U(VI) adsorption onto covalent organic frameworks-TpPa-1

Article abstract of DOI:10.1016/j.jssc.2019.06.044

Covalent organic frameworks (COFs) represent an exciting new type of porous organic materials, which are constructed with organic building units via strong covalent bonds. Here in, the COF-2,4,6-Triformylphloroglucinol p-Phenylenediamine (COF-TpPa-1) was

Full text of DOI:10.1016/j.jssc.2019.06.044

Accepted Manuscript
U(VI) adsorption onto covalent organic frameworks-TpPa-1
Zhuo Dai Li, Huai Qiang Zhang, Xiao Hong Xiong, Feng Luo
PII:
S0022-4596(19)30334-2
https://doi.org/10.1016/j.jssc.2019.06.044
YJSSC 20839
DOI:
Reference:
To appear in: Journal of Solid State Chemistry
Received Date: 14 May 2019
Revised Date: 20 June 2019
Accepted Date: 30 June 2019
Please cite this article as: Z.D. Li, H.Q. Zhang, X.H. Xiong, F. Luo, U(VI) adsorption onto covalent
organic frameworks-TpPa-1, Journal of Solid State Chemistry (2019), doi: https://doi.org/10.1016/
j.jssc.2019.06.044.
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Graphical Abstract:

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U(VI) Adsorption onto Covalent Organic
Frameworks-TpPa-1
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Zhuo Dai Lia,b, Huai Qiang Zhanga,b,*, Xiao Hong Xionga,c, Feng Luoc,*
a Fundamental Science on Radioactive Geology and Exploration Technology Laboratory, East
China University of Technology, Nanchang, 330013, China
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b School of Nuclear Science and Engineering, East China University of Technology, Nanchang,
330013, China
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c School of Biology, Chemistry and Material Science, East China University of Technology,
Nanchang, 330013, China
Abstract: Covalent organic frameworks (COFs) represent an exciting new type of
porous organic materials, which are constructed with organic building units via strong
covalent bonds. Here in, the COF-2,4,6-Triformylphloroglucinol p-Phenylenediamine
(COF-TpPa-1) was synthesized by solvothermal method for the removal of U(VI)
from aqueous solution. Effects of pH, adsorption dose, contact time, uranium solution
concentration, temperature and adsorption and desorption cycle on the efficiency of
COF-TpPa-1 removal of U(VI) are investigated. SEM, XRD, TGA and FT-IR were
employed to characterize the samples and analyze adsorption mechanism. The results
manifested COF-TpPa-1 has the high adsorption capacity (qm=152 mg/g), quick
adsorption kinetic, high selectivity, outstanding recycle performance and good
resistance to acids, bases and high temperature.
Keywords: Covalent organic framework; COF-TpPa-1; U(VI); Adsorption;
desorption;
* Corresponding author. E-mail address: zhanghq821@163.com (H Q. Zhang).
* Corresponding author. E-mail address: ecitluofeng@163.com (F. Luo).

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26 1. Introduction
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With the development of economy, the problems of energy shortage and
environmental pollution bring challenge to sustainable development of human
economy. Nuclear power is more and more irreplaceable in energy system as a kind of
clean and efficient energy [1]. As usage of nuclear power reactors developing [2,3],
which had leaded to several safety accidents and produced lots of radioactive wastes,
especially the containing uranium, plutonium and other radionuclides waste water,
had caused very serious environmental problems. Thus, separation, enrichment and
recovery of uranium from nuclear industrial effluents or other liquid are not only
significant in effective utilization of resources or environmental security [4], but also
reduce the potential threat of radionuclides to environment and human health [5–7].
In the past few decades, several efficient separation technologies, such as
chemical precipitation, solid-phase extraction, membrane separation, ion-exchange
and adsorption, have been developed for the capture and recovery of U(VI) from the
natural environment [8–10]. Among these technologies, the adsorption has been
widely employed as the primary method of recovery of uranium aqueous solution due
to its simplicity and continuity of operation, mature method, high efficiency, and
environmental friendly [11–17].
In radiation-related ions researches, kinds of materials have been developed to
collect radioactive ions, for example, optode membrane [18], MOFs [19] and
mesoporous silica [20]. So far, various materials, such as carbon-based materials
[21,22], clay materials [23,24], graphene-based materials [24], nanoscale zero-valent
iron materials [25,26] and metal organic frameworks (MOFs) [27,28], have been used
as adsorbents to capture U(VI) from aqueous solutions. However, carbon-based
nanomaterials like graphene and carbon nanotubes were costly and the preparation
process was quite complicated. Clay minerals have chemical stability but low
adsorption capacities and removal rates. Zero-valent iron materials were unstable and
non-reusable, also harmful to the surrounding environment. And most of MOFs own

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bad chemical stability. Therefore, developing a new type of materials with high
efficiency, low cost, high stability is of great significance to remove U(VI) in practical
applications.
As an emerging porous crystalline material, covalent organic frameworks (COFs)
[29] are prepared by various coupling reactions and have periodic two-dimensional or
three-dimensional structures [30–32]. Since their discovery, COFs have received a lot
of attention as they are highly crystalline and light weight materials possessing
exceptionally high surface area with a definite pore size distribution pattern [33,34].
Due to its unique structure and nature, COFs has been applied in gas storage [35,36],
catalysis [37,38], electricity [39], etc. Furthermore, COFs have great potential for the
adsorption and separation metal ions due to its sufficient functional points [40–42].
Many COF materials have been reported in past few years. For example, a kind of
graphene-synergized 2D covalent organic framework (GS-COF) obtained via an in-situ
loading of a covalent organic framework (TDCOF) on graphene sheets has been
reported with the maximum adsorption capacity of 220 mg/g [32]. Several other COFs
also have been reported by the same group. They showed the stability and functionality
of COFs in condition of high acidity and strong radiation existing in nuclear industry
[30–32,43].
In this work, COF-TpPa-1 was prepared to remove of uranium from aqueous
solution, the effects of pH, adsorption dose, contact time, uranium solution
concentration, temperature, adsorption and desorption cycle were investigated
detailedly. The SEM, XRD, TGA and FT-IR were also employed to characterize the
samples and analyze adsorption mechanism. The results show that COF-TpPa-1 has
high adsorption capacity, good acid and base resistance It can be used for treating
uranium-containing radioactive wastewater.
79 2. Experimental detail
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2.1 Reagents and instruments

