Hydroxyl-based hypercrosslinked microporous polymers and their

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Hydroxyl-based hypercrosslinked microporous polymers and their excellent performance for CO2 capture Yin Liu, Xin Chen, Xiangkun Jia, Xinlong Fan, Baoliang Zhang, Aibo Zhang, and Qiuyu Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05004 • Publication Date (Web): 30 Nov 2018 Downloaded from http://pubs.acs.org on December 2, 2018

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Industrial & Engineering Chemistry Research

Hydroxyl-based hypercrosslinked microporous polymers and their excellent performance for CO2 capture Yin Liu, Xin Chen, Xiangkun Jia, Xinlong Fan, Baoliang Zhang, Aibo Zhang, Qiuyu Zhang*

MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, Department of Applied Chemistry, School of Nature and Applied Science, Northwestern Polytechnical University, Xi'an 710072, China

KEYWORDS: benzyl alcohol; microporous polymers; external cross-linker; CO2 capture

CORRESPONDING AUTHOR

Qiuyu Zhang*, Email: [email protected]

1

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 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

ABSTRACT A series of benzyl alcohol (BA)-based hypercrosslinked microporous polymers (HCPs) were designed and synthesized via facile Friedel-Crafts alkylation using formaldehyde dimethyl acetal (FDA) as external cross-linker promoted by anhydrous ferric chloride (FeCl3). Results demonstrated that Brunauer-Emmett-Teller (BET) specific surface area and pore volume for the HCPs could be controlled by adjusting the amount of FDA and FeCl3. The HCPs obtained under optimal conditions showed a BET specific surface area up to 1101 m2/g, whose capacity of CO2 uptake could be as high as 3.03 mmol/g at 273 K/1.0 bar. The isosteric heats of CO2 sorption for the BA-based HCPs exceed 27 kJ/mol at the low coverage. In addition, the polymer networks possessed high CO2/N2 selectivity of 42. Compared with those BA-based HCPs which is without FDA, the prepared material has higher BET specific surface area and superior CO2 adsorption properties. These results demonstrated that these prepared HCPs are promising for CO2 capture and sequestration.

2


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Introduction In recent years, the global climate change caused by exhaust emission of CO2, especially from coal-fired plants, has attracted widespread public concern. In order to stabilize the concentration of CO2 in the atmosphere and prevent global warming, developing a viable CO2 capture and storage (CCS) technology is very significant 1, 2. Microporous organic polymers (MOPs) combining high surface areas, tunable pore sizes, high chemical stability with diverse synthetic approaches have exhibited hopeful prospect in CO2 uptake 3-5. Various synthesis methodologies have been exploited to the synthesis of MOPs, according to the chemical structure and the type of reactions involved, MOPs can be divided into four categories: polymers of intrinsic microporosity (PIMs) frameworks (COFs)

6, 7,

10, 11,

hypercrosslinked polymers (HCPs)

8, 9,

covalent organic

and conjugated microporous polymers (CMPs)

12, 13.

These

microporous polymers have been widely used in CO2 capture and exhibited excellent adsorption performance. However, the successful preparation of the most above MOPs requires noble metal catalysts and tedious synthesis procedures 14-16. Thus, the high cost and rigorous conditions would limit the practical applications of most MOPs. Compared with the other three kinds of MOPs, the preparation process of HCPs is very simple, which can be prepared directly by the Friedel-Crafts alkylation reaction and is easy to industrialize. HCPs are constructed by the hypercrosslinking of polymer chains, which effectively prevents the polymer chains from collapsing into a dense nonporous state

17,

thus preventing the dense accumulation of interchains and forming

microporous structures. The preparation method of HCPs has been developed for a long time and now the synthesis of HCPs could avoid the need for monomers with unique chemical structures and functional groups when an external cross-linking agent such as formaldehyde dimethyl acetal (FDA) is employed. This method greatly expands the range of the monomers involved and makes HCPs competitive in CO2 capture, which has been a topic of immediate concern. For example, benzene based HCPs exhibited high BET specific surface areas up to 1270 m2/g with a CO2 adsorption performance of 2.78 mmol /g (1.0 bar and 273 K) 18, tetraphenylmethane based HCPs with high BET specific surface areas of 1314 m2/g

