Mechanochemical Synthesis of Tannic Acid-Fe Coordination

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Mechanochemical synthesis of tannic acid-Fe coordination compound and its derived porous carbon for CO2 adsorption Chao Cai, Ning Fu, Ziwei Zhou, Mengchen Wu, Zhenglong Yang, and Rui Liu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02352 • Publication Date (Web): 18 Sep 2018 Downloaded from http://pubs.acs.org on September 20, 2018

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Mechanochemical synthesis of tannic acid-Fe coordination compound and its derived porous carbon for CO2 adsorption Chao Cai, Ning Fu,Ziwei Zhou, Mengchen Wu, Zhenglong Yangand Rui Liu* Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, School of Materials Science and Engineering, and Institute for Advanced Study, Tongji University, Shanghai, 201804, China

ABSTRACT Tannic acid-Fe coordination compound has been prepared via a simple mechanochemical method. The compound could be used as precursors for the fabrication of porous carbon, which was successfully applied as adsorbent for CO2 capture. The obtained porous adsorbent, NFePC-10-A, exhibited relatively high CO2 uptake capacities of 5.8 and 3.4 mmol g−1 at 0 and 25 °C, respectively. In addition, the initial isosteric heat of adsorption and selectivity for CO2/N2 were as high as 63.16 kJ mol-1 and 22.7 (0 °C). Meanwhile, the adsorbent underwent an efficient reusability, indicating a good potential for practical use. This feasible strategy might provide a novel precursor for the large-scale production of bio-derived carbonaceous adsorbents with tailored texture and porosity for CO2 capture and storage.

Keywords: coordination, porous carbon, tannic acid, Fe, CO2 adsorption

1. INTRODUCTION Mitigation of carbon dioxide (CO2) emission is becoming one of the main 1

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exigencies due to the significant global warming and environmental deterioration.1-5 Considering that the number of main CO2 contributors is difficult to be lessened, the development of efficient CO2 abatement and sequestration technology is of great importance.6-10 In recent years, great efforts have been undertaken for developing CO2 capture, including physical absorption, chemical adsorption, cryogenic techniques and membrane processes.11-18 To date, physi-sorption by porous solid adsorbents is widely acknowledged and various types of physical adsorbents have been intensively developed, including zeolites,13, 19 functionalized porous silica,20, 21 and metal-organic framework materials (MOFs).22-25 Among all types of adsorbents, porous carbonaceous materials are regarded as the most promising candidates due to their specific features such as inexpensive cost,26 ease of preparation27 and regeneration, excellent thermal and chemical stability, and the possibility of tailoring their textural or chemical properties through pre- or post-synthesis methods.28-36 Porosity of adsorbents plays a key role in CO2 adsorption. Recent studies have shown that the micropores with size between 0.34 and 0.70 nm greatly contribute to CO2 uptake capacity of a porous carbonaceous material under ambient conditions (1 bar).37 On the basis of this point, various methods (e.g., template,38, 39 activation,40, 41 and self-pyrolysis42) have been developed to synthesize porous carbonaceous adsorbents with abundant micropores. For example, Bao et al. have reported a novel N-doped microporous carbon from rationally designed polypyrrole precursor, which exhibited ultra-high Henry’s law CO2/N2 selectivity.43 Yuan and the coworkers have synthesized an ultra-microporous carbon from polycondensed framework and 2


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investigated the effect of microporosity on CO2 adsorption, which have proved that the microporosity below critical size (0.7 nm at 298 K and 1.08 nm at 273 K) greatly determined CO2 uptake capacity.44 However, the reported synthesis is usually unable to realize large-scale production or avoid the use of toxic reagent and organic solvent. Therefore, the development of a facile and feasible approach with a suitable precursor to prepare porous carbonaceous CO2 adsorbent still remains to be a challenge. In this contribution, we demonstrate a mechanochemical method to fabricate tannic acid (TA)-Fe coordination compound as a precursor for porous carbon with a large surface area and abundant micropores. TA (molecular structure in Figure S1) is an eco-friendly and ubiquitous natural polyphenol distributing in species throughout the whole plant kingdom.45 The polyphenolic structure of TA contains inherent pyrogalloyl or catechol chelating site, which can coordinate with a great range of transition metals (e.g., Fe, Coor Mn).46 In this work, TA-Fe coordination compound from mechanochemical synthesis has successfully converted into porous carbon via sequential carbonization, Fe-extraction and KOH-activation process. The obtained porous carbon has been successfully applied as an efficient adsorbent for CO2 physi-sorption, which exhibited a high CO2 capture capacity and excellent CO2/N2 selectivity.

