Role of Structure in the Ammonia Uptake of Porous Polyionic Liquids

Abstract

In this work, tunable NH 3 uptake of polyionic liquids (PILs) are reported through regulating the size of the cross-linking agent R, the metallic anion M(II) (SCN) 4 2− , where M are Co, Zn, and Cu, and the cationic polymer framework of PILs. Combined with NH 3 uptake experiments, spectroscopic analysis, and DFT calculation, the NH 3 uptake was proposed as the coordination with M(II) to generate M(NH 3 ) n 2+ , where n = 6 when M = Co and n = 4 when M = Cu and Zn, which suggests that the NH 3 capacity is dominated by the metal center for different coordinative numbers. The increase in the size of R benefits the high capacity of NH 3 uptake for more metallic anions to be exchanged and promotes NH 3 desorption for the enhancement of porosity of PILs; however, the oversize of R goes against porosity and NH 3 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 m 2 /g and total volume of pores of 0.011−0.695 cm 3 /g) and NH 3 uptake properties (capacity of 11.6−20.1 mmol/g PIL) as well as feasible NH 3 desorption of PILs are realized for the flexible structural design of PILs. Furthermore, the adsorbed H 2 O and SO 2 on NH 3 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.

A Mini-Review on NH3 Separation Technologies: Recent Advances and Future Directions

“…They further studied the effects of crosslinking agent and metal ions on the adsorption of NH 3 by POPs in detail. 135 Being different from MOFs, in which the metal ions are connected in the major frameworks, the POPs mentioned above have the metal ions attached to the major frameworks. Therefore, the interaction of metal ions with NH 3 does not affect the major frameworks of POPs, and the POPs do not have the problems of framework collapse after NH 3 adsorption.…”

“…The hydrogen-bond interaction of C(2)–H in imidazolium cation with NH 3 , and coordination interaction of Co 2+ with NH 3 , benefit to the high NH 3 adsorption capacity of synthesized POPs. They further studied the effects of cross-linking agent and metal ions on the adsorption of NH 3 by POPs in detail . Being different from MOFs, in which the metal ions are connected in the major frameworks, the POPs mentioned above have the metal ions attached to the major frameworks.…”

“…Therefore, the interaction of metal ions with NH 3 does not affect the major frameworks of POPs, and the POPs do not have the problems of framework collapse after NH 3 adsorption Table summarizes the functional types and NH 3 adsorption capacities of representative POPs reported in the literature. − …”

Few-Layered Hexagonal Boron Nitrides as Highly Effective and Stable Solid Adsorbents for Ammonia Separation

“…Liquid absorbents need to be circulated in absorption and desorption towers, thus the practical application of ILs and DESs is greatly limited. Alternatively, zeolites, , activated carbons, , porous organic polymers, − and metal–organic frameworks − with intrinsic nanoporosity were investigated as solid adsorbents for NH 3 separation. They have large surface areas for contacting with NH 3 and can be functionalized with Lewis/Brønsted acidic , and open metal sites. ,,, Solid adsorbents are fixed in towers for successive adsorption and desorption and do not have the viscous issue-like liquid absorbents.…”

“…Alternatively, zeolites, , activated carbons, , porous organic polymers, − and metal–organic frameworks − with intrinsic nanoporosity were investigated as solid adsorbents for NH 3 separation. They have large surface areas for contacting with NH 3 and can be functionalized with Lewis/Brønsted acidic , and open metal sites. ,,, Solid adsorbents are fixed in towers for successive adsorption and desorption and do not have the viscous issue-like liquid absorbents. Therefore, special interest is directed toward the exploration of solid adsorbents for effective separation of NH 3 .…”