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

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.