2. EXPERIMENTAL SECTION 2.1 Materials Iron(III) chloride hexahydrate (FeCl3·6H2O,99.0 wt %), hydrochloric acid (HCl, 3


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37 wt %) and potassium hydroxide (KOH, 85 wt %) were purchased from Sinopharm Chemical Reagent Co., Ltd. Tannic acid was supplied by Aladdin Industrial Corporation. Deionized water with specific resistivity of 18.0 MΩ.cm was prepared by Direct-Q®3. 2.2 Synthesis of NFePC-x-A In a typical synthesis, TA and FeCl3·6H2O were mixed with different molar ratio (1:5, 1:10 and 1:15) by a simple grinding. After the solid powder transformed into a black liquid, the mixture was aged for several days at 60 °C and a black powder TA-Fe was obtained. Then, TA-Fe was carbonized at 800 °C under flowing nitrogen in a tubular furnace with a heating rate of 5 °C min−1 and left for 2 h. The carbonated samples were denoted as FePC-x, where x is the molar ratio of FeCl3·6H2O to TA. FePC-x were washed by 1 M HCl under stirring for 24 h to remove the residual iron, and the obtained samples were designated as NFePC-x (non-Fe porous carbon). The post-activation process was performed by the impregnation of 0.2 g of NFePC-x with a KOH solution containing 0.2 g KOH followed by a heat treatment. The thermal treatment was conducted under a nitrogen flow in a tubular furnace at 800 °C(ramp rate: 5 °C min−1) and maintained for 1 h. Then, the samples were liberated by washing with 1 M HCl and deionized water until the pH value was neutral. Finally, the sample was dried at 60 °C overnight and denoted as NFePC-x-A (NFePC-x after activation). 2.3 Characterization Fourier transform infrared (FT-IR) spectra measurement was recorded on a Bruker EQUINOX 55 spectrometer (Equinox 55 Bruker Banner Lane, Coventry, 4


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Germany).Thermogravimetric (TG) measurement was performed on a TGA Q500 Thermogravimetric Analyzer (PerkinElmer) at 20 °C min−1. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) images were obtained using a Quanta200 (FEI, Hillsboro, Oregon, USA) and a JEM-2100 Felectron microscope (JEOL, Japan), respectively. X–ray diffraction (XRD, D/max 2550V, Rigaku, Tokyo, Japan) with Cu–Kα radiation using a Ni filter (λ=0.154059 nm at 30 kV and 15 mA) was used to identify the existence of Fe. Raman spectra were recorded by Raman spectrometer (DXR, GX-PT-2412, Thermo, USA), which were recorded from 100 to 3000 cm−1. X–ray photoelectron spectroscopic (XPS) was performed on a Thermo Fisher Scientific ESCALAB250Xi spectrometer operated at 120 W. Brunauer–Emmett–Teller (BET) surface area was quantified by calculating N2 adsorption isotherm data recorded on a Quantachrome adsorption instrument (Autosorb-iQ2; Quantachrome, America). The sample was degassed at 150 °C for 6 h in advance. The total pore volume (Vtotal) was derived from the amount gas adsorbed at the relative pressure of 0.99. The micropore specific surface area (St-plot) was determined by the t-plot method, while the pore size distribution (PSD) was measured by non-local density functional theory (NLDFT) and Horvath-Kawazoe (H-K) method, respectively. 2.4 CO2 Adsorption Measurement The CO2 adsorption equilibrium measurement was conducted by a static volumetric method using a Quantachrome gas adsorption instrument (Autosorb-iQ2; Quantachrome, America). The adsorption isotherms of N2 or CO2 were recorded at 0 5


