Versatile Platform of Ion Conducting 2D Anionic Germanate Covalent Organic Frameworks with Potential for Capturing Toxic Acidic Gases

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.