Unravelling gas sorption in the aluminum metal‐organic framework CAU‐23: CO₂, H₂, CH₄, SO₂sorption isotherms, enthalpy of adsorption and mixed‐adsorptive calculations

Abstract

The report is the first broader evaluation of the gas sorption properties of CAU-23 for the adsorptives CO 2 , H 2 , CH 4 , and SO 2 . CAU-23 is of intermediate porosity among Al-MOFs with specific BET surface areas of the order of MIL-100 > MIL-53 > CAU-23 > MIL-160 > MIL-53-TDC > Alfum > CAU-10-H and total pore volumes of the order of MIL-100 > MIL-53 > CAU-23 > Alfum = MIL-160 > MIL-53-TDC > CAU-10-H. CO 2 uptake (3.97 mmol g À 1 , 293 K) and H 2 uptake (10.25 mmol g À 1 , 77 K) of CAU-23 are second in the series and only slightly smaller than for MIL-160. The CH 4 uptake of CAU-23 (0.89 mmol g À 1 , 293 K) is unremarkable in comparison with the other Al-MOFs. The SO 2 uptake (8.4 mmol g À 1 , 293 K) follows the porosity and higher SO 2 uptakes were only observed for MIL-53 and MIL-100. CAU-23 is one of the best Al-MOFs for high-pressure sorption of CO 2 , with an uptake of 33 wt.-% at 20 bar, 293 K. Gas sorption measurements at two different temperatures gave near zero-coverage enthalpy of adsorptions, ~Hads 0 for CO 2 of À 22 kJ mol À 1 and of SO 2 for À 38 kJ mol À 1 which is at the low end of the other Al-MOFs (À 22 to À 39 kJ mol À 1 for CO 2 ; À 41 to À 51 kJ mol À 1 for SO 2 ), yet ~Hads increases for CAU-23 with CO 2 and SO 2 to À 25 and À 57 kJ mol À 1 , respectively. For CO 2 /CH 4 and SO 2 /CO 2 separation, ideal adsorbed solution theory (IAST) predicted gas selectivities of 5 and 27-50 (depending on molar ratio and model), respectively, in line with 4.5-6.3 and 17-50, respectively, with most of the other Al-MOFs, where only MIL-53-TDC with 83 and MIL-160 with 126 gave a higher SO 2 /CO 2 selectivity at a molar ratio of 0.5.

Enhanced sorption in an indium-acetylenedicarboxylate metal–organic framework with unexpected chains of cis-μ-OH-connected {InO6} octahedra

“…The CH 4 adsorption capacity of HHUD-4 at 293 K is 0.72 mmol g −1 , which is an increase of about 29% compared to that of In-fum (0.56 mmol g −1 ), thus bringing HHUD-4 into the range of the above-mentioned Al-MOFs (0.57–1.14 mmol g −1 ). 31,61,62 In contrast to the maximum uptake both HHUD-4 and In-fum show a significantly higher Q 0 st for CH 4 of about 26 and 30 kJ mol −1 than MIL-53, Al-fum, MIL-160, CAU-23 and CAU-10-H (8–16 kJ mol −1 ), 31,62 indicating attractive interactions between the In-based MOFs and CH 4 . The kinetic diameter of CH 4 is 3.8 Å.…”

“…The CO 2 uptake of HHUD-4 is also comparable to that of the structurally related Al-MOFs MIL-53 (2.11 mmol g −1 ), CAU-10-H (2.76 mmol g −1 ) and Al-fum (2.52 mmol g −1 ) but lower than that of MIL-160 (4.22 mmol g −1 ) and CAU-23 (3.97 mmol g −1 ). 31,57 The high CO 2 uptake of HHUD-4 in comparison with In-fum illustrates the advantageous role of the C–C triple bond for CO 2 adsorption. The isosteric heat of adsorption for HHUD-4 and In-fum was calculated from the isotherms obtained at 273 and 293 K (Fig.…”

“…Dalton Transactions fraction of 0.5, respectively. An IAST selectivity of 6.9 with HHUD-4 for CO 2 /CH 4 separation is also better than that of Alfum (4.5, 273 K), 64 CAU-23 (5.3, 293 K), 31 MIL-160 (6, 295 K) 65 and MIL-53 (6.3, 298 K). 66 The H 2 adsorption capacity at 77 K and 1 bar is 10% higher for HHUD-4 with 6.36 mmol g −1 than for In-fum (5.78 mmol g −1 ).…”

“…19,20,24,25 The MOFs Al-MIL-53, MIL-160, CAU-10-H and CAU-23 are frequently investigated for their properties such as structural flexibility, 26 sensing and selective separation of volatile organic compounds like xylene, [27][28][29] high thermal and water stability with high water uptake and promising gas sorption properties with high uptakes for H 2 , CO 2 and SO 2 and potential for the separation of gases. 25,30,31 Herein we present the successful synthesis and characterization of a new In-adc MOF, named HHUD-4 which shows cis-µ-OH connected {InO 6 } octahedra, unexpected for linear ligands.…”

“…The MOFs Al-MIL-53, MIL-160, CAU-10-H and CAU-23 are frequently investigated for their properties such as structural flexibility, 26 sensing and selective separation of volatile organic compounds like xylene, 27–29 high thermal and water stability with high water uptake and promising gas sorption properties with high uptakes for H 2 , CO 2 and SO 2 and potential for the separation of gases. 25,30,31…”