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and 25 °C with a gas pressure up to 1 bar. A Dewar bottle was used as a thermostatic bath while the temperature of 0 and 25 °C was acquired with icy water and ambient water, respectively. Prior to the adsorption analysis, the samples were degassed at 200 °C for 10 h to ensure the complete removal of impurity. After the temperature was adjusted to the desired temperature, single component gas, pure CO2 (99.995%) or N2 (99.999%), was introduced into the adsorption system. In the end of the analysis, a certain sample was put into the next cycle at 0 or 25 °C to investigate the recycling ability for four times. 2.5 CO2/N2 Selectivity The selectivity of CO2 over N2 (SCO2/N2) of was determined by single-component gas adsorption data conducted at 0 and 25 °C. The selectivity based on ideal adsorption solution theory (IAST) was calculated through the following equation:47, 48 ⁄

/ = ⁄

(1)

where q1 and q2 were the adsorbed amount of CO2 and N2 at their respective equilibrium partial pressures p1 and p2, respectively. Herein, SCO2/N2 was obtained by calculating the ratio of CO2 adsorption capacity at 0.15 bar to N2 adsorbed amount at 0.85 bar following the earlier literature.49

The initial slopes of CO2 and N2

adsorption isotherms measured at 0 and 25 °C were calculated and used for the low-pressure selectivity.50

3. RESULTS AND DISCUSSION The overall preparation process was illustrated in Figure 1. Under the solid state, 6


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TA and FeCl3·6H2O powders transformed into a black liquid by coordination crosslinking between TA and Fe ions. FePC was obtained by a direct thermal treatment with the presence of flowing nitrogen. After sequentially extracting the residual Fe, a carbonated porous sample NFePC was obtained. A subsequent KOH activation process led to the formation of NFePC-A.51,52 FT-IR spectra of pure TA and TA-Fe-10 (FeCl3·6H2O/TA molar ratio = 10) were presented in Fig. 2a. In contrast to pure TA, the characteristic stretching bands between 600 and 1800 cm-1 showed apparent position shifts or intensity changes in TA-Fe-10, which was believed to be in accordance with the interaction of –OH with the iron ions. Furthermore, the different XRD patterns between TA-Fe-10 and FeCl3 proved the coordination interaction between TA and Fe ions (Figure S2a).53, 54 TGA curves of TA and TA-Fe-10 were performed from 30 to 900 °C under N2 atmosphere and illustrated in Fig. 2b. The yield of TA and TA-Fe-10 after decomposition was 6 and 23%, respectively, indicating the successful conversion into carbonaceous materials. XRD patterns and Raman spectra of FePC-10 (Figure S2) showed that a considerable amount of maghemite (Fe2O3, PDF # 39-1346) crystals formed after carbonizing at 800 °C, which was also proved by the formation of nanoparticles in TEM (Figure S3). In contrast, no diffraction peaks related to the crystal structure of iron or the corresponding iron oxides could be observed in NFePC-10-A (Figure 3a), which implied the successful extraction of iron element in the final product. XPS was performed to investigate the surface elemental state and chemical compositions of 7


