A superhydrophobic zeolitic imidazolate framework (ZIF-90) with high steam stability for efficient recovery of bioalcohols

Article abstract of DOI:10.1039/c5cc10171a

A superhydrophobic zeolitic imidazolate framework (ZIF-90) with high steam stability is prepared through post-functionalization via an amine condensation reaction. The developed superhydrophobic ZIF-90 is highly promising as an effective and reusable adsorbent for bio-alcohol recovery.

Full text of DOI:10.1039/c5cc10171a

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DOI: 10.1039/C5CC10171A
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Superhydrophobic Zeolitic Imidazolate Framework ZIF‐90 with
High Steam Stability for Efficient Recover of Bioalcohols
Received 00th January 20xx,
Accepted 00th January 20xx
Chuanyao Liu, Qian Liu and Aisheng Huang*
DOI: 10.1039/x0xx00000x
www.rsc.org/
7‐12
Superhydrophobic zeolitic imidazolate framework ZIF‐90 with high separation, chemical sensor, and drug delivery.
In
steam stability is prepared through post‐functionalization via an particular, zeolitic imidazolate frameworks (ZIFs), a subfamily
amine condensation reaction. The developed superhydrophobic of MOFs based on transition metals and imidazolate linkers, 13,
14
ZIF‐90 shows highly promising as an effective and reusable
adsorbent for bio‐alcohols recovery.
have emerged as a novel type of porous material for the
fabrication of molecular sieving membranes due to their
zeolite‐like properties such as permanent porosity, uniform
15‐21
Due to the emerging scarcity of fossil resources and the critical
environment concerns, the development of renewable and
clean energy sources such as bioalcohols has drawn increasing
interest in the recent years. 1 Bioalcohols are usually produced
from biomass through fermentation with a low alcohol
concentration in aqueous medium. Therefore, it is prerequisite
to extract and recover the bioalcohols from the fermentation
broth before it can be used as biofuels. Distillation is a
conventional technology for the separation of alcohol/water
mixture. However, it involves high energy‐consuming boiling
and condensing processes. Adsorptive separation by using
porous materials is regarded as one of the most competitive
methods due to its energy‐saving and environmentally friendly.
So far, various materials including activate carbons, polymeric
resins and zeolites have been developed for the separation of
alcohol/water mixture. 2‐6 However, these adsorbents have a
strong affinity to water, resulting in a low adsorption capacity
and effectiveness. Therefore, the development of a novel
adsorbent with high adsorption performance remains an
urgent challenge.
pore size, exceptionally thermal and chemical stability.
Further, ZIFs are also promising adsorbents for the recovery of
bio‐alcohols due to their tunable pore size and adjustable
internal surface properties. 22, 23 It is well recognized that the
adsorption performances of the adsorbents is determined no
only by their open pore structures and surface areas, but also
3, 24
their hydrophobicity.
Therefore, the development of
superhydrophobic absorbents with open pore structures, high
stability and large surface areas is of special interest. To the
best of our knowledge, so far no studies on synthesis and
application of superhydrophobic ZIFs have been reported.
NH2
F
F
F
F
F
Methanol, 70 ºC, 24 h
In the past ten years, metal–organic frameworks (MOFs)
have received considerable interest because of their potential
applications in gas adsorption and storage, membrane
ZIF-90
Superhydrophobic ZIF-90
Fig. 1. Scheme of the synthesis of superhydrophobic ZIF‐90 via an amine
condensation reaction.
Institute of New Energy Technology, Ningbo Institute of Material Technology and
Engineering, CAS, 1219 Zhongguan Road, 315201 Ningbo, P. R. China. E‐mail:
huangaisheng@nimte.ac.cn
Electronic Supplementary Information (ESI) available: Experimental and simulation
details; FESEM, XRD, EDXS and XPS of ZIF membranes; Separation performances
for seawater desalination of the ZIF membranes. See DOI: 10.1039/x0xx00000x
Recently, Yaghi and co‐workers have developed a novel SOD
topology ZIF‐90 through solvothermal reaction of Zinc (II) and
imidazolate‐2‐carboxyaldehyde (ICA). ZIF‐90 shows not only
25
highly stable but also permanent microporosity with a narrow
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pore size (~3.5 Å) and high BET surface area (1270 m2∙g‐1). and X‐ray photoelectron spectroscopy (XPS). As shown in Fig.
