isotherms at 25°C showed the saturation of the
adsorbent pore system at a very low relative pressure (0.05 P/P0), with a marked steepness, from
which we derived apparent surface areas and pore
volumes, respectively, of 258 m2/g and 0.102 cm3/g
for AlFFIVE-1-Ni and 324 m2/g and 0.129 cm3/g for
FeFFIVE-1-Ni. The Qst of CO2, determined from
variable temperature adsorption isotherms (figs.
S14A and S15A) for AlFFIVE-1-Ni and FeFFIVE-
1-Ni, was estimated to be 45 ± 2.2 kJ/mol (fig.
S14B) and 48 ± 2.5 kJ/mol, respectively (fig.
S15B); this value was also measured directly by
calorimetry for the aluminum (43 kJ/mol) and
iron (45.7 kJ/mol) analogs (Fig. 3F and figs. S8
and S9). By comparison with the Qst associated
with H2O adsorption (63 kJ/mol), the framework-CO2 interactions (45 kJ/mol) are much weaker
than the framework-H2O interactions (63 kJ/
mol). The DFT calculations showed that CO2
preferentially adsorbs in a distinct site from
H2O (Fig. 3A). The electropositive C interacts
with F atoms of pillars (F···CCO2 = ~2.8 Å), and
the electronegative O is surrounded by pyrazine
H (H···OCO2 = ~2.6 Å) (Fig. 3A). This geometry
is reminiscent of that previously reported for
NbOFFIVE-1-Ni, although the presence of open
metal sites in AlFFIVE-1-Ni prevents CO2 to
interact simultaneously with the four F centers, thus leading to a slightly lower Qst than for
NbOFFIVE-1-Ni (~54 kJ/mol) (20).
Breakthrough adsorption column experiments
were carried out on AlFFIVE-1-Ni for a H2O vapor
(single component) and in the presence of N2,
CH4, and CO2 adsorbates using a similar total
flow of 23 cm3/min and an RH of 75%. The H2O
retention times in the column were relatively similar (500 to 600 min/g within experimental error)
and unaltered by the presence of CH4 and/or CO2
in the hydrated mixed-gas CO2/CH4: 1/99 mixture (Fig. 4A and fig. S16B). After multiple cycles of
the adsorption column breakthrough test with a
hydrated CO2/CH4: 1/99 gas mixture, the performance of AlFFIVE-1-Ni was unaltered (fig. S17). A
reduction in dehydration performance (nearly 50%)
was observed for zeolite 4A when the desorption
temperature was reduced from 250° to 105°C
(fig. S18). Increasing the CO2 concentration in
the CO2/N2 mixture to 1, 10, and 50% (Fig. 4, B
to D) caused no noticeable changes on the H2O
vapor retention time in the column (500 to
600 min/g within experimental error). Thus, the
same H2O vapor adsorption behavior and uptake
occurred independently of the CO2
concentration and the composition of the evaluated gas
mixtures (e.g., CO2/CH4: 1/99, CO2/N2: 1/99, CO2/
N2: 10/90, and CO2/N2: 50/50). However, although
CH4 (humid condition; Fig. 4A) and N2 (both dry
and humid conditions; fig. S16, A and C, and Fig.
4, B to D) did not show any noticeable uptake, the
retention time in the column for CO2 during
moisture-containing tests revealed a nominal difference (within experimental error) when compared with the corresponding dry tests for all of
the evaluated gas mixtures. Although the H2O
adsorption energetics in AlFFIVE-1-Ni particularly
favor the H2O adsorption, concomitant adsorption
of the CO2 molecules occurred in its presence.
Subsequent post–in situ temperature-programed
desorption studies were performed by progressively heating the column to 100°C, initially saturated with a CO2/H2O/N2: 9.2/2/88.8 gas feed
mixture, at three adsorbed phase states: (i) just
after the breakthrough time of CO2 25 min/g;
(ii) at half breakthrough time of H2O 300 min/g;
and, finally, (iii) after full breakthrough time of
H2O 600 min/g (Fig. 3, G to I). The H2O and CO2
molecules simultaneously desorbed from the column with CO2/H2O adsorbed phase compositions
of 0.67/0.33 (Fig. 3G), 0.24/0.76 (Fig. 3H), and
0.11/0.89 (Fig. 3I) at adsorbed phase states i,
ii, and iii, respectively, indicative of coadsorbed
CO2 and H2O in the pore system of the AlFFIVE-1-
Ni. Both H2O and CO2 could be simultaneously
removed with a H2O/CO2 selectivity ranging from
2 to 39. Single-crystal structure refinement of
AlFFIVE-1-Ni simultaneously exposed to air moisture and pure CO2 after activation showed oc-cupancies of 26 and 74% for CO2 and H2O,
respectively (Fig. 3B and table S3). DFT calculations were performed for AlFFIVE-1-Ni containing diverse amounts of H2O and CO2 adsorbed in
mixture (see supplementary materials). As a model
mixture case (1 H2O + 1 CO2 per formula unit), Fig.
3A confirms that both species occupy the same
adsorption sites as single components. Calorimetric
measurements of a hydrated gas mixture (CO2/
N2:1/99) showed similar CO2 and H2O Qst values
as compared with those for the single-adsorbate
cases (Fig. 3F and fig. S8).
To ascertain the prospective molecular exclusion cutoff for MFFIVE-1-Ni imposed by the
adsorbent pore-aperture size and shape and subsequently modulating the access to the confined
square-shaped channels, we explored the adsorption of slightly larger and relatively bulkier
probe molecules such as n-C4H10, iso-C4H10,
1-propanol, and isopropanol (figs. S19 and S20).
