Sr(II) and Ba(II) Alkaline Earth Metal–Organic Frameworks (AE-MOFs) for Selective Gas Adsorption, Energy Storage, and Environmental Application

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) / 1250 m2 g−1 (N2), and UPJS-16 does not adsorb mentioned gases. From the environmental application, the materials were studied as CO2 adsorbents, and both compounds adsorb CO2 with a maximum capacity of 22.4 wt.% @ 0 °C; 14.7 wt.% @ 20 °C and 101 kPa for UPJS-15 and 11.5 wt.% @ 0°C; 8.4 wt.% @ 20 °C and 101 kPa for UPJS-16. According to IAST calculations, UPJS-16 shows high selectivity (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 MTA linker. 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 °C and 101 kPa. The enhanced CO2/H2 selectivity could be used to scavenge carbon dioxide from hydrogen in WGS and DSR reactions. 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.

Molecular Modeling of Cu-, Ag-, and Au-Decorated Aluminum Nitride Nanotubes for Hydrogen Storage Application

“…The highest occupied molecular orbital (HOMO) is the outermost orbital containing electrons, which often acts as an electron donor, while the lowest unoccupied molecular orbital (LUMO), which is the innermost vacant orbital, always accepts the electrons donated by the HOMO; these two orbitals are the orbitals which make up the frontier molecular orbitals (FMOs). According to electronic studies and works of literature, the FMO study is a prerequisite factor in determining the electronic properties of a system .…”

Ideal Adsorbed Solution Theory (IAST) of Carbon Dioxide and Methane Adsorption Using Magnesium Gallate Metal-Organic Framework (Mg-gallate)

“…In this approach, the adsorbed phase is considered ideal without any interaction in the multicomponent system. Generally, IAST provides reliable predictions of the adsorption and selectivity of a gas mixture and has been used for various solid adsorbents such as zeolites, activated carbon and metal-organic frameworks (MOFs) [ 3 , 4 , 5 , 6 ]. Recently, MOFs are considered as emerging porous materials for gas adsorption and separation due to their large surface area and porosity, tunable structure and functionalities [ 7 ].…”

Alkoxy-Functionalized Hydroxamate/Zinc Metal–Organic Frameworks and the Effects of Substituents and Acid Addition on Their Structures

“…As shown in Figure b, a maximum CO 2 uptake of 63.4 cm 3 g –1 (12.5 wt %), which is higher than that of a previously reported Co-hydroxamate MOF (49.1 cm 3 g –1 , 9.6 wt %), was observed at 298 K and 100 kPa . This value is not as high as those of the reported benchmark MOFs, such as Mg-MOF-74 (27.5 wt.%), but higher than those of other important MOFs, such as ZIF-8 (4.3 wt.%) and MOF-5 (8.5 wt.%), and comparable to those of recently reported UPJS-16 (8.4 wt.% at 293 K) . The amount of CO 2 adsorption after 5 cycles under the same conditions was 66.2 cm 3 g –1 which the overall volume almost unchanged compared to the first cycle of the adsorption process (Figure S45).…”

“…34 This value is not as high as those of the reported benchmark MOFs, such as Mg-MOF-74 (27.5 wt.%), 45 but higher than those of other important MOFs, such as ZIF-8 (4.3 wt.%) 46 and MOF-5 (8.5 wt.%), 47 and comparable to those of recently reported UPJS-16 (8.4 wt.% at 293 K). 48 The amount of CO 2 adsorption after 5 cycles under the same conditions was 66.2 cm 3 g −1 which the overall volume almost unchanged compared to the first cycle of the adsorption process (Figure S45). The low-coverage isosteric heat of adsorption (Q st ) value of Zn-i PrOBDHA-III (33.5 kJ mol −1 ) is relatively high, but similar to that of a previously reported Co-hydroxamate MOF (34 kJ mol −1 ).…”