Development of Adsorbents for Selective Carbon Capture: Role of

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Development of Adsorbents for Selective Carbon Capture: Role of Homo- and Cross-coupling in Conjugated Microporous Polymers and Their Carbonized Derivatives Sachin Mane, Yu-Xia Li, Xiao-Qin Liu, Mingbo Yue, and Lin-Bing Sun ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05323 • Publication Date (Web): 26 Oct 2018 Downloaded from http://pubs.acs.org on October 29, 2018

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ACS Sustainable Chemistry & Engineering

Development of Adsorbents for Selective Carbon Capture: Role of Homo- and Cross-coupling in Conjugated

Microporous

Polymers

and

Their

Carbonized Derivatives Sachin Mane,† Yu-Xia Li,† Xiao-Qin Liu,† Ming Bo Yue,‡ and Lin-Bing Sun*,† State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical

†

Engineering, Nanjing Tech University, 5 Xinmofan Road, Nanjing 210009, China.

‡

School of

Chemistry and Chemical Engineering, Qufu Normal University, Shandong, China. *Corresponding author. E-mail: [email protected].

ABSTRACT: Selective adsorption of CO2 from natural gas results in increased calorific value, decreased gas volume, and reduced corrosion. For this purpose, the development of highperformance adsorbents with regard to both adsorption capacity and CO2/CH4 selectivity receives great attention. Herein, two new conjugated microporous polymers (CMPs) were prepared by Yamamoto homo-coupling and Sonogashira-Hagihara cross-coupling reaction. The significant role of homo- and cross-coupling in CMPs in selective CO2 separation was investigated. Notably, the cross-coupled CMP (NUT-15, NUT means Nanjing Tech University) shows CO2 uptake around twice than homo-coupled CMP (NUT-14) under the analogous conditions. Furthermore, the importance of KOH-activation and temperature-controlled

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carbonization in efficient CO2 capture was studied. For this, NUT-15 was further subjected to carbonization and highly active porous carbons (PCs) were obtained. It is noteworthy that, PC800 with high carbonization yield (78%) and suitable pore structure demonstrates excellent CO2 uptake (5.4 mmol.g−1) and selectivity (22.0) over CH4 at 273 K and 1 bar. Such CO2 uptake is higher than some benchmarks including activated carbon (2.8 mmol.g−1), PTz4 (3.6 mmol.g−1), and UTSA-50a (4.6 mmol.g−1) at 273 K and 1 bar. The high production yield, excellent CO2 uptake and high selectivity make the present PCs as promising candidates for selective CO2 separation from natural gas. KEYWORDS: Selective CO2 separation, Porous polymers, Carbonization, Porous carbons, Coupling reaction, Adsorption

INTRODUCTION Natural gas is a clean source of energy and its demand is constantly increasing.1 Raw natural gas mainly consists of methane as a major composition with undesirable CO2 impurity that needs to be removed prior to storage and utilization.2 On the one hand, traditional amine wet scrubbing absorption method is still considerably used in CO2 separation from natural gas. However, corrosion, solvent loss, degradation issue, unpleasant toxic smell, and energy-intensive regeneration are the major disadvantages of amine absorption.3 On the other hand, solid sorbents possess energy-saving regeneration, ease of preparation, and high recycle performance and are the main advantages over traditional absorption process in natural gas purification. To date, different types of sorbents such as molecular sieves,4,5 metal organic frameworks (MOFs),6,7 zeolites,8–13 and polymers14−22 have been developed for gas mixture separation and other applications. Among various alternatives, conjugated microporous polymers (CMPs) attract 2 ACS Paragon Plus Environment