Both AlFFIVE-1-Ni and FeFFIVE-1-Ni (KAUST-8
and KAUST-9) showed no noticeable adsorption
for isobutane and isopropanol, indicative of prospective efficient dehydration of gases and vapors
with equal and larger sizes than isobutane and
isopropanol via full molecular sieving. Overall,
these results highlight the potential of the KAUST-8
adsorbent-desiccant to congruently adsorb CO2
and H2O and could be used for the on-demand
simultaneous removal of CO2 and H2O by varying
the adsorption-desorption cycle times.
REFERENCES AND NOTES
1. A. Karimi, M. A. Abdi, Chem. Eng. Process. 48, 560–568
2. P. Gandhidasan, A. A. Al-Farayedhi, A. A. Al-Mubarak, Energy
26, 855–868 (2001).
3. S. S. B. M. Rohani, Natural Gas Dehydration Using Silica Gel:
Fabrication of Dehydration Unit (University of Malaysia Pahang,
4. T. Devic, C. Serre, Chem. Soc. Rev. 43, 6097–6115
5. H. Furukawa, K. E. Cordova, M. O’Keeffe, O. M. Yaghi, Science
341, 1230444 (2013).
6. V. Guillerm et al., Chem. Soc. Rev. 43, 6141–6172
7. Y. He, B. Li, M. O’Keeffe, B. Chen, Chem. Soc. Rev. 43,
8. S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. Int. Ed. 43,
9. N. C. Burtch, H. Jasuja, K. S. Walton, Chem. Rev. 114,
10. J. Canivet, A. Fateeva, Y. Guo, B. Coasne, D. Farrusseng,
Chem. Soc. Rev. 43, 5594–5617 (2014).
11. P. Küsgens et al., Micropor. Mesopor. Mater. 120, 325–330
12. H. Reinsch et al., Chem. Commun. 48, 9486–9488
13. Y.-K. Seo et al., Adv. Mater. 24, 806–810 (2012).
14. A. Khutia, H. U. Rammelberg, T. Schmidt, S. Henninger,
C. Janiak, Chem. Mater. 25, 790–798 (2013).
15. G. Akiyama et al., Micropor. Mesopor. Mater. 157, 89–93
16. H. Furukawa et al., J. Am. Chem. Soc. 136, 4369–4381
17. A. Cadiau et al., Adv. Mater. 27, 4775–4780 (2015).
18. M. F. de Lange, K. J. F. M. Verouden, T. J. H. Vlugt, J. Gascon,
F. Kapteijn, Chem. Rev. 115, 12205–12250 (2015).
19. A. Cadiau, K. Adil, P. M. Bhatt, Y. Belmabkhout, M. Eddaoudi,
Science 353, 137–140 (2016).
20. P. M. Bhatt et al., J. Am. Chem. Soc. 138, 9301–9307
21. O. Shekhah et al., Nat. Commun. 5, 4228 (2014).
22. P. Nugent et al., Nature 495, 80–84 (2013).
23. O. Shekhah et al., Chem. Commun. 51, 13595–13598
24. K. Adil, M. Leblanc, V. Maisonneuve, J. Fluor. Chem. 130,
25. A. Cadiau et al., Solid State Sci. 13, 151–157 (2011).
26. A. Cadiau, S. Auguste, F. Taulelle, C. Martineau, K. Adil,
CrystEngComm 15, 3430–3435 (2013).
27. A. Le Bail, H. Duroy, J. L. Fourquet, Mater. Res. Bull. 23,
28. L.-Z. Zhang, H.-X. Fu, Q.-R. Yang, J.-C. Xu, Energy 65, 430–440
29. F. Bouyer, G. Picard, J.-J. Legendre, Int. J. Quantum Chem.
52, 927–934 (1994).
30. U. Gross, D. Müller, E. Kemnitz, Angew. Chem. Int. Ed. 42,
Research reported in this publication was solely performed
at KAUST and was supported by KAUST funds, KAUST
funding grants (CCF/1/1972-02-01, CCF/1/1972-8-01, and
OSR-2017-CPF-3325), and Aramco. The data reported in the
paper are presented in the main text and the supplementary
materials. Crystal structures of the as-synthesized AlFFIVE-1-Ni,
the dehydrated AlFFIVE-1-Ni, AlFFIVE-1-Ni (rehydrated),
AlFFIVE-1-Ni·1.48H2O·0.26CO2, and FeFFIVE-1-Ni are available
free of charge from the Cambridge Crystallographic Data Centre
(CCDC) under reference nos. CCDC 1538217, 1538215,
1538216, 1538219, and 1538218. A.C., Y.B., K.A., P.M.B., M.E.,
and KAUST have filed provisional patents (WO2016/162834A1
and WO2016/162835A1) pertaining to the results presented
herein. K.A., M.E., and A.C. conceptualized the design and the
construction of the reported MOF materials; A.C. carried out
the materials synthesis; K.A., A.C., and A.S. conducted and
interpreted the crystallographic experiments; P.M.B., Y.B.,
and A.C. conducted and interpreted low-pressure adsorption
experiments; Y.B. and P.M.B. contributed to conceptualizing,
designing, conducting, and interpreting calorimetric and mixed
adsorption experiments; R.S.P. and G.M. performed and
analyzed the DFT calculations; C.M.-C. conducted and analyzed
the solid-state NMR experiments; and K.A., Y.B., A.C., and M.E.
wrote the manuscript.
Materials and Methods
Figs. S1 to S26
Tables S1 to S5
Data S1 to S5
23 January 2017; accepted 25 April 2017