A Water-Stable Twofold Interpenetrating Microporous MOF for Selective CO2 Adsorption and Separation

Article abstract of DOI:10.1021/acs.inorgchem.7b02136

Self-assembly of bent dicarboxylate linker 4,4′-sulfonyldibenzoic acid (H₂SDB) and flexible N,N-donor spacer 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L) with Co(NO₃)₂·6H₂O forms a twofold interpenetrated {[Co₂(SDB)₂(L)]·(H₂O)₄·(DMF)}_n, (IITKGP-6) network via solvothermal synthesis with SQL(2,6L1) topology, which is characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, powder X-ray diffraction (XRD), and single-crystal XRD. The framework is microporous with a solvent-accessible volume of 25.5% and forms a one-dimensional channel along [1-1 0] direction with the dimensions of -3.4 × 5.0 ?². As the stability of metal-organic frameworks (MOFs) in the presence of water is a topic of significant importance while considering them for practical applications, this framework reveals its high stability toward water. The desolvated framework shows modest uptake of CO₂ (50.6 and 37.4 cm³ g^-1 at 273 and 295 K under 1 bar pressure, respectively), with high selectivity over N₂ and CH₄. Ideal adsorbed solution theory calculations show that the selectivity values of CO₂/N₂ (15:85) are 51.3 at 273 K and 42.8 at 295 K, whereas CO₂/CH₄ (50:50) selectivity values are 36 at 273 K and 5.1 at 295 K under 100 kPa. The high CO₂ separation selectivity over N₂ and CH₄ along with its water stability makes this MOF a potential candidate for CO₂ separation from flue gas mixture and landfill gas mixture as well.

Full text of DOI:10.1021/acs.inorgchem.7b02136

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX
A Water-Stable Twofold Interpenetrating Microporous MOF for
Selective CO2 Adsorption and Separation
Arun Pal, Santanu Chand, and Madhab C. Das*
Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, WB, India
S
* Supporting Information
ABSTRACT: Self-assembly of bent dicarboxylate linker 4,4′-sulfonyldiben-
zoic acid (H2SDB) and flexible N,N-donor spacer 1,4-bis(4-pyridyl)-2,3-diaza-
1,3-butadiene (L) with Co(NO3)2·6H2O forms a twofold interpenetrated
{[Co2(SDB)2(L)]·(H2O)4·(DMF)}n, (IITKGP-6) network via solvothermal
synthesis with sql(2,6L1) topology, which is characterized by Fourier
transform infrared spectroscopy, thermogravimetric analysis, elemental
analysis, powder X-ray diffraction (XRD), and single-crystal XRD. The
framework is microporous with a solvent-accessible volume of 25.5% and
forms a one-dimensional channel along [1−1 0] direction with the dimensions
of ∼3.4 × 5.0 Å2. As the stability of metal−organic frameworks (MOFs) in the
presence of water is a topic of significant importance while considering them
for practical applications, this framework reveals its high stability toward water.
The desolvated framework shows modest uptake of CO2 (50.6 and 37.4 cm3 g−1 at 273 and 295 K under 1 bar pressure,
respectively), with high selectivity over N2 and CH4. Ideal adsorbed solution theory calculations show that the selectivity values
of CO2/N2 (15:85) are 51.3 at 273 K and 42.8 at 295 K, whereas CO2/CH4 (50:50) selectivity values are 36 at 273 K and 5.1 at
295 K under 100 kPa. The high CO2 separation selectivity over N2 and CH4 along with its water stability makes this MOF a
potential candidate for CO2 separation from flue gas mixture and landfill gas mixture as well.