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All common chemicals used in this study were purchased from Aladdin
(Shanghai, China) and are of analytical grade. The 721 spectrophotometer (Shanghai,
China) was used for the detection of the U(VI). SEM measurements was carried out
using a Nova Nano SEM 450 (Czech Republic), equipped with Oxford X-Max
spectrometer. X-ray diffraction were collected by a Bruker AXS D8 Discover powder
diffractometer (Germany). Thermal analysis was carried out by TGA Q500 thermal
analysis system (TA Instruments, USA). The FT-IR spectra were performed on a
Nicolet 380 (Thermo, USA). Nitrogen adsorption and desorption isotherms were
measured at 77 K using an BELSORP-max analyzer.
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2.2 Synthesis of 2,4,6-Triformylphloroglucinol
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Hexamethylenetetraamine (15.098 g, 108 mmol) and phloroglucinol (6.014 g, 49
mmol) was added into 90 mL trifluoroacetic acid under N2. The solution was heated at
100 for 2.5 h. Then 150 mL of 3 M HCl was added and the solution was heated at
100 for 1 h. After cooling to room temperature, the solution was filtered through
Celite, extracted with 350 mL dichloromethane, dried over magnesium sulfate, and
filtered. Rotary evaporation of the solution afforded 1.23g (5.87 mmol ,11%) of an
off-white powder. The pure sample was obtained by sublimation. 1H NMR (400 MHz,
CDCl3) data indicated near 99% purity, giving 14.12 (s, 3H, OH), 10.15 (s, 3H, CHO)
ppm.
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2.3 Synthesis of COF-TpPa-1
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0.3 mmol (63 mg) of 2,4,6-Triformylphloroglucinol (TP), 0.45 mmol (84.7 mg)
p-Phenylenediamine (Pa-1) was added into a Pyrex tube with 1.5 mL butyl alcohol
and 1.5mL 1,2-dichlorobenzene. The mixture was sonicated for 20 min, followed by
addition of 0.5 mL of 3 M aqueous acetic acid. After that, the tube was degassed by
freeze-pump-thaw cycles for three times, sealed under vacuum and heated at 120 °C
for 3 days. The reaction mixture was cooled to room temperature and washed with
deionized water, dimethylacetamide and acetone. The resulting dark red powder was

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dried at 120 °C under vacuum for 12 hours.
2.4 Uranium adsorption experiments
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Uranium adsorption experiments were performed in batches method.
COF-TpPa-1 was added into 50 mL plastic centrifuge tubes containing 20 mL of
U(VI) solution with specific initial U concentration(C0) with stirring. The pH was
adjusted by HCl/Na2CO3. The adsorption experiments were carried out by putting the
plastic centrifuge tubes into a thermostatic shaker bath at 25 for 150 min, with
rotation speed of 250 rpm. Then, 1 mL solution withdrawn from centrifuge tubes was
centrifuged at 10000 rpm for 8 min. the concentration of U(VI) at time t (Ct) was
detected by arsenazo (III) spectrophotometric method at 650 nm. The desorption rate,
distribution coefficient (Kd) and equilibrium adsorption capacity(qe) were calculated by
the Eqs. (1), (2) and (3), respectively [44,45]:
(C0 − Ce )
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(1)
(2)
Remove rate =
m
V
(C0 − Ce ) V
qe =
w
C0 −Ce V
Kd =
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(3)
Ce
w
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where C0 (mg/L) is the initial concentration, Ce (mg/L) denotes the equilibrium
concentration, V (L) is solution volume and w (g) is adsorbent weight. All data of
batch experiments were obtained in triplicates.
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2.5 Chemical stability studies
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COF-TpPa-1 was added into four glass bottles of 15 mg each. 6 M HCL, 6M
NaOH, 1M HNO3 and H2O were added respectively to for samples. The first three
were placed at room temperature for 72 hours and the fourth was keep at 100 for
same 72 hours. Then, samples were washed several times with deionized water for
XRD.
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2.6 Desorption studies

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After each adsorption study, the solid liquid separation by high-speed centrifuge to
recover the spent COF-TpPa-1, which was then washed several times with acidic
solution (HCL, 1 mol/L) to remove the U(VI). The recovered COF-TpPa-1 was
thoroughly washed with deionized water and methyl alcohol, dried at vacuum, and
used for further adsorption investigation. During the repeated adsorption studies,
U(VI) adsorption capacity (qe) was calculated. The adsorption and desorption
processes were repeated up to 4 times, to further ascertain the recyclability of
COF-TpPa-1.
141 3. Results and Discussion
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3.1 Characterizations of COF-TpPa-1
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Chemical stability experiments were performed by soaking COF-TpPa-1 in 1
mol/L HNO3, 6 mol/L NaOH and HCl, and 100 deionized water for there days. then
these samples was analyzed by XRD. The results were shown in Fig. 1. Compared
with the Fig. 2, it can be easily concluded that COF-TpPa-1 possesses good chemical
and temperature stability.
To confirm the chemical stability of the samples during adsorption of U(VI),
powder X-ray diffraction (XRD) of pristine and U(VI)-loaded samples were tested. As
shown in Fig. 2, The diffraction peaks between the samples before and after
adsorption were no significantly different before adsorption. Major XRD patterns for
the U(VI)-loaded samples basically the same as the pristine samples, suggesting its
high chemical stability even after loading of U(VI). Moreover, the XRD Spectrum of
COF-TpPa-1 before and after adsorption matched well with its simulated data. The
simulated data was obtained by theoretical calculation and MS software simulation.
There is no corresponding JCPDS card with this kind of COF material. But our
simulation data matches well with the eclipsed model in the paper of Suvendu Karak
et al. [46].

