Anionic
covalent organic framework is an emerging class of functional
materials in which included ionic species of the opposite charges
play an important role in the ion conduction and selective gas adsorption.
Herein, we reported a facile method to construct a series of germanate-based
anionic COFs (Ge-COFs) by reticulating dianionic hexa-coordinated
GeO6 nodes with anthracene building blocks adopting a hcb topology in an extended 2D framework. A systematic change
of pore properties in Ge-COFs was observed through the incorporation
of three different alkali metal cations: Li+, Na+, and K+. The intrinsically negatively charged backbone
provides a host matrix with a homogeneous distribution of counter
cations and poses variable and exciting features for gas adsorption
and ionic conduction. Among the series, K+-based Ge-COF-K
with a surface area of 1252 m2/g and pore volume of 0.84
cm3/g shows a maximum CO2 uptake of 126 cm3/g (247.4 mg/g) at 273 K and 1 bar, an IAST selectivity of
140 over N2. Ge-COF-K also exhibits a high SO2 kinetic breakthrough capacity of 154 mg/g at low ppm of SO2 concentration under ambient conditions among recently reported porous
materials. Moreover, reasonably high lithium, sodium, and potassium
ionic conductivities were observed with the values of 1.2 × 10–4, 3.4 × 10–5, and 2.2 ×
10–5 S/cm for propylene carbonate infiltrated Ge-COF-Li,
Ge-COF-Na, and Ge-COF-K at 100 °C, respectively.
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