those materials for their stability in water.10 Sadly, many
reported MOFs are water-unstable except for some examples of
imidazolate-based zeolitic imidazolate frameworks (ZIFs),
INTRODUCTION
■
The benefits in simple construction and structural inves-
tigations of metal−organic frameworks (MOFs) have mani-
Materials of Institut Lavoisier based on the trivalent metal
festly decreased during the past several years; however, research
ions, zirconium(IV)-based MOFs, and a few more.10c In
interest in extending MOF applications1 is rapidly increasing in
diverse fields such as gas storage,1b,2 gas separation,1b,3 proton
general, MOFs ligated with N-coordination exhibit better
conduction,4 drug delivery,5 catalysis,6 sensing,7 photolumines-
stability toward water, as the basicity of those ligands are higher
than their carboxylate counterparts.11 While comparing the
cence,8 and many others9 due to their permanent porosity,
traditional hydrophobic adsorbents such as activated carbons
and zeolites to their MOF counterparts, the easily hydrolyzable
nature of metal−carboxylate bonds along with high suscepti-
bility of coordinatively unsaturated metal nodes toward water
flexible pore surface, fine-tuning pore size, and extra-high
surface areas. While considering new porous materials including
MOFs for practical applications, in particular, adsorption-based
gas separation and purification systems, the stability of an
adsorbent in humid environments is a serious issue that must
be taken into account with the obvious high adsorption
loadings and selectivities for the target gas molecule, as water is
are the main deterrents of MOF materials for successful
implementations in practical applications.10a
Several factors such as adsorption energy of CO2, the
framework polarity, and shape/size of the pores determine the
omnipresent in various industrial streams. For example, water is
aforementioned selectivities.12 Additionally, the separation
a major component of flue gas (CO2/N2 = 15/85) of coal-fired
power plants and must not be ignored while examining the
potential of adsorbent materials for CO2 capture and separation
from flue gas stream. Purification of landfill gas (CO2/CH4 =
selectivity can be controlled by modifying the network
structures thorough immobilization of different polar function-
ality onto the pore surface.13 Hence, the introduction of polar
parts like open metal sites or direct incorporation of polar
50/50) also needs to deal with varying amount of water content
functionality on the framework backbone is a very useful
during separation process by adsorbent materials. Obviously,
practice to improve adsorption selectivity for CO2 with a large
hydrostability of the MOF-based adsorbent will be a serious
quadrupole moment.12 For example, existence of a polar group
issue for successful implementation in carbon capture
technology, as the material may degrade over time because of
like H2O onto the pore surface of an MOF can have significant
lack of stability in the presence of water. Although much has
been studied on porous MOFs for their above-mentioned
diverse applications, less focus has been made to investigate
Received: August 18, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02136
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FT-IR spectra (KBr pellets) were recorded on a PerkinElmer RX1
spectrophotometer. Powder X-ray diffraction (PXRD) data were
collected (Cu Kα radiation of 1.5418 Å) on a Bruker D8 Advance
diffactometer. Thermogravimetric analysis (TGA) was executed with a
TG 209 F3 Tarsus (Netzsch), and the sample was heated from room
impact on CO2 adsorption and separation properties as
demonstrated by Chen et al.14 Additionally, by taking
advantage of Lewis acidic nature of CO2 itself, the selectivity
for CO2 adsorption can also be enhanced by judicious selection
of N-rich spacers such as hydrazine derivatives of N,N donor
spacers for enhanced interactions with CO2. Keeping those
facts in mind, we designed our MOF bearing a −SO2 polar
functionality on a V-shaped organic linker and N-rich sites on a
linear spacer for enhanced interactions of CO2 molecules with
excellent separation selectivity toward CO2/N2 and CO2/CH4.
