Facile synthesis of porous organic polymers for the absorption of Pd(II) ions and organic dyes

Article abstract of DOI:10.1039/c6ra17790e

Porous organic polymers (POPs) were prepared via two-step reactions. In the first step, dialdehyde compounds were synthesized using the Suzuki-Miyaura coupling reaction, and in the second step, the dialdehyde compounds reacted with hydrazine hydrate to fo

Full text of DOI:10.1039/c6ra17790e

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Facile Synthesis of Porous Organic Polymers for the Absorption of
Pd(Ⅱ) Ions and Organic Dyes
Yanmei Luoa, Junhui Rana, Rong Chenb, and Xinjian Chenga*
aSchool of Textiles and Garments, Southwest University, Chongqing, P. R. China,
400715
bSchool of Chemical Engineering and Pharmacy, Wuhan Institute ofTechnology,
Wuhan, P. R. China 430073
Abstract: Porous organic polymers (POPs) were prepared via two-step reactions. In
the first step, dialdehyde compounds were synthesized by Suzuki-Miyaura coupling
reaction. And in the second step, the dialdehyde compounds reacted with hydrazine
hydrate to form polymers by the Schiff's base formation reactions. These POPs are
layer-nanosheet structured, crystalline and fluorescent. They are studied by FTIR,
Fluorescence spectra, UV-Vis, SEM, TEM, XRD, DSC, and TGA. It is found that the
pore parameters, such as specific surface areas and pore diameters of the POPs could
be adjusted by changing the reaction time and temperature. The specific surface areas
increased with the increasing of reaction time and temperature. The maximum
specific surface area could reach 715.6 m2/g. Furthermore, the POPs could detect and
remove Pd(Ⅱ) ions and organic dyes. When contact with Pd( Ⅱ) ions, the
fluorescence of the POPs quenched, and the POPs could absorb Pd(Ⅱ) ions as well.
The maximum absorption capacity for Pd(Ⅱ) ions could reach 20.6 mg/g within 5min.
* Corresponding author, Dr. Cheng, chxj606@163.com
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Meanwhile, the POPs could absorb two model dyes, rhodamine B (RhB) and
methylene blue (MB), with high efficiency within 5min.
Keywords: POPs nanosheet, absorption of Palladium ions, absorption of organic dyes
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1. Introduction
In recent years, organic dyes and heavy metal ions are becoming serious pollutants
to environments and creatures with the development of the industry. Palladium is
often employed as high-performance catalyst in most organic reactions. And
sometimes the pollutions caused by Pd are neglected. Pd could lead to disease when it
is enriched in human body. Rhinoconjunctivitis, allergy and asthma could be caused
by it[1]. Therefore, detection and recycling of Pd ions are very important.
Fluorescent sensors have attracted considerable attention due to their ability to
detect and remove some metal ions. Some chemosensors have been proved can detect
Pd(Ⅱ)ions with high sensitivity and selectivity[2-4].Ezoddin et al [5] have prepared
hydrophilicity-switchable solvent for the recognition of palladium by air-assisted
liquid-liquid micro-extraction. The recognition limit value reaches 0.07 ꢀg/L. Yan et
al [6] have synthesized a fluorometric and colorimetric NBD-PMA chemosensor for
selective detection of palladium(Ⅱ) ions. These sensor could selectively coordinate
with palladium(Ⅱ) ions with a color change from yellow to pink. And the change
could be detected by the naked eyes. In our previous work, fluorescent nanoparticles
and glass were prepared and used for detection and removal of Pd(Ⅱ) ions[7]. In
addition, fluorescent conjugated polymers have attracted much attention due to the
“molecular wire” effect. When contact with metal ions, the fluorescence could be
magnified. These conjugated polymers could detected Pd ions with high sensitivity.
Bai’s group [8, 9] have prepared this kind of conjugated polymers for the detection of
palladium ions.
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Organic dyes are widespread because of their splendid colors with the development
of garments industry. Meanwhile, they are hazardous materials to our water resource,
soils and atmosphere.For the treatment of organic dye pollutants, degradation and
adsorption are the frequently used methods. For example, in our previous work[10], a
composite nano-fiber mat was prepared and employed to treat MB pollutants. The
mat could photo-degradeMB under UV light. Zhu et al.[11] have prepared porous
coordination polymers for the degradation of organic dyes. The as-prepared porous
polymers could treat rhodamine B (RhB), methylene blue (MB) and safranine T (ST),
the dyes degraded in neutral aqueous solution with high efficiency.