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much attention due to their low skeletal density, synthetic diversity, and tailorable surface properties. A variety of monomers have been employed for the construction of CMPs through either homo- or cross-coupling, leading to the formation of CMPs with different structure and subsequently, different adsorption performance. Therefore, investigations on the role of homoand cross-coupling in CMPs in selective carbon capture are highly expected. In the meanwhile, CMPs are good choice of precursors for the preparation of porous carbons (PCs). Upon carbonization at different conditions, PCs with tunable pore structure can be synthesized. Owing to facile preparation, enhanced surface area, and high physicochemical stability, these PCs are highly promising for the adsorption of CO2. PCs have been reported by various groups through the carbonization of polymer precursors. For example, Shao et al.23 developed the TPOP-1 polymer as a precursor to obtain NPC-1-500 (9.8% yield at 500 oC). Li et al.24 prepared melamine coated poly(EGDMA-co-MAA) spheres which were converted into Ndoped

carbons

(25.0%

yield

at

600

oC).

Sun

et

al.25

developed

sulfonated

poly(styrene−divinylbenzene) and subsequently converted into porous carbon (45.9% yield at 800 oC). Furthermore, Hirst et al.26 converted air-carbonized sawdust derived carbon (ACSD) to activated carbon (50.0% yield at 800 oC). Although a number of PCs have been reported, the carbonization yield is far from satisfactory, which limits their applications seriously. From the viewpoint of natural gas purification, the development of PC adsorbents with high production yield as well as high CO2 uptake and CO2/CH4 selectivity is an ultimate need. Herein, we report the fabrication of two new CMPs (NUT-14 and NUT-15, NUT means Nanjing Tech University) through Yamamoto coupling of tetrakis(4-brmophenyl)ethylene) and Sonogashira coupling of tetrakis(4-brmophenyl)ethylene and 1,3,5-triethynylbenzene. Further, NUT-15 was used as the precursor to fabricate PCs by temperature-controlled carbonization for



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the first time. The carbonization yield of NUT-15 is 85% at 600 oC, 82% at 700 oC, and 78% at 800 oC, which are the quite high carbonization yields. These yields are notably higher than the reported carbonization yields of polypyrrole (4.6% at 600 oC),27 poly(resorcinol-formaldehyde) (28.0% at 600 oC),28 porous imine-linked polymer (31.0% at 600 oC),29 NC-800 (47.8% at 600 oC),30

and microporous imine-liked polymer (50.1% at 500 oC).31 Our results demonstrate the

significant role of coupling-type, KOH-activation, and temperature-controlled carbonization in selective carbon capture. It is worth noting that cross-coupled NUT-15 shows CO2 uptake (2.9 mmol.g−1) around twice higher than homo-coupled NUT-14 (mmol.g−1) under the analogous conditions. Remarkably, PC-800 displayed high CO2 uptake (5.4 mmol.g−1) over benchmarks such as activated carbon (2.8 mmol.g−1), PTz4 (3.6 mmol.g−1), and UTSA-50a (4.6 mmol.g−1) as well as a series of carbon-based adsorbents under the comparable conditions. Moreover, PC-800 demonstrates high CO2/CH4 selectivity of 22.0 as well. The present PCs might act as a promising adsorbent for selective CO2 separation from gas mixtures like natural gas.

EXPERIMENTAL SECTION Materials Synthesis Chemicals.

The

following

chemicals

were

used

for

the

fabrication

of

PCs.

Bis(cyclooctadiene)nickel(0) (RG) was received from Acros. Tetrakis(4-brmophenyl)ethylene (TBE, 97%) and 1,3,5-triethynylbenzene (TEB, 98%) were procured from Tianjin Heowns Biochemical Technology Co. Ltd. Copper(I)iodide (>99%) and 2,2ˈ-bipyridyl (>99%) were purchased from Adamas-beta. 1,5-Cyclooctadiene (>98%) was obtained from TCI. Potassium hydroxide, and methanol (anhydrous) was procured from Sinopharm Chemical Reagent Co., Ltd. Ethanol was obtained from Wuxi City Yasheng Chemical Co., Ltd. Tetrahydrofuran (THF) was purchased from H. V. Chemical Co. Ltd. These chemicals were used as they received. 4 ACS Paragon Plus Environment