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NaOH
HNO3
HCL
100 , H2O
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10
15
20
25
30
2-Theta (degree)
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Fig. 1 XRD patterns of the samples after HCL (6 M, soaked for 72 h), HNO3 (1M,
soaked for 72 h), NaOH (6 M, soaked for 72 h) and H2O (100 , soaked for 72 h)
treatment.
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Fig. 2 XRD patterns of the samples before and after adsorption.
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Scanning electron microscopy (SEM) an accelerating voltage of 10 kV was used
to observe the microscopic morphology before and after adsorption. It is obvious that
COF-TpPa-1 shows a radial cluster structure in the SEM images. There are no
significant differences between the surface of U(VI)-loaded samples and pristine
samples.

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Fig. 3 SEM results of pristine and U(VI)-loaded samples. (a), (b) and (c) are
COF-TpPa-1 samples before adsorption; (d), (e) and (f) are COF-TpPa-1 samples
after adsorption.
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N2 adsorption and desorption experiments were carried out at 77 K to investigate
the surface area and porosity of COF-TpPa-1. The N2 adsorption and desorption
isotherm of it is shown in Fig. 4. From the isotherm the Brunauer-Emmett-Teller
(BET) surface area was found to be 704 m2/g. According to the inset of Fig. 4, the
result suggests the average pore diameter was 1.86 nm.
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Fig. 4 N2 adsorption/desorption isotherms of COF-TpPa-1 at 77 K. Pore size
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distribution is shown in the inset.

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To determine the thermal stabilities of COF-TpPa-1, thermogravimetric analysis
(TGA) for COF-TpPa-1 was performed. The results are shown in Fig. 5. In the range
of 25-100 , the rapid reducing of weight can be attributed to the volatilization of
physically adsorbed water and residual solvent outside and inside its pores. After that,
the COF-TpPa-1 was stabile before 300 . In the range of 300-400 , the weight loss
sharply increases due to the pyrolysis of some functional groups on the surface of
COF-TpPa-1. The most significant weight loss occurs after 400 , which suggests the
destruction and decomposition of the basic skeleton of COF-TpPa-1 [14].
Before adsorption
After adsorption
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0
100 200 300 400 500 600 700 800
Temperature (°C)
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Fig. 5 Thermal gravimetric analysis (TGA) of the samples before and after
adsorption.
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The samples were also analyzed by Fourier transform infrared spectroscopy
(FT-IR) in the wavenumbers range between 4000 and 500 cm-1, and the obtained
results had been illustrated in Fig. 6. The adsorption bands at 3355 cm-1 is assigned to
the O-H stretching vibration. The band at 1256 cm-1 is attributed to the C-N bending
vibration of COF-TpPa-1. The aromatic -C=C- stretching frequency of the benzene
ring appears at 1450 cm-1. The band at 1574 cm-1 is assigned to the C=C bending
vibration. The strong peaks at 1256 cm-1 (-C-N) and 1574 cm-1 (-C=C) have clearly
shown the formation of the β-ketoenamine-linked framework structures [46].

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Comparing the spectrum of COF-TpPa-1 samples before and after adsorption, it can
be found that there is a very weak adsorption band at 916 cm-1. This is because U=O
bonds were formed after adsorption. The adsorption band is not obvious for its low
ratio to others.
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Fig. 6 FTIR spectra of COF-TpPa-1 before and after adsorption.
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3.2 Effect of pH value on U(VI) adsorption
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pH value is one of the most important parameters. It determines the speciation of
uranium ions [47]. The effect of pH value on adsorption capacity (qe) of U(VI) are
described in Fig. 7. The adsorption capacity of U(VI) is strongly dependent on pH
values because of the morphological distribution of uranium at different pH values.
When pH value is lower than 4, uranium exists predominantly as uranyl ions. When the
pH value increases to more than 4, there begins to form uranium hydrolyzate, such as
UO2(OH)+, (UO2)3(OH)52+, (UO2)2(OH)22+. When pH increases to more than 5, another
uranium hydrolyzate of UO2(OH)2·H2O is formed. Then, more than pH=8, anionic
form becomes to be the major form. Thereby, COF-TpPa-1 primarily adsorbs the
uranium hydrolysate. The U(VI) adsorption capacity increases slowly from pH=1 to
pH=4, then a sharply increase was observed in the pH range of 4-6, subsequently
rapidly decreases at pH=6-9 was observed. At pH=6, COF-TpPa-1 shows up strongest

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ability to adsorb uranium. Thus, this pH value is chosen for the further study.
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Fig. 7 E ect of pH on the U(VI) adsorption for the COF-TpPa-1 adsorbent. (C0=100
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mg/L, m=10 mg, t=12 hours, T=298 K).
3.3 Adsorption kinetics and adsorption mechanism analysis
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To obtain the kinetic parameters of adsorption, the effect of contact time on U(VI)
adsorption on COF-TpPa-1 is studied. The results are shown in Fig. 8. The adsorption
capacity rapidly increased in the first 100 mins, then increased slowly from 100 min
to 5 hours. There is no significant changing of adsorption capacity after 5 hours,
indicating the adsorption reaction reached equilibrium. The rapid growth of
adsorption capacity is attributed to the relatively higher concentration of U(VI) during
the initial time of adsorption reaction. In order to analyze the kinetic at length,
pseudo-first-order and pseudo-second-order were employed to fit the experimental
data [44,48]. The result is shown in Fig. 9. The resultant fitness represents the
corresponding adsorption mechanism [49]. The pseudo-first-order and
pseudo-second-order models can be described by following two equations:
k1t
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(4)
(5)
log(qe − qt ) = log qe −
2.303
t
1
t
=
+
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q
k2qe2 qe
t

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where the k1 (min-1) and k2 (g·mg-1·min-1) are the adsorption rate constants in the
pseudo-first-order and pseudo-second-order adsorption kinetic models, respectively. qt
(mg·g-1) and qe (mg·g-1) are the adsorption quantities at time t and at adsorption
equilibrium, respectively. Kinetic parameters of two kinetic models are listed in Table
1.
The linear correlation coefficient (R2) is used to check the validity of each model.
In Table 1, fitting result indicates that the correlation coefficient R2 of
pseudo-second-order kinetic model was larger than pseudo-first-order kinetic model.
And the adsorption capacity calculated by pseudo-second-order kinetic model
(qe,cal=97.2 mg/g) is closer to the experiment value (qe,exp=94.1 mg/g). Therefore, the
pseudo-second-order kinetic model could better describe the adsorption process of
COF-TpPa-1 on U(VI) and demonstrated that the adsorption process was chemical
adsorption.
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Fig. 8 Adsorption kinetics of COF-TpPa-1 for U(IV) adsorption (pH=6, V=20 mL,
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C0=100 mg/L, m=10 mg).

