Amide-functionalized ionic indium-organic frameworks for efficient separation of organic dyes based on diverse adsorption interactions

Article abstract of DOI:10.1039/C9CE00065H

By varying the solvents, two ionic indium-organic frameworks (1 and 2) were achieved. Both MOFs are constructed from the same indium monomer building units and amide-functionalized linker, but they present distinct topologies along with varied channel sizes and shapes. Importantly, the adsorption potential of the two anionic frameworks towards organic dyes with different charges and sizes was thoroughly examined. Both frameworks exhibited highly selective adsorption of the cationic dye methylene blue (MB) based on preferential electronic affinity and the size-exclusion effect. Besides MB, 1 and 2 also exhibited uptake of cationic dyes rhodamine B (RhB) and rhodamine 6G (R6G) but an inert reaction to the cationic dye crystal violet (CV), and thus additional hydrogen-bonding interactions of the amide groups and dyes during adsorption were suggested. The results also revealed that the adsorption capacity and kinetic constant of 1 are greater than those of 2, showing the importance of porosity and pore structure during adsorption. The adsorption capacity of 1 towards MB is as high as 281 mg g^?1 and thus it can potentially serve as a column-chromatographic filler for separating dye molecules.

Full text of DOI:10.1039/C9CE00065H

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DOI: 10.1039/C9CE00065H
Journal Name
ARTICLE
Amide-functionalized ionic indium-organic frameworks
for efficient separation of organic dyes based on diverse
adsorption interactions†
Received 00th January 20xx,
Accepted 00th January 20xx
Huiyan Liu,* Guimei Gao, Jie Liu, Fenlin Bao, Yuhui Wei and Haiying Wang*
DOI: 10.1039/x0xx00000x
Based on varying solvents, two ionic indium-organic frameworks (1 and 2) were achieved. Both MOFs are constructed
from the same indium monomer building units and amide-functionalized linker, but they present distinct topology along
with varied channel size and shape. Importantly, the adsorption potential of two anionic frameworks towards organic dyes
with different charge and size was thoroughly examined. Both frameworks exhibited highly selective adsorption towards
cationic dye methylene blue (MB) based on preferential electronic affinity and size-excluded effect. Besides MB, 1 and 2
also exhibited uptakes towards cationic dyes rhodamine B (RhB) and rhodamine 6G (R6G) but inert action to cationic dye
crystal violet (CV), and thus additional hydrogen-bonding interactions of amide groups and dyes over the adsorption were
suggested. The results also revealed that the adsorption capacity and kinetic constant of 1 are greater than those of 2,
showing the importance of porosity and pore structure during the adsorption. The adsorption capacity of 1 towards MB is
as high as 281 mg g−1 and can potentially serve as column-chromatographic filler for separating dye molecules.
www.rsc.org/
between the host and incoming guest molecules. Moreover,
by the ion-exchange, ionic MOFs can be easily modified and
accommodate other charged guest molecules, including ions,
Introduction
Currently, organic dyes are extensively used in many industries
with the advance of industrialization and, accordingly, the
removal of organic dyes from waste water has been a severe
issue from an environmental point of view.1 So far, various
methods have been explored for the remove of organic dyes,
and adsorption has been regarded as one of the most
competitive methods.1b, 2
organic dyes or small coordinated molecules. Thus, such ionic
MOFs materials are expected to be an ideal platform for
different applications as functional materials. A handful of
MOF materials have been evaluated to demonstrate
adsorptive capabilities towards organic dyes.1,5 For efficient
adsorption, not only adequate porosity/pore size but also pore
functionality along with special interaction sites is suggested.6
Then, by tuning pore size and incorporating functionality
groups into ionic frameworks permit the encapsulation of ionic
receptors and thereby make it feasible to investigate the
Metal−organic frameworks (MOFs) have been a fascinating
class of hybrid materials for their intriguing structural
diversities as well as promising potential applications in gas
sorption and separation, molecular sensing and ion-exchange.3
Given their intrinsic features of high porosity and easy
tenability of pore size and shape, MOFs towards high-
performance in organic dyes decontamination have become a
hot research subject more recently.4 Especially, ionic metal-
organic frameworks, as a fraction of MOFs with either
positively or negatively charged frameworks, have been
various host-guest interactions during
the adsorption
progress. Generally, for charged MOFs, strong electrostatic
interactions are mainly interactions for efficiently and
selectively separate dyes with different charges as
demonstrated in many works. Meanwhile, non-valence
interactions, such as hydrogen-bonding interactions and π-π
stacking interactions are common intermolecular interactions
which play important role in the preferred dyes adsorption
attracting significant attentions.2e, The charged species in
these ionic architectures facilitate the improved interactions
5
7
processes.6a-c, However, little has been known about the
presence or how these weak forces combine or collaborate
with strong electrostatic interactions during the dyes
adsorption processes for the charged MOFs.