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Synthesis of CMP by Yamamoto Homo-coupling Reaction. In a typical procedure, bis(1,5cyclooctadiene)nickel(0) (2.23 g, 8.11 mmol) and 2,2ˈ-bipyridyl (1.26 g, 8.07 mmol) were added to a 200 mL round bottomed flask in nitrogen atmosphere. To this, anhydrous DMF (∼120 mL) was added to the flask. To the resultant solution, 1,5-cyclooctadiene (0.89 g/1 mL, 8.23 mmol) was added and stirred for 1 h at 80 oC. To this solution, the tetrakis-(4-bromophenyl)ethylene (1 g, 1.55 mmol) was added. The solution was stirred at 80 oC for 24 h. After completion of a reaction, the reaction mixture was cooled to room temperature and quenched with concentrated HCl (20 mL). The resultant reaction mixture was stirred for overnight. The floating precipitate was collected by filteration and washed with chloroform (50 mL), tetrahydrofuran (50 mL), and water (50 mL). Finally, the polymer was dried at 80 oC in oven. The obtained polymer is abbreviated as NUT-14. Synthesis of CMP by Sonogashira-Hagihara Cross-coupling Reaction. In a typical procedure, tetrakis-(4-bromophenyl)ethylene (1 g, 1.54 mmol), 1,3,5-triethynylbenzene (0.349 g, 2.32 mmol), tetrakis(triphenylphosphine)palladium(0) (0.1 g, 0.09 mmol), and copper iodide (0.030 g, 0.16 mmol) were added to a 200 mL round bottom flask in a nitrogen atmosphere. Anhydrous DMF (50 mL) was added via syringe, followed by anhydrous diisopropylamine (50 mL). The reaction mixture was heated at 80 oC for 24 h. After reaction completion, the resultant mixture was cooled, filtered washed with chloroform (50 mL), tetrahydrofuran (50 mL), methanol (50 mL), and acetone (50 mL). Finally, the polymer was dried at 80 oC in an oven. The obtained polymer was abbreviated as NUT-15. The structures of used monomers and fabricated CMPs are presented in Figure 1. Synthesis of PCs via Carbonization. PCs were prepared by carbonization of NUT-15. In a typical process, NUT-15 was pre-carbonized at 200 oC for 100 min in an air atmosphere to avoid 5 ACS Paragon Plus Environment


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the quick collapse of the polymer framework at high temperature. The resulting black powder was then immersed in KOH-ethanol solution (1/3, mass ratio) with stirring, followed by drying at 70 oC. Carbonization of the black residue was carried out in nitrogen atmosphere (99.99%) from temperatures 600 oC, at a heating rate of 3 oC/min and holding the final temperature for 1 h. After carbonization, the black solids were treated with 2 N HCl to remove residual KOH, followed by washing with deionized water four times. The same procedure was used for carbonization at 700 and 800 oC. The resultant materials were denoted as PC-X, where X indicates the carbonization temperature 600, 700, and 800 oC. To examine the effect of KOH, a reference sample PC-700r was also prepared by carbonization of NUT-15 at 700 oC. The procedure was identical to that of PC-X except that no KOH was added and indicated by PC700r.

Materials Characterization The fabrication of CMPs and PCs was confirmed by infrared (IR) spectra which were performed on a Nicolet Nexus 470 spectrometer with KBr wafer. Solid state

13C

nuclear magnetic

resonance (NMR) spectra were recorded on a Bruker AVANCE 400 spectrometer; a Bruker 4 mm MAS probe was used to acquire 13C CP MAS NMR spectra at 12 kHz spinning. Elemental analyses (C and H) were carried out on an Elementar Vario EL elemental analyzer. The thermogravimetric (TG) analysis was studied by using a thermobalance (STA-499C, NETZSCH). About 5 mg of sample was heated from room temperature to 1000 oC in a flow of nitrogen (20 mL·min–1) and air (20 mL·min–1), with a heating rate of 10 °C·min–1. Scanning electron microscopy (SEM) images were recorded on a Hitachi S4800 electron microscope operating at 2.0 kV and 30kX magnification to observe morphology. Transmission electron