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(a)
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7
6
5
4
3
2
1
0
(b)
0
100 200 300 400 500 600
t (min)
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Fig. 9 The fitting by (a) pseudo-first-order and (b) pseudo-second-order models (the
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black points and red line present the experimental and simulated values, respectively).
Table 1 Kinetic parameters of pseudo-first-order and pseudo-second-order models.
pseudo-first-order
pseudo-second-order
q
e,exp (mg/g)
Adsorbent
q
,
e cal (mg/g)
k
1 (min-1)
R2
q
,
e cal (mg/g)
k
2 (g·mg-1·min-1)
R2
COF-TpPa-1
94.054
41.849
0.00177 0.9646
97.182
0.0005501
0.9995
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3.4 Adsorption isotherm
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In order to obtain its maximum adsorption capacity, the adsorption capacity of
COF-TpPa-1 for U(VI) was performed by taking different the uranium concentration

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from 0 to 300 mg/L at 25 . As shown in Fig. 10, with the increasing of uranium
concentration, the adsorption capacity increases. The adsorption gradually reaches
saturation when the initial uranium concentration is more than 150 mg/L. the
maximum adsorption capacity is up to 152 mg/g, which is comparable with the value
observed in the most reported porous materials. The adsorption capacity and optimal
pH value of some other porous materials are shown in Table. 2.
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60
40
20
0
0
50 100 150 200 250 300
C0 (mg/L)
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Fig. 10 Adsorption isothermal of COF-TpPa-1 for U(IV) (pH=6, V=20 mL, t= 480
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min, m=10 mg, T=25 °C).
Table 2 A comparison among some other porous materials for U(VI) removal.
Adsorption
Optimal
Compounds
capacity
(mg/g)
330
Adsorption site Reference
pH value
SX-LDH
MOF-76
6
Polysulfide anions
Unclear
[5]
298
3
[28]
[50]
[51]
[52]
[53]
[54]
[31]
UiO-68-P(O)(OEt)2 217
2.5
5.5
4.5
2
Phosphorylurea
Amine
MIL-101-DETA
ED-MIL-101
Zn(HBTC)(L)
Co-SLUG-35
COF-HBI
350
200
115
118
211
Amine
Carboxyl
5
Ion exchange
Benzimidazole
4.5
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To learn more about the adsorption, the common isothermal adsorption model of
Langmuir and Freundlich model are also utilized. Assuming that there is no interaction

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between adsorbates, and all the adsorption sites of solid surface are same and distribute
uniformly, then it results uniform monolayer adsorption and conforms to the Langmuir
adsorption model. Supposing that the adsorbate arrives at the non-uniform surface of
the adsorbent from the liquid phase, and the adsorbent has di erent adsorption sites on
the surface, thus leading to di erent adsorption energies and unevenly distributed
surface adsorption heat, then the adsorption is uneven multilayer adsorption and in
accordance with the Freundlich model. In this system, Langmuir and Freundlich
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models were selected, and the fitting results were shown in Fig. 11. Its linear
expressions are as following [55]:
Ce
1
Ce
=
+
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(6)
(7)
qe qmb qm
1
log qe = log KF + log Ce
n
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where qe (mg/g) is the adsorption capacity when adsorption reaches equilibrium, qm
(mg/g) is the theoretical saturation adsorption capacity, Ce (mg/L) is the equilibrium
concentration, b (L/mg) is the Langmuir adsorption-related constant, n and KF (L/mg)
are Freundlich equilibrium constants.
(a)
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(b)
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Fig. 11 Fitting the adsorption isotherm by (a) Langmuir and (b) Freundlich models
(the black points and red line present the experimental and simulated values,
respectively).
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In order to get the saturated adsorption capacity of the COF-TpPa-1 and
determine the adsorption type, Langmuir and Freundlich model were used to fit the
experimental data. The results are illustrated in Fig. 11 (a), (b) and Table 3.
The results of calculation and simulation indicated that the behavior of U(VI)
adsorption onto COF-TpPa-1 are fitted well by the Langmuir model, suggesting that
the adsorption behavior is monolayer-type. However, the Freundlich model is widely
used in describing multilayer adsorption process [56]. The fitting line of the
Freundlich model is not matching well with the behavior of U(VI) adsorption onto
COF-TpPa-1, which is monolayer-type. And the correlation coefficient R2 of
Langmuir adsorption isotherm model was greater than the Freundlich model. It means
the Langmuir model was more suitable than the Freundlich model for describing the
adsorption process of COF-TpPa-1 on U(VI), which demonstrated that the adsorption
of U(VI) onto this adsorbent was dependent on the completion of the chemisorption
monolayer.
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Table 3 Isotherm parameters of Langmuir and Freundlich models