Based on above consideration and as a continuation of our
effort to construct polyfunctional carboxylate based MOFs for
gas separation and molecular sensing,8 herein, by varying
School of Chemistry & Materials Science, Jiangsu Key Laboratory of Green Synthetic
Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou 221116, P. R.
China.
E-mail: liuhuiyan72@163.com; wanghy@jsnu.edu.cn
†Electronic supplementary Information (ESI) available: CCDC reference numbers
1863820 and 1881138. The supplementary tables, figures, and additional
characterization data. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/x0xx00000x
solvents
we
access
two
ionic
frameworks,
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[(CH3)2NH2][In(L)]·4H2O·2DMF
[(CH3)2NH2][In(L)]·H2O·3DMF (2) with amide-functionalized 1505, 1446, 1334, 1241, 1103, 907, 763, 732, 665.
(1)
and Selected IR data (KBr, cm−1): 3311, 3057, 1709,Vi1ew60Ar6ti,cle1O5n5lin0e,
DOI: 10.1039/C9CE00065H
tetracarboxylate
linker
(5-(3,5-dicarboxybenzamido)
isophthalic acid) (H4L). Noticeably, incorporating amide Synthesis of 1
functional group into framework not only accesses distinct A mixture of In(NO3)3·6H2O (10.0 mg, 0.024 mmol), H4L (5.0 mg,
network as well as modified pore structure, but also serves as 0.013 mmol) and HNO3 (0.6 mL, 2.7 M in DMF) in DMF (1 mL)
special interaction sites for dyes adsorption.
was placed in a 23 mL glass vial and heated at 75 °C for 36 h.
Mainly, the anionic nature of frameworks of 1 and 2 induces The colorless polyhedron crystals were obtained and washed
strong electrostatic affinity which facilitates outstanding size- with DMF (yield: 80% based on ligand). Anal. Calcd (Found) for
selective adsorption towards cationic organic dye methylene C28H38InN5O13: C, 43.82 (43.78); H, 4.99 (5.02); N, 9.12 (9.22)%.
blue (MB). Moreover, besides the preferential electrostatic Selected IR data (KBr, cm–1): 3417, 3086, 2801 1624, 1559,
affinity observed, additional hydrogen-bonding interactions of 1443, 1363, 1283, 1190, 1104, 1019, 905, 777, 742.
amide groups and dye molecules were found, which show a
beneficial effect on the dyes adsorption. Both frameworks, Synthesis of 2
especially 1, display large adsorption capacity and can A mixture of In(NO3)3·6H2O (40.0 mg, 0.096 mmol), H4L (10.0
potentially serve as column-chromatographic filler for mg, 0.026 mmol) and HNO3 (0.09 mL) in a mixed solvents of
separating dyes molecule. In addition, the adsorption DMSO (1mL) and DMF (1 mL) was placed in a 23 mL glass vial
isotherms and kinetics characteristic of dye adsorption onto and heated at 85 °C for 36 h. The colorless polyhedral crystals
the two MOFs were also investigated.
were obtained and washed with DMF (yield: 80% based on
ligand). Anal. Calc. (Found) for C25H37InN4O15: C, 40.12 (40.22);
H, 4.98 (5.08); N, 7.49 (7.40)%. Selected IR data (KBr, cm–1):
3078, 2806, 1622, 1557, 1503, 1361 1281, 1238, 1197, 1104,
1018, 777, 740.