To this end, we report a water-stable twofold inter-
penetrating MOF, {[Co2(SDB)2(L)]·(H2O)4·(DMF)}n,
(IITKGP-6, IITKGP stands for Indian Institute of Technology
Kharagpur), constructed by 4,4′-sulfonyldibenzoic acid
(H2SDB), flexible N,N-donor linear spacer 1,4-bis(4-pyridyl)-
2,3-diaza-1,3-butadiene (L) and Co(NO3)2·6H2O. This frame-
work has polar functionality exposed toward the channel along
[1−1 0] direction and unbound N-sites on the spacer. Gas
sorption analysis of the desolvated IITKGP-6a shows modest
uptake of CO2 (50.6 and 37.4 cm3 g−1 at 273 and 295 K,
respectively) under 1 bar pressure with good selectivity over N2
and CH4. IAST calculations based on dual-site Langmuir−
Freundlich fittings of single component isotherms indicate that
the selectivity values of CO2/N2 (15:85) are 51.3 at 273 K and
42.8 at 295 K and that the selectivity values of CO2/CH4
(50:50) are 36 at 273 K and 5.1 at 295 K under 100 kPa, which
makes this MOF a potential contender for separation of flue gas
and purification of landfill gas mixture.
temperature to 800 °C at 5 °C min−1 rate under N2 gas flow. 1H, 13
C
NMR spectrum was recorded using a Bruker Avance II 400
spectrometer. Mass spectrum was obtained using a Bruker MALDI-
TOF/TOF spectrometer. Gas sorption experiments were performed
using a Micromeritics 3-Flex Surface Characterization Analyzer (with
micropore ports) at different temperatures. All the guest solvents in
the framework were exchanged with dry chloroform at least 10 times
within 3 d, and the framework was evacuated at 373 K for 12 h until an
outgas rate of 5 μmHg min−1 was achieved. The measurement
temperatures for sorption isotherms at 273 and 295 K were
maintained with an ice−water bath and water bath, respectively.
Single Crystal X-ray Diffraction. The cell parameters and
refinement data are collected in Table S1 (Supporting Information).
Particular bond lengths and angles are listed in Table S2. A suitable
size single crystal protected with mineral oil was mounted on a fiber
glass tip and cemented using epoxy resin. Bruker SMART APEX II
CCD diffractometer equipped with graphite-monochromated Mo Kα
radiation (λ = 0.710 73 Å) is used for data collection at 298 K. The
structure was solved by direct method (SIR97),16 and the data were
refined using full-matrix least-squares technique on F2 (WINGX,
v2014.1) and SHELXL-2014.17 Riding model was used to place all H
atoms in calculated positions with fixed isotropic displacement
parameters. Highly disordered solvent molecules could not be
modeled with certainty, and thus, SQUEEZE/PLATON18 is used to
generate a new set of F2 (hkl) values without solvent contributions,
which was used for further refinements of the structure. CCDC
1569337 contains the full crystallographic data with embedded hkl, res,
and SQUEEZE files.
EXPERIMENTAL SECTION
■
Materials. Co(NO3)2·6H2O (Merck India), pyridine-4-carboxalde-
hyde (Alfa Aesar), 4,4′-sulfonyldibenzoic acid (H2SDB; Sigma-
Aldrich), hydrazine hydrate (Merck), and organic solvents (dime-
thylformamide (DMF), chloroform) were used without additional
purification.
RESULTS AND DISCUSSION
■
The reaction of bent dicarboxylate linker 4,4′-sulfonyldibenzoic
acid (H2SDB) and flexible N,N-donor spacer 1,4-bis(4-
pyridyl)-2,3-diaza-1,3-butadiene (L) with Co(NO3)2·6H2O
under solvothermal condition gave reddish crystal of
IITKGP-6. The molecular formula was established as
{[Co2(SDB)2(L)]·(H2O)4·(DMF)}n by the combination of
elemental analysis, TGA, and single-crystal XRD. The result of
single-crystal X-ray analysis revealed that it crystallizes in a
Synthesis of 1,4-Bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L).