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Langmuir model
Freundlich model
Adsorbent
q
m (mg/g)
b
(L/mg)
R2
K
F (mg1-n
·
g-1
·
Ln)
1/n
R2
COF-TpPa-1
168.1
0.0672
0.9965
32.3288
0.3198
0.8405
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3.5 Thermodynamics
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The effect of the temperature which was studied at T=298, 308, 318, 328, 333 K
on U(VI) adsorption by COF-TpPa-1 is shown in Fig. 12. As can be seen, the
adsorption capacity of COF-TpPa-1 increasing rapidly with the temperature from 298
K to 333 K, denoting an endothermic process. The thermodynamic analysis is
calculated according to Eqs. (8) and (9):
∆S ∆H
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(8)
(9)
ln Kd =
−
R
RT
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∆G = ∆H −T∆S
where ∆S is entropy change (J/mol·K), ∆G is Gibbs free energy change (kJ/mol), T is
temperature (K), ∆H is enthalpy change (J/mol·K), R is gas constant of 8.314
J/(mol·K), and Kd is partition coe cient.
To acquire the thermodynamic data of the adsorption process, the plot of lnKd
versus 1/T was used to calculate the enthalpy of the adsorption process according to
the slope and intercept of its linear equation. Calculation results were listed in Table 4.
324
ΔH is positive and greater than 40kJ/mol. It means that this reaction is mainly a
325
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328
chemical endothermic process. Positive ∆S indicates that the adsorption reaction can
be proceed in the ambience. ∆G is negative, so the reaction can proceed spontaneously.
Gibbs free energy decreases with increasing temperature, indicating that an increase
in temperature promotes the reaction.

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(b)
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Fig. 12 (a) Effect of temperature on U(VI) adsorption, (b) lnKd versus 1/T.
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333
334
(C[U(VI)]=150 mg/L, pH=6; V=20 mL, t=480 min)
Table 4 The thermodynamics parameters of U(IV) adsorption.
∆G/kJ·mol-1
Adsorbent
∆H (kJ/mol)
∆S (J·K-1·mol-1)
298.15
308.15
318.15
328.15
333.15
COF-TpPa-1
48.605
221.77
-17.515
-19.733
-21.950
-24.168
-25.277
335
3.6 Recycle
336
337
Adsorption and desorption experiments were performed for 4 times, the repeated
availability of COF-TpPa-1 was shown in Fig.13. As can be seen, the remove rate of

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U(VI) by COF-TpPa-1 have not reduced during cycles from 1 to 4 in sequence. The
remove rate of U(VI) by COF-TpPa-1 was about 70% during four cycles, it has not
reduced. This indicated that the chemical stability of COF-TpPa-1 was very well. The
desorption e ciency was about 96% in four cycles. The elution process did not
damage the material and it was reused for four cycles with no observation of
extraction capacity loss.
344
345
Fig. 13 Recycling for the adsorption of U(VI) by COF-TpPa-1.
346
3.7 Effect of competitive ions
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352
In practical applications, the system of uranium adsorption usually contains many
other metal ions. Thus, the selective separation ability of COF-TpPa-1 towards
uranium was confirmed using batch adsorption experiments in solution containing 6
coexisting ions (UO2+, Cr3+, Sr2+, Cd3+, Cs+, Mg2+). As shown in Fig. 14, the qe for
U(VI) is up to about 150 mg/g, which is far more than others. The results
demonstrated the high selectivity of COF-TpPa-1 for U(VI).

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(b)
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Fig. 14 The competitive sorption capacities and selectivity of COF-TpPa-1 for U(VI)
over competing ions (C0≈50 mg/L for all cations, t=480 min, m=10 mg, T=25 °C).
356
357
358 Conclusions
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363
For effective adsorption of U(VI) from aqueous solution, the COF-TpPa-1 was
prepared through solvothermal method. The results show that such adsorbent can
effectively adsorption U(VI), leading to high adsorption capacity up to 152 mg/g. The
value is comparable with some COFs for such purpose. The adsorption process of
COF-TpPa-1 strongly depended on pH value and temperature. Adsorption processes

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corresponded to the Freundlich model and pseudo-second order kinetic model. The
calculation results of thermodynamic study show that the adsorption process was
endothermic, freedom increase, and spontaneous reaction. In adsorption and
desorption experiments, the adsorbent shows good chemical stability and recyclability.
The selectivity experiments results demonstrated the high selectivity of COF-TpPa-1
for U(VI). XRD patterns for the U(VI)-loaded samples matches well with the pristine
samples, suggesting its high chemical stability even after loading of U(VI). The SEM
images shows a radial cluster structure of COF-TpPa-1. FT-IR have clearly shown the
formation of the β-ketoenamine-linked framework structures. Overall, COF-TpPa-1
shows high adsorption capacity for U(VI), good chemical stability, high selectivity
and recycle performance. It can be used for treatment radioactive waste water
containing uranium.
376 Acknowledgements
377
378
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380
This work was supported by the NSF of China (21661001 and 21661002), the
Foundation of Key Laboratory for Radioactive Geology and Exploration Technology,
Fundamental Science for National Defense and State Key Laboratory for Nuclear
Resources and Environment (RGET1309).
381 References
382
383
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390
[1] J. Veliscek-Carolan, Separation of actinides from spent nuclear fuel: A review, J.
Hazard. Mater. 318 (2016) 266–281. doi:10.1016/j.jhazmat.2016.07.027.
[2] J.R. Lovering, A. Yip, T. Nordhaus, Historical construction costs of global
nuclear power reactors, Energy Policy. 91 (2016) 371–382.
doi:10.1016/J.ENPOL.2016.01.011.
[3] J. De Decker, K. Folens, J. De Clercq, M. Meledina, G. Van Tendeloo, G. Du
Laing, P. Van Der Voort, Ship-in-a-bottle CMPO in MIL-101(Cr) for selective
uranium recovery from aqueous streams through adsorption, J. Hazard. Mater.
335 (2017) 1–9. doi:10.1016/J.JHAZMAT.2017.04.029.