19,

and ferrocene based HCPs with high BET 3



specific surface areas of 729 m2/g 20. To meet the requirements of practical application, the CO2 uptake capacity and selectivity of the microporous polymers are crucial parameters for CO2 capture, and materials with very high surface areas may not be optimal. Such as the PAF-1 with much higher BET specific surface area of 4077 m2/g but lower CO2 uptake capacity of 2.65 mmol/g 14. Several strategies have been adopted to improve CO2 uptake capacity and selectivity of MOPs, for example open metal-sites, post synthetic modification, introduce organic heterocycles and incorporate polar functional groups, such as hydroxyl 21, 22 and amine 23, 24 into the polymer network to advance the binding affinity for CO2. For example, thiophene-based heterocyclic HCPs possessed CO2 uptake capacity of 2.89 mmol/g and CO2/N2 adsorption selectivity of 39:1 25, Nitrogen-Doped RFL-500 showed CO2 uptake capacity of 3.01 mmol/g and CO2/N2 adsorption selectivity of 29:1 under ambient conditions

26.

Therefore, efficient synthetic

approaches for the preparation of HCPs with higher specific surface areas and polar functional groups are desired. Here, we report a series of simple hydroxyl-based HCPs with high BET specific surface area and large CO2 uptake ability, which was prepared by simple one-step Friedel-Crafts reaction. In this reaction, BA was used as building blocks and FDA was served as the external crosslinker. Actually, without FDA, BA could also be used as alkylating agents, and extensive crosslinking could also occur between molecules in the presence of an acid catalyst. However, the reactive activity of hydroxymethyl is weaker than that of FDA. Therefore, the addition of FDA can not only improve the crosslinking degree of the final HCPs, but also retain some hydroxyl groups to improve the CO2 uptake capacity and selectivity. Therefore, a facile efficient synthetic approach for generating HCPs with high BET specific surface areas and improved CO2 sorption performance is proposed. Experimental sections Materials Benzyl alcohol (BA) and formaldehyde dimethyl acetal (FDA) were purchased from J&K Scientific Ltd. 1,2-dichloroethane(DCE), anhydrous ferric chloride(FeCl3), 4


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methanol and acetone were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemicals were used as received without further purification. Deionized water was used throughout the whole process. Synthesis of hypercrosslinked polymer networks All of the HCPs were synthesized by Friedel-Crafts alkylation of BA using FDA as external crosslinker and promoted by anhydrous FeCl3. The detailed recipes in this article were listed in Table S1, several reaction conditions including reaction time, addition amount of FeCl3 and FDA were studied to identify polymers with optimized BET specific surface area and pore structures. The detailed experimental conditions were as follows (Scheme 1), briefly, a 100 mL flask was charged with 30 mL DCE and some amount of BA and FDA, the resultant solution was heated to 80 °C, and then was treated with a solution of anhydrous FeCl3 in DCE (30 mL). The resulting mixture was maintained at 80 °C for 24 h. After cooling, the precipitated polymer networks were filtered and subsequently washed with methanol, acetone and water until the filtrate turned clear. The resultant polymer networks were dried under reduced pressure to obtain HCPs as brown powder. OH