This ligand was synthesized according to a literature report.15 To a 30
mL dry ethanol solution of pyridine-4-carboxaldehyde (3.79 mL, 40
mmol), hydrazine hydrate (0.97 mL, 20 mmol) was added dropwise
and was allowed to stir for 24 h under nitrogen. The yellow product
that appeared as precipitate was filtered, washed with hexane/ethanol
1
triclinic crystal system, with a space group of P1, and the
̅
(1:1, 20 mL), and treated under vacuum. Yield: 90%. H NMR (400
MHz, CDCl3, ppm): δ 8.70 (d, 4H), 8.50 (s, 2H), 7.64 (d, 4H). 13C
NMR (100 MHz, CDCl3, ppm): δ 123.84, 142.29, 152.32, 162.13.
Mass (matrix-assisted laser desorption/ionization time of flight
(MALDI-TOF)): m/z 211.495 (M+1). Fourier transform infrared
(FT-IR; KBr, cm−1): 1624.8(s), 1590.8(m), 1553.5(m), 1414(s),
1339.5(w), 1308.5(s), 1237.2(s), 1209.3(w), 1082.2(s), 973(s),
955.01(s), 877.5(s), 815.5(s), 744.19(s), 716.28(s), 679.1(s),
508.53(s).
{[Co2(SDB)2(L)]·(H2O)4·(DMF)}n, IITKGP-6. Co(NO3)2·6H2O (0.1
mmol, 0.0291 g), H2SDB (0.1 mmol, 0.031 g), and L (0.1 mmol, 0.021
g) were dissolved in 5 mL of DMF and kept in a 15 mL Teflon-lined
stainless steel container. This was heated to 110 °C for 2 d and
allowed to cool to room temperature over a period of 12 h. Reddish
crystals were obtained in 75% yield. Elemental analysis for
C43H41Co2N5O17S2, Calcd: C, 47.71%; H, 3.79%; N, 6.47%; S,
5.92%. Found: C, 47.39%; H, 3.71%; N, 6.52%; S, 5.83%. FT-IR
(cm−1): 3443.0(b), 3094.2(w), 3069.8(w), 2930.2(m), 2850.0(w),
1681.4(s), 1632.6(s), 1566.3(s), 1489.5(m), 1409.3(s), 1329.1(m),
1297.7(s), 1252.3(w), 1227.9(w), 1165.1(s), 1140.7(s), 1102.3(s),
1064.0(w), 1015.1(s), 948.8(w), 868.6(m), 847.7(m), 826.7(m),
781.4(s), 743.0(s), 722.1(s), 694.2(s), 662.8(w), 617.4(s), 586.1(m),
512.8(s), 443.0(m).
asymmetric unit contains two Co(II) ions, one L spacer, and
two SDB2− linkers. The coordination geometry around the
dinuclear Co(II) units with a Co−Co separation distance of
2.81 Å is depicted in Figure 1a. The Co(II) ions display
distorted square-pyramidal geometries by coordination of four
oxygen atoms [Co−O = 2.003(4)−2.086(4) Å] from four
linkers and a nitrogen atom [Co−N = 2.033(5)−2.053(5) Å]
of the L spacer. The framework is composed of paddle-wheel
{Co2(COO)4} secondary building units that are bridged by
both the ligands to form a layer structure. While considering
the central sulfur atoms of the SDB2− ligands as two-connected
nodes and the paddle wheel unit as six-connected nodes, the
framework can be evaluated as a 2,6-connected two-dimen-
sional (2D) net with sql(2,6L1) topology with point symbol:
{(42.68.8.104)(4)2} (Figure 1b).19 The linkers L with length of
17.99 Å connect the looped chains of rhombic grids (8.63 ×
8.65 Å) leading to the formation of a twofold interpenetrating
parallel network as represented in Figure1c. Total potential
solvent-accessible volume is 604 Å3 (25.5%) per unit cell
volume of 2371.1 Å3 as estimated by PLATON.18 Despite
interpenetration, IITKGP-6 shows lozenge-shaped channels of
approximate size of 3.4 × 5.0 Å2 (considering van der Waals
Physical Measurements. Elemental analyses (C, H, N, S) were
performed on an Elementar, Vario Micro Cube elemental analyzer.