Porous organic polymers (POPs) have attracted much attention due to their unique
structures. Most POPs have large surface area[12], high chemical stabilities and low
skeleton density[13].They can be applied to gas storage and separation [12-15],
adsorption of CO2[15-18], catalysis[19-22] and chemical sensing[23-25]. For example,
Yu et al[13] have synthesized microporous polyphenylenes via ethynyl trimerization
reaction with aromatic ethynyl monomers. Their pore diameter and BET surface areas
reached 0.7 nm and 1246 m2/g respectively.These microporous polyphenylenes could
be used to store hydrogen. In general, POPs have porous network structures or
three-dimensional organic frameworks.This structure provides a wide interface for gas
capture, so POPs can be used as chemosensor[26-30]for many chemicals. Conjugated
microporous polymers were prepared by Adams et al[28] via Ni-catalyzed Yamamoto
polymerization between 1,3,6,8-tetrabromopyrene and 1,4-dibromobenzene. The
as-prepared microporous polymers have high luminescence and the emission colour
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could be tuned by introducing varying comonomers. Most of POPs have π-conjugated
characteristics so that they are sensitiveto electron-deficient compounds[31-34].
Zheng et al [35] have synthesized POPs with high thermostability due to the rigid
macro-cyclic structures. Suh et al [36] have synthesized POPs of considerable surface
areas (830 m2/g) with as high CO2 capture ability as 3.14 mmol/g.In addtion, chang et
al [37] have synthesized indole-based microporous organic polymer by the reaction of
1,3,5-tris-(4-fluorobenzoyl)benzene and 3,3 ´-diindolylmethane via nucleophilic
substitution reaction. The preparative strategy of the microporous organic polymer
exhibits cost-effective advantages. The polymer have considerable BET surface area
(2090 m2/g), large adsorption capacity (16.0 wt%) for carbon dioxide and hydrogen
storage (2.48 wt%). Its good performance shows application vision in the
environmental technology. Moreover, mannitol-based and ketal-linked porous organic
polymers were prepared by Ding et al [38]through condensation reaction between
mannitol and aromatic acetyl monomers. They demonstrated high carbon dioxide
uptake (11.5 wt%) due to hydroxyl-rich structures and the predominant micropores.
In this work, two fluorescent POPs were prepared.They exhibited sensing and
separation ability to Pd ions. Also they exhibited high-performance to absorb organic
dyes. Firstly, two intermediate dialdehydes were prepared with 1,4-benzenediboronic
acid and 4-bromobenzaldehyde by Suzuki-Miyaura coupling reaction. And then, two
porous organic polymers was synthesized via Schiff's base formation reaction. In the
process of polymerization, POPs (two kinds of polymers are named as P1 and P2
series) were obtained. P1 and P2 exhibit excellent ability to detect Pd(Ⅱ) ions, the
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fluorescence quenched dramatically when contact Pd(Ⅱ) ions. In addition,these POPs
could rapidly absorb organic dyes in aqueous solution with high efficiency.
2. Experimental section
2.1 Materials
6-bromo-3-pyridinecarboxaldehyde, 4-bromobenzaldehyde, 1,4-benzenediboronic
acid, tetrakis(triphenylphosphine)palladium(0),hydrazine hydrate, rhodamine B, and
methylene blue were purchased from J&K China Chemical Ltd. All metal salts
(Fe(Ⅲ), Cr(Ⅲ), Mn(Ⅱ), Co(Ⅱ), Cd(Ⅱ), Zn(Ⅱ), Ag(Ⅰ), Pb(Ⅱ), Ca(Ⅱ), Ni(Ⅱ),
Cu(Ⅱ), Na(Ⅰ), K(Ⅰ), Hg(Ⅱ), Mg(Ⅱ), Fe(Ⅱ) and Pd(Ⅱ)) were purchased from
Aladdin chemical co., Ltd and used as received. All solvents were also purchased
from Aladdin chemical co., Ltd. They were dried before using.
