Self-Repairing [MEDTA]2- functionalized poly(ionic liquid)s in the application of NH3 adsorption through reversible NH3 insertion

Abstract

MOFs have high adsorption performance of ammonia (NH3) because of its porosity and abundant coordination sites, especially MOFs containing carboxylic acid ligands have emerged as effect NH3 adsorbents. But, it’s troublous for reversible ammonia adsorption for the strong metal-NH3 coordination or the collapse of adsorbents. [MEDTA]2- is a very stable and classic carboxylic acid-containing complex, but there was no relevant report. Therefore, this work carried out the design and synthesis of PVIm-R8-MEDTA based on the use of the coordination structure of [MEDTA]2- and the stability of PILs’ skeleton. The characterization indicated the [MEDTA]2- could be introduced into PILs successfully for the hydrogen bonding interactions with the imidazolium cation, and the obtained PVIm-R8-MEDTA presented enhanced NH3 capacity (10.4–14.7 mmol/g) than their precursor PVIm-R8-Br (7.8 mmol/g). The mechanism of NH3 adsorption was proposed by DFT calculation, spectroscopic method, and the calorimetric test, it indicated the NH3 was fixed by imdazolium cation through hydrogen bonding and inserted into two of the carboxylate and metal bonds of [MEDTA]2-. Because of the multi-meshing coordination of [EDTA]4- and metal ions, the disconnected carboxylate ions could easily coordinate with metal ions again and repair the chelating structure of [MEDTA]2-, which caused the ammonia easily be desorbed. In the process of gas adsorption, there was no bonding breakage of the skeleton of PILs, which helped the PVIm-R8-MEDTA be recovered under moisture and NH3 atmosphere. Thanks for the designability of PILs, such as the cationic structure, structure and size of cross-linking agent, the choice of complex anion and so on, it provides a new design idea and theoretical basis for efficient and reversible ammonia adsorption materials.