Sr(II) and Ba(II) Alkaline Earth Metal–Organic Frameworks (AE-MOFs) for Selective Gas Adsorption, Energy Storage, and Environmental Application
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Date
2023-01
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Abstract
Two new alkaline earth metal–organic frameworks (AE-MOFs) containing Sr(II) (UPJS-15)
or Ba(II) (UPJS-16) cations and extended tetrahedral linker (MTA) were synthesized and characterized
in detail (UPJS stands for University of Pavol Jozef Safarik). Single-crystal X-ray analysis (SC-XRD)
revealed that the materials are isostructural and, in their frameworks, one-dimensional channels
are present with the size of ~11 10 Å2. The activation process of the compounds was studied
by the combination of in situ heating infrared spectroscopy (IR), thermal analysis (TA) and in situ
high-energy powder X-ray diffraction (HE-PXRD), which confirmed the stability of compounds after
desolvation. The prepared compounds were investigated as adsorbents of different gases (Ar, N2,
CO2, and H2). Nitrogen and argon adsorption measurements showed that UPJS-15 has SBET area
of 1321 m2 g 1 (Ar)/1250m2 g 1 (N2),andUPJS-16 does not adsorb mentioned gases. From the
environmental application, the materials were studied as CO2 adsorbents, and both compounds
adsorb CO2 withamaximumcapacityof22.4wt.%@0 C;14.7wt.%@20 Cand101kPaforUPJS-15
and 11.5 wt.% @ 0C; 8.4 wt.% @ 20 C and 101 kPa for UPJS-16. According to IAST calculations,
UPJS-16 showshighselectivity (50 for CO2/N2 10:90 mixture and 455 for CO2/N2 50:50 mixture) and
can be applied as CO2 adsorbent from the atmosphere even at low pressures. The increased affinity
of materials for CO2 was also studied by DFT modelling, which revealed that the primary adsorption
sites are coordinatively unsaturated sites on metal ions, azo bonds, and phenyl rings within the
MTAlinker. Regarding energy storage, the materials were studied as hydrogen adsorbents, but the
materials showed low H2 adsorption properties: 0.19 wt.% for UPJS-15 and 0.04 wt.% for UPJS-16 @
196 Cand101kPa. Theenhanced CO2/H2 selectivity could be used to scavenge carbon dioxide
from hydrogen in WGS andDSRreactions. The second method of applying samples in the area of
energy storage was the use of UPJS-15 as an additive in a lithium-sulfur battery. Cyclic performance at a cycling rate of 0.2 C showed an initial discharge capacity of 337 mAh g 1, which decreased
smoothly to 235 mAh g 1 after 100 charge/discharge cycles.