Achieving selective transport of monovalent metal ions
with high
precision and permeability analogues to biological protein ion channels
has long been explored for fundamental research and various applications,
such as ion sieving, mineral extraction, and energy harvesting and
conversion. However, it still remains a significant challenge to construct
artificial nanofluidic devices to realize the trade-off effects between
selective ion transportation and high ion permeability. In this work,
we report a bioinspired functional micropipet with in situ growth
of crown ether-encapsulated metal–organic frameworks (MOFs)
inside the tip and realize selective transport of monovalent metal
ions. The functional ion-selective micropipet with sub-nanochannels
was constructed by the interfacial growth method with the formation
of composite MOFs consisting of ZIF-8 and 15-crown-5. The resulting
micropipet device exhibited obvious monovalent ion selectivity and
high flux of Li+ due to the synergistic effects of size
sieving in subnanoconfined space and specific coordination of 15-crown-5
toward Na+. The selectivity of Li+/Na+, Li+/K+, Li+/Ca2+, and
Li+/Mg2+ with 15-crown-5@ZIF-8-functionalized
micropipet reached 3.9, 5.2, 105.8, and 122.4, respectively, which
had an obvious enhancement compared to that with ZIF-8. Notably, the
ion flux of Li+ can reach up to 93.8 ± 3.6 mol h–1·m–2 that is much higher than
previously reported values. Furthermore, the functional micropipet
with 15-crown-5@ZIF-8 sub-nanochannels exhibited stable Li+ selectivity under various conditions, such as different ion concentrations,
pH values, and mixed ion solutions. This work not only provides new
opportunities for the development of MOF-based nanofluidic devices
for selective ion transport but also facilitates the promising practical
applications in lithium extraction from salt-like brines, sewage treatment,
and other related aspects.