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Capture and reversible storage of volatile iodine by novel conjugated microporous polymers containing thiophene units Xin Qian, Zhaoqi Zhu, Hanxue Sun, Feng Ren, Peng Mu, Weidong Liang, Lihua Chen, and An Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b06569 • Publication Date (Web): 26 Jul 2016 Downloaded from http://pubs.acs.org on July 28, 2016
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ACS Applied Materials & Interfaces
Capture and Reversible Storage of Volatile Iodine by
Novel
Conjugated
Microporous
Polymers
Containing Thiophene Units Xin Qian†, Zhao-Qi Zhu†,Han-Xue Sun†, Feng Ren†, Peng Mu†, Weidong Liang†, Lihua Chen*,‡, An Li*,† †
College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, P.
R. China ‡
Experimental Center, Northwest University for Nationalities, Lanzhou 730030, P.R. China
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ABSTRACT Conjugated microporous polymers having thiophene building blocks (SCMPs) which originated from ethynylbenzene monomers with 2,3,5-tribromothiophene, were designedly synthesized through Pd(0)/CuI catalyzed Sonogashira-Hagihara cross-coupling polymerization. The morphologies, structure and physicochemical properties of the as-synthesized products were characterized through scanning electron microscope (SEM), thermogravimeter analysis (TGA), 13
C CP/MAS solid state NMR and Fourier transform infrared spectroscope (FTIR) spectra.
Nitrogen sorption-desorption analysis shows that the as-synthesized SCMPs possesses a high specific surface area of 855 m2 g-1. Owing to their abundant porosity, π-conjugated network structure as well as electron-rich thiophene building units, the SCMPs show better adsorption ability for iodine and a high uptake value of 222 wt% was obtained, which can compete with those nanoporous materials such as silver-containing zeolite, metal-organic frameworks (MOFs) and conjugated microporous polymers (CMPs), etc. Our study might provide a new possibility for the design and synthesis of functional CMPs containing electron-rich building units for effective capture and reversible storage of volatile iodine to address environmental issues. KEYWORDS: Conjugated microporous polymers; Thiophene; Porosity; Iodine uptake; Storage
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1. Introduction Recently, the development of novel microporous materials has generated much more interest in both fundamental research and practical applications. Owing to their large surface areas1,2, structural modularity and excellent physicochemical properties, microporous materials have been proven to be useful materials for diverse applications. Of particular success are MOFs3,4 and covalent organic frameworks (COFs)5-8 because of their tunable micropores and structure diversity which rend them promising candidates as porous mediums for diverse applications such as catalysis and separation. Both MOFs and COFs have uniform and defined microporous architectures formed in crystalline structure. However, in the most cases, the crystalline structure is not necessary for real applications. In contrast to those crystalline MOFs and COFs, microporous polymers which usually formed as amorphous structures have recently received more and more attention. To date, several classes of microporous polymers have been developed, including polymers of intrinsic microporosity (PIMs)9, hyper-cross-linked polymers (HCPs)10 and CMPs11-13. CMPs, one sub-class of microporous polymers, are composed of π-conjugated structures originated from rigid aromatic rings inter-connected with carbon carbon triple bonds. Based on such specific structures, CMPs possess excellent thermal and chemical stability in addition to their high BET surface areas and desirable porosities. Since first reported in 2007, CMPs are highly promising in a variety of applications, including electrodes14, light harvesting15, catalysis16,17, carbon dioxide capture18,19 and superhydrophobic separation20. etc. For synthesis of CMPs, the cross-coupling strategy is highly versatile, of which palladiumcatalyzed crosscoupling or homocoupling chemistry are typical approaches to construct CMPs with extended structure and permanently microporous. Compared to those traditional porous materials (e.g. zeolite or activated carbon), CMPs have particular advantage of the designable