Experimental section
General methods
All reagents were commercially obtained and used as received.
H4L ligand was prepared according to the procedure reported
with modification.3e Elemental analyses (C, H and N) were
performed on a PerkinElmer 240 analyzer. 1H NMR spectra
X-ray Crystallography
The X-ray diffraction data for 1 and 2 were performed on a
Bruker Apex II CCD diffractometer at 291 K using graphite
monochromated Mo Kα radiation (λ = 0.71073 Å) and Bruker
SAINT program was used to data reduction.9a The structure
was solved by direct methods and refined with full-matrix least
squares technique using the SHELXTL package.9b Displacement
parameters were refined anisotropically, and the positions of
the hydrogen atoms were generated geometrically assigned
isotropic thermal parameters and allowed to ride on their
parent carbon atoms before the final cycle of refinement. The
diffused electron densities resulting from highly disordered
solvent molecules were removed from the data set using the
SQUEEZE routine of PLATON and refined further using the data
generated. The contents of the solvent region are not
represented in the unit cell contents in the crystal data. Details
of the crystal parameters, data collection, and refinements for
1 and 2 are summarized in Table 1 (CCDC reference numbers
1863820 (1) and 1881138 (2)).
were recorded on
a
Bruker DRX-500 spectrometer.
Thermogravimetric analyses (TGA) were carried out under N2
atmosphere using a 2960 SDT thermogravimetric analyzer. IR
spectra were obtained on a Bruker Tensor 27 spectrometer
with KBr pellets in the range of 4000-400 cm-1. UV-vis spectra
were recorded on a UV-vis spectra were collected on a
PerkinElmer Lambda 365 UV/VIS spectrophotometer. A Bruker
D8 ADVANCE diffractometer with Cu Kα radiation (λ = 1.5418 Å)
was used to collected powder X-ray diffraction (PXRD) data at
room temperature. NanoBrook 90PlusPALS size and zeta
potential analyzer was used to determine the zeta potential.
Synthesis of H4L ligand
3,5-bis(methoxycarbonyl)benzoic acid (2.38 g，10 mmol) and
SOCl2 (50 mmol) were added to a mixture of CH2Cl2 (40 mL)
and DMF (0.1 mL). Then the mixture was refluxed for 12 h
under N2 atmosphere. The excess SOCl2 was removed under
vacuum.
The
resultant
was
dissolved
in
N,N-
Dye absorption and separation measurements
dimethylacetamide (DMA) (20 mL) and added dropwise to a
solution of dimethyl 5-aminoisophthalate (2.09 g, 10 mmol) in
DMA (20 mL) at 0 oC. After the completion of the addition, the
mixture was stirred at 50 oC for another 12 h and then poured
into water to obtain the crude product. The crude product was
hydrolyzed by refluxing in LiOH (1 M) followed by acidification
Freshly prepared crystalline samples of 1 and 2 (15 mg) were
transferred into solution of methylene blue (MB), methyl
orange (MO), solvent yellow 2 (SY2), acid red 2 (AR2), crystal
violet (CV), rhodamine B (RhB) and rhodamine 6G (R6G) in
MeOH (5 mL), respectively. The concentration of dyes was 40
mg L−1. The selective dyes adsorption ability was carried out by
placing fresh crystalline samples (15 mg) in the mixed dyes
solutions with the same concentration (10 mL). UV−vis spectra
were used to measure the adsorption ability towards dyes and
selective adsorption ability of 1 and 2.
1
with HCl (3M) to afford H4L (yield 90%). H NMR (400 MHz,
DMSO-d6, δ ppm): 13.47 (s, COOH), 10.97 (s, NH), 8.82 (d, 2H, J
= 4.0 Hz, ArH), 8.70 (d, 2H, J = 4.0 Hz, ArH), 8.65 (t, 1H, J = 4.0
Hz, ArH), 8.25 (t, 1H, J = 4.0 Hz, ArH). Anal. Calcd (Found) for
C17H11NO9: C, 54.70 (54.62); H, 2.97(2.86); N, 3.75 (3.82)%.