ACCEPTED MANUSCRIPT
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
[4] Y. Arai, C.C. Fuller, Effects of sulfate ligand on uranyl carbonato surface
species on ferrihydrite surfaces, J. Colloid Interface Sci. 365 (2012) 268–274.
doi:10.1016/J.JCIS.2011.09.026.
[5] S. Ma, L. Huang, L. Ma, Y. Shim, S.M. Islam, P. Wang, L.-D. Zhao, S. Wang, G.
Sun, X. Yang, M.G. Kanatzidis, Efficient Uranium Capture by
Polysulfide/Layered Double Hydroxide Composites, J. Am. Chem. Soc. 137
(2015) 3670–3677. doi:10.1021/jacs.5b00762.
[6] M. Salvatores, G. Palmiotti, Radioactive waste partitioning and transmutation
within advanced fuel cycles: Achievements and challenges, Prog. Part. Nucl.
Phys. 66 (2011) 144–166. doi:10.1016/J.PPNP.2010.10.001.
[7] M.-L. Feng, D. Sarma, X.-H. Qi, K.-Z. Du, X.-Y. Huang, M.G. Kanatzidis,
Efficient Removal and Recovery of Uranium by a Layered Organic–Inorganic
Hybrid Thiostannate, J. Am. Chem. Soc. 138 (2016) 12578–12585.
doi:10.1021/jacs.6b07351.
[8] Y. Sun, S. Lu, X. Wang, C. Xu, J. Li, C. Chen, J. Chen, T. Hayat, A. Alsaedi, N.S.
Alharbi, X. Wang, Plasma-Facilitated Synthesis of Amidoxime/Carbon
Nanofiber Hybrids for Effective Enrichment of 238 U(VI) and 241 Am(III),
Environ. Sci. Technol. 51 (2017) 12274–12282. doi:10.1021/acs.est.7b02745.
[9] S. Yu, X. Wang, H. Pang, R. Zhang, W. Song, D. Fu, T. Hayat, X. Wang, Boron
nitride-based materials for the removal of pollutants from aqueous solutions: A
review, Chem. Eng. J. 333 (2018) 343–360. doi:10.1016/J.CEJ.2017.09.163.
[10] L. Zhu, C. Xiao, X. Dai, J. Li, D. Gui, D. Sheng, L. Chen, R. Zhou, Z. Chai, T.E.
Albrecht-Schmitt, S. Wang, Exceptional Perrhenate/Pertechnetate Uptake and
Subsequent Immobilization by a Low-Dimensional Cationic Coordination
Polymer: Overcoming the Hofmeister Bias Selectivity, Environ. Sci. Technol.
Lett. 4 (2017) 316–322. doi:10.1021/acs.estlett.7b00165.
[11] A. Rout, K.A. Venkatesan, T.G. Srinivasan, P.R. Vasudeva Rao, Liquid–liquid
extraction of Pu(IV), U(VI) and Am(III) using malonamide in room temperature

ACCEPTED MANUSCRIPT
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
ionic liquid as diluent, J. Hazard. Mater. 221–222 (2012) 62–67.
doi:10.1016/J.JHAZMAT.2012.04.007.
[12] P. Hu, L. Qian, Y. He, H. Wang, W. Wu, Solvent extraction of uranium(VI) and
thorium(IV) by N,N′-di-p-tolylpyridine-2,6-dicarboxamide from nitric acid
solution, J. Radioanal. Nucl. Chem. 297 (2013) 133–137.
doi:10.1007/s10967-012-2352-3.
[13] J.E. Birkett, M.J. Carrott, O.D. Fox, C.J. Jones, C.J. Maher, C. V. Roube, R.J.
Taylor, D.A. Woodhead, Recent Developments in the Purex Process for Nuclear
Fuel Reprocessing: Complexant Based Stripping for Uranium/Plutonium
Separation, Chim. Int. J. Chem. 59 (2005) 898–904.
doi:10.2533/000942905777675327.
[14] L.-Y. Yuan, Y.-L. Liu, W.-Q. Shi, Z. Li, J.-H. Lan, Y.-X. Feng, Y.-L. Zhao, Y.-L.
Yuan, Z.-F. Chai, A novel mesoporous material for uranium extraction,
dihydroimidazole functionalized SBA-15, J. Mater. Chem. 22 (2012) 17019.
doi:10.1039/c2jm31766d.
[15] S. Yu, X. Wang, X. Tan, X. Wang, Sorption of radionuclides from aqueous
systems onto graphene oxide-based materials: a review, Inorg. Chem. Front. 2
(2015) 593–612. doi:10.1039/C4QI00221K.
[16] S. Yu, X. Wang, W. Yao, J. Wang, Y. Ji, Y. Ai, A. Alsaedi, T. Hayat, X. Wang,
Macroscopic, Spectroscopic, and Theoretical Investigation for the Interaction of
Phenol and Naphthol on Reduced Graphene Oxide, Environ. Sci. Technol. 51
(2017) 3278–3286. doi:10.1021/acs.est.6b06259.
[17] L. Zhu, L. Zhang, J. Li, D. Zhang, L. Chen, D. Sheng, S. Yang, C. Xiao, J. Wang,
Z. Chai, T.E. Albrecht-Schmitt, S. Wang, Selenium Sequestration in a Cationic
Layered Rare Earth Hydroxide: A Combined Batch Experiments and EXAFS
Investigation, Environ. Sci. Technol. 51 (2017) 8606–8615.
doi:10.1021/acs.est.7b02006.
[18] M. Akamatsu, H. Komatsu, A. Matsuda, T. Mori, W. Nakanishi, H. Sakai, J.P.

