivity "trade-off". In addition, the synthesized membrane possessed the excellent structural stability even in polar organic solvent of tetrahydrofuran. Our new strategy for constructing high-performance nanofiltration membrane via intermediate-layer-tuned formation/polymerization of the selective layer can provide an alternative potential avenue to fabricate next-generation molecular separation membranes towards environmental remediation and resource recovery.