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flexibility of their π-conjugated architecture by varying molecular structure or chemical constitution of CMPs building blocks21, which make it possible to precisely control over its chemical nature, specific surface area and the introduction of specific molecular recognition or active sites for construction of multifunctional porous CMPs materials for specific purposes. To date, a variety of novel CMPs with tunable porosity and a large diversity of functionalities have been manufactured22-24, which have shown a great diversity of potentials for catalysis, adsorption, separation and so on. In particular, in regard to them used as an absorbent, the reversible capture and storage of volatile iodine has attracted an increasingly attention because of the severe environmental issues arising from nuclear energy and nuclear technology which involves health effects of radiation, safe nuclear waste management and radiation protection25,26. So far, a variety of absorbents have been developed for efficient volatile iodine capture and storage, including silver-containing zeolite27, MOFs28, porous organic polymers (POP) and CMPs29-31, etc. Owing to their large surface area, pore volume and high affinity of the πconjugated CMPs networks to iodine, CMPs have been proven as one of promising candidates for efficient volatile iodine capture and storage32. So far, CMP nanotubes32 and porous carbon33 have been employed as functional absorbents for efficient iodine capture by us. Also, the iodine uptake of 208 wt% for CMP nanotubes has been reported as one of the highest values for iodine absorption32. Along this line, the design and synthesis of new functional CMPs for further improvement of volatile iodine capture and storage should be of special interest. It is suggested that both high specific area and suitable porous characteristics of porous polymers to iodine are the important influence factors for their volatile iodine uptakes based on the previous studies31,32. In addition to the porosity, high affinity of absorbent to iodine molecules would also result in an enhanced iodine uptake caused by the enhancement of the
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interaction between the adsorbents and adsorbates26,34. From a design point of view, the introduction of electron-rich heterocyclic into new CMPs networks would expect to improve their iodine affinity and thus increase their iodine uptakes due to the high interaction between CMPs and iodine molecules originated from lone pair electrons of heteroatoms. In this regards, here we employed 2,3,5-tribromothiophene and a rigid molecular linker (1,3,5-triethynylbenzene and 1,4-diethynylbenzene) as monomer, two novel functional CMPs incorporated with electronrich heterocyclic were synthesized by palladium-catalyzed Sonogashira-Hagihara crosscoupling reaction. As a kind porous medium, the absorption performance for volatile iodine of these two absorbents has been investigated and a high iodine uptake of 222 wt% for the resulting SCMPs was obtained. The findings obtained from this study may provide useful guidance for development of novel sulfur-substituted CMPs as well as expanding their application aspects, especially for potential application for removal of radioactive iodine. 2. Experimental section Materials. 2,3,5-tribromothiophene was purchased from J&K, 1,3,5-triethynylbenzene and 1,4diethynylbenzene were all purchased from TCI, copper (I) iodide and tetrakis (triphenylphosphine) palladium(0) were purchased from J&K. All starting chemicals and solvents were used had a purity of 97% or greater used as received. Synthesis of SCMPs. 2,3,5-tribromothiophene (320.8 mg, 1 mmol), 1,4-diethynylbenzene (283.4 mg, 2.25 mmol), tetrakis (triphenyl-phosphine) palladium(0) (100 mg), and copper (I) iodide (30 mg) were added in the mixture of N,N-dimethylformamide (DMF) (5 ml) and Et3N (5 ml). The mixture solution was heated to 80 oC and stirred for 24 h under a nitrogen atmosphere after degassing with nitrogen gas for 0.5 h. After the reaction was ending, the mixture was
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cooled to ambient temperature and the resulting polymer was filtered and washed by dichloromethane, acetone, water and methanol for several times to remove any unreacted monomers and catalyst. The further purification of the procedure was performed Soxhlet extraction with methanol for 72 h. The resulting polymer was dried at 70 oC for 24 h to a constant weight and named as SCMP-1. The SCMP-2 was synthesized using the same method as mentioned
above
using
2,3,5-tribromothiophene
(320.8
mg,
1
mmol)
and
1,3,5-