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NFePC-10-A. Figure S4 illustrated the common carbon and oxygen functionalities and their corresponding binding energies. The C 1s spectra with binding energies at 284.6, 285.9 and 288.3 eV were assigned to sp2-hybridized graphitic C-C, phenolic/alcohol groups (C-O), and carbonyl/quinone groups (C=O), respectively. The peak of 284.6 eV (C-C) possessed the maximum relative area percentage, suggesting the existence of graphite-dominated carbon. The O 1s spectra could be fitted into two peaks of O=C (531.7 eV) and O-C (533.5 eV).55-58 The relatively high carbon content (94.9 at.%) rendered the surface super hydrophobic, which made NFePC-10-A being favorable for CO2 capture and avoiding the competitive adsorption of H2O in the practical usage.56 SEM and TEM were employed to study the microscopic morphology of NFePC-10-A. As seen in TEM (Figure 3a and b) and SEM (Figure 3c and d), the NFePC-10-A showed a bulky and flaky morphology with a random, amorphous and foam-like pore structure, which was formed during the pre-extraction and activation process.59 No trace of iron clusters or iron residuals were observed in the TEM images of NFePC-10-A, in good agreement with XRD and Raman analysis. Nitrogen adsorption/desorption isotherm at 77 K was conducted to evaluate the specific surface area and porosity. As shown in Figure 4a, NFePC-x exhibited a typical type-I isotherms, suggesting that a characteristic micropore-forming process was occurred during HCl treatment. However, the isotherms of NFePC-x-A exhibited a shape considered as an intermediate between type I and type IV isotherms with an obvious plateau at lower relative pressure. This proved that a small quantity of 8


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mesopores were developed during the KOH activation process. Detailed texture parameters were summarized in Table 1. Remarkably, compared to NFePC-5, -10 and -15, the specific surface area of NFePC-5-A, NFePC-10-A, and NFePC-15-A increased significantly to 1393, 1414, and 1801 m2 g-1, respectively. Pore size distribution (PSD) was presented in Figure 4. In comparison with other reported activated carbon

60-62

, our materials exhibited a narrow PSD mainly located between

0.4 and 0.7 nm, indicating a great potential for CO2 adsorption. Meanwhile, part of meso- or macro-pores were developed through the KOH activation process and confirmed

by

the

cumulative

pore

volume

values

in

Figure

S5.

N2

adsorption/desorption capacity of pure TA derived carbon was also measured for comparison (Figure S6). The pure TA derived carbon exhibited a specific surface area of 728 m2 g-1 and a total pore volume of 0.30 cm3g-1, both of which were apparently lower than those of NFePC-x-A, indicating the significance of Fe in the pore-forming and pore-modifying in the above-mentioned samples. CO2 adsorption of the prepared samples was investigated at 0 and 25 °C under 1 bar. The corresponding CO2 adsorption isotherms for NFePC-x and NFePC-x-A were plotted in Figure 5. Along with the pressure growth, CO2 uptake capacities of all samples increased steadily. In these isotherms, no obvious plateau was observed under various applied pressure, indicating a possibility to adsorb more CO2 at a higher pressure. Detailed adsorption results at 0 and 25 °C were summarized in Table 2.The CO2 adsorption capacities varied with the feeding ratio and activation process. NFePC-10-A showed the highest CO2 uptake capacity, which was recorded as 5.8 and 9


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3.4 mmol g−1 at 0 and 25 °C, respectively. The effect of specific surface area and micro-porosity of the derived adsorbent on CO2 adsorption capability was plotted in Figure 6a. In comparison with NFePC-x, the samples treated with KOH activation process, NFePC-x-A possessed the relatively higher surface areas and provide more binding site for CO2. Consequently, NFePC-x-A owned a greater uptake capability. Among all the NFePC-x-A samples, NFePC-10-A exhibited the greatest efficiency for CO2 adsorption, which might be ascribed to its largest St-plot/SBET (Table 1 and Figure 6).1, 63,64 In contrast, pure TA derived carbon showed a CO2 adsorption capacity of 4.4 and 2.9 mmol g−1 at 0 and 25 °C, respectively. The relatively low values strongly indicated the significance of Fe in modifying the micro-structure of the above-mentioned carbonaceous materials, which was in good agreement with BET results. Moreover, NFePC-10-A also exhibited a relatively high CO2 uptake capacity compared to other porous carbonaceous adsorbents (Table S1). The selectivity of CO2 over N2 was measured to evaluate the competitive adsorption ability.65,66 Both CO2 and N2 isotherms measured at 0 and 25 °C were presented in Figure S7 and the corresponding IAST CO2/N2 selectivity was plotted in Figure 6b. It was observed that the CO2/N2 selectivity of NFePC-x-A was higher than that of NFePC-x. While among NFePC-x-A adsorbents, NFePC-15-A exhibited the highest efficiency of CO2/N2 selectivity, which may be ascribed to the greatest as-developed Vmicro. 43, 67 In addition, the low-pressure selectivity was also calculated and presented in Figure S8 to evaluate the selectivity behavior from more dilute streams. The low-pressure selectivity was calculated to be 27.7, 27.4, 29.4 at 0 °C and 10


