Highly Selective and Stable Carbon Dioxide Uptake in Polyindole

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Highly selective and stable carbon dioxide uptake in polyindole-derived microporous carbon materials Muhammad Saleh, Jitendra N. Tiwari, K. Christian Kemp, Muhammad Yousaf, and Kwang S. Kim Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es3052922 • Publication Date (Web): 26 Apr 2013 Downloaded from http://pubs.acs.org on April 28, 2013

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Environmental Science & Technology

Highly selective and stable carbon dioxide uptake in polyindole-derived microporous carbon materials Muhammad Saleh, Jitendra N. Tiwari,* K. Christain Kemp, Muhammad Yousaf and Kwang S. Kim* Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea

ABSTRACT. Adsorption with solid sorbents is considered to be one of the most promising methods for the capture of carbon dioxide (CO2) from power plant flue gases. In this study, microporous carbon materials used for CO2 capture were synthesized by the chemical activation of polyindole nanofibers (PIF) at temperatures from 500-800 °C using KOH, which resulted in nitrogen (N) doped carbon materials. The N doped carbon materials were found to be microporous with an optimal adsorption pore size for CO2 of 0.6 nm and a maximum (BrunauerEmmett-Teller) BET surface area of 1185 m2 g-1. The PIF activated at 600 °C (PIF6) has a surface area of 527 m2 g-1 and a maximum CO2 storage capacity of 3.2 mmol g-1 at 25 °C and 1 bar. This high CO2 uptake is attributed to its highly microporous character and optimum N content. Additionally, PIF6 material displays a high CO2 uptake at low pressure (1.81 mmol g-1 at

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0.2 bar and 25 °C), which is the best low pressure CO2 uptake reported for carbon based materials. The adsorption capacity of this material remained remarkably stable even after 10 cycles. The isosteric heat of adsorption was calculated to be in the range of 42.7-24.1 kJ mol-1. Besides the excellent CO2 uptake and stability, PIF6 also exhibits high selectivity values for CO2 over N2, CH4 and H2 of 58.9, 12.3 and 101.1 at 25 °C respectively, these values are significantly higher than reported values.

Introduction The combustion of fossil fuels is playing a major role in the rapidly growing concentration of carbon dioxide (CO2) in the atmosphere [1]. The Intergovernmental Panel on Climate Change (IPCC) suggests that Carbon Capture and Storage (CCS) are good options to reduce CO2 concentrations in the atmosphere. The cost of transport and storage is small in CCS processes, when compared to the CO2 capture costs [2]. Presently, selective CO2 sorption and removal is of major importance worldwide. However, one of the major problems facing post combustion CO2 capture from flue gas is the associated low pressures (ca. 1 atm). Additionally, the low concentration of CO2 in flue gas (ca. 15%) requires selective separation from the large volume of other component gases, mainly N2 [3]. Expensive chemical adsorption processes (i.e. amine scrubbing, ammonia solution) are currently used for industrial CO2 capture [4-6]. While other chemisorbents such a CaO are expensive, and corrode and degrade the adsorption equipment during chemical recycling [6]. A variety of solid based materials have been considered for CO2 capture such as metal organic


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frameworks (MOF) [7], covalent organic frameworks (COF) [8], zeolites [9], activated carbon [10-16], functionalized graphene [17], carbon molecular sieves [18], chemically modified mesoporous materials [19] etc. Among these, activated carbons are important due to their recycling ability, availability and high adsorption capacity. However, the adsorption capacity of carbonaceous materials decreases rapidly at high temperatures. Thus the methods that enhance the interaction between gas molecules and adsorbent have constantly been explored. This can be done by either with increasing the surface area, tuning the pore size/volume or heteroatom doping [20-24]. The adsorption capacity of high adsorption capacity materials at low CO2 partial pressures is still very small, because of less nitrogen (N) content (~4.7%) [25]. Therefore, by doping N into activated carbons, capturing as well as selectivity capacities comparable to MOF, COF, zeolites and industrial liquid-phase processes can be achieved. Here we report a simple method to synthesize microporous carbon materials that show a nanostructure with a high surface area, large microporosity and N doping. For the preparation of microporous carbon materials, first the polyindole nanofibers (PIF) were synthesized by the polymerization of indole using ammonium persulfate (APS) and cetyl trimethylammonium bromide (CTAB). Then, PIF were chemically activated using KOH at 500-800 °C which results in the formation of N-doped microporous carbon materials. The PIF activated at 600 °C (PIF6) displayed a high CO2 adsorption capacity. Additionally, the material showed a high degree of reversibility during recycling experiments as well as adsorption selectivity towards CO2 over H2, N2 and CH4. Moreover, these properties make us believe that the PIF6 material could be a promising candidate for selective CO2 capture from power plant flue gas.