2 | J. Name., 2012, 00, 1-3
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ARTICLE
where ce, V, and m denote the equilibrium concentration of
DOI: 10.1039/C9CE00065H
adsorbate, the volume of system and the mass of added
adsorbent, respectively.
The experiment data for adsorption of two MOFs were fitted
with the Langmuir isotherm model, which is represented by
equation 2.10a
Dye-releasing experiments were performed by immersing the
fully MB loaded samples (MB@1 and MB@2) in pure MeOH or
DMF and a saturated solution of NaCl in MeOH or DMF,
respectively. UV−vis spectra were also used to measure the
release ability of two frameworks.
Reusability experiments for MB adsorption were further
conducted. The sample after MB fully released was filtered out
and washed thoroughly, and the above adsorption−desorption
cycle was repeated.
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Ce Ce
1
=
+
(2)
qe
qm KLqm
The equilibrium adsorption capacity (qe) is calculated based
on the difference in the dye concentrations in solution before
and after the adsorption process according to the following
equation 1.1g, 10a
where qm (mg g−1) and KL (L mg−1) are the maximum adsorption
capacity of the adsorbent and Langmuir constant, respectively.
The values of qm and KL were calculated from the slope and
intercept of the Ce/qe vs Ce plot.
(
)
C0 - Ce V
qe =
(1)
m
Table 1 Crystallographic data for 1 and 2.
MOFs
1
2
empirical formula
formula wt
C38H30In2N4O18
1060.30
C19H15InN2O9
530.15
cryst syst
monoclinic
P21/c
monoclinic
C2/c
space group
a (Å)
b (Å)
9.957(2)
14.212(2)
14.062(2)
24.444(2)
c (Å)
35.537(2)
90.337(3)
22.5060(11)
91.135(3)
β(deg)
V (Å3)
8649.2(19)
4
4496.9(10)
4
Z

calcd (g cm3)
 (mm-1)
F(000)
0.814
0.572
2112
0.783
0.551
1056
-12  h  12
-24  k  31
-35  l  46
-18  h  18
-18  k  15
-29  l  29
index ranges
Rint
0.0900
0.875, 0.894
19754/1/563
1.025
0.019
0.880, 0.900
5124/1/149
1.095
Tmax, Tmin
data/restraints/parameters
Goodness of fit
R1 a, wR2 b (I > 2(I))
R1, wR2 (all data)
0. 0440, 0.1042
0. 0497, 0.1055
1.71, -1.39
0.0488, 0.1427
0.0521, 0.1455
0.884, -0.986
(Δ)max, (Δ)min (e A-3)
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2 2
2 2 1/2
R1a = ||Fo| − |Fc||/Fo|, wR2b = [w(Fo2 − Fc ) /w(Fo ) ]
View Article Online
DOI: 10.1039/C9CE00065H
The pseudo-first-order and the pseudo-second-order kinetic
models were applied to fit kinetic data obtained. The models
(a)
(b)
can be expressed as equation
respectively.10b
3
and equation 4,
(
)
ln qe - qt = ln qe - K1t (3)
t
1
K2q2e
t
=
+
(4)
qt
qe
(c)
where qe (mg g−1) and qt (mg g−1) are the amount of dyes
adsorbed at equilibrium and at any time (min), respectively. K1
and K2 are the rate constants of the pseudo-first-order (min−1)
and pseudo second-order adsorption (g mg−1 min−1) models,
respectively.
Chromatographic column is made of bottomless NMR sample
tube and samples were filled in the NMR sample tube as
stationary phase. The MeOH solutions of mixed dyes were
passed through the chromatographic column at room
temperature. Then pure MeOH were traversed the
chromatographic column.
(d)
(e)
Results and discussion
Crystal structure and framework stability
Solvothermal reaction between H4L and In(III) in different
solvents afforded crystals of 1 and 2, respectively. Both
structures are based on the same indium monomer building
units but present distinctly different frameworks (Figs. 1 and 2).