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‐1
DOI: 10.1039/C5CC10171A
Especially, the presence of free aldehyde groups in the ZIF‐90 S4, the C=O band of the aldehyde at 1678 cm is replaced by
framework allows the covalent functionalization of ZIF‐90 with the C=N bond of the imine at 1630 cm‐1. The presences of
amine groups via an imine condensation reaction. Based on aromatic C‐C band at 1510 cm‐1 and F‐C band at 1030, 1125,
the imine condensation reaction, we have developed a 1235 cm‐1 suggest that pentalfluorobenzylamine has been
covalent post‐functionalization strategy to enhance the grafted on the ZIF‐90 after post‐modification. As shown in Fig.
molecular sieve performances of the ZIF‐90 membrane. 26, 27 S5 and Table S1, after post‐modification, the intensity of O1s
Indeed, the postsynthetic modification of MOFs is well known and Zn2p peaks reduce much and a new F1s peak emerges
as an effective and versatile strategy to improve their physical with high intensity, confirming that pentalfluorobenzylamine
28‐32
and chemical properties.
Due to the presence of the free has successfully reacted with the aldehyde groups of ZIF‐90.
aldehyde groups in the ZIF‐90 framework, ZIF‐90 is an ideal Since the kinetic diameters of pentalfluorobenzylamine is
candidate for the post‐functionalization through host‐guest much larger than the pore size of the ZIF‐90, the
reactions, generating a large number of topologically identical pentalfluorobenzylamine is difficult to go into the ZIF‐90 cage.
but functionally diverse ZIF‐90 with fine‐tuned and optimized Therefore, the post‐synthetic modification reaction mainly
properties. 25‐29 In the present work, we report the synthesis of occurs at the external surface of the ZIF‐90 particles, as shown
superhydrophobic ZIF‐90 for bioalcohols recovery through in Fig. S6. 35 The successful post‐functionalization of ZIF‐90 was
post‐functionalization of ZIF‐90 with pentalfluorobenzylamine further confirmed by N2 adsorption isotherm. As shown in Fig.
via amine condensation reaction (Fig. 1 and Fig. S1). It can be S7a, the N2 adsorption isotherm for ZIF‐90 showed a steep rise
expected that the fluorinated ZIF‐90 will show high in the low‐pressure region, indicating the permanent porosity
hydrophobicity and thus is promising for bioalcohols recovery.
of the ZIF‐90 framework. 34 The calculated BET surface area of
ZIF‐90 in the present work is about 1182 m2∙g‐1, which is in
good agreement with the previous report. 34 However, after
post‐functionalization, the pore aperture of the fluorinated
ZIF‐90 is severely constricted, leading to a low N2 adsorption
(Fig. S7b).
(a)
(b)
After post‐functionalization, no remarkable differences in
the ZIF‐90 morphology are found between the as‐prepared
and the fluorinated ZIF‐90 (Fig. 2b). As deduced from the X‐ray
diffraction (XRD) pattern (Fig. 2c), the high crystallinity of the
ZIF‐90 structure is kept unchanged after post‐modification,
even after being boiled in water for 24 h (Fig. S8). Further,
from thermogravimetric analysis (TGA) (Fig. S9), both the as‐
prepared and fluorinated ZIF‐90 show a similar plateau region
without significant weight loss in the temperature range
80~300 oC, even after the measurement of water stability (Fig.
S10). These results indicate that the fluorinated ZIF‐90 shows
high thermal and chemical stability.