triethynylbenzene (225.3 mg, 1.5 mmol) as monomers. Yield: for SCMP-1, 396.7mg, 82% (theory 483.34 mg). For SCMP-2, 321.9 mg, 87% (theory 404.7 mg). Microanalysis: for SCMP1, C 75.71% H 3.06% S 6.14%. For SCMP-2, C 68.98% H 2.49% S 6.33%. The uptake of iodine. The solid iodine adsorption experiments were conducted as follows. The SCMPs samples were placed into a sealed vessel which filled with nonradioactive iodine vapor at 350 K and atmospheric pressure for a period of time, followed by cooled down to room temperature and weighed. The uptake of iodine for SCMPs sample was calculated according following equation: α=(m2-m1)/m1×100 wt% where α is the iodine uptake, m1 and m2 represent the quality of SCMPs samples before and after adsorption of iodine. To investigate the adsorption capacity of iodine in cyclohexane, both of samples were added into the iodine/cyclohexane solution (20 mL) and keep for a period of time. Then the supernatant (~2 mL) was measured by using UV-Vis at various time intervals. Characterization. The morphologies of SCMPs were examined by scanning electron microscope (SEM, JSM-6701F, JEOL, Ltd.). A thin layer of Au film was applied to the samples before measurement. Fourier transform infrared (FTIR) spectra were recorded on a Nicolet
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Nexus 670 spectrum instrument using the pellet technique with the wavelength rang from 4000400 cm-1. 13C CP/MAS NMR experiments were carried out on a Bruker AVANCE III 400 MHz NMR spectrometer at a resonance frequency of 100.6 MHz and recorded using a MAS probe 4 mm in diameter and a spinning rate of 14 kHz. The pore structures and Brunauer-Emmett-Teller (BET) surface areas of resulting SCMPs were measured using a micromeritics ASAP 2020 apparatus at 77 K. All samples were degassed at 120 oC overnight under vacuum before analysis. UV/Vis spectrum was recorded from in the range of 190-600 nm on a spectrophotometer (UV2102PC, Unico) with the wavelength range from.The existential form of iodine element loaded in SCMPs were recorded on a ESCALAB 250Xi X-ray photoelectron spectroscopy. The thermal stability was investigated by thermogravimeter analysis from ambient temperature to 800 oC at a heating and cooling rate of 10 oC min-1 under the protection of nitrogen. Elemental analysis was characterized in an Elementar Vario EL elemental analyzer. 3. Results and Discussion Structure analysis. The two novel functional CMPs incorporated with electron-rich heterocyclic were designedly synthesized by Pd(0)/CuI-catalyzed Sonogashira-Hagihara crosscoupling polymerization, ethynyl to bromo functionalities at a 1.5:1 molar ratio of and DMF as a solvent35-37. The detailed synthetic routes of SCMPs are shown in Scheme 1. The probable molecular level structures of both SCMP-1 and SCMP-2 were confirmed by FTIR and
13
C
CP/MAS solid-state NMR., For SCMP-1, as shown in Fig. 1, the absorption band at around 2900 cm-1 is the stretching vibration of –Ar–H. In addition, the peak is assigned to the C≡C bond stretching vibration near 2200 cm-1 .The peak around 1400-1650 cm-1 is ascribed to skeletal vibration of benzene ring and the peak at 650-880 cm-1 is assigned to the C-H bending vibration of benzene ring. The peak at around 1100 cm-1 and 800 cm-1 corresponds to =CH bond Inner-
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plane deformation vibrations of thiophene ring23,32,38. Similar spectra were also viewed in SCMP-2. To further confirm the structures of resulting SCMPs, the
13
C CP/MAS solid-state
NMR were conducted. As shown in Fig. 2a, the resonances at 176.4 ppm can be ascribed to the thiophene ring. The resonances of proton-bearing atoms atoms located at 122.9 ppm and 131.9 ppm can be assigned to the thiophene and phenylene groups39,40. The resonances at 95.3 ppm and 83.5 ppm can be ascribed to the -C≡C- linkages, The low-intensity lines at approximately 70-80 ppm can be ascribed to the -C=CH end group41, 42. The NMR spectrum of SCMP-1 is similar with that of SCMP-2, as shown in Fig. 2b, the significantly difference is SCMP-2 has increased population of carbon resonances42. Morphology. SCMP-1 was received as a light yellow precipitate, SCMP-2 was brown. Both of SCMP-1 and SCMP-2 are insoluble not only in a great number of organic solvent, for instance, acetone, toluene, DMF and THF, but in base and acid, such as NaOH and HCl. These results show that as-prepared polymers are high chemical stability. Besides, the thermal property of these two polymers were shown in Fig. S1. The powder X-ray diffraction patterns of SCMP-1 and SCMP-2 are shown in Fig. S2. As shown in Fig. 3, the morphologies of SCMPs were characterised by SEM. SCMP-1 is composed of agglomerated microgel particles with a size ranging from tens to hundreds of nanometers, along with interwoven micron rods. For SCMP-2, it also has a porous morphology consisting of agglomerated microgel particles to construct a three-dimensional network structures. Such macroscopically porous three-dimensional network structures of SCMP-2 would benefit to uptake of iodine. On the other hand, the difference observation of SCMPs by SEM images suggests that the choice of building blocks have great effect on the morphologies of resulting polymers, as seen elsewhere23,36,43.