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27.1, 24.0, 28.3 at 25 °C for NFePC-5-A, NFePC-10-A, NFePC-15-A, respectively. The remarkable results on both IAST and low-pressure selectivity revealed the reported NFePC-x-A adsorbents a great potential for real applications.68 The isosteric heat of adsorption (Qst) was evaluated from the CO2 sorption isotherms at 0 and 25°C, using the Clausius−Clapeyron equation to investigate the interaction strength between the adsorbate (CO2) and adsorbent (NFePC-x-A or NFePC-x).As shown in Figure 7a, all samples exhibited a decreasing trend with two stages. At the low CO2 uptake region, NFePC-x-A and NFePC-x presented an ultra-high Qst and indicated a strong interaction of these carbonaceous adsorbents with CO2 molecules, which might be ascribed to the considerable amount of developed micropores. While at a high CO2 loading, Qst showed a constant but a slower drop, which indicated a significant decrease of the interaction strength between the adsorbent and CO2 molecules. Notably, a high Qst was observed for NFePC-10-A, which was in good agreement with the relatively high CO2 uptakes result. The reusability of CO2 adsorbent is of great importance for the practical application.69 The CO2 adsorption capability of NFePC-10-A at 0 and 25 °C in four regeneration cycles was presented in Figure 7b. No obvious loss on CO2 adsorption was observed after each cycle at both temperatures, indicating a high efficiency of the reported adsorbent in the reusability for CO2 adsorption.

4. CONCLUSIONS In conclusion, we have presented a mechanochemical method for the fabrication of a 11


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tannic acid-Fe coordination compound derived porous carbon with a large surface area (up to 1801m2 g-1) and pore volume (up to 2.58 cm3 g-1).The eco-friendly and ubiquitous TA was used as carbon source. The adjustment of feeding ratio was an efficient method to tune the micro- and meso-structure. The obtained porous carbon, NFePC-10-A, exhibited an excellent CO2 uptakes capacity (5.8 mmol g−1 at 0 °C and 3.4 mmol g−1 at 25 °C, 1 bar). The outstanding adsorption capacity might be mainly ascribed to the high specific surface area, abundant micropores and narrow pore size distribution. In addition, the high initial isosteric heat of adsorption (63.16 kJ mol-1), good selectivity for CO2/N2, and efficient reusability afforded the adsorbent a great potential for the practical application. The reported porous carbon might be a promising adsorbent for CO2 capture and storage. ■ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Molecular structure of tannic acid, XRD patterns, Raman spectra, TEM images, XPS surveys, textural properties (pore size distributions, cumulative pore volumes, N2 adsorption/desorption isotherms), CO2 and N2 adsorption isotherms, CO2/N2 selectivity, and comparison of CO2 uptake and selectivity with other porous carbon materials.(PDF) ■AUTHOR INFORMATION Corresponding Authors 12


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*[email protected]

■ ACKNOWLEDGMENTS This work was supported by Shanghai Municipal Natural Science Foundation (17ZR1432200), National Natural Science Foundation of China (21774095), the Fundamental Research Funds for the Central Universities (0400219376), the start-up funding from Tongji University and the Young Thousand Talented Program.