2 µm
2 µm
(c)
(d)
Superhydrophobic ZIF-90
As-synthesized ZIF-90
Simulated ZIF-90
10
20
30
2 Theta / Degree
40
50
The hydrophobicity of the fluorinated ZIF‐90 was evaluated
by the measurement of water contact angle (CA). As shown in
Fig. 2d, the surface of fluorinated ZIF‐90 shows a water CA of
about 152.4°, while water CA of the surface of the as‐prepared
ZIF‐90 is 93.9° (Fig. S11), suggesting that the hydrophobicity of
the ZIF‐90 can be significantly enhanced through post‐
functionalization with pentafluorobenzylamine. Such surface
superhydrophobicity should be attributed to the cooperation
of both microporous morphological structures and strongly
hydrophobic chemical compositions of the fluorinated ZIF‐90,
which are two well‐known key factors for the surface
superhydrophobicity. 24, 36
The hydrophobicity of the fluorinated ZIF‐90 was further
confirmed by the removal of alcohols from alcohol/water
mixtures. To evaluate the adsorption capacity of the
fluorinated ZIF‐90 for recovery of alcohols from alcohol/water
mixtures, the superhydrophobic ZIF‐90 powders were added
into ethanol/water mixture which was dyed by red oil for
clarity, and then keeping stirring for 2 h. After a following
selective adsorption of ethanol for 20 h, the fluorinated ZIF‐90
Fig. 2. FESEM images of ZIF‐90 (a) and superhydrophobic ZIF‐90 (b), XRD
patterns of ZIF‐90 and superhydrophobic ZIF‐90 (c), measurement of contact
angle with water for the superhydrophobic ZIF‐90 (d).
Pentalfluorobenzylamine was synthesized according to the
procedure reported elsewhere with minor modification (Fig. S2,
33
the details see Supporting Information).
The formation of
pentalfluorobenzylamine is confirmed by Fourier transform
infrared (FT‐IR) and 1H‐NMR nuclear magnetic resonance
(NMR) spectra (Fig. S3). The ZIF‐90 was prepared by the
solvothermal reaction of zinc (II) nitrate tetrahydrate, sodium
34
formate, and ICA in methanol.
As shown Fig. 2a, well‐
defined ZIF‐90 crystals with dodecahedral morphology and size
of about 2.0±0.5 µm are prepared after solvothermal synthesis
o
for 24 h at 85 C. For covalent post‐functionalization, the as‐
prepared ZIF‐90 crystals were immersed in a solution of
pentalfluorobenzylamine in methanol, and then refluxed for
24 h at 70 oC. The post‐functionalization of ZIF‐90 with
pentalfluorobenzylamine was confirmed by FT‐IR spectroscopy
2 | J. Name., 2012, 00, 1‐3
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powders which have adsorbed ethanol were separated by a (ethanol, iso‐propanol and butanol) can be reVcioewveArrteicdle Oanlninde
simple filtration. As shown in Fig. S12c, the mother solution removed from bio‐alcohol/water mixtuDreO.I: T10h.1e0s3e9/Cp5rCoCp1e0r1t7ie1As
become colourless and transparent after the removal of recommend the superhydrophobic ZIF‐90 as a promising
fluorinated ZIF‐90 powders by filtration, indicating ethanol has candidate for industrial bio‐alcohols recovery.
been fully recovered and removed by the fluorinated ZIF‐90. In
This work was financially supported by the Ningbo Science
deeded, according to the analysis of gas chromotograph (GC), and Technology Innovation Team (2014B81004), and Ningbo
98% ethanol has been removed from the ethanol/water Municipal Natural Science Foundation (2015A610046).
mixture (Fig. 3). On the contrary, only 7% ethanol can be
removed from the ethanol/water mixture by using the as‐
prepared ZIF‐90 as adsorbent (Fig. S13). Besides ethanol, the
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effective and reusable adsorbent for bio‐alcohols recovery
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In conclusion, based on an amine condensation reaction
between the aldehyde groups of ZIF‐90 and amine groups of
pentafluorobenzylamine, we have developed a facile post‐
functionalization road for preparation of superhydrophobic
ZIF‐90. After post‐functionalization, the water CA can be
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recovery of bio‐alcohols. At 20oC, more than 98% bio‐alcohols
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