Substituent Engineering-Enabled Structural Rigidification and Performance Improvement for C₂/CO₂ Separation in Three Isoreticular Coordination Frameworks

Abstract

Construction of porous solid materials applied to the adsorptive removal of CO 2 from C 2 hydrocarbons is highly demanded thanks to the important role C 2 hydrocarbons play in the chemical industry but quite challenging owing to the similar physical parameters between C 2 hydrocarbons and CO 2 . In particular, the development of synthetic strategies to simultaneously enhance the uptake capacity and adsorption selectivity is very difficult due to the trade-off effect frequently existing between both of them. In this work, a combination of the dicopper paddlewheel unit and 4-pyridylisophthalate derivatives bearing different substituents afforded an isoreticular family of coordination framework compounds as a platform. Their adsorption properties toward C 2 hydrocarbons and CO 2 were systematically investigated, and subsequent IAST and density functional theory calculations combined with column breakthrough experiments verified their promising potential for C 2 /CO 2 separations. Furthermore, the substituent engineering endowed the resulting compounds with simultaneous enhancement of uptake capacity and adsorption selectivity and thus better C 2 /CO 2 separation performance compared to their parent compound. The substituent introduction not only mitigated the framework distortion via fixing the ligand conformation for establishment of better permanent porosity required for gas adsorption but also polarized the framework surface for host−guest interaction improvement, thus resulting in enhanced separation performance.

Optimized Pore Nanospace through the Construction of a Cagelike Metal–Organic Framework for CO2/N2 Separation

“…Recently, nonthermal-driven adsorption and separation technology based on porous solid materials has presented great potential in the CCS field due to its cost and energy efficiency, high capture capacity, and high selectivity. − In this respect, metal–organic frameworks (MOFs) have shown tremendous potential for CCS as a result of their structural diversity, function tunability, and high surface area. − Up to now, a great deal of effort has been devoted to improving the CO 2 uptake capacity and separation performance from flue gas via various crystal engineering strategies, in which pore-nanospace engineering represents an effective protocol for CCS achieved by tuning the pore size, volume, shape, and surface. − Generally, a MOF with a small pore size usually shows a high CO 2 selective adsorption performance but adversely leads to a low capture capacity, whereas a high pore volume can bestow the MOF with high uptake capacity but might reduce the adsorptive selectivity. , Therefore, engineering a MOF nanospace with the characteristics of small pore size and large pore volume might be an effective approach for achieving the trade-off between the adsorptive selectivity and uptake capacity, which can be accomplished through the construction of a cagelike MOF featuring a small window size and a large cavity. − Additionally, the window shape and internal cavity environment also play an important role in the selective adsorption process. In this regard, Feng, Zhou, and other groups have made pioneering contributions, demonstrating that pore-nanospace engineering via the construction of a cagelike MOF with suitable pore size/volume/shape/surface is an effective method to enhance the selective adsorption performance. − However, the elaborate design of a cage-based MOF with the appropriate pore volume/surface and precise window size falling between CO 2 and N 2 remains highly challenging.…”

Creating an Ethane Trap in a Ketone-Decorated MOF for One-Step Ethylene Separation from C2 Hydrocarbons

“…The BET surface area and Langmuir surface area of NTUniv-63 were evaluated to be ∼518 m 2 g –1 and 565 m 2 g –1 , respectively. The BET values were higher than those of ZJNU-130 (228/251 m 2 g –1 ), and were lower than those of ZJNU-132 (753/811 m 2 g –1 ), ZJNU-133 (790 and 839 m 2 g –1 ), ZJNU-140 (1051 and 1193 m 2 g –1 ) . In addition, a pore-size distribution ranging from 4 Å to 6 Å (Figure a) could be derived from the adsorption isotherm of the CO 2 at 195 K, based on the Horvath–Kawazoe model, which agreed well with the crystal structure.…”

Exquisitely Constructing a Robust MOF with Dual Pore Sizes for Efficient CO2 Capture

“…For instance, Mg-MOF-74 [12,13], with abundant OMS, reached a dramatic capacity of 8.0 mmol/g at 1 bar, 296 K. However, this MOF suffers from high Q st value and vulnerability to moisture as a side-effect of the introduced OMS. Besides the above-mentioned strategies, molecular sieving through crystal engineering strategies on MOF, particularly for pore engineering by tuning the pore size, volume, shape, and surface, provides as an alternative way with a low Q st value [14][15][16][17][18][19][20][21][22]. Generally, a MOF with a confined pore size (<4 Å) usually exhibits high selectivity but low adsorption capacity, while an expanded pore size (>4 Å) usually shows high adsorption capacity but low selectivity [19].…”