OH

FeCl3 O

O OH

OH

OH

OH OH

Scheme1. The synthesis process of HCPs Characterization N2 adsorption/desorption analysis (77.3K), pore size distributions and CO2 uptake volumetric analysis (1 bar, 273 K and 298 K) were measured using a Micrometrics TriStar II 3020 surface area and porosity analyzer. Prior to the analysis, the samples 5



were outgassed at 100 °C for 12 h under vacuum (10-5 bar). The specific surface area was determined using BET model, total pore volume (Vt) was evaluated from the amount of nitrogen adsorbed at around P/P0 = 0.99, pore size distribution was obtained from the density functional theory (DFT) model. Heat of adsorption was determined from CO2 adsorption isotherms up to a pressure of 1.0 bar at both 273K and 298K temperatures. Fourier transforms infrared spectroscopies (FTIR) of BA and the final HCPs were collected with a TENSOR27 FTIR spectrometer (Bruker, Germany) using KBr disks. Field emission scanning electron microscope (FE-SEM) micrographs of polymer networks were measured using a JSM 6700F (JEOL, Japan). Transmission electron microscopy (TEM) image of the obtained HCPs were carried out on a JEM 2010 TEM (JEOL, Japan) at an accelerating voltage of 200 kV. The thermal properties of the prepared HCPs were evaluated using a Q50 thermal gravimetric analyzer (TGA, TA Instruments) by heating each sample from 25 °C to 800 °C with a heating rate of 20 °C /min in air atmosphere. Solid-state 13C cross-polarization magic angle spinning (CP-MAS) NMR spectrum was carried out on a Bruker Avance III model 400 MHz NMR spectrometer at a MAS rate of 5 kHz. The elemental analysis data was collected using a Vario Micro cube Elemental Analyzer (Elementar, Germany). Results and discussion All of the HCPs were prepared via one-pot Friedel-Crafts alkylation of BA with different doses of the FDA and FeCl3, using DCE as reaction medium at 80 oC. The obtained HCPs were insoluble in conventional organic solvents such as acetone, DCM and THF, indicating the existence of hypercross-linked structures. As can be seen from SEM image of as-synthesized HCPs (Figure 1 a), irregular spherical small particles with pronounced rough surface were observed, and the diameter of spherical small particle is not uniform, and the average particle size is 35 nm. The voids formed by loose accumulation of small particles might be responsible for the mesoporous and macropores structures which were detected by N2 adsorption/desorption analysis. From the TEM image (Figure 1 b), nanoparticles possess porous structures and rough surfaces could also be seen, and snatchy nanopore channels were observed distributed throughout the entire networks. These small pores were of importance to the produce 6


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of high surface area and large adsorption capacity of CO2. Figure 1 c showed the FTIR spectra of BA and final HCPs prepared with FDA (BAHCP-7) and without FDA (BAHCP-12), by comparing the three FTIR spectra, it could deduce two important differences in the molecular structure before and after the reaction. The first was the characteristic bonds at 3330 cm-1 and 740 cm-1 which were assigned to -OH stretching vibration and bending vibration of -CH2OH weakened significantly in the spectra of the polymers, during the Friedel-Craft reaction, hydroxymethyl group would form a methylene bridge by elimination of one water molecule. In addition, it could be seen from the peak intensity at 3330 cm-1 that there were more hydroxyl group remained in BAHCP-7 after the reaction. This phenomenon proved that the addition of FDA could preserve more hydroxyl groups in final polymer networks. The latter was the increased intensity of -CH2- bond and the increased substitution sites of the benzene ring. The peak at 2923 cm-1 was attributed to C-H stretching bond of -CH2- bond increased after the hypercrosslinking procedure 27. BA only has one functional group on the benzene ring, while there might be more than two substitutions on benzene ring after reaction. The peak at 881 cm-1 appeared after the reaction, representing the vibration of C-H band of the para-type functional group on benzene ring, further indicating the presence of hypercrosslinking strutcture. The peak at 1585 cm-1 and 1450 cm-1, signed to the C = C stretching vibration in the benzene ring 28,

The bands at 1278 cm-1 and 1081 cm-1 were attributed to the bending band of C-C

and C-O moieties, respectively. 13C CP/MAS NMR spectrum of the obtained HCPs was collected to further analyze the chemical constitution (Figure 1 d). The carbon signal 137 and 129 ppm was assigned to the substituted aromatic carbons and the non-substituted aromatic carbons