2.2 Synthesis of 4''-Aldehyde-[1,1',4',1'']terphenyl-4-carbaldehyde (compound 1)
and 6-[4-(5-Aldehyde-pyridin-2-yl)-phenyl]-pyridine-3-carbaldehyde (compound
2)
Compound 1 was prepared by Suzuki-Miyaura coupling reaction[39] using the
following procedure: mix 4-bromobenzaldehyde (1 mmol), 1,4-benzenediboronic acid
(0.6 mmol), Na2CO3 (1.5 mmol) in deionized water (10 mL) and DMF (10 mL) with
nitrogen atmosphere at room temperature. After being stirred for 0.5 h,
tetrakis(triphenylphosphine)palladium(0) (0.1% mmol) was added. The reaction
mixture was stirred for 8h at 80 ℃. Thereafter, the mixture was extracted with
trichloromethane (20 mL, 3 times). The extract was dried by the anhydrous Na2SO4,
and then the solvent was evaporated to obtain crude product. It was purified through
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column chromatography with CHCl3/petroleum ether as eluent. White solid was
obtained, its yield was 72.5%. 1H NMR spectra data (Supporting information, Fig. S1)
of compound 1 are as follows (DMSO-d6, 600 MHz): 10.079 (s, 2H), 8.027 (s, 8H),
7.945 (s, 4H). Using the same procedure, Compound 2was obtained, its yield was
53.2%. 1H NMR spectra data (Fig. S2) of compound 2 are as follows (DMSO-d6, 600
MHz): 10.168 (s, 2H), 9.207(d, 2H), 8.394 (s, 6H), 8.336 (s, 2H).
2.3 Synthesis of porous organic polymericnano-sheet
POP nanosheet (P1) was synthesized with the reaction between compound 1 and
hydrazine hydrate (0.98 : 1, molar ratio) in DMF. Four different reaction conditions
were investigated and different products were obtained. That is under 80oC for 24h
(named as P1-1), under 160oC for 24h (named as P1-2), under 160oC for 40h (named
as P1-3), and under 160oC for 24h (named as P1-4) respectively. The crude product
were washed by DMF and water for three times. The other series of porous organic
polymer nano-sheet (P2-1 to P2-4) was synthesized using the same method.
2.4 Characterization
1H NMR was analyzed by AVANCE III 600 MHz instrument (Bruker), Fourier
transform infrared spectra (FTIR, 4000-400cm−1 ) were performed on a Nicolet
NEXUS 470 spectrometer. Fluorescence spectra were measured on a Shimadzu
F-4600 FL spectrophotometer. UV-Vis absorption was measured on a UV-5900PC
spectrophotometer (METASH). Differential scanning calorimetry was measured by
DSC 214 Polyma instrument. The POPs were observed by the scanning electron
microscopy (SEM, JEOL JSM-7600F) and Transmission electron microscope (TEM,
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JEOL JEM-2100). Zeta potentials were recorded on a Zeta Plus S/N21479
(Brookhaven Instrument Corporation). Thermogravimetric Analysis (TGA) was
conducted on a 209F3 Tarsus NETZSCH instrument. Porous structure was analyzed
by BET (Quantachrome Instruments version 4.01). Elemental analysis were measured
by a Elementar Vario Micro Select instrument (Germany). Atomic Absorption
spectrometry (AAS) were measured by an ICP single channel scanning spectrometer
(Z-5000).
3. Result and discussion
3.1 Synthesis and characterization of P1 and P2
The synthesis procedure of POPnanosheet (P1 and P2) was presented in Scheme 1.
In step 1, compound 1 was prepared via Suzuki-Miyaura coupling reaction between
4-bromobenzaldehyde and 1,4-benzenediboronic acid. Compound 2 was also prepared
via Suzuki-Miyaura reaction between 1,4-benzenediboronic acid and
6-bromo-3-pyridinecarboxaldehyde. Instep 2, POPs(P1 and P2) were prepared via
polycondensations between compound 1/compound 2 and hydrazine hydrate.
Step 1
Br
CHO
Compound 1
1. DMF, H2O
2. Na2CO3
+
OHC
CHO
3. Pd[P(C6H5)3]4
OH
HO
B
B
OH
HO
NH2
NH2
Step 2
DMF
HN NH
n
n
CH
NH NH
C
N
N
C
H
H
m
P1
Scheme. 1 Synthesis procedure of compound 1 and P1.
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P1 and P2 couldn’t be dissolved incommon solvents, such as DMF, DMSO, ethanol,
methanol, THF, acetone, trichloromethane and dichlormethane and so on. The
structures of compound 1,compound 2,P1, and P2 were confirmed by FTIR and
shown in Fig. 1. The strong absorption bands of aldehyde groups in compound 1 and
compound 2 at 1687 cm-1could be seen clearly. When the polymers were formed,
peaks at 1687 cm-1 became weaker, it indicated aldehyde groups reacted with
NH2NH2. Besides, the characteristic absorption of imine linkage (-C=N-), aliphatic
(-C-N-) and amine (N-H) were observed at 1620 cm-1, 1217 cm-1 and 3380 cm-1.These
peaks further confirmed the successful preparation of the POPs.