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microscopy (TEM) images were captured with a JEM-2010 UHR electron microscope. X-ray diffraction (XRD) patterns were recorded on a Bruker D8 advance diffractometer with Cu Kα radiation in the 2θ range from 5o to 80o at 40 kV and 40 mA. The contact angles were determined using a DropMeter A-100P contact-angle system (MAIST Vision Inspection & Measurement Co., Ltd., China) in sessile drop mode to quantify the wettability of CMPs. A 5-μL water droplet was dropped carefully onto the CMP surface, and the images of the droplet were recorded by a video camera at a rate of 100 frames per second. The contact angles were calculated from these images with the software named “Dropmeter”. The apparent surface areas were calculated using the Brunauer–Emmett–Teller (BET) model. Prior to the adsorption-desorption analysis, samples were evacuated at 120 °C for 6 h. N2 adsorption-desorption analysis was carried out at 77 K using BELSORP-mini analyzer.

Adsorption Tests The adsorption of CO2 and CH4 was carried out using a Micromeritics ASAP 2020 analyzer. The high purity gases, CO2 (99.999%) and CH4 (99.99%) were used for adsorption measurements whereas free space was measured using helium (99.999%). Adsorption isotherms were carried out at 273 K (ice–water bath) and 298 K (water bath). The isosteric heats of adsorption (Qst) were calculated from the CO2 adsorption isotherms at temperatures of 273 and 298 K. The ideal adsorption solution theory (IAST) selectivity of CO2 over CH4 was measured at 273 and 298 K.

RESULTS Structural Characterization of Adsorbents



Two CMPs, NUT-14 and NUT-15, were synthesized by Yamamoto homo-coupling and Sonogashira-Hagihara cross-coupling reaction of TBE and TEB. The carbonization of NUT-15 at different temperatures with/without KOH leads to a series of PCs. Various methods were then employed to characterize these CMPs and PCs. Figure 2-a presents IR spectra of the CMPs, PCs, as well as the monomers (TBE, TEB). IR peaks of the first monomer (TBE) were observed at 3047 cm−1 assigned to phenyl −C−H, 822 cm−1 attributes to para di-substituted −C−H, 1400, 1490, and 1587 cm−1 shows the existence of aromatic conjugated −C=C− in phenyl ring, and 1652 cm−1 revealed the presence of tetra-substituted >C=CC=C 0.8 bar indicating the predominant existence of micropores (Figure 5-a). Figures 5-b displays uniform pore size which can also be confirmed by TEM images. These evidences clearly indicate the existence of large surface areas and plentiful micropores in PCs, which is beneficial to adsorption as demonstrated below.

Gas Adsorption Performance The adsorption performance of CO2 and CH4 on CMPs and PCs was systematically investigated at 273 and 298 K. Figures 6-a,b indicates that NUT-14 and NUT-15 have CO2 uptake of 1.7 and 2.9 mmol.g−1 (273 K, 1 bar) and 0.9 and 2.1 mmol.g−1 (298 K, 1 bar), respectively (Table 1). This clearly demonstrates that cross-coupled NUT-15 remarkably increases CO2 capture than homo-coupled NUT-14 at 273 and 298 K. This is mainly due to the fact that homo- (NUT-14) and cross-coupled (NUT-15) CMP forms by a longer and smaller chain length, which results into larger and smaller pore size whereas smaller and larger pore volume, respectively. Thus, the adsorbent with small pore size and larger pore volume often facilitates CO2 capture. In case of PCs, PC-700 demonstrates 5.2 mmol.g−1 CO2 capture which is higher than PC-700r (4.4 mmol.g−1) (Figures 6-c,e). This is due to the fact that KOH-assisted carbonization promotes the 12 ACS Paragon Plus Environment