29,

respectively. Peak near 36 ppm further indicated the formation of -CH2- bond. The peak near 17 ppm of the HCPs was attributed to the carbon of remaining ethanol adsorbed in the micropores or ultra-micropores. Since micropores were very small, there was usually a small amount of solvent remaining in the polymer network which was difficult to completely remove. The content of residual hydroxyl groups in the final polymer was obtained by 7



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elemental analysis. The result show that the residual oxygen content in the final polymer is in the range of 4.09 % to 8.66 % (Table S2), which suggests that some hydroxyl groups are also involved in the reaction, in addition, the higher oxygen content in the obtained polymer also leads to the superior CO2 adsorption performance of the obtained polymer.

C

d

BAHCP-12

Ar (non-H) Ar (H)

BAHCP-7

-CH2BA

CH3OH

3750

3000 2250 1500 -1 Wavenumber (cm )

750

200

150

100  (ppm)

50

0

Figure 1. Typical SEM (a) and TEM (b) images of obtained HCPs; FTIR spectra of BA and HCPs (c); 13C CP/MAS NMR spectrum of the obtained HCPs (d). Effect of the reaction time Reaction time was an important factor for the preparation of HCPs. The influence of reaction time on the porosity properties of HCPs was investigated. As shown in Table 1, the BET specific surface areas of the HCPs were mainly in the range of 600-900m2/g, and several basic trends could be deduced from the result. Figure S1 showed the change 8


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of BET specific surface area varied with reaction time. The rule of the change was to increase first and then remain stable, and the optimum reaction time was 22 h. The reason for this change might be that the initial reaction was mainly condensation polymerization, the rate of crosslinking reaction was slow, hence, the BET specific surface areas of HCPs increased rapidly. Along with the increase of reaction time, the rate of crosslinking reaction was accelerated and the polymer skeleton was gradually formed, therefore, after 22 h of the reaction, porosity properties of HCPs almost remained stable with the increase of the reaction time. Table 1 Porosity properties of the HCPs obtained with different reaction times. Polymer

a

Time(h)

SBET a (m2/g) SMicrob (m2/g)

VTotalc (cm3/g)

VMicrod (cm3/g)

BAHCP-1

16

675

329

0.73

0.0982

BAHCP-2

18

756

376

0.79

0.1015

BAHCP-3

20

839

418

0.83

0.1352

BAHCP-4

22

863

412

0.83

0.1410

BAHCP-5

24

866

415

0.87

0.1415

BAHCP-6

26

868

417

0.87

0.1416

Specific surface area calculated from nitrogen adsorption isotherms using BET equation (SBET). b

Micropore surface area calculated from the N2 adsorption isotherm using t-plot method based on the Harkins-Jura Equation. c Total pore volume calculated from nitrogen isotherm at P/P0 =0.99. d The micropore volume derived from the t-plot method.

Effect of the amount of FeCl3 and FDA The BET specific surface areas and pore volumes of final HCPs were very sensitive to the addition amount of FeCl3 and FDA. In this work, several different addition amount of FeCl3 and FDA were investigate to obtain HCPs with the best performance. BET specific surface areas and pore volumes of HCPs produced by different addition amount of FeCl3 were presented in Table S3. As can be seen from the results, when the addition amount of the FDA remained unchanged, increasing the amount of FeCl3, BET specific surface area of obtained HCPs increased at first and then decreased. When the molar ratio of FeCl3 with respect 9