1.4
1.2
P1
P2
1.2
1.0
1.0
Compound 2
compound 1
0.8
0.8
1.2
0.6
1.2
0.6
0.9
0.4
0.2
0.0
0.4
0.2
0.0
0.8
0.6
0.4
0.3
1500
1200
2500
900
2000
4000
3500
3000
2500
2000
1500
1000
500
4000
3500
3000
1500
1000
500
Wavenumber cm-1
Wavenumber cm-1
(a)
(b)
Fig. 1 FTIR spectra of (a) compound 1and P1 and (b) compound 2 and P2.
The elemental analysis data of P1 and P2 were listed in the table 1. It can be seen
that the measured mass fractions (in P1) of C, H and N elemental were 84.0%, 5.2%
and 10.6% respectively. Similarly, in table 1, the elemental composition data of P2
was displayed. It indicated the measured mass fractions (in P2) of C, H and N
elemental were 72.2%, 4.5% and 16.8% respectively. However, according to the
theoretical calculation,ifthere was only C=N bond in the P1, the mass fraction of C, H
and N elemental should be 85.1%, 5.0% and 9.9%. While ifthere was only C-N in the
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P1, the mass fraction of C, H and N elemental should be 76.5%, 5.7% and 17.8%
respectively. These data indicated that there were both -C-N-bond and -C=N- bond in
P1. Similarly, there were both C-N bond and C=N bond in P2.
Table 1 The elemental analysis of P1 and P2.
Entry
P1
C(%)
84.0
72.2
H(%)
5.2
N(%)
10.6
16.8
P2
4.5
3.2 The morphology, structure and thermostability of P1 and P2
To study the morphology and structure of materials, SEM and TEM are often
employed [40, 41]. SEM and TEM photographs of P1 and P2 were obtained and
shown in Fig. 2. From the high resolution TEM, the sheets of POPs could be seen
clearly. And by the selected area electron diffraction (SAED) pattern (inset in Fig. 2a),
the crystalline structures could be observed. However, compared with some inorganic
mareriaals, the difraction pattern is weaker. For the sake of more accuracy, X-ray
diffraction measurement was conducted in the following. From Fig. 2b, c, d, e and f,
it could be seen that P1 and P2 exhibit layered nanosheet structures, and the layers are
parallelly pilled up. There were many pores between the layers. The distance between
layersof P1-2, P1-3, P2-1, P2-2 and P2-3 were approximately calculated. And they are
44 5nm, 32 5nm, 68 5nm, 42 5nm and 30 5nm respectively. The results indicated
that the distance between layers decreased with the increase of reaction time and
reaction temperature.
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(a)
(b)
(c)
(d)
(e)
(f)
Fig. 2TEM (inset is the diffraction
Pattern) image of (a) P1-1, and SEM of (b) P1-2, (c) P1-3, (d) P2-1, (e) P2-2 and (f)
P2-3.
XRD measurements of P1 and P2 were conducted.And the data were measured at a
scanning rate of 4° min-1 in the 2θ range of 5° to 70°. In Fig. 3, P1 and P2 show sharp
peaks, it indicates the crystalline structures. P1 and P2 possess three peak at 2θ values
of about 20°/20°, 23°/25° and 28°/30°.
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6000
5000
4000
3000
2000
1000
0
P2
P1
10
20
30
40
50
60
70
2 Theta (degree)
Fig. 3 Powder X-ray diffraction of P1 and P2.
Compound 1, compound 2, P1, and P2 were investigated by TGA under N2
atmosphere. As shown in the Fig. 4 (a), the decomposing temperature of compound 1
o
o
was 311 C, the decomposing temperature of the polymers were 408 C. It indicated
the high thermal stability of P1 when compound 1waspolymerized. Similarly, thermal
stability of P2 (402 oC) were higher than compound 2 (300 oC).
100
80
60
40
20
0
100
80
60
40
20
0
(a)
(b)
P2-3
P2-2
P1-3
P1-2
P1-1
P2-1
Compound 1
Compound 2
100
200
300
400
500
600
700
200
400
600
Temperature (oC)
Temperature (oC)
Fig. 4 TGA cures of (a) compound 1, P1-1, P1-2 and P1-3 and (b) compound 2, P2-1,
P2-2 and P2-3.
Differential scanning calorimetry (DSC) curves of P1 and P2 were analyzed at a
o
heating rate of 10 °C min-1 in the temperature range of -50 C to 500oC. Each sample
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was tested for three times. As shown in the Fig. 5, there is not a noticeable glass
transition for P1. This may be caused by a relatively high degree of cross-linking.
There was a exothermic peak at 418 oC, it could be attributed to the crystallization. In
addition, there was a glass transition peak for P2 at 85 oC and at a crystallization peak
at 410 oC.