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Experimental Section Materials All chemicals were purchased from the local suppliers and used without purification. Hydrochloric acid (37%, Sigma-Aldrich), CTAB (99.0%, Sigma-Aldrich), Ammonium persulphate (Aldrich), Indole (99%, Aldrich) and Potassium hydroxide (90%, flakes, SigmaAldrich). Synthesis of PIF PIF was synthesized using oxidative template assembly route. In a typical synthesis, CTAB, (C16H33)N(CH3)3Br, (3.0 g) was dissolved in HCl (60 mL, 0.1 mol L− 1) at room temperature. To this solution 5 g ammonium persulfate (APS) was added slowly, resulting in the formation of a white oxidative template, whereafter the mixture was stirred for 30 minutes. To this solution 1 g indole dissolved in 3.2 mL absolute alcohol was added drop-wise with constant stirring. The polymerization reaction was allowed to proceed for 24 h at 25 °C. The dark green polyindole precipitate was washed with 1M HCl solution and then deionized water until a neutral pH was observed. Finally, the precipitate was washed with acetone and vacuum dried overnight. Porous N doped carbon materials were synthesized by chemical activation of PIF. 20 ml of a 7M solution of KOH and 150 mg PIF were mixed and stirred at 800 rpm for 24 hrs. This mixture was filtered and then dried at 80 °C overnight. The dried samples were activated in a tube furnace at temperatures ranging from 500-800 °C for 1h under a N2 atmosphere, heating rate of 5 °C/min. The activated sample was neutralized using 2M HCl solution and subsequently washed using deionized water until a neutral pH was observed. Finally, the sample was dried overnight at 85° C in an oven. Physicochemical characterization


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X-ray diffraction patterns (XRD) were recorded on a Riguka, Japan, RINT 2500V X-ray diffraction-meter using Cu Kα irradiation (λ = 1.5406 Å). Fourier transformed infrared (FTIR) spectra were recorded in KBr pellets using a Bruker FTIR. Raman spectra were carried out using a Senterra Raman Scope system with a 532 nm wavelength incident laser light and power 20mW. Scanning electron microscopy (SEM) images of the product were taken on a field emission scanning electron microscope (FESEM, JEOL, FEG-XL 30S). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) analyses were made with a JEM-2200F (Cs corrected TEM) electron microscope with an accelerating voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) analyses were performed using an ESCALAB-220IXL (THERMO-ELECTRON, VG Company) device. Photoemission was stimulated by a nonmonochromatized Mg Kα source (1253.6 eV) for all samples. Gas adsorption measurements Gas adsorption measurements were carried out using a Belsorp mini II (Japan) device. Before each measurement the samples were heat treated at 130 °C in vacuum for 24 hours. BET (Brunauer-Emmett-Teller) surface area and pore size was calculated from N2 adsorptiondesorption isotherms measured at 77K. CO2 adsorption isotherms were measured at 25 °C and up to 1 bar pressure.

Results and discussion Material synthesis and characterization PIF was synthesized by the polymerization of indole in the presence of ammonium persulphate and CTAB. As shown in Figure 1, indole solution prepared in ethanol was polymerized by adding it dropwise to an APS/CTAB/0.1M HCl template (the chemical reaction is shown in Figure S1). The white template of APS/CTAB acts as oxidative template that helps in