to BA was within the range of 2 to 4, the prepared HCPs possessed better porosity properties. In the following work, we adjusted the molar ratio of FeCl3 to BA at 2, 3 and 4, and investigated the effect of amount of FDA to the porosity properties of the obtained HCPs. The results were shown in Table S4. When the molar ratio of FeCl3 to BA was 2, the optimum molar ratio of FDA to BA was 2, and the BET specific surface area of the prepared HCPs was 1101 m2/g. When the molar ratio of FeCl3 to BA was 3 and 4, the highest BET specific surface area of prepared HCPs was 1066 and 1038 m2/g, respectively. The results showed that when the molar ratio of FeCl3 to BA was fixed, the BET specific surface area of the prepared HCPs increased at first and then decreased with the increase of the addition amount of FDA. Furthermore, by comparing porosity performance of HCPs obtained with FDA and those without FDA, it was possible to deduce that the FDA was significant for the porosity properties of HCPs. Through the investigation of the addition amount of FeCl3 and FDA, we found that there was a threshold concentration of FeCl3 and FDA for producing HCPs with excellent porosity properties. When the concentrations of FeCl3 and FDA were below the threshold, it would lead to low BET specific surface areas and small pore volume, whereas much higher FeCl3 and FDA concentrations were detrimental to the porosity properties of HCPs. The reason might be that low dosage of FeCl3 and FDA would result in low crosslinking degree of HCPs, and eventually lead to poor porosity properties. Once the concentration of FeCl3 and FDA were beyond thresholds, the whole reaction system would be confined into a limited area, the growth of the polymer chains were restricted, and then the crosslinking reaction was caged into a concentrated region, limiting the construction of pores

17.

Moreover, the residual FeCl3 and FDA

would block the channel of obtained HCPs and hardly to be removed. Thermal analysis of HCPs with high BET specific surface area (BAHCP-7, 18, 22) was shown in Figure S2. The weight loss of all samples was low below 100 °C, which could be attributed to the loss of residual organic solvent and physically adsorbed water. When temperature was below 400 °C, all samples have no obvious weight loss, which indicated that all the samples have great thermal stability. The rapid rate of weight loss 10


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in the temperature range between 400 and 800 °C was caused by the thermal decomposition of polymers. For BAHCP-7 which retained more than 36 % of its mass even at 800 °C in air atmosphere, whereas BAHCP-18 and 22 retained 34 % and 31 % of their mass, respectively. The good thermal stabilities could be attributed to the crosslinked structure and aromatic polymer skeletons, and the diversity in residual mass might be due to the difference in degree of crosslinking. The BET specific surface areas and porosity parameters of the three samples with high BET specific surface area were measured by nitrogen sorption analysis at 77 K. Figure 2 presented the nitrogen adsorption isotherms and pore size distribution of the three samples (BAHCP-7, 18, 22) with high BET specific surface area. As shown in Figure 2a, the adsorption isotherms of the all samples displayed sharp uptakes at low relative pressure (P/P0 < 0.001), thus reflecting the existence of abundant microporous structure in prepared HCPs, which could be confirmed by the pore size distributions. All the samples showed slight hysteresis loops at medium and high pressure regions, suggesting the existence of mesopores and macropores, these macropores might be attributed to loose packing of tiny particles and irreversible bind of nitrogen molecules to the pore surface. Figure 2b showed the pore size distribution for the three samples. All of samples exhibited several families of pores, such as, dominant micropores at 1.4 nm and 1.7 nm, and a smaller peak of mesopores at around 2.2 nm. Thus, the most prevalent pores were mainly centered below 2 nm, indicating that the polymers were predominantly microporous.

11


a

b

BAHCP-22

Volume adsorbed (cm3/g) STP

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

0.0

BAHCP-18

BAHCP-7

0.2 0.4 0.6 0.8 1.0 Relative Pressure (P/P0)

Differential pore volume (cm3/g Å)


Page 12 of 20

BAHCP-22

BAHCP-18

BAHCP-7

12.5 15.0 17.5 20.0 22.5 25.0 Pore width (Å )