B
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as-synthesized pattern (Figure S3, Supporting Information)
confirming its water stability. Recently, effect of catenation/
interpenetration on the water stability of MOFs was
demonstrated by Walton et al.20 Thus, absence of coordina-
tively unsaturated metal centers, which is mostly responsible for
framework degradation,10 presence of N coodinations11 to the
paddle-wheel {Co2(COO)4} structural building unit (SBU) and
interpenetrating nature,20 possibly makes this MOF a water-
stable material.
To evaluate the permanent porosity, the as-synthesized
sample was immersed in dry chloroform for 3 d to remove the
high-boiling guest solvents. PXRD showed good agreement
among the simulated pattern, the as-synthesized pattern, the
chloroform-exchanged pattern, and the activated pattern
indicating retention of the porous structure after solvent
exchange and successive elimination of exchanged solvent
molecules from the channels (Figure S2, Supporting
Information). Approximately 70 mg of exchanged sample was
activated at 100 °C for 12 h for the adsorption study. The N2
sorption isotherm of activated sample (IITKGP-6a) displays an
uptake of 83.4 cm3 g−1 at 1 bar pressure with steep increase in
adsorption amounts under low relative pressure (P/P0 < 0.01)
as depicted in Figure S5 (Supporting Information). The
Brunauer−Emmett−Teller (BET) surface area was estimated
to be 279 m2 g−1 from the low-pressure adsorption region with
pore volume of 0.12 cm3 g−1 (Figure S6, Supporting
Information). Moreover, the N2 sorption isotherm of water-
treated and dried sample displays an uptake of 76 cm3 g−1 at 1
bar and 77 K (Figure S7, Supporting Information) exhibiting
negligible loss in BET surface area compared to the pristine
sample (254 vs 279 m2 g−1) and thus unambiguously
establishing the water stability of IITKGP-6. The hydrogen
sorption isotherm indicates an uptake of 0.76 wt % at 77 K/1
bar (Figure S8, Supporting Information).
Figure 1. (a) View of paddle-wheel unit and surrounding environment
in IITKGP-6. (b) An illustration of a layer with the sql(2,6L1)
topology. (c) A schematic representation of twofold interpenetrated
network. (d) Packing diagram showing pore surfaces decorated with
−SO2 functionality along [1−1 0] direction.
radii) along [1−1 0] direction as depicted in Figure 1d, which
are filled by solvent molecules. Moreover, five intermolecular
C−H···O contacts among the components are accountable for
stabilizing the whole framework (Table S3, Supporting
Information).
The phase purity of the bulk material was established by
PXRD study, which revealed a good agreement with the
corresponding simulated patterns obtained from single-crystal
data (Figure S1, Supporting Information). The TGA showed
∼14.3% weight loss until 200 °C, which is ascribed to the
release of lattice solvent molecules (four water molecules and
one DMF molecule; Figure S4, Supporting Information). No
weight loss from 200 to 375 °C could be seen before
degradation of the framework indicating its good thermal
stability. To assess the water stability, IITKGP-6 was immerged
in water for 48 h, filtered, and dried. The PXRD pattern of the
dried sample after soaking in water reveals exact similarity with
We further investigated the sorption behaviors of IITKGP-6a
for CO2, CH4, and N2 to test its CO2/CH4 and CO2/N2
separation selectivity at ambient conditions. Single-component
gas sorption isotherms performed at 273 and 295 K are
presented in Figure 2a,b, respectively. CO2 uptake values at 273
and 295 K/1 bar are 50.6 cm3 g−1 (9.9 wt %) and 37.4 cm3 g−1
(7.3 wt %), respectively. It is of particular interest that the
Figure 2. CO2, CH4, and N2 sorption isotherms of IITKGP-6a (a) at 273 K and (b) at 295 K (CO2: red, CH4: blue, N2: magenta, solid and open
symbols represent adsorption and desorption, respectively).