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polymerization of indole. The resulting dark green precipitates were washed with HCl, distilled water and acetone to obtain the pure material. The PIF material was chemically activated using KOH at temperatures ranging from 500-800 °C (PIF5-PIF8). The FTIR spectrum of the PIF sample is shown in Figure S2. The broad peak at 3485 cm−1 is assigned to the N–H stretching peak. The adsorption bands at 1500-1600, 1453, 1375 and 747 cm-1 present in the PIF sample can be assigned to the C-C, C-N, C=N and C-H bonds, respectively [26]. The observation of these FTIR peaks shows the successful synthesis of PIF. The X-ray diffraction (XRD) pattern of PIF shows the characteristic broad band of polyindole between 21° and 27° (Figure S3). On activation, the broad band disappears and a single peak at 23° emerges. When the activation temperature exceeds 600 °C, a new peak appears at 43 °. These two peaks at 23 ° and 43 ° are representative of the (002) and (100) planes of graphite respectively, which suggests that activated PIF(s) possess a low degree of graphitization. As shown in Figure S4, PIF exhibits two distinctive Raman bands, the G-band at 1592 cm− 1 associated with the E2g mode of graphite, while the D-band at 1330 cm− 1 corresponds to the defect-induced mode [27]. After activation, the D and G bands, as well as the ID/IG ratio increases, which are attributed to the development of defects and pores [28]. FESEM and TEM images of the PIF samples are shown in Figures 2 and S5. FESEM and TEM images of the PIF (Figures 2a-c) show a nanostructured morphology made of interconnected polymer fibers of variable sizes and dimensions that make a web type structure. After activation, the nitrogen containing polymeric framework converts into a more structured carbon framework as can be seen for the PIF5-8 samples in Figures S5 and 2d. The TEM and HRTEM images of the PIF6 sample are shown in Figures 2 (e-i) that indicates the clear micro porous structure. Figures 2 (h and i) show the nitrogen and carbon mapping of the PIF6 sample from which we can see that there is an even distribution of elements after activation.


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In order to determine the elemental state the XPS analysis of all adsorbents was performed. Full survey spectra of PIF samples show the presence of the C1s peak, N1s peak and O1s peak at 284, 400 and 530 eV, respectively, as shown in Figure S6a [29]. Two peaks were observed arising from Si2s and Si2p at 104 and 154 eV, respectively, due to non-uniform film thickness of sample on Si wafer [30]. The surface atomic concentrations of C, O and N were calculated from the corresponding peak areas of the XPS spectra and are summarized in Table S1. Deconvolution of the C1s peak of PIF and activated samples show the presence of the C–C peak (284.7 eV) and C–N peak (285.9 eV), as shown in Figure S6b. Deconvolution of N1s peaks located at about 400 and 399 eV which are attributed to pyrrolic and pyridinic N are shown in Figure S6c [31]. The PIF sample shows only the presence of pentagonal pyrrolic N, while on activation the hexagonal pyridinic N is observed. This conversion of pentagonal pyrrolic N to hexagonal pyridinic N confirms the occurrence of N doping in activated materials [32]. Figure 3a shows the N2 adsorption-desorption isotherms of the PIF samples. It is clear that N2 uptake increases strongly beyond a relative pressure of 0.85 in all cases suggesting multilayer formation. The isotherms of PIF and PIF5 are classical type III according to the IUPAC classification [33]. At activation temperatures ranging 600-800 °C the adsorption isotherms of PIF6-PIF8 showed type I behavior, as they have significant uptake at a relative lower pressure of 0.1. At relative pressures higher than 0.1, adsorption isotherms become approximately flat. Moreover, adsorption isotherms do not contain hysteresis loop indicating the absence of a mesoporous character. PIF and PIF5 do not show any characteristic micropore distribution, while the pore size distribution of PIF6-PIF8 becomes intense around 0.6-1.2 nm as shown in Figure 3b, calculated using the non-local density function theory model. The textural properties of the resultant microporous carbon materials are summarized in Table S1. A BET surface area of 38.38 m2 g-1 was observed in the case of PIF which increases to 120.6 m2 g-1 for PIF5.


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Furthermore, the materials activated at temperatures from 600-800 °C show specific surface areas of 527-1185 m2 g-1. PIF6 has a micropore volume of 0.2 cc g-1 while PIF7 and PIF8 have micropore volumes of 0.57 and 0.64 cc g-1, respectively. This indicates that with an increasing temperature a larger microporous volume is developed in the carbon materials. From Table S1, it is also clear that the N content also decreases with the increasing activation temperature, which is in good agreement with the literature [33].