Figure 2. Nitrogen adsorption and desorption isotherms at 77 K (a) and pore size. distributions (b) of the three samples with high BET specific surface area. Gas adsorption properties The high BET specific surface area and the microporous nature of the obtained HCPs inspired us to investigate their performance in gas storage. CO2 capture or separation from flue gases or coal-fired plants has attracted widespread public attention due to environmental and economical reasons. Hence, CO2 adsorption performance for the obtained HCPs was investigated. As shown in the Table 2, The CO2 uptakes of the polymer networks were measured up to 1.0 bar at 273 and 298 K, respectively. As expected, BAHCP-7 and BAHCP-18 possessed higher CO2 adsorption properties than that of BAHCP-22, which could be explained by the higher BET specific surface area. The adsorption curves of the three HCPs for CO2 were shown in Figure 3a and 3b. It was noteworthy that, for the all samples, the adsorption-desorption curves were reversible. This property was quite favorable for the release of CO2 gas and reusability of the adsorbents. Moreover, no saturation was observed in the studied pressure range for all of the samples, which indicated that larger CO2 capture capacities could be obtained by increasing the pressure above 1.0 bar. As far as we know, the CO2 uptake of 3.03 mmol/g for BAHCP-7 was not only higher than some of the previously reported microporous polymers, such as the tetraphenylmethane-based HCPs (2.27 mmol/g at 1.0 bar/273 K) 27, the HCP-BA without FDA as external crosslinker (1.92 mmol/g at 12


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1.0 bar/273 K) 29, the aromatic porous PAF-1 with high BET specific surface area of 4077 m2/g (2.65 mmol/g at 1.0 bar and 273 K) 14, but also comparable to the reported tetraphenylethylene-based HCPs (3.63 mmol/g at 1.0 bar/273 K)

30

and binaphthol-

based HCPs (3.96 mmol/g at 1.0 bar and 273 K) 31, but still lower than that of some other MOPs with high CO2 uptake ability, such as the nitrogen-doped polymer networks (e.g. 4.48 mmol/g for SNS2-20) 32, 33. The higher CO2 uptake capacity of the obtained HCPs were considered to the existence of residual alcohol groups which could provide adsorption sites through dipole-quadrupole interactions, thus advancing the CO2 uptake capacity of polymer networks 34. These results confirmed that in addition to the BET specific surface area, the chemical property of the monomer was also a significant factor for the CO2 adsorption properties of MOPs. Therefore, the selection of suitable building blocks was very crucial for the design of MOPs. In order to further explore the adsorption properties of CO2, isosteric heat of adsorption (Qst) was calculated from CO2 isotherms collected at 273 K, 288K and 298 K. The isosteric heats of CO2 adsorption for the three samples (Figure 3c) were calculated to be 26-28 kJ/mol at low coverage. These values exceed those reported MOPs, such as the tetraphenylethylene-based HCP of Network-1 (24.1 kJ/mol), the BA-based HCP of HCP-BA without the addition of FDA (24-27 kJ/mol)

35

and are

comparable to the acid-functionalized porous polymers (PPN-6-SO3H, 30.4 kJ/mol) 36. These results proved that the presence of alcohol groups could improve the binding affinity between the polymer network and CO2 molecules. It has been reported that the electron-rich atoms, e.g. oxygen, can yield strong dipole-quadrupole interaction with CO2, leading to a significant increase in the adsorption enthalpy 37. The Qst values of the three samples in our work remained nearly constant with the increased quantities of adsorbed CO2, which suggested that the absorption of CO2 could be significantly increased by enhancing the micropore volume and micro-surface area of the final HCPs 38.

Furthermore, it was worth noting that the Qst values remain well below the energy

of the chemical bond and demonstrates the strong physisorption, which was desirable for facile CO2 release and reusability of the adsorbents. As for CO2 adsorption, high gas selectivity of CO2/N2 was also essential for an 13



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adsorbent which would be used in the adsorption-based separation processes, in addition to high CO2 uptake capacity. The CO2 and N2 adsorption isotherms were therefore measured at 273 K for the three samples (Figure 3d, 3e and 3f). The selectivity of the samples were calculated using experimental single-component gas sorption isotherms and the ratios of the Henry's law constant which were collected from the initial slopes for both CO2 and N2 at 273 K at a low pressure coverage (< 0.15 bar). That 39.