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The porosity of SCMP-1 and SCMP-2 were obtained by calculating the data of nitrogen adsorption and desorption at 77 K from which the specific surface area was calculated. As shown in Fig. 4a, we can observe that the two networks revealed mixed type-II/IV gas sorption isotherms according to the IUPAC classification. Strong nitrogen gas adsorption exists in the relative pressure range from 0.8 to 1.0, demonstrating the coexisting of mesropores and macropores in the polymers. The specific surface areas of these two polymers were found to be 413 m2 g-1 and 855 m2 g-1 by applying BET equation. The micropore surface areas were calculated to be 172 m2 g-1 for SCMP-1 and 308 m2 g-1 for SCMP-2 by using the t-plot method. The pore size distributions (PSD) curves demonstrated that both SCMP-1 and SCMP-2 has similar continuous curves (Fig. 4b). The total pore volumes were calculated to be 0.23 m3 g-1 for SCMP-1 and 1.50 m3 g-1 and SCMP-2. Iodine capture. To investigate the adsorption performance of SCMP-1 and SCMP-2, the I2, a dangerous radioisotope existing in nuclear waste, was chosen as host molecules for measurement. Recent researches focusing on iodine capture and adsorption have drawn great attention, especially the Nuclear Security Summit was held to promote the people’s reflect to nuclear waste. Nowadays, research interests mainly concentrated on the exploitation of silver-contained zeolites and many organic solids, including, MOFs, POPs and CMPs. Excitingly, we found the SCMPs have highly effect on iodine adsorption. The iodine uptake capacity of SCMPs was tested by placing the samples into a sealed vessel which filled with nonradioactive iodine vapor at 353 K and normal atmosphere. As the iodine was captured, the quality of SCMPs after capture was weighted by an electronic balance at various time intervals. The adsorption equilibrium of those two SCMPs samples were reached quickly (1~3 h) and as the SCMPs sample were occupied with the iodine molecule the adsorption reached saturated after 5h. An obvious color change of
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the samples from brown to black was observed (Fig. 5a insert). As shown in Fig. 5a, the equilibrium uptake of iodine was measured to be 188 wt% and 222 wt% for SCMP-1 and SCMP2. With this value, SCMP-2 could compete with silver-loaded zeolite27, MOFs28, CMPs32, and so on. In viewing of capture of volatile iodine by porous polymeric absorbents26,32, it is well known that the capture of iodine is a trapping and physical deposition of volatile iodine into the framework. Also, findings obtained from previous studies have proven that high specific surface area as well as open porous structures and strong affinity of absorbents to iodine molecules would lead to an increase in iodine uptake26,32. In this study, as expected, the designed SCMP-2 shows a high iodine uptake, which may be attributed to an comprehensive effect by its inherent π-π conjugated structures and electron-rich thiophene building units of SMCPs in combination with its high specific surface area. Iodine molecule could be easily released from SCMPs. To this end, the iodine-loaded samples (named as I2@SCMPs) were immersed in several organic solvents including ethanol, methanol and cyclohexane, etc. When the I2@SCMPs was immersed in ethanol, an apparent color change for organic solvents was observed from colorless to yellow. In order to investigate the process of release, the absorbency of solvent was measured at various time intervals. As shown in Fig. 5b, the I2 delivery is empirically adjusted as zero order. The delivery of I2 in ethanol increases linearly in the first 25 min, implying that the I2 release is dominated by a hostguest interaction (see Fig. 5c and Fig. 5d insert). With the process continued, the absorbency decrease gradually, suggesting that the iodine molecules were released and the delivery in this stage is mainly controlled by a free diffusion. Thus, after washing and controlled releasing, the SCMPs samples can be regenerated and reused for next round of adsorption.