ACCEPTED MANUSCRIPT
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
Hill, K. Ariga, Visual Detection of Cesium Ions in Domestic Water Supply or
Seawater using a Nano-optode, Bull. Chem. Soc. Jpn. 90 (2017) 678–683.
doi:10.1246/bcsj.20170046.
[19] J. Li, X. Wang, G. Zhao, C. Chen, Z. Chai, A. Alsaedi, T. Hayat, X. Wang,
Metal–organic framework-based materials: superior adsorbents for the capture
of toxic and radioactive metal ions, Chem. Soc. Rev. 47 (2018) 2322–2356.
doi:10.1039/C7CS00543A.
[20] I. Saptiama, Y.V. Kaneti, H. Oveisi, Y. Suzuki, K. Tsuchiya, K. Takai, T. Sakae,
S. Pradhan, M.S.A. Hossain, N. Fukumitsu, K. Ariga, Y. Yamauchi,
Molybdenum Adsorption Properties of Alumina-Embedded Mesoporous Silica
for Medical Radioisotope Production, Bull. Chem. Soc. Jpn. 91 (2018) 195–200.
doi:10.1246/bcsj.20170295.
[21] S. Yu, J. Wang, S. Song, K. Sun, J. Li, X. Wang, Z. Chen, X. Wang, One-pot
synthesis of graphene oxide and Ni-Al layered double hydroxides
nanocomposites for the efficient removal of U(VI) from wastewater, Sci. China
Chem. 60 (2017) 415–422. doi:10.1007/s11426-016-0420-8.
[22] X. Wang, S. Yang, W. Shi, J. Li, T. Hayat, X. Wang, Different Interaction
Mechanisms of Eu(III) and 243 Am(III) with Carbon Nanotubes Studied by Batch,
Spectroscopy Technique and Theoretical Calculation, Environ. Sci. Technol. 49
(2015) 11721–11728. doi:10.1021/acs.est.5b02679.
[23] † A. Kowal-Fouchard, *,† R. Drot, † and E. Simoni, J.J. Ehrhardt‡, Use of
Spectroscopic Techniques for Uranium(VI)/Montmorillonite Interaction
Modeling, (2004). doi:10.1021/ES0348344.
[24] L.D. Troyer, F. Maillot, Z. Wang, Z. Wang, V.S. Mehta, D.E. Giammar, J.G.
Catalano, Effect of phosphate on U(VI) sorption to montmorillonite: Ternary
complexation and precipitation barriers, Geochim. Cosmochim. Acta. 175 (2016)
86–99. doi:10.1016/J.GCA.2015.11.029.
[25] B. Hu, X. Mei, X. Li, J. Hu, D. Xu, J. Ma, Y. Huang, Decontamination of U(VI)

ACCEPTED MANUSCRIPT
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
from nZVI/CNF composites investigated by batch, spectroscopic and modeling
techniques, J. Mol. Liq. 237 (2017) 1–9. doi:10.1016/J.MOLLIQ.2017.04.084.
[26] Z. Zhang, J. Liu, X. Cao, X. Luo, R. Hua, Y. Liu, X. Yu, L. He, Y. Liu,
Comparison of U(VI) adsorption onto nanoscale zero-valent iron and red soil in
the presence of U(VI)–CO3/Ca–U(VI)–CO3 complexes, J. Hazard. Mater. 300
(2015) 633–642. doi:10.1016/J.JHAZMAT.2015.07.058.
[27] L. Li, W. Ma, S. Shen, H. Huang, Y. Bai, H. Liu, A Combined Experimental and
Theoretical Study on the Extraction of Uranium by Amino-Derived Metal–
Organic Frameworks through Post-Synthetic Strategy, ACS Appl. Mater.
Interfaces. 8 (2016) 31032–31041. doi:10.1021/acsami.6b11332.
[28] W. Yang, Z.-Q. Bai, W.-Q. Shi, L.-Y. Yuan, T. Tian, Z.-F. Chai, H. Wang, Z.-M.
Sun, MOF-76: from a luminescent probe to highly efficient UVI sorption
material, Chem. Commun. 49 (2013) 10415. doi:10.1039/c3cc44983a.
[29] * Adrien P. Côté, Hani M. El-Kaderi, Hiroyasu Furukawa, and Joseph R. Hunt,
O.M. Yaghi*, Reticular Synthesis of Microporous and Mesoporous 2D Covalent
Organic Frameworks, (2007). doi:10.1021/JA0751781.
[30] S. Zhang, X. Zhao, B. Li, C. Bai, Y. Li, L. Wang, R. Wen, M. Zhang, L. Ma, S.
Li, “Stereoscopic” 2D super-microporous phosphazene-based covalent organic
framework: Design, synthesis and selective sorption towards uranium at high
acidic condition, J. Hazard. Mater. 314 (2016) 95–104.
doi:10.1016/j.jhazmat.2016.04.031.
[31] J. Li, X. Yang, C. Bai, Y. Tian, B. Li, S. Zhang, X. Yang, S. Ding, C. Xia, X. Tan,
L. Ma, S. Li, A novel benzimidazole-functionalized 2-D COF material:
Synthesis and application as a selective solid-phase extractant for separation of
uranium, J. Colloid Interface Sci. 437 (2015) 211–218.
doi:10.1016/j.jcis.2014.09.046.
[32] R. Wen, Y. Li, M. Zhang, X. Guo, X. Li, X. Li, J. Han, S. Hu, W. Tan, L. Ma, S.
Li, Graphene-synergized 2D covalent organic framework for adsorption: A

ACCEPTED MANUSCRIPT
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
mutual promotion strategy to achieve stabilization and functionalization
simultaneously, J. Hazard. Mater. 358 (2018) 273–285.
doi:10.1016/j.jhazmat.2018.06.059.
[33] R. Gomes, A. Bhaumik, A new triazine functionalized luminescent covalent
organic framework for nitroaromatic sensing and CO 2 storage, RSC Adv. 6
(2016) 28047–28054. doi:10.1039/C6RA01717G.
[34] S. Kanti Das, S. Mishra, K. Manna, U. Kayal, S. Mahapatra, K. Das Saha, S.
Dalapati, G.P. Das, A.A. Mostafa, A. Bhaumik, A new triazine based
π-conjugated mesoporous 2D covalent organic framework: its in vitro anticancer
activities, Chem. Commun. 54 (2018) 11475–11478.
doi:10.1039/C8CC07289B.
[35] H. Furukawa, O.M. Yaghi, Storage of Hydrogen, Methane, and Carbon Dioxide
in Highly Porous Covalent Organic Frameworks for Clean Energy Applications,
J. Am. Chem. Soc. 131 (2009) 8875–8883. doi:10.1021/ja9015765.
[36] N. Huang, X. Chen, R. Krishna, D. Jiang, Two-Dimensional Covalent Organic
Frameworks for Carbon Dioxide Capture through Channel-Wall
Functionalization, Angew. Chemie Int. Ed. 54 (2015) 2986–2990.
doi:10.1002/anie.201411262.
[37] Y. Zhang, S.N. Riduan, Functional porous organic polymers for heterogeneous
catalysis, Chem. Soc. Rev. 41 (2012) 2083–2094. doi:10.1039/C1CS15227K.
[38] Q. Fang, S. Gu, J. Zheng, Z. Zhuang, S. Qiu, Y. Yan, 3D Microporous
Base-Functionalized Covalent Organic Frameworks for Size-Selective Catalysis,
Angew. Chemie. 126 (2014) 2922–2926. doi:10.1002/ange.201310500.
[39] S. Wan, F. Gándara, A. Asano, H. Furukawa, A. Saeki, S.K. Dey, L. Liao, M.W.
Ambrogio, Y.Y. Botros, X. Duan, S. Seki, J.F. Stoddart, O.M. Yaghi, Covalent
Organic Frameworks with High Charge Carrier Mobility, Chem. Mater. 23
(2011) 4094–4097. doi:10.1021/cm201140r.
[40] N. Huang, L. Zhai, H. Xu, D. Jiang, Stable Covalent Organic Frameworks for