3
P2
85 oC
2
410 oC
1
0
P1
-1
-2
-3
-4
418 oC
-5
0
100
200
300
400
500
Temperature (oC)
Fig. 5Differential Scanning Calorimetry (DSC) analysis of P1 and P2.
The zeta potentials of P1 and P2 were measured in the range of pH from 2 to12.
When P1 and P2 were in a lower pH value, the protonation on the N atoms occurred,
and the nano-sheets were positively charged. And in a higher pH value, the
deprotonation on the N atoms occurred, the nano-sheets were negatively charged. As
shown in the Fig. S3, zeta potential vspH curves were plotted. P1 and P2 have almost
the same isoelectric points of 4.4 and 4.3.
3.3 Porous Structure of Polymers (P1 and P2)
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The porous structures of polymers (P1 and P2) were measured by nitrogen sorption
at 77 K (Fig. 6), which revealed P1 and P2 are of the mesoporous structures. And
indicated typical type-
Ⅲ mesoporous materials. The isotherms of all POPs exhibited
the adsorbing volumes increased with the increase of relative pressure.
70
60
50
40
30
20
10
0
140
120
100
80
(b)
(a)
60
40
20
0
0.0
0.2
0.2
0.2
0.4
0.6
0.8
0.8
0.8
1.0
1.0
1.0
0.0
0.2
0.2
0.2
0.4
0.6
0.8
0.8
0.8
1.0
1.0
1.0
Relative pressure
(P/Po
)
)
)
Relative pressure
(P/Po
)
)
)
250
200
150
100
50
(c)
80
60
40
20
0
(d)
0
0.0
0.4
0.6
0.0
0.4
0.6
Relative pressure
(P/Po
Relative pressure (P/Po
100
80
60
40
20
0
140
120
100
80
(e)
(f)
60
40
20
0
0.0
0.4
0.6
0.0
0.4
0.6
Relative pressure
(P/Po
Relative pressure (P/Po
Fig. 6 Nitrogen gas adsorption and desorption isotherms (measured at 77 K) for (a)
P1-1, (b) P1-2, (c) P1-3, (d) P2-1, (e) P2-2 and (f) P2-3.
The BET surface area (SBET) of (a) P1-1, (b) P1-2, (c) P1-3, (d) P2-1, (e) P2-2 and
(f) P2-3 were calculated by adsorption and desorption isotherms data and shown in
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table 2. The maximum BET surface area (SBET) could reach 716 m2/g. The minimum
average pore size could be 21nm.
Table 2 Porosity parameters of P1 and P2.
Entry
P1-1
304
42
P1-2
618
27
P1-3
716
24
P2-1
404
38
P2-2
587
30
P2-3
660
21
SBET (m2/g)
Average pore size(nm)
Compared with the adsorption ability of (a)P1-1, (b) P1-2 and (c) P1-3, the
maximum adsorbed volume increased. P2-1, P2-2 and P2-3 have the same trends. It
means that the maximum adsorbed volume could be tuned by adjusting the
preparation conditions of the POPs. With the increase of temperature and reaction
time, the high specific surfaces areas of POPs could be obtained.
3.4 Detectingmetal ions by compound 1 and compound 2
To investigate the detecting ability of the compound 1 and compound 2, a series of
experiments were conducted. Compound 1 and compound 2 turned from colorless to
colored when contact with Fe(
(Cr( ), Mn( ), Co( ), Cd(
Na( ), K( ), Hg( ), and Mg(
compound 1 and compound 2could detect Fe(
Ⅲ
), Fe(
), Zn(
) showed no color change. It indicated that
), Fe( )and Pd( ) ions. And the
), Fe( )and Pd(
Ⅱ
)and Pd(
Ⅱ
) ions. Other heavy metal ions
Ⅲ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
), Ag( ), Pb(
Ⅰ
Ⅱ
), Ca( ), Ni( ), Cu( ),
Ⅱ
Ⅱ
Ⅱ
Ⅰ
Ⅰ
Ⅱ
Ⅱ
Ⅲ
Ⅱ
Ⅱ
fluorescence became weaker when being contacted with Fe(
Ⅲ
Ⅱ
Ⅱ)
ions.
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Fig. S4 shows the UV–Vis spectra. The absorbance peaks of compound 1
([Compound 1]=5 µ ) with Fe( ), Fe( )and Pd( )ions shifted (Fig. S4 a). It could
be seen clearly the peak of about 317nm disappeared when compound 1contacted
with Fe( ), Fe( )and Pd( )ions, the peaks of 331nm 333nm and 335nm appeared.