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Iodine adsorption. In addition, iodine in solution also can be the uptake by using SCMPs. when the SCMPs (10 mg) were added into iodine/cyclohexane solution (50 mg L-1~250 mg L-1, 20 mL), the dark purple solution gradually fade to vary pale red with adsorption process prolong. The XPS spectrum (see Fig. 6 and Fig. S3) indicates that the iodine-loaded with a valance of zero loading on SCMPs, which suggests that the iodine exists as molecule. The measurement for adsorption kinetics of iodine at ambient temperature was conducted and the results are shown in Fig. 7a and Fig. 7b, it can be demonstrated that the contact time and the initial solution concentration are the two factors for affecting the adsorption capacity. The adsorption capacity increased quickly in first 100 min, and then gradually became slowly until achieve equilibrium after 490 min. The maximum adsorption capacity was found to be 145 mg g-1 (for SCMP-1) and 184 mg g-1 (for SCMP-2) with the initial concentration of 250 mg L-1. In these experiments, the removal efficiencies of 58.3% for SCMP-1 and 73.6% for SCMP-2 were achieved. It is noteworthy that this value of 73.6% for iodine removal efficiencies is higher than other porous materials. To analyse the adsorption kinetics of iodine onto SCMPs, we adopt four models that are pseudo-first order kinetics, modified pseudo-first order kinetics, pseudo-second order kinetics and intra-particle diffusion model (see Table 1 and Table S1). Results suggest that the adsorption process of SMPs to iodine fits well in pseudo-second order kinetics model and a good linear correlation coefficient (R2 greater than 0.99) was achieved. It is confirmed that the iodine adsorption process was dominated by pseudo-second order kinetics in this work. What is more, the adsorption isotherm of iodine onto SCMPs is another factor determining the maximum adsorption capacity. As shown in Fig. 8a and 8b, it is obvious that two stages of adsorption exists in the adsorption isotherms. At low concentration, the adsorption capacity is in proportion to the initial concentration. Then, with the adsorption process continued, the adsorption reached
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saturation and the adsorption capacity does not increase with the increasing of the concentration of iodine/cyclohexane. Simulation results (Langmuir adsorption isotherm see Table 2 and Table S2, Freundlich adsorption isotherm see Table 3 and Table S3) suggesting that Langmuir adsorption isotherm could be well describe the iodine adsorption by SCMPs. It is clear that the adsorption process dominated by a monolayer and homogeneous of iodine molecule on the surface of SCMPs. From the adsorption isotherm, the maximum adsorption capacity varying from 139.57 mg g-1 to 150.55 mg g-1 (for SCMP-1) and 184.31 mg g-1 to 191.62 mg g-1 (for SCMP-2) were obtained. It is shown that the adsorption process is endothermal and warming is advantageous to this process. Indeed, the separation factor of Langmuir adsorption isotherm (named as RL) ranged from 0 to 1 for the range of concentration of experiment research, it is shown that the adsorption of iodine onto SCMPs is a favourable adsorption. The Changes of adsorptions enthalpy (∆H), Gibbs free energy (∆G) and entropy (∆S) for SCMPS were shown in Table 4 and Table S4. The native values of ∆G indicated that the iodine adsorption process is a spontaneous process, and the positive values of ∆H and ∆S for the adsorption of the iodine from cyclohexane solution demonstrated that this process is an endothermic process which indicated that the temperature was a beneficial factor on the adsorption kinetics and the spontaneity of adsorption process is driven by an increase in entropy. The ∆H values involve in iodine adsorption process was 5.3 kJ mol-1 at the range of 293 K-313 K which indicated that the adsorption process was dominated by physisorption. 4. Conclusions CMPs networks containing thiophene moieties which originated from ethynylbenzene monomers with 2, 3, 5-tribromothiophene, were designedly synthesized through Pd(0)/CuI catalyzed Sonogashira-Hagihara cross-coupling polymerization. The resulting SCMPs show good
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physicochemical stability because of their strong π-conjugated networks. The choice of ethynylbenzene monomer has a great impact on the specific surface areas of the as-prepared CMPs. The highest BET surface area of 855 m2 g-1 (SCMP-1) was obtained. Taking advantage of the unique π-π conjugated structures and electron-rich thiophene building units of SMCPs by combining its high specific surface area, a high iodine uptake of up to 222 wt% was obtained, which rend the resulting SCMPs promising candidates for remediation of radioactive iodine to address environmental issues.