Single-crystal structure analysis reveals that 1 is crystallized in
the monoclinic P21/c with cell parameters a = 9.957(2) Å, b =
24.444(2) Å, c = 35.537(2) Å and V = 8649.28(19) Å3, while 2 is
crystallized in the monoclinic C2/c with cell parameters a =
14.212(2) Å, b = 14.062(2) Å, c = 22.506(11) Å and V = 4496.9(9)
Å3 (Table 1). Both anionic frameworks of 1 and 2 are
constructed from negatively charged [In(CO2)4] building blocks,
Fig. 1 (a) The monomeric [In(CO2)4] building-block in 1. (b) The coordination
mode of the L4− ligand. (c) Space-filling representation of the framework of 1
showing the channels along the [100] direction. (d, e) Ball-and-stick and natural
tiling representations of (4,4,4,4)-connected net of 1. (color code: In, turquoise;
C, gray; O, red; N, blue).
The framework of 2 displays 1D square channels along c axis
with an aperture size of approximately 6.0 × 6.0 Å2 (Fig. 2c and
S3). The bridging L4- ligands and In(III) ions in 2 can be
topologically simplified as square-planar nodes and tetrahedral
nodes, respectively, giving PtS network with the topological
point symbol of (42·84) (Figs. 2d and 2e).
Two nets are constructed from the same indium monomer
building units with four carboxylate groups bind the metal in a
chelating fashion. Evidently, the generation of different
networks of 1 and 2 is related to conformational flexibility of
the organic ligands originated from the incorporation of amide
group into ligand (Fig. S4), which leads to different
configurations in the interconnection of metal ions and thus
different 3D nets. The total potential solvent-accessible
volumes for 1 and 2 were 61.8 % and 53.6 %, respectively, as
estimated by PLATON software.
+
and contain (CH3)2NH2 cations to balance the charge. Each
In(III) center is eight-coordinated by bi-dentate chelating
carboxylate oxygen atoms from four separate L4− ligands, while
each ligand binds to four separate In(III) centers (Figs. 1a and
2a). Notably, both frameworks contain amide functional
groups in the channels, which are expected to serve as special
sites and facilitate selectively adsorption of organic dyes.
In 1, viewing along a axis, there exist two types of channels,
rectangular and triangular in shape and measure about 7.2 ×
5.4 Å2 and 5.4× 5.0 Å2, respectively (point-to-point and
excluding van der Waals radii) (Figs. 1c and S1). After applying
symmetry operation, there are two types of bridging L4- ligands
as well as two types of In(III) ions in 1, but which can be
topologically simplified as equal square-planar nodes and
tetrahedral nodes, respectively (Fig. S2). Consequently, 1
adopts
a distinct 4,4,4,4-connnected network with the
topological point symbol of (4·62·83) (4·63·82) (42·62·82) (42·84)
(Figs. 1d and 1e).
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weight loss of 35.3% (calcd 35.7%) for 1 and 36.9% (calcd
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(b)
(a)
DOI: 10.1039/C9CE00065H
36.7%) for 2 between 25 and 200 °C, corresponding to the loss
+
of (CH3)2NH2 cations, and guest H2O and DMF molecules in
the cavity. Further heating above 300 °C may lead to the
release of organic ligands. The bulk identity of 1 and 2 were
confirmed by powder X-ray diffraction (PXRD) measurements
(Fig. S7). The PXRD patterns for as-synthesized samples match
well with the simulated patterns from crystal data,
demonstrating that the crystal is representative of the pure
bulk sample.
(c)
Organic dye adsorption and separation
To explore the potential application of two anionic frameworks
in organic dye removal, 1 and 2 were employed to capture
different types of dyes in MeOH solutions. In addition, size and
charge of the organic dye are the two most important factors
during the process of dye capture. Based on these
consideration, seven organic dyes were chosen for this study
including methylene blue (MB), solvent yellow 2 (SY2), acid red
2 (AR2), methyl orange (MO), crystal violet (CV), rhodamine B
(RhB) and rhodamine 6G (R6G) (Scheme S1).