CO2 adsorption Owing to the presence of basic N groups, the PIF samples were applied as sorbents for CO2 capture. Figure 4a shows the CO2 adsorption-desorption isotherms up to 1bar at 25 °C for the PIF samples. As PIF5 has a higher surface area and larger microporous character than PIF, it displays good CO2 capturing properties. It can be seen that the PIF7 exhibits the highest adsorption capacity of 3.42 mmol g-1 due to the presence of large microporosity and optimum N content, while PIF6 and PIF8 show a CO2 adsorption capacity of 3.2 and 2.75 mmol g-1, respectively. The lower adsorption of PIF6 and PIF8 compared to PIF7 is due to their micropore volume and N content. An inverse relation between N content and micropore volume leads to a decrease in the CO2 uptake of the two adsorbents (Table S1). PIF6 has a larger N content (4.17%) than PIF7 (2.64%) and PIF8 (1.98%), so it is strongly believed that this feature causes the major CO2 uptake, especially at low pressure. PIF6 shows very high CO2 adsorption capacity in the lower pressure regime, showing its potential to be used as an adsorbent for post combustion applications. The adsorption capacity of PIF6 is greater than many adsorbents as tabulated in Table 1 [34-48]. In selectivity studies, the N content in the adsorbent is of key importance for adsorption of CO2 at low pressure. Since the flue gases from power plants contain about 20% CO2 and about 70%


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N2 under normal pressure, competitive adsorbents display fast adsorption kinetics, good selectivity, easy regeneration and more ideally high CO2 uptake at low pressure. N doped carbon materials have been analyzed under repeated adsorption–desorption cycles in order to explore their versatility. Cyclic adsorption-desorption via a combination of thermal treatment at 150 °C and vacuum were performed for PIF6 and its adsorption capacity after 10 consecutive adsorptiondesorption cycles is presented in Figure 4b. Interestingly, the adsorption capacity of this material is highly reversible, with negligible loss (~4.5%) of adsorption capacity even after 10 cycles. The loss in adsorption capacity is attributed to the reduction of BET surface area (475 m2 g-1) of the PIF6 after 10 cycles (Figure 4c). The consistent performance of the adsorbent exhibited that the activated material is highly stable. PIF6 was chosen to be a good candidate as its adsorption capacity at low pressure (0.2 bar) is far better than that of PIF7. PIF6 has a CO2 uptake of 1.81 mmol g-1 at 0.2 bar which is so far the best result for any carbon based material at 25 °C. To the best of our knowledge the highest result reported to date is 1.75 mmol g-1 at 0.2 bar [49]. At 0.2 bar the adsorption capacity of PIF6 is much higher than the PIF7 capacity (1.14 mmol g-1), see Figure 4a. This indicates that efficient doping of N in the PIF6 helps to adsorb a high CO2 volume at low pressure regions. Although PIF7 has a marginally higher CO2 uptake than PIF6, it has a lower CO2 adsorption in the low pressure region, which makes PIF6 a more promising candidate for adsorption studies. Figure 5a represents the selective CO2 adsorption of PIF6 over N2, CH4 and H2 at 25 °C and 1 bar. PIF6 has a very small N2 adsorption capacity ~0.4 mmol g-1. Similarly, CH4 and H2 adsorption on PIF6 shows a very small adsorption capacity of 1.1 mmol g-1 and less than 0.01 mmol g-1, respectively. This shows that PIF6 has a good potential for selective CO2 adsorption. Henry’s law for single-component adsorption isotherms is extensively used to calculate gas selectivities [50]. Selectivity of CO2 over N2, CH4 and H2 was calculated (from the ratio of the