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Figure 3. Loading amounts in mixed gas phase and separation selectivities at 273 K (a, b) and 295 K (c, d) predicted by IAST for CO2/CH4 (50:50)
and CO2/N2 (15:85).
present CO2 uptake capacities are similar to the uptake
amounts of well-known MOFs such as SIFSIX-2-Cu, [Cu-
(bcppm)H2O], [Zn2(BME-bdc)2(bipy)]n, and activated car-
bon21,22c,25d but higher than familiar MOFs, to name a few such
as ZIFs-25, -71, -93, -95, -97, and -100, IRMOF-3, and MOF-
177.22 Interestingly, it adsorbed high amounts of CO2 at 0.5 bar
(1.66 mmol g−1 at 273 K and 1.08 mmol g−1 at 295 K), which is
the partial pressure of CO2 in landfill gas mixture. Therefore,
steep uptakes in the low-pressure regions indicate a high CO2
affinity toward the polar pore surfaces. On the one hand, in
addition to well-established quadrupole−quadrupole interac-
tions among CO2 molecules and presence of high density of N
atoms for Lewis base−Lewis acid interactions, plausible
dipole−quadrupole interactions of CO2 gas molecules with
the polar pore surface decorated with −SO2 groups that are
exposed toward the channels (Figure 1d) may also correspond
to the present uptake capacity.12−14 On the other hand, it takes
up much lower amount of CH4 (13.8 cm3 g−1, 0.98 wt % at 273
K; 9.2 cm3 g−1, 0.66 wt % at 295 K) and N2 (6.2 cm3 g−1, 0.78
wt % at 273 K; 4.1 cm3 g−1, 0.52 wt % at 295 K) under 1 bar
pressure.
N2, respectively, indicating the gas affinity in the decreasing
order of CO2 > CH4 > N2. The enthalpy value of CO2 is
comparable to the values for MIL-53-Al (20.1 kJ mol−1), PCN-
88 (27 kJ mol−1), MOF-5 (17 kJ mol−1), and NOTT-140 (25
kJ mol−1). The fairly constant enthalpy values specify
homogeneity of CO2 binding sites over the entire loading
range within the pores. On the one hand, the higher CO2
affinity may be attributed to the strong interactions of CO2 with
the −SO2 groups and the confined channel structure. On the
other hand, the high difference in polarizability between CH4
and N2 could be the reason for stronger interaction of CH4
with the pore surface and thus result in comparatively better
uptake than N2.
We further studied the potential of IITKGP-6a for gas
separations. The mixture selectivities at two different temper-
atures (273 and 295 K) were calculated based on ideal
adsorbed solution theory (IAST) developed by Myers and
Prausnitz for mixed CO2/CH4 (50:50, landfill gas composi-
tion), and CO2/N2 (15:85, flue gas composition) with
pressures up to 100 kPa.23 Pure-component adsorption data
at particular temperatures are taken as inputs to the IAST
calculation, whereas the output predicts mixture adsorption
equilibrium over a desired pressure range. The precision of the
IAST calculations for loading approximation of gas components
present in binary mixtures in a diverse range of MOFs and
zeolites are well-recognized in comparison with the Configura-
tional-Biast Monte Carlo (CBMC) simulations for calculation
To evaluate quantitative binding strengths of CO2, CH4, and
N2 gas molecules with the framework, the coverage-dependent
adsorption enthalpies were calculated from their adsorption
isotherms at 273 and 295 K by using Clausius−Clapeyron
equation (Figure S9, Supporting Information). The enthalpies
at zero loading are 23, 18.4, and 5.1 kJ mol−1 for CO2, CH4, and
D
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of mixture adsorption studies.24 The results of IAST