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22. Xue, D. X.; Cairns, A. J.; Belmabkhout, Y.; Wojtas, L.; Liu, Y.; Alkordi, M. H.; Eddaoudi, M., Tunable Rare-Earth fcu-MOFs: A Platform for Systematic Enhancement of CO2 Adsorption Energetics and Uptake. J. Am. Chem. Soc.2013, 135 (20), 7660-7667. 23. Zhang, Z.; Zhao, Y.; Gong, Q.; Li, Z.; Li, J., ChemInform Abstract: MOFs for CO2 Capture and Separation from Flue Gas Mixtures: The Effect of Multifunctional Sites on Their Adsorption Capacity and Selectivity.Chem. Commun.2013, 49 (7), 653-661. 24. Hao, G. P.; Li, W. C.; Qian, D.; Lu, A. H., Rapid Synthesis of Nitrogen-Doped Porous Carbon Monolith for CO2 Capture. Adv. Mater.2010, 22 (7), 853-857.. 25. Chandra, V.; Yu, S. U.; Kim, S. H.; Yoon, Y. S.; Kim, D. Y.; Kwon, A. H.; Meyyappan, M.; Kim, K. S., Highly Selective CO2 Capture on N-Doped Carbon Produced by Chemical Activation of Polypyrrole Functionalized Graphene Sheets. Chem. Commun.2011, 48 (5), 735-737. 26. Tiwari, D.; Goel, C.; Bhunia, H.; Bajpai, P. K., Dynamic CO2 Capture by Carbon Adsorbents: Kinetics, Isotherm and Thermodynamic Studies.Sep. Purif. Technol.2017, 181, 107-122. 27. Tiwari, D.; Bhunia, H.; Bajpai, P. K., Synthesis of Nitrogen Enriched Porous Carbons from Urea Formaldehyde Resin and Their Carbon Dioxide Adsorption Capacity.J. CO2 Util. 2017, 21, 302-313. 28. Sevilla, M.; Valle‐Vigón P.; Fuertes, A. B., N-Doped Polypyrrole-Based Porous Carbons for CO2 Capture. Adv. Funct. Mater.2011, 21 (14), 2781-2787. 16


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29. To, J. W. F.; Zheng, C.; Yao, H.; He, J.; Kim, K.; Chou, H. H.; Pan, L.; Wilcox, J.; Yi, C.; Bao, Z., Ultrahigh Surface Area Three-Dimensional Porous GraphiticCarbon from Conjugated Polymeric Molecular Framework. Acs Cent. Sci.2015, 1 (2), 68-76. 30. Shen, W.; Fan, W., Nitrogen-Containing Porous Carbons: Synthesis and Application. J. Mater. Chem. A2013, 1 (4), 999-1013. 31. Goel, C.; Bhunia, H.; Bajpai, P. K., Development of Nitrogen Enriched Nanostructured Carbon Adsorbents for CO2 Capture.J. Environ. Manage2015, 62, 20-29. 32. Yang, S. J.; Antonietti, M.; Fechler, N., Self-Assembly of Metal Phenolic Mesocrystals and Morphosynthetic Transformation toward Hierarchically Porous Carbons. J. Am. Chem. Soc. 2015, 137 (25), 8269-8273. 33. Iqbal, N.; Wang, X.; Babar, A. A.; Yu, J.; Ding, B., Highly Flexible NiCo2O4/CNTs Doped Carbon Nanofibers for CO2 Adsorption and Supercapacitor Electrodes. J. Colloid Interface Sci. 2016, 476, 87-93. 34. Goel, C.; Bhunia, H.; Bajpai, P. K., Novel Nitrogen Enriched Porous Carbon Adsorbents for CO2 Capture: Breakthrough Adsorption Study.J. Environ. Chem. Eng.2016, 4(1), 346-356. 35. Bing, X.; Wei, Y.; Wang, M.; Xu, S.; Long, D.; Wang, J.; Qiao, W.; Ling, L., Template-Free Synthesis of Nitrogen-Doped Hierarchical Porous Carbons for CO2 Adsorption and Supercapacitor Electrodes. J. Colloid Interface Sci. 2017, 488, 207-217. 36. Goel, C.; Kaur, H.; Bhunia, H.; Bajpai, P. K., Carbon Dioxide Adsorption on 17