M
Ⅲ
Ⅱ
Ⅱ
Ⅲ
Ⅱ
Ⅱ
Similarly, compound 2([compound 2]=5 µ
1(in Fig. S4b).
M) shows the same change as compound
The fluorescence properties of compound 1 and compound 2with different heavy
metal ions were shown in Fig. S5.Taking compound 1 (Fig. S5 (a)) as an example, the
fluorescence intensity decreased when compound 1 contacted with Fe(
Pd( ) ions respectively. The fluorescence changes of compound 2 were similar to
compound 1 in Fig. S5(b). The results further demonstrated that compound 1 and
compound 2 could selectively recognize Fe( ), Fe( )and Pd( ) ions by
fluorescence measurement. Meanwhile, the fluorescence intensity of compound 2
gradually decreased with increasing Fe( ) concentrations at about 426 nm (Fig. S5
(c)). Also, from Figure S4(d), it could be seen that the fluorescence intensity of
compound 2 decreased with increasing Pd( ). And when the concentration of Pd(
ions lowered to 5 µ , change of color and fluorescence of compound 1 and
compound 2 still could be seen.
3.5 Detecting Pd( ) ion by P1 and P2
Ⅲ), Fe(Ⅱ) and
Ⅱ
Ⅲ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅱ)
M
Ⅱ
First, the influences of pH value to the polymer were tested using Britton-Robinson
buffer solutions. And it can be seen that no notable changes in UV-Vis spectra and
fluorescence spectra in the pH value range of 2 to11. Then all the experiments were
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measured in the pH of 6.8 Briton-Robinson buffer solution. The sensing ability of the
fluorescent P1 and P2 were investigated. 5 equivalent metal ion solution ((Cr(
Mn( ), Co( ), Cd( ), Zn( ), Ag( ), Pb( ), Ca( ), Ni( ), Cu( ), Na(
K( ), Hg( ), Mg( ), Fe( ), Fe( ) and Pd(
P2([Polymer]=2.5µ in repeat units) suspensions at room temperature. Taking P1 (Fig.
S6) as an example, the color of P1 suspension changed dramatically from yellow to
orange upon addition of Pd( ) ions, and the color of adding other ions didn’t change
under UV light and natural light. In Fig. S6, the color changed via interaction between
Pd( ) ions and P1 rather than intrinsic color of Pd( ) solution. Similarly, the P2
suspension had the same change. It indicated that P1 and P2 could be employed to
detect Pd( ) ions as polymeric chemosensors. The mixed suspension containing
metal ions and Polymer (P1 and P2) were measured by the UV–Vis and fluorescence.
Fig. S7 shows the UV–Vis spectra. The absorbance peaks of P1 with Pd( ) ions
shifted (Fig. S7a). It could be seen clearly the peak of about 423nm disappeared when
P1 combined with Pd( )ions, the peak of about 453nm appeared. Similarly, P2
Ⅲ
),
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅰ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅰ
),
Ⅰ
Ⅱ
Ⅱ
Ⅲ
Ⅱ
Ⅱ)) were added to P1 and
M
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
shows the same change as P1(Fig. S7b).
The fluorescence spectra (λex = 390 nm, Slit 10/20 nm) of P1([P1]=2.5µ
M in
repeating units) were measured. As is shown in the Fig. 7 (a), it can be seen
fluorescence intensity decreased notably upon the addition of Pd( ), but other metal
Ⅱ
ions did not cause any noteworthy change comparing with P1. P2 shows the same
change as P1 in the Fig. 7 (b).As shown in Fig. 7 (c), fluorescence intensity of P1
decreased with the increasing concentration of Pd(
Ⅱ) ions. Moreover, when the
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concentration of Pd(
still could be seen. As shown in Fig. 7 (d), fluorescence intensity of P2 decreased
with the increasing concentration of Pd( ) ions. And when the concentration of
Ⅱ) ions lowered to 2.5 µM, color change and fluorescence of P1
Ⅱ
Pd(Ⅱ
) ions lowered to 2.5 µ
M
, color change and fluorescence of P2 still could be
seen as well.
(b)
467nm
486nm
(a)
500
400
300
200
100
600
P2, P2+Other ions
P1, P1+other ions
Fe3+
400
3+
Fe
Pd2+
200
2+
Pd
0
450
500
550
600
650
700
450
500
Wavelength (nm)
550
600
Wavelength (nm)
700
600
500
400
300
200
100
0
467nm
P2
486nm
P1
(c)
(d)
0 equi.
500
400
300
200
100
0 equi.
Pd2+
Pd2+
10 equi.
10 equi.