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generation of micropores with enhanced surface area and pore volume in the carbon framework.37−40 This clearly indicates the importance of KOH-assisted carbonization. Moreover, PC-800 (5.4 and 4.6 mmol.g−1) revealed the excellent CO2 capture of than PC-700 (5.2 and 3.6 mmol.g−1) and PC-600 (4.7 and 3.3 mmol.g−1) at 273 and 298 K, respectively (Figures 6-d,e,f). This is mainly due to the fact that, with the increase of carbonization temperature, larger pores collapse into the smaller pores which results into high surface area and pore volume. From above discussion it was concluded that cross-coupling and KOH-assisted carbonization at elevated temperature remarkably enhance CO2 capture. As compare to CO2 uptake, all CMPs and PCs scarily adsorb CH4 under the analogous conditions. Thus, CMPs and PCs show higher CO2 uptake whereas CH4 adsorb barely. This is mainly due to the presence of plentiful micropores that greatly facilitate small sized CO2 (3.30 Å) capture and separation over large sized CH4 (3.80 Å).41 For PC-800, uptake of CH4 is only 0.6 mmol.g−1 whereas other adsorbents demonstrate further decrease in CH4 uptake at all the recorded temperature and pressure. A list of recently reported adsorbents show lower adsorption capacity for CO2 than those in the present work under the comparable conditions.42 The obtained CO2 capture capacity is obviously higher than recently reported adsorbents such as S3-MIPs (1.1 mmol.g−1),43 PVIm-n-SCD (3.5 mmol.g−1),44 HIP-Cl-1 (3.8 mmol.g−1),45 NPCM-1-700 (3.9 mmol.g−1),46 NT-POP-@800-4 (4.0 mmol.g−1),47 BILP-1 (4.3 mmol.g−1),48 PC-700 (4.7 mmol.g−1)23 (273 K, 1 bar) and S3-MIPs (0.6 mmol.g−1),43 HIP-Cl1 (2.3 mmol.g−1),45 BILP-1 (3.0 mmol.g−1),48 PC-700 (3.0 mmol.g−1)23 KOH/PPy-700-2 (3.1 mmol.g−1),49 (298 K, 1 bar). In addition, PC-800 (5.4 mmol.g−1) displayed comparable CO2 uptake to those of benchmarks like activated carbon (2.8 mmol.g−1),50 PTz4 (3.6 mmol.g−1),51 UTSA-50a (4.6 mmol.g−1).37 RN-400-4 (4.8 mmol.g−1),52 C-650-3 (5.0 mmol.g−1),53 and GC-



650-4 (5.7 mmol.g−1).54 Further, a comparison of CO2 uptake of PCs with recently reported adsorbents are tabulated in Table S1. The IAST model was employed to determine CO2/CH4 selectivity. Figure 7 clearly indicates that cross-coupled NUT-15 has selectivity around three times higher than homocoupled NUT-14. This is mainly due to the formation of longer and smaller chains in NUT-14 and NUT-15, respectively. This clearly indicates that cross-coupling has significant role in selective CO2 capture. PC-800 demonstrates CO2/CH4 selectivity as high as 22.0 which is undoubtedly higher than PCTF-1 (5.0), PAF-1-450 (9.0) and PECONF-3 (10.0) at 273 K (Figure 7-a, Table S1). Similarly, PC-800 also shows the higher selectivity of 19 than reported benchmarks PAF-26-COOH (4.0), PPs-BN-1-800 (5.1) and TBILP-1 (9.0) at 298 K (Figure 7-b, Table S1). A comparison of CO2/CH4 selectivity of PCs with recently reported adsorbents are tabulated in Table S1. Thus, excellent CO2 capture and high selectivity indicates that PCs are highly promising adsorbents for selective carbon capture from natural gas. The isosteric heats of adsorption (Qst) (Figure 8) and nonlinear curve fitting (Figure S6) were calculated by CO2 adsorption data collected at 273 and 298 K. For the initial adsorption of CO2, CMPs and PCs demonstrates the −Qst in the range of 20−40 kJ.mol−1. It was observed that with increase in CO2 uptake, −Qst gets declined, mainly due to occupied active sites of CMPs and PCs. The moderate −Qst (20−40 kJ.mol−1) obtained in the present work, indicates the existence of weak interaction (physisorption) between adsorbent−adsorbate which attributes for energy-saving regeneration of the adsorbent.