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Br
S Br +
Br
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S
Pd(0)/CuI
S
o
Et3 N/DMF,80 C
S
Br
Pd(0)/CuI
S Br +
Br
S
Et3N/DMF,80o C
S
Scheme 1. The synthesis of SCMP-1 and SCMP-2.
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SCMP-1
% Transmittance
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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SCMP-2
4000
2000 3000 -1 Wavenumbers(cm )
1000
Fig. 1 FTIR spectra of the SCMP-1 and SCMP-2 samples.
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(b)
131.9
(a)
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123.8 SCMP-2
SCMP-1
133.1
122.9
83.5
*
*
95.7 82.5
*
*
*
*
95.2 77.5
300
250
200
150
100
50
0
300
250
δ/ppm
200
150
δ/ppm
100
50
0
Fig. 2 (a) 13C CP/MAS NMR spectra of SCMP-1. (b) 13C CP/MAS NMR spectra of SCMP-2.
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(a)
(b)
Fig. 3 SEM images of (a) SCMP-1 and (b) SCMP-2. Scale bar: (a) 1 µm. (b) 1 µm.
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0.16
(a)
SCMP-1 SCMP-2
)
-1
dV/dD(cm3 g-1 nm-1)
1500 1200
3
N2 absorbed (cm g
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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900 600 300
(b) 0.12
SCMP-1 SCMP-2
0.08 0.04 0.00
0 0.0
0.2
0.4
0.6 P/P0
0.8
1.0
0
20 40 60 80 100 120 140 160 Pore diameter (nm)
Fig. 4 (a) Nitrogen adsorption and desorption isotherms of SCMP-1, and SCMP-2 measured at
77.3 K. (b) PSD curves for SCMP-1 and SCMP-2, calculated according to desorption data.
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SCMP-1 SCMP-2
2h
0h
150
SCMP-1
120
SCMP-2
Absorbance
210 180
(b)
0.98
4h
0.91 0.84 SCMP-1 SCMP-2
0.77 0.70 0.63
90
3.2 2.4 1.6
2 3 Time (h)
4
0
5
4.0
(c) 0.80 A bsorbance
4.0
1
0.75 0.70 y=0.0096x+0.60173 0.65 4
0.8
8
12 16 20 Time (min)
24
0.0 240
360 480 Wavelength(nm)
5min 10min 15min 19min 24min 29min 45min 56min 66min 76min 86min 96min 106min
600
20
0.93
3.2 2.4
40 60 80 Time/min
(d) Absorbance
0
Absorbance
I2 uptake (wt%)
1.05
(a)
240
Absorbance
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0.90 0.87 0.84 y=0.00567x+0.80230
1.6 4
8
12 16 20 Time (min)
24
0.8
100
5min 10min 15min 20min 25min 36min 46min 56min 66min 76min 86min 96min 106min
0.0 240
360 480 Wavelength (nm)
600
Fig. 5 (a) Gravimetric uptake of iodine as a function of time at 80 oC. Insert photographs
showing the colour change when SCMP-1 and SCMP-2 were exposed to iodine vapour 4 hour. (b)The controlled delivery of iodine of SCMPs. Temporal evolution of UV/vis absorption spectra of the I2 released from the loaded SCMP-1 (C) and SCMP-2 (d) in 20 mL EtOH. Insert: fit curves of the controlled of I2 in the first 25min.
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90
I3d5
(a)
Counts (x1,000)/s
I3d3
40 30 20 10 640 28
I3d3
60 45 30 15
635
630 625 620 615 Binding energy (eV)
640
610
635
630 625 620 615 Binding energy (eV)
35
(c) I3d3
20 16
635
630 625 620 615 Binding energy (eV)
610
30
610
I3d5
(d)
I3d5
24
12 640
I3d5
(b)
75
Counts (x1,000)/s
Counts (x1,000)/s
50
Counts (x1,000)/s
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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I3d3
25 20 15 640
635
630 625 620 615 Binding energy (eV)
610
Fig. 6 XPS spectrum of SCMP-1 (a) and SCMP-2 (b) after iodine capture. XPS spectrum of I2-
loaded SCMP-1 (c) and SCMP-2 (d).