(d)
(e)
At first, four types of dyes (MB, SY2, AR2 and MO) featuring
the similar size and molecular weight but different charges
were selected to conduct adsorption process. The crystalline
samples of 1 and 2 were immersed in MeOH solution of
different kinds of dyes, respectively. The content of dyes in the
solution was monitored by certain time intervals through UV-
vis spectroscopy. As shown in Fig. 3, two frameworks can
adsorb 99.6% in 90 mins and 94.5% of MB in 120 mins,
respectively, demonstrating rapid and high-efficiency removal
capacity of MB. At the same time, the color of the solution
gradually becomes transparent. On the contrary, the neutral
SY2 and AR2, and anionic MO cannot be effectively adsorbed
(Figs. S8a-S8c and S9a-9c).
Fig. 2 (a) The monomeric [In(CO2)4] building-block in 2. (b) The coordination
mode of the L4− ligand. (c) Space-filling representation of the framework of 2
showing the channels along the b and c direction, respectively. (d, e) Ball-and-
stick and natural tiling representations of PtS net of 2.
The thermal stability of 1 and 2 has been evaluated in the
temperature range of 25−600 °C (Fig. S5). TG curve reveals a
(a)
(b)
Fig. 3. UV-vis spectra of MB in MeOH solution at different time during the adsorption with 1 (a) and 2 (b) as the host. The insets are the corresponding photographs
before and after adsorption.
ability of 1 and 2 (Figs. 4a-4c and 5a-5c). As expected, only the
The desirable adsorbent material should possess not only cationic MB was effectively absorbed in the mixture solutions.
the outstanding adsorption property towards the dyes but also The color of the solutions essentially came to as the same as
the eminent capability of selective removal and separation. the pure SY2, AR2 and MO solution after 30 mins. Meanwhile,
Then the mixtures of MB/SY2, MB/AR2 and MB/MO solutions the color of samples changed from colorless to blue, indicating
were used to further demonstrate the selective adsorption selective trapping of MB within the pore. The selective
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absorption of cationic dyes could be attributed to enhanced the molecule size might not the major way to control the
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interaction between the anionic frameworks and cationic dyes, uptake of RhB.
DOI: 10.1039/C9CE00065H
+
as well as the ion-exchange between free (CH3)2NH2 cations
present in the framework and cationic dyes. Therefore, by ion-
exchange processes, 1 and 2 can be a potential material for
selectively separating the organic dyes with similar sizes but
different charges.
It is evident from literature that the amide groups on the
linkers are both hydrogen-bonding donors and acceptors that
can facilitate hydrogen bonding interactions in MOFs.3e, 5b, 11 It
is reasonable to speculate that the presence of amide groups
within the pore surfaces and carboxylate groups in RhB might
contribute to form hydrogen-bonding interactions and further
facilitate RhB adsorption. To further confirm this claim,
another cationic R6G with large size was employed to compare
the adsorption performance. As same to that of RhB, 1 and 2
show somewhat slow but complete R6G removal after 24 h
(Figs. S8f and S9f). These results further confirm that the
formation of hydrogen-bonding interactions may be beneficial
for the adsorption of dye molecules.
To demonstrate the size effect, another two kinds of
cationic dyes, CV and RhB, with the same charge but different
molecular sizes, were chosen to carry out the absorption
experiments. Compared with the results in Fig. 3, for the large
size CV and RhB, an unexpected and different adsorption
behavior was observed (Figs. S8d-8e and S9d-9e). Although the
size of RhB is slightly large than that of CV, 1 and 2 show
somewhat slow but complete RhB removal after 20 h, while no
obvious adsorption towards CV even after 12 h, indicating that
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 4 UV-vis spectra of MB/SY2 (a), MB/AR2 (b), MB/MO (c), MB/CV (d), MB/RhB (e) and MB/R6G (f) in MeOH solution at different time during the adsorption with 1
as the host. The insets are the corresponding photographs before and after the adsorption.