DISCUSSION


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CMPs were fabricated through Yamamoto homo-coupling and Sonogashira-Hagihara crosscoupling reaction. DTG peaks of NUT-14 and NUT-15 were observed at 800 and 850 oC (Figure S2-b) which demonstrates their excellent thermostability and is mainly due to high rigidity in CMPs. High contact angles at around 150o demonstrate the remarkable hydrothermal stability of CMPs and PCs. The textural properties were determined by N2 adsorption-desorption isotherm at 77 K. NUT-14 and NUT-15 demonstrates the surface areas of 302 and 415 m2.g–1, pore volumes of 0.18 and 0.24 cm3.g–1, and pore sizes of 23.2 and 23.1 Å, respectively. This clearly indicates the large surface area, high pore volume, and small pore size of NUT-15 over NUT-14. This is because cross-coupling in NUT-15 generated by smaller chains which results into high surface area and increased pore volume.49 On the other hand, homo-coupling in NUT-14 generated by longer chains which results into small surface area and decreased pore volume.55 In the present work, role of coupling-type, KOH activation, and carbonization temperature in high CO2 capture was successfully investigated. First, CO2 uptake result shows that the cross-coupled NUT-15 has high CO2 uptake over homo-coupled NUT-14 under the analogous adsorption conditions. This is mainly due to the fact that homo- and cross-coupling CMPs forms by a longer and smaller chain length, which results into small and large surface area and pore volume, respectively (Table 1). Thus, the adsorbent with large surface area and high pore volume undoubtedly enhance the CO2 capture. This clearly supports the high efficiency of cross-coupled NUT-15 over homo-coupled NUT-14. Second, KOH functions as a chemical activator as well as acts as a hard template which results into the formation of micropores and prevent the collapse of the framework, respectively.37−40 This clearly indicates the importance KOH-assisted carbonization. Third, with the increase of carbonization temperature, larger pores collapse into the smaller pores which results into the formation of micropores with high surface area and pore volume. Due to the



formation of small pore size and increased pore volume at higher temperature, PC-800 demonstrates excellent CO2 uptake (5.4 mmol.g−1) which decreases for PC-700 (5.2 mmol.g−1) and further decreases for PC-600 (4.7 mmol.g−1) under the analogous conditions. Similarly, high selectivity was also observed with similar trends like CO2 uptake. From above discussion it was concluded that cross-coupled CMP, KOH-assisted carbonization, and high carbonization temperature promote the generation of large surface area, high pore volume, and micropores in the carbon framework which attributes for enhanced CO2 capture and selectivity over CH4. Thus, remarkable hydrothermal stability, excellent CO2 uptake, and high selectivity make the fabricated PCs as promising adsorbents in selective CO2 separation from natural gas.