calculations have shown that, under 100 kPa, the selectivity
for CO2/N2 mixture is 51.3 at 273 K and 42.8 at 295 K; the
selectivity for CO2/CH4 mixture is 36 at 273 K and 5.1 at 295
K (Figure 3a−d). All of these four values are significantly higher
than those of many well-known MOFs: PCN-88 (CO2/N2: 18/
296 K, CO2/CH4: 5/296 K), PCN-61 (CO2/N2: 15/298 K),
ZJNU-44a (CO2/N2: 15/296 K), UTSA-34a (CO2/CH4: 5.1/
296 K), SIFSIX-2-Cu (CO2/N2: 13.7/298 K), Cu24(TPBTM)8
(CO2/N2: 22/298 K), PMOF-3a (CO2/N2: 29.2/273 K and
23.4/296 K, CO2/CH4: 8/273 K and 5.1/296 K), MOF-177
(CO2/N2: 3.6/296 K), Cu-BTTri (CO2/N2: 21/298 K), en-
Cu-BTTri (CO2/N2: 25/298 K), JUC-141 (CO2/N2: 21.6/273
K and 27.6/298 K, CO2/CH4: 4.2/273 K), NOTT-202a (CO2/
N2: 26.7/273 K and 4.3/293 K, CO2/CH4: 2.9/273 K and 1.4/
293 K), many ZIF materials (ZIF-68, CO2/N2: 18.7/298 K,
CO2/CH4: 5/298 K; ZIF-69, CO2/N2: 19.9/298 K, CO2/CH4:
5.1/298 K) and benchmark zeolite MFI (CO2/N2: 11.2/296 K,
CO2/CH4: 2.5/296 K).14,25 Both CO2/N2 and CO2/CH4
selectivity at different pressures and temperatures with the
type of selectivity calculations (IAST, Henry Law, isotherm
slopes) based on literature survey is tabulated in Table S5
(Supporting Information). It needs to be pointed out that
IITKGP-6a has the modest CO2 uptake capacity but displays a
higher CO2/N2 and CO2/CH4 selectivity, underlying the
uniqueness of this new water-stable interpenetrating MOF for
carbon dioxide capture and separation from flue gas as well as
landfill gas mixture.
functional groups in combination with adjusting the pore size
should be appealing from the practical application point of view
for carbon dioxide separation.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02136.
Crystallographic data, PXRD, TGA, IAST calculation
details, related plots, and tabulated data of IAST
selectivity (PDF)
Accession Codes
CCDC 1569337 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: mcdas@chem.iitkgp.ernet.in.
■
ORCID
Madhab C. Das: 0000-0002-6571-8705
Notes
Besides gas separation selectivity, capacity consideration of
adsorbed amount of the desired gas in mixed gas phase is
important to assess the capability of a given adsorbent material
in a pressure-swing adsorption (PSA) unit. The loading
capacity of CO2 in the mixed gas phase at equilibrium (CO2/
N2: 15/85 and CO2/CH4: 50/50) within the porous framework
at 273 K (Figure 3a,b) and 295 K (Figure 3c,d) was calculated
up to 100 kPa pressure. At this pressure, we note that maximum
CO2 loadings from binary CO2/N2 mixture are 0.7 and 0.33
mmol g−1 at 273 and 295 K, respectively. The loading value of
0.33 mmol g−1 at 296 K is higher than MOF-177 (0.16 mmol
g−1 at 295 K/100 kPa) and zeolite MFI (0.26 mmol g−1 at 295
K/100 kPa).14 For the case of binary CO2/CH4 gas mixture
these values are 1.54 and 0.77 mmol g−1 at 273 and 295 K,
respectively, which is comparable to Zn4O(FMA)3 (0.89 mmol
g−1 at 296 K/2 bar) and zeolite MFI (1.07 mmol g−1 at 296 K/
2 bar).14
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
A.P. thanks UGC for SRF fellowship. This work is funded by
SERB, New Delhi, through Early Carrier Research Award
(ECR/2015/000041) scheme. We thank Dr. J.-B. Lin (Univ. of
Calgary) for helpful discussion.
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To conclude, a new water-stable twofold interpenetrating
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