Hyperfine adjustment of flexible pore-surface pockets enables smart recognition of gas size and quadrupole moment

Abstract

Continuous pore-size adjustments are achieved in a series of ultramicroporous MOFs, giving flexible pore-surface pockets for the smart recognition of highly similar gases and high gas separation/storage performances.

Fine pore engineering in a series of isoreticular metal-organic frameworks for efficient C2H2/CO2 separation

“…Among these SIFSIX-type materials, a flexible MOF [Zn(dps) 2 (SiF 6 )] (UTSA-300-Zn, SIFSIX-dps-Zn) was able to completely differentiate C 2 H 2 and CO 2 gas molecules. However, flexible MOFs usually show negligible gas uptake before gate-opening, which might lead to capture leakage when applied to the breakthrough separation of gas mixture 34 – 38 . In this context, flexible-robust MOFs with permanent small pores as well as specific binding sites have been employed to selective take up targeted gas molecules, whereas minimizing the co-adsorption of counterpart gases by tuning the gate-opening pressure, which has been demonstrated by [Cu(dps) 2 (SiF 6 )] (SIFSIX-dps-Cu) for size-exclusive adsorption of C 2 H 2 from C 2 H 4 39 .…”

Electrostatically Driven Selective Adsorption of Carbon Dioxide over Acetylene in an Ultramicroporous Material

“…Even for adsorbents with chemisorptive CO 2 ‐binding sites, there is still a significant C 2 H 2 adsorption with minor uptake difference comparing to CO 2 [13] . Motivated by the complementary electrostatic interaction for determining the binding orientation of a variety of biological molecular recognitions, like protein folding and substrate binding, [14] the dramatically different charge distributions of both gas molecules (opposite quadrupole moments, −13.4×10 −40 C m 2 for CO 2 and +20.5×10 −40 C m 2 for C 2 H 2 ) facilitate the applicability to exclusively recognize CO 2 or C 2 H 2 through similar mechanism [15] . However, in wide open pore space with size beyond those of both molecules, both CO 2 and C 2 H 2 can get their own optimal binding configurations in different orientations, making it impossible to differentiate them by their molecular charge distributions.…”

“…[13] Motivated by the complementary electrostatic interaction for determining the binding orientation of av ariety of biological molecular recognitions,like protein folding and substrate binding, [14] the dramatically different charge distributions of both gas molecules (opposite quadrupole moments, À13.4 10 À40 Cm 2 for CO 2 and + 20.5 10 À40 Cm 2 for C 2 H 2 )f acilitate the applicability to exclusively recognize CO 2 or C 2 H 2 through similar mechanism. [15] However,i nw ide open pore space with size beyond those of both molecules,b oth CO 2 and C 2 H 2 can get their own optimal binding configurations in different orientations,m aking it impossible to differentiate them by their molecular charge distributions.Inthis context, restricting the molecular orientations in the rigid confined space make the charge-distribution recognition become possible,w hereas charge distribution on the pore surface complementary to CO 2 can ensure the CO 2 -selective recognition. Ultramicroporous materials featuring compact pore space (close to the molecular size of CO 2 and C 2 H 2 )a nd positive charge distribution at both ends are thus targeted to maximize the inverse selectivity and sieving effect of CO 2 over C 2 H 2 .…”

Optimal Pore Chemistry in an Ultramicroporous Metal–Organic Framework for Benchmark Inverse CO2/C2H2 Separation

“…Notably, there is a huge difference in quadrupole moment between CO 2 (−13.4×10 −40 C m 2 ) [9] and C 2 H 2 (+20.5×10 −40 C m 2 , Figure S1), [2d, 10] enlightening us to judiciously tune the pore chemistry with inverse electrostatic potential to leverage the quadrupole moment difference between CO 2 and C 2 H 2 , thus leading to inverse CO 2 /C 2 H 2 separation. For this reason, the metal node in MOFs should be in a high oxidation state to withdraw the electrons from ligands, producing a more polar pore surface to recognize CO 2 molecules preferentially.…”