CONCLUSIONS To investigate the role of homo- and cross-coupling in CMPs toward selective CO2 capture, NUT polymers (NUT-14 and NUT-15) were fabricated through Yamamoto homo-coupling and Sonogashira-Hagihara cross-coupling reaction. KOH-activation of NUT-15 results into the formation of PCs with high carbonization yield (78−85%), large surface area (800−1700 m2.g−1) and plentiful micropores. These properties obviously enhance CO2 uptake which can be confirmed from CO2 uptake of PC-700 (5.2 mmol.g−1) and PC-700r (4.4 mmol.g−1) at 273 K and 1 bar. With the increase of carbonization temperature, CO2 uptake increases since at higher temperature larger pores collapse into the smaller pores which results into large surface area and increased pore volume. This can be confirmed from CO2 uptake of PC-800 (5.4 mmol.g−1) which decrease for PC-700 (5.2 mmol.g−1) and further decreases for PC-600 (4.7 mmol.g−1) at 273 K and 1 bar. Among PCs investigated, PC-800 exhibits maximum CO2 uptake of 5.4 mmol.g−1 at 273 K and 1 bar, which is obviously much higher than reported benchmarks including activated


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carbon (2.8 mmol.g−1), PTz4 (3.6 mmol.g−1), and UTSA-50a (4.6 mmol.g−1) as well as a series of carbon-based adsorbents under the analogous conditions. Moreover, PC-800 demonstrates CO2/CH4 selectivity as high as 22.0 which is undoubtedly higher than a variety of reported adsorbents. Our PCs might provide promising adsorbents for the purification of various gas mixtures like natural gas.

ASSOCIATED CONTENT The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.xxxxxx.

13C

NMR, TG, DTG, SEM, TEM, XRD, contact angle, CO2

adsorption and selectivity comparison, and nonlinear curve fitting of the resultant CMPs and PCs (PDF).

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. ORCID Lin-Bing Sun: 0000-0002-6395-312X Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS



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We thank the Science and Engineering Research Board (SERB) New Delhi, India for providing the Postdoc Fellowship, Award No.: SB/OS/PDF-341/2015-16. In addition, we acknowledge financial support of this work by the National Natural Science Foundation of China (21676138, 21722606, and 21576137) and the Project of Priority Academic Program Development of Jiangsu Higher Education Institutions.

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Figure 1. The chemical structures of used monomers (a,b) and the resultant CMPs (NUT-14 and NUT-15).



Figure 2. (A) IR spectra of the monomers (a) TBE, (b) TEB, (c) NUT-14, (d) NUT-15, (e) PC700r, (f) PC-600, (g) PC-700, and (h) PC-800, and (B) 13C solid-state NMR spectra of (a) NUT14 and (b) NUT-15.


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Figure 3. SEM images of (a) PC-700r, (b) PC-600, (c) PC-700, and (d) PC-800.



Figure 4. TEM images of (a) PC-700r, (b) PC-600, (c) PC-700, and (d) PC-800.


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Figure 5. (a) N2 adsorption-desorption isotherms and (b) corresponding pore size distributions at 77 K.



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Table 1. Textual parameters and gas adsorption performance of the resultant CMPs and PCs. Adsorbent

SBET

(m2.g–1)

Vp

(cm3.g–1)

Gas uptake at 273 K, 1 bar (mmol.g−1) CO2

CH4

SCO2/CH4a

NUT-14

302

0.18

1.7

0.3

5.0

NUT-15

415

0.24

2.9

0.4

12.4

PC-700r

817

0.47

4.4

0.5

11.4

PC-600

953

0.55

4.7

0.5

11.0

PC-700

1280

0.70

5.2

0.6

16.0

PC-800

1666

0.95

5.4

0.6

22.0

a Selectivity

of CO2/CH4 at 273 K.


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Figure 6. Adsorption isotherms of CO2 and CH4 on (a) NUT-14, (b) NUT-15, (c) PC-700r, (d) PC-600, (e) PC-700, and (f) PC-800.



Figure 7. IAST selectivity of CO2/CH4 on CMPs and PCs at (a) 273K and (b) 298K.


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Figure 8. CO2 isosteric heat of adsorption of CMPs and PCs.



For Table of Contents Use Only Synopsis: Porous carbons produced from conjugated microporous polymers show high yield, excellent CO2 adsorption capacity and notable CO2/CH4 selectivity.


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Development of Adsorbents for Selective Carbon Capture: Role of

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