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initial slopes of adsorption isotherms as shown in Figure S7) as 58.9, 12.3 and 101.1 respectively at 25 °C, which is significantly high and much better than that of previously reported carbon based materials (see Table S2 ). In order to determine the isosteric heat of adsorption (Qst) the CO2 adsorption was measured for PIF6 at 0 and 25 °C, as shown in Figure S9. It was found that the isosteric heat of adsorption is in the range of 42.7-24.1 kJ mol-1, with the corresponding amount of CO2 adsorbed in the range of 1.42-71.27 cc g-1 (0.1 to 2.8 mmol g-1), as shown in Figure 5b. This result indicates that the maximum amount of energy is released during the initial adsorption of CO2 in the adsorbent, which is due to the strong interaction between the CO2 and the N containing carbon materials. However, these Qst values are much lower than the covalent bond energy, so the process of desorption is much easier and reversible. The initial decrease and then almost stabilizing of the Qst value with the increasing adsorption of CO2 indicates that high energy N- sites are occupied once and then reach a saturation level after a certain amount of CO2 uptake. These isosteric heats of adsorption are also higher than any previously reported data for activated carbon based material (10.5-28.4 kJ mol-1) [51] and graphene oxide based carbons (17-22 kJ mol-1) [43], except for the recently reported IBN9-C1 (44.1 kJ mol-1 ) [49] and ACM-5 (65.2 kJ mol-1) [ 47] respectively. This higher Qst value is attributed to the high N content that also plays a major role in high CO2 uptake over N2 at low pressure i.e. selectivity. In Summary, a rapid and simple one step method has been demonstrated for the preparation of polyindole by a template route that produced a unique nanofibrous structure. On activation, this fibrous material was converted to N doped carbon materials. The obtained microporous carbon materials have a high surface area of 527–1185 m2 g-1 with large microporous volume of 0.2-0.64 cc g-1. It has been demonstrated that PIF6 is an excellent adsorbent for CO2 capturing, with a capacity of 3.2 mmol g-1 at 25 °C and 1 bar. Furthermore, it has much higher CO2 uptake at 0.2


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bar than other materials reported to date, which makes it the best candidate for selective adsorption at low pressure. It has remarkably high stability during recycling experiments with insignificant change in adsorption capacity over 10 cycles and can be easily regenerated. The isosteric heat of adsorption of PIF6 shows a range of 42.7-24.1 kJ mol-1, with the adsorbed amount of CO2 ranging from 0.1-2.8 mmol g-1. Moreover, this material also shows very high selective adsorption of CO2 over N2, CH4 and H2. This easy procedure offers a pathway to produce N doped microporous carbon materials that possess industrial applications.

ASSOCIATED CONTENT Supporting Information Raman, FTIR, XPS, XRD, SEM images and micropore distribution data, Texture properties for PIF and PIF5-PIF8. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (ksk); [email protected]. (jnt); Tel: (+82)-54-279-2110, Fax (+82)-54-279-8137. ACKNOWLEDGMENT This work was supported by NRF (National Honor Scientist Program: 2010-0020414). Dr. NamSuk Lee is gratefully acknowledged for measurement of High Resolution (HR)-TEM, which was done in National Center for Nanomaterials Technology (NCNT) at POSTECH, Korea.


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(31) Dommelea, S.; Izquirdoa, A. R.; Brydsonb, R.; Jonga, K. P.; Bitter, H. Tuning nitrogen functionalities in catalytically grown nitrogen-containing carbon nanotubes. Carbon 2008, 46, 138-148. (32) Qie, L.; Chen, W. M.; Wand, Z. H,; Shao, Q. G.; Li, X.; Yuan. Nitrogen-doped porous carbon nanofiber webs as anodes for lithium ion batteries with a super high capacity and rate Capability. Adv. Mater. 2012, 24, 2047-2050. (33) Liu, L.; Deng, Q.; Hou, X.; Yuan, Z. User-friendly synthesis of nitrogen-containing polymer and microporous carbon spheres for efficient CO2 capture. J. Mater. Chem. 2012, 22, 15540-15548. (34) Himeno, S.; Komatsu,T.; Fujita, S. J. High pressure adsorption equilibria of methane and carbon dioxide on several activated carbons. J. Chem. Eng. Data 2005, 50, 369-376. (35) Wang, B.; Ceote, A. P.; Furukawa, H.; O’Keeffe, M.; Yaghi, O. M. Colossal cages in zeolitic imidazolate frameworks as selective carbon dioxide reservoirs. Nature 2008, 453, 207-212. (36) Saha, D.; Deng, S. Adsorption equilibrium and kinetics of CO2, CH4, N2O, and NH3 on ordered mesoporous carbon. J. Colloid Interface Sci. 2010, 345, 402-409. (37) Chandrasekar, G.; Son, W. J.; Ahn, W. S. Synthesis of mesoporous materials SBA-15 and CMK-3 from fly ash and their application for CO2 adsorption J. Porous Mater. 2009, 16, 545-551. (38) Dawson, R.; Adams, D. J.; Cooper, A. I. Chemical tuning of CO2 sorption in robust nanoporous organic polymers Chem. Sci. 2011, 2, 1173-1177. (39) Pachfule, P.; Balan, B. K.; Kurungot, S.; Banerjee, R. One-dimensional confinement of a nanosized metal organic framework in carbon nanofibers for improved gas adsorption, Chem. Commun. 2012, 48, 2009–2011. (40) Xia, Y.; Zhu,Y.; Tang, Y. Preparation of sulfur-doped microporous carbons for the storage of hydrogen and carbon dioxide. Carbon 2012, 50, 5543-5553.


