Construction
of nanofluidic devices with an ultimate ion selectivity
analogue to biological ion channels has been of great interest for
their versatile applications in energy harvesting and conversion,
mineral extraction, and ion separation. Herein, we report a three-dimensional
(3D) sub-1 nm nanofluidic device to achieve high monovalent metal
ion selectivity and conductivity. The 3D nanofluidic channel is constructed
by assembly of a carboxyl-functionalized metal–organic framework
(MOF, UiO-66-COOH) crystals with subnanometer pores into an ethanediamine-functionalized
polymer nanochannel via a nanoconfined interfacial
growth method. The 3D UiO-66-COOH nanofluidic channel achieves an
ultrahigh K+/Mg2+ selectivity up to 1554.9,
and the corresponding K+ conductivity is one to three orders
of magnitude higher than that in bulk. Drift-diffusion experiments
of the nanofluidic channel further reveal an ultrahigh charge selectivity
(K+/Cl–) up to 112.1, as verified by
the high K/Cl content ratio in UiO-66-COOH. The high metal ion selectivity
is attributed to the size-exclusion, charge selectivity, and ion binding
of the negatively charged MOF channels. This work will inspire the
design of diverse MOF-based nanofluidic devices for ultimate ion separation
and energy conversion.
Two metal−organic framework (MOF) materials, that is, α-cyclodextrin (α-CD)-MOF-Na and α-CD-MOF-K, were successfully synthesized and exhibited excellent adsorption capacity and storage stability for ethylene gas. The ethylene encapsulation capacity of α-CD-MOF-Na and α-CD-MOF-K reached 47.4 and 52.9% (w/w), respectively, which was significantly higher than those of other materials reported such as α-CD and V-type starch. The release characteristics of ethylene inclusion complexes (ICs) were determined under different temperatures and relative humidity conditions. The ethylene gas could be stably encapsulated in α-CD-MOF-ethylene ICs at 25 °C for up to 30 days. The crystal structure of α-CD-MOFs was determined to explain their high capacity and stability for ethylene storage. Molecular simulation was used to model the location of ethylene molecules in α-CD-MOFs. Alpha-CD-MOF-Na and α-CD-MOF-K showed "8"-shaped and spindle-shaped cavity, respectively, which effectively adsorbed and stored the ethylene gas. Accelerated ripening experiments showed that 5 mg of α-CD-MOF ICs could ripen bananas within 4 days, with an effect similar to that of free ethylene gas. We suggest that α-CD-MOF materials are an excellent material for ethylene storage with potential application in industrial and agricultural areas.
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