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150
(a)
125 100 75 50 50mg/L 150mg/L 250mg/L
25 0 0
100
200 300 Time/min
100mg/L 200mg/L
400
500
Iodine uptake (mg g-1)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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Iodine uptake ( mg g-1)
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175 150 125 100 75 50 25 0
(b)
50mg/L 150mg/L 250mg/L
0
100
200 300 Time/min
100mg/L 200mg/L
400
500
Fig. 7 The kinetic studies of iodine adsorption by SCMP-1 (a) and SCMP-2 (b) in cyclohexane
solutions with different concentration of 50 to 250 mg·L-1.
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160
200
(a)
180
120 100 293K 303K 313K
80 60 40
qe(mg g-1)
140 qe(mg g-1)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
(b)
160 140
293K 303K 313K
120 100 80 60
50 100 150 200 250 300 350 ρe(mg L-1)
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50
100 150 200 250 300 350 ρe(mg L-1)
Fig. 8 The thermodynamics studies of iodine adsorption by SCMP-1 (a) and SCMP-2 (b) in
cyclohexane solutions with different concentration of 50 to 350 mg L-1 and different temperature from 293K to 313K.
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Table 1 Results from linear regression of adsorption rate experiments of SCMP-1 Pseudo-first order kinetics
ρ0 (mg L-1) 250 200 150 100 50
Modified pseudo-first order kinetics
Pseudo-second order kinetics
Intra-particle diffusion model
K1/min-1
R2
K1/min-1
R2
K×106/min-1
R2
KP/(mg·(g·min)-1)
R2
0.00729 0.00834 0.00709 0.00840 0.00789
0.9670 0.9891 0.9610 0.9789 0.9772
0.00649 0.00751 0.00618 0.00712 0.0064
0.9592 0.9872 0.9456 0.9778 0.9533
375.51 457.52 358.42 459.79 342.83
0.9988 0.9992 0.9981 0.9994 0.9967
3.2200 2.7627 3.0402 2.2090 2.1312
0.9161 0.9114 0.9436 0.9014 0.9542
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Table 2 Regression equation for Langmuir isotherms of SCMP-1
⋅
⋅
Temperature/K
Regression equation ρe/qe
R2
qm(mg g-1)
b(L mg-1)
293
0.00489ρe+0.77673
0.99536
204.50
0.00630
303
0.00462ρe +0.69764
0.99098
216.45
0.00662
313
0.00446ρe +0.61640
0.99429
224.16
0.00724
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Table 3 Regression equation for Freundlich isotherms of SCMP-1 Regression equation lnqe
R2
K
n-1
0.53193lnρe +1.88400
0.98909
6.58
0.53193
303
0.52605lnρe +1.96007
0.98304
7.10
0.52605
313
0.46925lnρe +2.31393
0.99096
10.11
0.46950
Temperature/K 293
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Table 4 Changes of adsorptions enthalpy (∆H), Gibbs free energy (∆G) and entropy (∆S) for
SCMP-1 Temperature/K
∆H/(kJ mol-1)
⋅
∆G(kJ mol-1)
⋅
∆S(J mol-1 K-1)
293
5.30
-16.28
73.64
303
5.30
-16.96
73.46
313
5.30
-17.75
73.64
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⋅
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ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at
http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author
*To whom correspondence should be addressed. Tel.: +86-931-7823125. Fax: +86-931-7823125. E-mail address:
[email protected] (A. Li),
[email protected] (L. Chen) ACKNOWLEDGMENT The authors are grateful to the National Natural Science Foundation of China (Grant Nos. 51263012, 51262019, 51462021, 51403092 and 41361070), Gansu Provincial Science Fund for Distinguished Young Scholars (Grant No. 1308RJDA012), Support Program for Hongliu Young Teachers (Q201411), Hongliu Elitist Scholars of LUT (J201401), Support Program for Longyuan Youth and Fundamental Research Funds for the Universities of Gansu Province. the Opened Fund of the State Key Laboratory on Integrated Optoelectronics (Grant No. IOSKL2014KF01) and the Fund of Chinese Petroleum Changqing Oilfield Company (14AQFW-014).