ACCEPTED MANUSCRIPT
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
Exceptional Mercury Removal from Aqueous Solutions, J. Am. Chem. Soc. 139
(2017) 2428–2434. doi:10.1021/jacs.6b12328.
[41] Z. Li, Y. Zhang, H. Xia, Y. Mu, X. Liu, A robust and luminescent covalent
organic framework as a highly sensitive and selective sensor for the detection of
Cu 2+ ions, Chem. Commun. 52 (2016) 6613–6616. doi:10.1039/C6CC01476C.
[42] J. Li, X. Yang, C. Bai, Y. Tian, B. Li, S. Zhang, X. Yang, S. Ding, C. Xia, X. Tan,
L. Ma, S. Li, A novel benzimidazole-functionalized 2-D COF material:
Synthesis and application as a selective solid-phase extractant for separation of
uranium, J. Colloid Interface Sci. 437 (2015) 211–218.
doi:10.1016/J.JCIS.2014.09.046.
[43] C. Bai, J. Li, S. Liu, X. Yang, X. Yang, Y. Tian, K. Cao, Y. Huang, L. Ma, S. Li,
In situ preparation of nitrogen-rich and functional ultramicroporous
carbonaceous COFs by “segregated” microwave irradiation, Microporous
Mesoporous Mater. 197 (2014) 148–155.
doi:10.1016/j.micromeso.2014.06.004.
[44] D. Liu, Z. Liu, C. Wang, Y. Lai, Removal of uranium(VI) from aqueous solution
using nanoscale zero-valent iron supported on activated charcoal, J. Radioanal.
Nucl. Chem. 310 (2016) 1131–1137. doi:10.1007/s10967-016-4892-4.
[45] Y. Dai, Y. Liu, A. Zhang, Preparation and characterization of a mesoporous
polycrown impregnated silica and its adsorption for palladium from highly acid
medium, J. Porous Mater. 24 (2017) 1037–1045.
doi:10.1007/s10934-016-0343-4.
[46] S. Karak, S. Kandambeth, B.P. Biswal, H.S. Sasmal, S. Kumar, P. Pachfule, R.
Banerjee, Constructing ultraporous covalent organic frameworks in seconds via
an organic terracotta process, J. Am. Chem. Soc. 139 (2017) 1856–1862.
doi:10.1021/jacs.6b08815.
[47] M.-J. Gang, B.-E. Han, P.-S. Han, RESEARCH PAPERSꢀ: PRECIPITATION
AND ADSORPTION OF URANIUM ( 4 ) UNDER VARIOUS AQUEOUS

ACCEPTED MANUSCRIPT
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
CONDITIONS, Environ. Eng. Res. 7 (2002) 149–157.
doi:10.4491/eer.2002.7.3.149.
[48] H. Parab, S. Joshi, N. Shenoy, R. Verma, A. Lali, M. Sudersanan, Uranium
removal from aqueous solution by coir pith: equilibrium and kinetic studies,
Bioresour. Technol. 96 (2005) 1241–1248. doi:10.1016/j.biortech.2004.10.016.
[49] L. Zhou, J. Liu, Z. Liu, Adsorption of platinum(IV) and palladium(II) from
aqueous solution by thiourea-modified chitosan microspheres, J. Hazard. Mater.
172 (2009) 439–446. doi:10.1016/j.jhazmat.2009.07.030.
[50] M. Carboni, C.W. Abney, S. Liu, W. Lin, Highly porous and stable metal–
organic frameworks for uranium extraction, Chem. Sci. 4 (2013) 2396.
doi:10.1039/c3sc50230a.
[51] Z.-Q. Bai, L.-Y. Yuan, L. Zhu, Z.-R. Liu, S.-Q. Chu, L.-R. Zheng, J. Zhang, Z.-F.
Chai, W.-Q. Shi, Introduction of amino groups into acid-resistant MOFs for
enhanced U( vi ) sorption, J. Mater. Chem. A. 3 (2015) 525–534.
doi:10.1039/C4TA04878D.
[52] J.-Y. Zhang, N. Zhang, L. Zhang, Y. Fang, W. Deng, M. Yu, Z. Wang, L. Li, X.
Liu, J. Li, Adsorption of Uranyl ions on Amine-functionalization of MIL-101(Cr)
Nanoparticles by a Facile Coordination-based Post-synthetic strategy and X-ray
Absorption Spectroscopy Studies, Sci. Rep. 5 (2015) 13514.
doi:10.1038/srep13514.
[53] L.L. Wang, F. Luo, L.L. Dang, J.Q. Li, X.L. Wu, S.J. Liu, M.B. Luo, Ultrafast
high-performance extraction of uranium from seawater without pretreatment
using an acylamide- and carboxyl-functionalized metal–organic framework, J.
Mater. Chem. A. 3 (2015) 13724–13730. doi:10.1039/C5TA01972A.
[54] J.Q. Li, L. Le Gong, X.F. Feng, L. Zhang, H.Q. Wu, C.S. Yan, Y.Y. Xiong, H.Y.
Gao, F. Luo, Direct extraction of U(VI) from alkaline solution and seawater via
anion exchange by metal-organic framework, Chem. Eng. J. 316 (2017) 154–
159. doi:10.1016/j.cej.2017.01.046.