450
500
Wavelength (nm)
550
600
450
500
550
600
650
700
Wavelength (nm)
Fig. 7 Fluorescence spectra (λex = 390 nm, Slit 10/20 nm) of (a) P1 (2.5µ
M
in
repeating units) and (b) P2 (2.5µm in repeating units) with different heavy metals ions
((Cr( ), Mn( ), Co( ), Cd( ), Zn( ), Ag( ), Pb( ), Ca( ), Ni( ), Cu( ),
Na( ), K( ), Hg( ), Mg( ), Fe( ), Fe( ) and Pd( )) in DMF/water, (c) P 1
with different concentration of Pd( ) ions and (d) P2 with different concentration of
Pd( ) ions.
To make clear whether other metal ions have interference to the detection of Pd(
Ⅲ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅰ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅰ
Ⅰ
Ⅱ
Ⅱ
Ⅲ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
Ⅱ
)
ions, equivalent other every mental ions with Pd(
Ⅱ) ions were simultaneously added
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to the P1 and P2suspension. The results indicated that they have no interference to the
recognition of Pd(
Ⅱ)(Fig. 8).
(a)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
(b)
(c)
1.0
0.8
0.6
0.4
0.2
0.0
(d)
1.0
0.8
0.6
0.4
0.2
0.0
Fig. 8 Fluorescent response of P1 (2.5µ
P1 with single metal ions, (b) P1 with other metal ions and Pd(
metal ions, (d) P2 with other metal ions and Pd(
3.6 Adsorption of RhB and MB
M
) and P2 (2.5µ
M
) with metal ions (5µ
), (c)P2 with single
).
M). (a)
Ⅱ
Ⅱ
Adsorption of Methylene blue and Rhodamine B by P1 and P2 for were measured
at room temperature. The adsorption efficiency of P1 and P2 serieswere measured as
follows. Added a series of P1 (5mg ) to 5mL RB solution (0.01g/L), adsorption
equilibrium could be reached within 5min. The adsorption percentages of P1 series
after 5min were as follows: 40.6% for P1-1, 86.0% for P1-2, 87.9% for P1-3and
98.2% for P1-4 respectively in the Fig. 9 (a). Similarly, the adsorption percentages of
P2 series after 5min were as follows: 39.3% for P2-1, 82.4% for P2-2, 89.0% for P2-3
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and 98.6% for P2-4 respectively and shown in Fig. 9 (c). Using the same method,
double weight of P1 and P2 experiments were conducted. As shown in Fig. 9 (b) and
(d), the adsorption percentages of P1 and P2 for RhB solution after 5min were as
follows: 56.5% and 61.1% for P1-1 and P2-1, 91.8% and 89.0% for P1-2 and P2-2,
92.1% and 90.1% for P1-3 and P2-3, 98.9% and 98.6% for P1-4 and P2-4 respectively.
And the adsorption efficiency of P1 and P2 for RhB was very close. The adsorption
efficiency can reach to 98.9% within 5min.
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.6
0.5
0.4
0.3
0.2
0.1
0.0
(a)
(b)
RhB
P1-1
P1-2
P1-3
P1-4
RhB
P1-1
P1-2
P1-3
P1-4
500
600
500
600
Wavelength (nm)
Wavelength (nm)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
(d)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
(c)
RhB
RhB
P2
P2
P2
P2
-1
-2
-3
-4
P2-1
P2-2
P2-3
P2-4
500
600
500
600
Wavelength (nm)
Wavelength (nm)
Fig. 9Adsorption of P1 and P2 for Rhodamine B: (a) 5mg P1, (b) 10mg P1, (c) 5mg
P2 and (d) 10mg P2.
Different POPs were used to study the dye adsorption abilities. Namely, P1-1 to
P1-4, P2-1 to P2-4 were used and the results were shown in Fig. 9. Both the P1 and
P2 series shown the same trends. The POPs obtained at higher temperature and longer
reaction time, the higher dye adsorption abilities obtained. In other words, P1-4 and
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P2-4 are the best ones. In this experiment, change the weight of POPs from 5mg to
10mg. the results showed that there were no notable efficiency increase between 5mg
to 10mg POPs. Which means that 5mg POP is enough to adsorb the RhB. As for the
adsorption of MB, the results are shown in Fig 10.It can be seen that under the same
conditions, RhB is much easier be adsorbed than MB. The maximum adsorption
efficiency for MB only 58.78%. It indicated the adsorption capacity of POPs were
different for different dyes.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(a)
(b)
MB
MB
P1-1
P1-2
P1-3
P1-1
P1-2
P1-3
500
600
700
500
600
700
Wavelength (nm)
Wavelength (nm)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(d)
(c)
MB
MB
P2
P2
P2
-1
-2
-3
P2-1
P2-2
P2-3
500
600
700
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 10Adsorption of P1 and P2 for Methylene blue: (a) 5mg P1, (b) 10mg P1, (c)
5mg P2 and (d) 10mg P2.