The capture abilities were further inspected under mixed 4d-4f and Figs. 5d-5f, only characteristic peaks of MB
solution of MB/CV, MB/RhB and MB/R6G. As shown in Figs. decreased significantly, while that of the CV remain unchanged.
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However, for the mixed solution of MB/RhB and MB/R6G, the maintained throughout the absorption process, and no major
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DOI: 10.1039/C9CE00065H
MB was almost completely adsorbed after about 30 min while changes to the PXRD and IR patterns of frameworks were
only a very small amount of the RhB or R6G can be adsorbed. detected after the exchange of dyes, as demonstrated by PXRD
The removal efficiency of MB in mixed solution of MB/RhB and and IR studies (Figs. S7 and S12).Furthermore, PXRD of 1 and 2
MB/R6G is lower than that in the single MB solution, which after release experiment confirmed their high stability (Fig.
may be due to the competitive adsorption of RhB and R6G.
S13). This high stability and reversible adsorption feature were
To further confirm that selective adsorption is mainly due to crucial to the MB removal application.
ionic interaction of dye with the anionic framework, dye-
The reusability experiments of 1 for MB adsorption show
releasing experiment with MB were carried out and indicated that 1 was found to be operational for three cycles with
by UV−vis spectroscopy (Figs. 6a and S10). As shown in Fig. 6a, somewhat lowered adsorption efficiency for MB (Fig. S14). The
the dye molecules in MB ＠1 can be efficiently released in the PXRD patterns indicate that the framework of 1 is basically
presence of NaCl and the color of the solution gradually turned unchanged after three adsorption−desorption cycles for MB
back to blue again. In contrast, the dye molecules are difficult (Fig. S13).
to release in pure MeOH and DMF for 1 and 2, respectively (Fig.
S11). It is worth noting that the integrity of the framework is
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 5 UV-vis spectra of MB/SY2 (a), MB/AR2 (b), MB/MO (c), MB/CV (d), MB/RhB (e) and MB/R6G (f) in MeOH solution at different time during the adsorption with 2
as the host. The insets are the corresponding photographs before and after the adsorption
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(b)
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DOI: 10.1039/C9CE00065H
Fig. 6 (a) The MB released from the MB@1 in a saturated solution of NaCl in MeOH monitored by UV-vis spectra. (b) Langmuir fitting plots for the adsorptions of MB
on 1.
Dye adsorption capacity is commonly influenced by the
concentration of the dye solutions. Therefore, by using UV−vis
spectroscopy to test the adsorption amount at different initial
dye concentrations for 24 h at room temperature, the
adsorption capacity of 1 and 2 towards MB can be deduced
from the dependence of saturate adsorption amount (qe) on
the initial concentration of adsorbate (c0) according to the
equation 1. In addition, Langmuir and Freundlich models are
used to fit the maximum adsorption isotherms and it is found
that the adsorptions can be described well by the Langmuir
isotherm model (Figs. 6b and S15). The maximum adsorption
amount for MB is 281 mg g-1 for 1 and 181 mg g-1 for 2, which
are really higher than other reported carbonaceous materials
(activated carbon, graphene oxide, and carbon nanotubes),2b,
From the combined information on the above dyes
adsorption experiments, it is realized that the different
interactions are combined or collaborative during dyes
adsorption progress as summarized in Table S1. The main and
preferential electrostatic affinity facilitated highly size-
selective and rapid adsorption towards cationic MB.
Meanwhile, inserting amide groups in frameworks may serve
as special interaction sites through hydrogen-bonding
interactions, which favored the adsorption towards cationic
RhB and R6G with large size. However, compared with the
strong electrostatic affinity, hydrogen-bonding interactions
were much smaller in this work and do not make such a big
contribution for adsorption, which resulted in that the
adsorption capacity of cationic RhB and R6G is very low.
In all, as shown in Fig. 7, the possible mechanisms involved
in the adsorption process could clarify its highly selective
adsorption towards MB as well as different adsorption
performance towards different dyes.
