Bottleneck Effect of N,N-Dimethylformamide in InOF-1: Increasing CO₂ Capture in Porous Coordination Polymers

Abstract

The bottleneck effect of confined N,N-dimethylformamide (DMF) molecules was observed in InOF-1 for the first time: CO capture was remarkably enhanced in samples of as-synthesized InOF-1, thermally activated in such a way that a small residual amount of DMF molecules remained confined within the pores (DMF@InOF-1). Dynamic CO adsorption experiments on DMF@InOF-1 exhibited a CO capture of 8.06 wt % [1.5-fold higher than that of a fully activated InOF-1 (5.24%)]. DMF@InOF-1 can reversibly adsorb/desorb 8.09% CO with no loss of CO capacity after 10 cycles, and the desorption is accomplished by only turning the CO flow off. Static CO adsorption experiments (at 196 K) demonstrated a 1.4-fold CO capture increase (from 5.5 mmol·g, fully activated InOF-1, to 7.5 mmol·g, DMF@InOF-1). Therefore, these CO capture properties are the result of the presence of residual-confined DMF molecules within the InOF-1 framework and their interactions via a very strong hydrogen bond with the In(μ-OH) groups, which prevent DMF leaching. The stability of this hydrogen bond is given by a perfect fit of the DMF molecule in the "dent" around the OH group that allows a nearly ideal orientation of the DMF molecule towards the OH group.

Confined toluene within InOF-1: CO2capture enhancement

“…S3, ESI †), resulting in a DH ads ¼ À46.81 kJ mol À1 . The DH ads value was higher than the molar enthalpy of vaporisation for toluene (DH vap ¼ 38.01 kJ mol À1 ), which is consistent with previously reported 25,26,28 values for other conned solvents in the same material, InOF-1 and within the range of previously reported MOFs with toluene sorptive capability. 36…”

“…We are know corroborating these ndings in studies with other small aromatic systems, such as benzene, and its effect on the adsorption of other substances like SO 2 , which will be published in future works. These computational analyses and DRIFTs experiments provided us a better understanding on the connement of small amounts of toluene within InOF-1 (intermolecular interactions), and evidenced a partial obstruction of the pores (similar to other polar molecules like H 2 O, EtOH, MeOH and DMF) which provided a "bottleneck effect" and a synergic effect between toluene and InOF-1, as we previously reported, 17,24,25,28 to enhance the CO 2 capture in InOF-1.…”

“…The inuence of the functionalisation of InOF-1 with toluene in the CO 2 capture can be rationalised in two ways: a "bottleneck" 17,24,25,28 effect, and simultaneous toluene/CO 2 and InOF-1/CO 2 interactions. The former implies a reduction in the pore size, caused by the presence of the adsorbed toluene molecules, that forces the CO 2 molecules to slow down, enhancing in this way its adsorption.…”

“…22 InOF-1 is a water-stable microporous MOF material, which is constructed from a exible BPTC (biphenyl-3,3 0 ,5,5 0 -tetracarboxylate) and based on a binuclear [In 2 (m 2 -OH)] building block. 23 Sequestration of CO 2 in InOF-1 has previously been demonstrated under anhydrous conditions and with the preadsorption (connement of small amounts) of different polar molecules, [24][25][26][27][28] resulting in the increase on the total CO 2 capture. In all these examples the hydrogen bond between these polar molecules and the hydroxo functional group, showed to be the dominant intermolecular interaction to enhance the CO 2 uptake.…”

Bottleneck Effect Explained by Le Bail Refinements: Structure Transformation of Mg-CUK-1 by Confining H2O Molecules

“…When there is one hydrogen-bonded H 2 O molecule per unit cell, the pore-window is reduced to approximately 4.43 Å and the distance between two water molecules increases to 20.5 Å (Table 1). This can provide enough free space for the CO 2 molecules to diffuse within the pore-window and, as we previously reported, a "bottleneck effect" occurs [16,17]. This effect is expected to accommodate the CO 2 molecules more efficiently, by partially obstructing the pore-windows of Mg-CUK-1.…”