As shown in the Fig. 11 (a) and (b), the colors of RhB and MB faded with the
addition of P1. As shown in Fig.11, the color of P1 and P2 powders changed from
yellow to orange and green, which indicated the adsorption of the organic dyes.
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Fig. 11the color change (a) Rhodamine B and (b) Methylene bluebefore and
afteradsorbed by P1.the color change of P1 and P2 before and after adsorb Rhodamine
B and Methylene blue.
3.7 Adsorption of Pd(Ⅱ)
The adsorptions of Pd(Ⅱ)were measured at room temperature. First, Pd(Ⅱ)
solution (10.64 mg/L) were prepared. 5mg and 10mg of P1 (P1-1 to P1-4) and P2
(P2-1 to P2-4) were added to 10mL Pd(Ⅱ) solution and stirred for 5min. The
concentrations of Pd(Ⅱ) before and after the addition of P1 and P2 were measured
by AAS. The adsorption performance of Pd(Ⅱ) ions on P1 and P2 were calculated
by the following formula,
C
0
−C
0
Ef
=
e ×100%
(1)
C
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DOI: 10.1039/C6RA17790E
(C
0
−C )×V
m
e
Q =
(2)
where Ef, Q, C0, Ce, V and m represent the adsorption efficiency (%), the adsorption
capacity (mg/g), the original concentration of Pd( Ⅱ) ions, the equilibrium
concentration of Pd(Ⅱ) ions, and the total volume and the quality respectively. The
adsorption performance of Pd(Ⅱ) ions on P1 and P2 was calculated by equations (1)
and (2). The results were presented in the table 3.
Table 3Adsorption efficiency (Ef) and adsorption capacity (Q) of different condition
of P1 with Pd(Ⅱ) ions.
Entry
P1-1
P1-2
P1-3
P1-4
P1-1
P1-2
P1-3
P1-4
P2-1
P2-2
P2-3
P2-4
POP (mg)
C0(mg/L)
10.64
10.64
10.64
10.64
10.64
10.64
10.64
10.64
10.64
10.64
10.64
10.64
Ce (mg/L)
6.5645
3.6822
3.149
Ef (%)
38.3
65.4
70.4
90.1
65.6
78.5
84.1
99.0
41.7
79.2
81.9
97.0
Q (mg/g)
8.2
5
5
14.0
15.0
19.2
7.0
5
5
1.0532
3.661
10
10
10
10
5
2.2888
1.6919
0.1082
6.2056
2.214
8.4
8.9
10.5
8.9
5
16.9
17.4
20.6
5
1.9295
0.3194
5
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P2-1
P2-2
P2-3
P2-4
10
10
10
10
10.64
3.376
0.7364
0.3299
0.2349
68.3
93.1
96.7
97.8
7.3
9.9
10.64
10.64
10.64
10.3
10.4
It could be concluded that P1-4 and P2-4 are the best ones concerning the
adsorption efficiency and capacity.
4. Conclusions
In conclusion, two kinds of porous organic polymers were synthesized. They are
layer-nanosheet structured, fluorescent and crystalline. The pore diameters and
specific surface areas of the POPs could be tuned by changing the reaction time and
temperature. The POP nanosheet showed relatively high thermal stability. They could
be used to adsorb organic dyes and Pd(Ⅱ) ions.Under longer reaction time and higher
temperatures, POPs with larger specific surface areas and smaller pore size could be
obtained. And these POPs have the best adsorption efficiency and capacity. They
might find real applications in the treatment of dye and metal ion pollutions in the
future.
Acknowledgements: The authors thank financial support of National Natural Science
Foundation of China (NSFC No. 41573106).
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Graphic Abstract
Text for Table of Contents
Yanmei Luo, Junhui Ran, Rong
Chen, and Xinjian Cheng*
Facile
Two kinds of layer-nanosheet
POPs were synthesized. They
exhibit unique porous
structures and considerable
specific surface areas. The
specific surface area and pore
diameters could be adjusted
via changing the reaction time
and temperature. The POPs
exhibit high adsorption
Synthesis of Porous Organic
Polymers for the Absorption
of Pd(Ⅱ) Ions and Organic
Dyes
capacity for RhB,
MB and Pd(Ⅱ) ions.
28