6c, 12a
and oxidized nanodiamond (OND-4.5) (Table S2). This
values are also higher than or comparable with that of various
MOFs, such as UiO-66 (90.9 mg g−1)10b, MOF-235 (187 mg
g−1),12b NH2-MIL-101-SO3H (141 mg g−1),6c JLU-liu39 (308 mg
g−1),12c {[Cd4(BPTC)2(DMA)4(H2O)2](DMA)}n (79.4 mg g−1),12d
and [(CH3)2NH2]1.5[Tb1.5(TATAT)(H2O)4.5] x(solvent) (147 mg
∙
g−1)12e (Table S2). In order to examine the adsorption
mechanism, the pseudo-first-order and the pseudo-second-
order kinetic models were applied to analyze data obtained
(Figs. S16 and S17). As indicated in Table S3, it is evident that
the fitting with pseudo-second-order kinetic model matches
well with experimental data by comparing the fitting
coefficient.
electrostatic
interactions
MB
MB
t
c
e
f
f
CV
e
d
e
d
u
l
c
x
e
-
e
z
i
s
At the same time, it is worth noted that the adsorption
capacity and adsorption kinetic constant of 1 are greater than
those of 2, demonstrating the effect of porosity and pore
structure during the adsorption.
RhB
h
y
d
e
r
i
n
o
R6G
g
t
e
n
r
a
b
c
o
t
i
o
n
d
n
i
n
s
g
SY2
Generally, zeta potential of adsorbents is another key factor
affecting their adsorption capacity.6b,10b Thus, we further
tested the zeta potential of two MOFs. The zeta potential of 1
and 2 are about −15.38 and −10.37 mV, respectively. The
result further demonstrated that the higher efficiency removal
of cationic dye may be attributed to the electrostatic
attraction interactions between the adsorbents and cationic
dye.
AR2
MO
r
e
p
u
l
s
i
v
e
e
l
e
c
t
r
o
s
t
a
t
i
c
e
f
f
e
c
t
Fig. 7 Proposed interaction mechanism during adsorption of dyes on 1.
Adsorption isotherm and kinetics for MB adsorption
8 | J. Name., 2012, 00, 1-3
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Ion chromatographic column filler for dyes separation
removal. Then, it is expected that this work will offer valuable
View Article Online
guidance in designing ideal porous MOFs that offer high
DOI: 10.1039/C9CE00065H
Encouraged by the excellent adsorption and separation
performance towards cationic dyes on two frameworks, we
performance for dyes removal in the real practice.
used
1 and 2 as the stationary phase of an ion
chromatographic column (Fig. 8). The mixed solutions of
MB/MO, MB/AR2, MB/RhB, MB/CV and MB/SY2 with the same
concentration were injected into the chromatographic column,
respectively. As displayed in Fig. 8, MB was adsorbed into
samples for a long time along with the MeOH stream, while
MO, AR2, RhB, CV and SY2 were passed through the column.
Consequently, the two kinds of dyes can be successfully
separated by passing through chromatographic column, which
could be easily observed by the naked eye. These experiments
highlight the potential of 1 and 2 serving as column-
chromatographic filler for the separation of dyes.
Acknowledgements
This work was supported by the Natural Science Foundation of
Jiangsu Normal University, China (No.17XLR044), PAPD of
Jiangsu Higher Education Institution and Postgraduate
Research & Practice Innovation Program of Jiangsu Province
(KYCX18_2109).
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functional group into framework not only access distinct
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DOI: 10.1039/C9CE00065H
Graphical Abstract
Amide-functionalized ionic indium-organic frameworks for
efficient separation of organic dyes based on diverse adsorption
interactions
Huiyan Liu,* Guimei Gao, Jie Liu, Fenlin Bao, Yuhui Wei and Haiying Wang*
MB
MB
CV
RhB
R6G
SY2
AR2
MO
Based on varying solvents, two anionic indium-organic frameworks were synthesized. Both MOFs
feature amide group functionalized anionic frameworks and different channel of size and shape,
which consequently afford diverse interactions during adsorption towards dyes of different charge
and size, and thus different adsorption potential. Especially, 1 demonstrated outstanding
adsorption toward small cationic organic dye methylene blue, and be applicable in
column-chromatographic separation of dyes.