Smart pH-Responsive Covalent Organic Framework Membrane for Charge-Driven Molecular Sieving

Water
purification has been identified as a far-sighted measure
that benefits global sustainable development, and the purification
technology based on membrane separation has gradually become the main
strategy due to its virtue of low energy consumption, small footprint,
convenient operation, and high separation efficiency. In this work,
we have constructed 160 nm-thick robust self-standing COF membranes.
For the first time, the as-synthesized imine-linked COF membrane not
only exhibits intelligent optical pH stimuli-responsive performance
(its color turns from bright red to black immediately when being exposed
to acidic solutions and turns to light red after a few minutes of
exposure to alkaline solutions) but also overcomes the ecumenical
limitation of selective removal. The charge-driven molecular sieving
effects induced by acid/base endow them with preeminent screening
performance toward organic dyes whose dimensions are much smaller
than the membrane pores and in separating oppositely charged persistent
organic pollutants with analogical sizes. This work opens up a new
avenue for developing smart pH-responsive 2D COF membranes, exploring
the neoteric removal modes of organic compounds, and discovering more
potential intelligent applications of self-standing COF membranes
in various frontier domains and functional devices.