Constructing ultra-permeable pillar[5]arene-based membrane with intramolecular water channels and precise molecular fractionation

Abstract

Designing membranes with synthetic water channels has become an emerging topic to overcome the ubiquitous selectivity/permeability trade-off effect. In this study novel ultra-permeable thin film composite membranes with precise molecular fractionation were successfully fabricated. Per-hydroxylated pillar [5]arene (P [5]A), a macrocycle with a highly regular, cylindrical, angstrom-scale intramolecular cavity was applied as the aqueous monomer in interfacial polymerization (IP) to construct water channels in a thin film composite membrane. The competing effects of esterification and alkali-induced hydrolysis during IP were validated by investigating the effect of fabrication conditions. With almost complete rejection of model dyes >99.0% (e.g., Congo Red & Direct Red 23) and low retention of salts (e.g., 4.5% for NaCl & 18.9% for Na2SO4), the optimal membrane exhibited an ultra-high water permeance up to 267.1 L m−2 h−1 bar−1, which is 3–10 times higher than most literature-reported membranes for similar applications. Also, the precision of dye/salt fractionation of the membrane was not affected by the increased feed salinity, with overall stable performance in 72 h continuous operation. A high flux recovery of >94.5% proved that the membrane had low fouling propensity. Overall, the new route explored in this study provided inspiration for designing ultra-permeable membranes with precise molecular separation for environmental applications.