was a typical partial pressure of CO2 in flue gas at 273 K

From these data, the

calculated CO2/N2 selectivity of the three samples were 35, 38, 42 at 273K, respectively (Table 2). Although the CO2/N2 adsorption selectivity was lower than that of some other porous polymers, such as the pyrrole-based HCP (117:1) CAU-1 (101:1)

40

25,amine-decorated

MOF

and covalent triazine framework (CTF-CSU37@post 145.9 :1)

41,

they were still comparable to many other types of porous polymer networks 42. It has been reported that high selectivity generally correlates with low uptakes. For example, Yao et al. synthesized a 1,1,2,2-tetraphenylethane-1,2-diol based HCPs which showed high ideal CO2/N2 adsorption selectivity of 119 : 1 at 273K and 1 bar 43, but the absolute CO2 uptake was 1.92 mmol/g, lower than that of the prepared HCPs in this paper. Ideally, high uptake and selectivity were both necessary for practical applications. As such, the large CO2 adsorption capacity and the high CO2/N2 adsorption selectivity of the prepared HCPs made them promising for post-combustion CO2 capture and storage. Table 2 Gas adsorption properties of the three samples with high BET specific surface area. Sample

g CO

2

CO2 uptake g

CO2 uptake h

CO2 uptake i

Selective j

(mmol/g)

(mmol/g)

(mmol/g)

(CO2 / N2)

BAHCP-7

3.03

2.52

1.96

35

BAHCP-18

3.02

2.51

1.89

38

BAHCP-22

2.89

2.40

1.86

42

uptake determined volumetrically using a Micromeritics TriStar II 3020 analyzer at 1.00 bar

and 273 K; h CO2 uptake determined volumetrically using a Micromeritics TriStar II 3020 analyzer at 1.00 bar and 288 K; i CO2 uptake determined volumetrically using a Micromeritics TriStar II 14


Page 15 of 20

3020 analyzer at 1.00 bar and 298 K; j The CO2 / N2 selectivity of the three samples at 1.00 bar and 273 K.

1.5

2.0

24

10:20:20 10:50:40

0.0 0.0

0.2

0.4 0.6 0.8 Pressure (bar)

0.35

CO2 N2

e Uptake (mmol/g)

0.30 0.25 0.20 0.15 0.10

10:40:30 10:50:40

0.0 0.0

1.0

0.05

0.2

0.4

0.6

0.8

1.0

0.35

CO2

0.30

N2

0.25 0.20 0.15 0.10

0.0

0.1 0.2 Pressure (bar)

0.3

10:20:20

18

10:40:30

16

10:50:40

0.0 0.5 1.0 1.5 2.0 Quantity Adsorbed (m mol/g STP)

Pressure (bar)

f

CO2

0.25

N2 y = a + b*x

Equation

0.20Weight

No Weighting 3.12993E-4

Residual Sum of Squares

0.15Pearson's r

0.99847 0.99652

Adj. R-Square

Value H

0.10H

Intercept Slope

Standard Error

0.0097

0.00355

6.92268

0.14469

0.05

0.05

0.00

20

10:20:20

0.5

10:40:30

0.5

22

Uptake (mmol/g)

1.0

28 26

1.0

1.5

30

Heat of Adsorption (KJ/mol)

2.5

d

c

2.0

CO2 Quantity Adsorbed (mmol/g)

b

3.0

CO2 Quantity Adsorbed (mmol/g)

a

Uptake (mmol/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


0.00 0.0

0.1 0.2 0.3 Pressure (bar)

0.4

0.00 0.0

0.1

0.2 0.3 Pressure (bar)

