Dispersing LiCl in Zwitterionic COF for Highly Efficient Ammonia Storage and Separation

Abstract

Efficient and inherently safe NH₃ storage and separation are of significant importance for the chemical industry. Herein, we proposed zwitterionic COF as a porous host to disperse LiCl for highly efficient NH₃ storage and separation with record adsorption capacity. The equivalently cationic and anionic groups in the channels of zwitterionic COF could act as two separated sites to facilitate the dispersion of LiCl, hence the optimal composite exhibits a high capture capacity of 44.98 mmol/g at 25 °C and 1 bar, far exceeding other existing porous materials. Notably, the adsorption capacity is completely reversible and the efficient separation of NH₃ from NH₃ /CO₂ /N₂ mixture is achieved through breakthrough experiments. DFT calculation combined with XPS and ⁷ Li NMR experimental results give insight into the interaction between zwitterionic COF and LiCl. This work extends possibilities for the development of efficient adsorbents for NH₃ storage and separation.

Keywords: NH3 storage and separation; covalent organic frameworks; dispersion of metal halide; zwitterionic material.