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(25) Ewing, R. C.; von Hippel, F. N. Nuclear Waste Management in The United States—Starting Over. Science 2009, 325, 151-152. (26) Sigen, A.; Zhang, Y.; Li, Z.; Xia, H.; Xue, M.; Liu, X.; Mu, Y. Highly Efficient and Reversible Iodine Capture Using A Metalloporphyrin-Based Conjugated Microporous Polymer. Chem. Commun. 2014, 50, 8495-8498. (27) Chapman, K. W.; Chupas, P. J.; Nenoff, T. M. Radioactive Iodine Capture in SilverContaining Mordenites through Nanoscale Silver Iodide Formation. J. Am. Chem. Soc. 2010, 132, 8897-8899. (28) Liu, Q.-K.; Ma, J.-P.; Dong, Y.-B. Highly Efficient Iodine Species Enriching and Guestdriven Tunable Luminescent Properties Based on A Cadmium (II)-triazole MOF. Chem. Commun. 2011, 47, 7185-7187. (29) Riley, B. J.; Chun, J.; Ryan, J. V.; Matyáš, J.; Li, X. S.; Matson, D. W.; Sundaram, S. K.; Strachan, D. M.; Vienna, J. D. Chalcogen-Based Aerogels as A Multifunctional Platform for Remediation of Radioactive Iodine. RSC Adv. 2011, 1, 1704-1715. (30) Sava, D. F.; Rodriguez, M. A.; Chapman, K. W.; Chupas, P. J.; Greathouse, J. A.; Crozier, P. S.; Nenoff, T. M. Capture of Volatile Iodine, A Gaseous Fission Product, by Zeolitic Imidazolate Framework-8. J. Am. Chem. Soc. 2011, 133, 12398-12401. (31) Huang, P.-S.; Kuo, C.-H.; Hsieh, C.-C.; Horng, Y.-C. Selective Capture of Volatile Iodine Using Amorphous Molecular Organic Solids. Chem. Commun. 2012, 48, 3227-3229. (32) Chen, Y.; Sun, H.; Yang, R.; Wang, T.; Pei, C.; Xiang, Z.; Zhu, Z.; Liang, W.; Li, A.; Deng, W. Synthesis of Conjugated Microporous Polymer Nanotubes with Large Surface Areas as Absorbents for Iodine and CO2 Uptake. J. Mater. Chem. A 2015, 3, 87-91.
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(41) Jiang, J.-X.; Trewin, A.; Su, F.; Wood, C. D.; Niu, H.; Jones, J. T.; Khimyak, Y. Z.; Cooper, A. I. Microporous Poly (Tri (4-ethynylphenyl) Amine) Networks: Synthesis, Properties, and Atomistic Simulation. Macromolecules 2009, 42, 2658-2666. (42) Jiang, J.-X.; Su, F.; Niu, H.; Wood, C. D.; Campbell, N. L.; Khimyak, Y. Z.; Cooper, A. I. Conjugated Microporous Poly (Phenylene Butadiynylene) s. Chem. Commun. 2008, 486-488. (43) Xu, Y.; Jin, S.; Xu, H.; Nagai, A.; Jiang, D. Conjugated Microporous Polymers: Design, Synthesis and Application. Chem. Soc. Rev. 2013, 42, 8012-8031.
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SCMP-1 SCMP-2
240 I2 uptake (wt%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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210 180
0h
2h
2 3 Time (h)
4
150
SCMP-1
120
SCMP-2
4h
90 0
1
5
Thiophene-containing conjugated microporous polymers (SCMPs) with a surface area of up to 855 m2 g-1 were synthesized. An excellent iodine uptake of 222 wt% for such SCMPs was obtained, which can compete with those nanoporous materials such as silver-loaded zeolite, MOFs, CMPs, POPs, and so on, showing great potentials for effective capture and reversible storage of volatile iodine to address environmental issues.
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