0.4

Figure 3. CO2 adsorption and desorption isotherms at 273 K (a); CO2 adsorption and desorption isotherms at 298 K (b); Isosteric heat of adsorption for CO2 at different CO2 loadings (c); Initial gas uptake slopes of BAHCP-7 at 273 K (d); Initial gas uptake slopes of BAHCP-18 at 273 K (e); Initial gas uptake slopes of BAHCP-22 at 273 K (f). Conclusion In summary, a series of BA-based HCPs were synthesized via facile Friedel-Crafts alkylation with FDA as cross-linker promoted by anhydrous FeCl3. The reaction conditions including the reaction time and the addition amount of FeCl3 and FDA both have great influence on the properties of the produced HCPs. The obtained HCPs possessed high BET specific surface area, good CO2 uptake properties, and enhanced isosteric heat for CO2 compared to many other porous materials. At 1.0 bar and 273 K, the HCPs obtained under optimal conditions exhibited high BET specific surface areas up to 1101 m2/g and a large CO2 uptake ability of 3.03 mmol/g. The cost-efficient HCPs with high surface area and outstanding CO2 sorption performances would be one of the most promising candidates for potential application in post-combustion CO2 capture and sequestration technology. 15



Acknowledgements The authors are grateful for the financial support provided by the State Key Program of National Natural Science of China (Grant No.51433008), the National Natural Science Foundation of China (Grant No.21704084), the International Cooperation and Exchanges NSFC (Grant No.51711530233) and the Fundamental Research Funds for the Central Universities (Grant No. 3102017jc01001). Supporting Information Table of Contents Table S1 The detailed experimental conditions of the preparation of HCPs. Table S2 Elemental analysis for the monomers and the corresponding polymers (wt%). Table S3 Porosity properties of HCPs produced by different addition amount of FeCl3. Table S4 Porosity properties of HCPs produced by different amount of FeCl3 and FDA. Figure S1. BET specific surface areas of the HCPs obtained with different reaction times. Figure S2. Thermal analysis of HCPs with high BET specific surface area. References 1. Singh, D. K.; Krishna, K. S.; Harish, S.; Sampath, S.; Eswaramoorthy, M., No More HF: Teflon-Assisted Ultrafast Removal of Silica to Generate High-Surface-Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor Performance. Angew. Chem. Int. Ed. 2016, 55 (6), 2032-2036. 2. Li, Y.; Zou, B.; Hu, C.; Cao, M., Nitrogen-doped porous carbon nanofiber webs for efficient CO2 capture and conversion. Carbon 2016, 99, 79-89. 3. Hussain, M. W.; Bandyopadhyay, S.; Patra, A., Microporous organic polymers involving thiadiazolopyridine for high and selective uptake of greenhouse gases at low pressure. Chem. Commun. 2017, 53 (76), 10576-10579. 4. Gu, S.; He, J.; Zhu, Y.; Wang, Z.; Chen, D.; Yu, G.; Pan, C.; Guan, J.; Tao, K., Facile carbonization of microporous organic polymers into hierarchically porous carbons targeted for effective CO2 uptake at low pressures. ACS Appl Mater Interfaces. 2016, 8 (28), 18383-18392. 5. Wang, S.; Song, K.; Zhang, C.; Shu, Y.; Li, T.; Tan, B., A novel metalporphyrinbased microporous organic polymer with high CO2 uptake and efficient chemical conversion of CO2 under ambient conditions. J Mater Chem. A 2017, 5 (4), 1509-1515. 6. Weng, X.; Baez, J. E.; Khiterer, M.; Hoe, M. Y.; Bao, Z.; Shea, K. J., Chiral polymers of intrinsic microporosity: selective membrane permeation of enantiomers. Angew. Chem. Int. Ed. 2015, 54 (38), 11214-11218. 7. Swaidan, R.; Ghanem, B.; Litwiller, E.; Pinnau, I., Physical aging, plasticization 16


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TOC OH

OH

FeCl3 O

O OH

OH

OH

OH OH

A series of benzyl alcohol (BA)-based hypercrosslinked microporous polymers (HCPs) were designed and synthesized via facile Friedel-Crafts. The prepared HCPs with high surface area and outstanding CO2 sorption performances would be one of the promising candidates for potential application in post-combustion CO2 capture and sequestration technology.

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Hydroxyl-based hypercrosslinked microporous polymers and their

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