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Figure and Figure captions

Figure 1. Scheme for the preparation of N-doped carbon materials.


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a

b

c

d

e

f

g

h

i

Figure 2. (a) PIF FESEM image, (b and c) TEM images. (d) PIF6 FESEM image, (e and f) TEM and HRTEM images, respectively. (g) PIF6 TEM mapping image, (h and i) carbon and nitrogen mapping, respectively.


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-1

500 400

4 -1

300 200 100 0

PIF PIF5 PIF6 PIF7 PIF8

3

-1

600

a



dVp/d dp (cc g nm )

700 N2 uptake (cc 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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2

b

1 0

0.0

0.2

0.4

0.6

0.8

1.0

0.5

P/P0

1.0 1.5 Pore diameter dp (nm)

2.0

Figure 3. (a) N2 adsorption-desorption isotherms (filled symbols: adsorption, open symbols: desorption) and (b) pore size distribution for the PIF samples.


20

-1

4 3



a

b

3 -1

5 CO2 uptake (mmole g )

2

2

1

1 0 0.0

0.2

0.4 0.6 Pressure (bar)

180 150

-1

N2 uptake (cc 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


CO2 uptake (mmol g )

Page 21 of 24

120 90 60

0.8

1.0

0

1

2

4 5 6 7 No. of cycles

8

9 10

c

Adsorption Desoption 2

3

-1

SSA = 495 m g -1 Total pore valume = 0.32 cc g Avearage pore diameter = 2.45 nm -1 Micropore volume = 0.20 cc g

30 0.0

0.2

0.4 0.6 P/P0

0.8

1.0

Figure 4. (a) CO2 adsorption-desorption isotherms for PIF and activated samples at 25 °C (filled symbols: adsorption, open symbols: desorption). (b) CO2 adsorption capacity for PIF6 at 25 °C for recycling of 10 cycles and (c) N2 adsorption-desorption isotherms for PIF6 after 10 cycles.


21


2 1 0 0.0

0.2

0.4 0.6 0.8 Pressure (bar)

1.0

b

40

-1

-1

3

a

CO2 CH4 N2 H2

Qst (kJ mol )

4 Gas uptake (mmole 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

Page 22 of 24

30 20 10 0

PIF6 0

20 40 60 3 -1 Adsorbed volume (cm g )

80

Figure 5. (a) Selective adsorption of CO2 over H2, N2 and CH4 for PIF6 at 25 °C and (b) isosteric heat of CO2 adsorption on PIF6 calculated from experimental adsorption isotherms at 0°C and 25 °C.


22

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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


Table 1. Comparison table showing CO2 capturing properties of different materials. Materials

CO2 adsorption at 25 °C

References

and 1 bar (mmol g-1) Activated carbons

< 2.0

34

Hybrid zeolitic imidazole frameworks ZIF-98

1.5

35

Soft template mesoporous carbons

2.4

36

Hard-templated CMK-3

1.7

37

CMP

1.2

38

Nanosized MOF in carbon nanofibers

1.6

39

Sulfur-doped microporous carbons

2.4

40

Halogen-decorated borazine-linked polymer

1.20

41

HKUST-1

2.95

42

Graphene oxide derived carbons

2.7

43

Silica supported poly(ethyleneimine) (PEI) materials

2.3

44

MOP

2.21

45

5.5 (at 0 °C)

46

5.14

47

Mg-MOF 74

~2

48

PIF6

3.2

Present work

Benzimidazole linked polymer BILP-4 Activated carbon monolith ACM-5


23


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Table of contents


24

Highly Selective and Stable Carbon Dioxide Uptake in Polyindole

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