Role of Structure in the Ammonia Uptake of Porous Polyionic Liquids

In this work, tunable NH3 uptake of polyionic liquids (PILs) are reported through regulating the size of the cross-linking agent R, the metallic anion M(II) (SCN)42–, where M are Co, Zn, and Cu, and the cationic polymer framework of PILs. Combined with NH3 uptake experiments, spectroscopic analysis, and DFT calculation, the NH3 uptake was proposed as the coordination with M(II) to generate M(NH3)n2+, where n = 6 when M = Co and n = 4 when M = Cu and Zn, which suggests that the NH3 capacity is dominated by the metal center for different coordinative numbers. The increase in the size of R benefits the high capacity of NH3 uptake for more metallic anions to be exchanged and promotes NH3 desorption for the enhancement of porosity of PILs; however, the oversize of R goes against porosity and NH3 desorption. There seems to be less effect of the cation on ammonia uptake, while the stable cationic polymer framework protects the PILs from collapse. Overall, the tunable porosity (surface area of 15.9–869.0 m2/g and total volume of pores of 0.011–0.695 cm3/g) and NH3 uptake properties (capacity of 11.6–20.1 mmol/g PIL) as well as feasible NH3 desorption of PILs are realized for the flexible structural design of PILs. Furthermore, the adsorbed H2O and SO2 on NH3 uptake of PVIm-R8-Co were investigated. The investigation in this work makes the role of the structure of PILs in ammonia uptake clearer and provides the designability of PILs for gas adsorption and other applications.