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Nitrogen Enriched Carbon Adsorbents: Experimental, Kinetics, Isothermal and Thermodynamic Studies. J. CO2 Util.2016, 16 (12), 50-63. 37. Qian, D.; Lei, C.; Wang, E. M.; Li, W. C.; Lu, A. H., A Method for Creating Microporous Carbon Materials with Excellent CO2-Adsorption Capacity and Selectivity.Chemsuschem 2014, 7 (1), 291-298. 38. Guan, B.; Wang, X.; Xiao, Y.; Liu, Y.; Huo, Q., A Versatile Cooperative Template-Directed Coating Method to Construct Uniform Microporous Carbon Shells for Multifunctional Core-Shell Nanocomposites. Nanoscale 2013, 5 (6), 2469-2475. 39. Liu, B.; Jin, L.; Zheng, H.; Yao, H.; Wu, Y.; Lopes, A.; He, J., Ultrafine Co-based Nanoparticles@Mesoporous

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Soc.2016, 138 (3), 1001-1009. 44. Tian, Z.; Huang, J.; Zhang, X.; Shao, G.; He, Q.; Cao, S.; Yuan, S., Ultra-Microporous N-Doped Carbon from Polycondensed Framework Precursor for CO2 Adsorption. Microporous Mesoporous Mater. 2017, 257, 19-26. 45. Zhang, X.; Liu, M.; Zhang, X.; Deng, F.; Zhou, C.; Hui, J.; Liu, W.; Wei, Y., Interaction of Tannic Acid with Carbon Nanotubes: Enhancement of Dispersibility and Biocompatibility. Toxicol. Research 2014, 4 (1), 160-168. 46. Rahim, M. A.; Björnmalm, M.; Suma, T.; Faria, M.; Ju, Y; Kempe, K.; Müllner, M.; Ejima, H.; Stickland, A. D.; Caruso, F., Metal–Phenolic Supramolecular Gelation.Angew. Chem., Int. Ed.2016,55 (44), 13803-13807. 47. Fu, N.; Wei, H.; Lin, H.; Li, L.; Ji, C.; Yu, N.; Chen, H.; Han, S.; Xiao, G., Iron Nanoclusters As Template/Activator for the Synthesis of Nitrogen Doped Porous Carbon and Its CO2 Adsorption Application. AcsAppl. Mater. Interfaces2017, 9 (11), 9955-9963. 48. Bandyopadhyay, S.; Anil, A. G.; James, A.; Patra, A., Multifunctional Porous Organic Polymers: Tuning of Porosity, CO2 and H2 Storage and Visible-Light-Driven Photocatalysis.ACS Appl. Mater. Interfaces2016, 8 (41), 27669-27678. 49. Deng, S. B.; Chen, T.; Zhao, T. N.; Yao, X. L.; Wang, B.; Huang, J.; Wang, Y. J.; Gang, Y.,Role of Micropores and Nitrogen-Containing Groups in CO2Adsorption on Indole-3-Butyric Acid Potassium Derived Carbons. Chem. Eng. J.2016, 286, 98-105. 50. Hao, G. P.; Li, W. C.; Qian, D.; Wang, G. H.; Zhang, W. P.; Zhang, T.; Wang, A. Q.; Schüth, F.; Bongard, H. J.; Lu, A. H., Structurally Designed Synthesis of 19


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Table 1. Texture parameters of NFePC-x-A and NFePC-x

SBET St-plota Vmicro 2 -1 2 -1 (m g ) (m g ) (cm3 g-1) NFePC-5-A 1393 926 (0.66) 0.53 NFePC-10-A 1414 984 (0.70) 0.53 NFePC-15-A 1801 800 (0.44) 0.55 NFePC-5 295 68 (0.23) 0.04 NFePC-10 776 398 (0.51) 0.21 NFePC-15 905 558 (0.62) 0.28 a The valuesin parentheses are the percentage of St-plot/SBET. Samples

Vtot (cm3 g-1) 1.50 1.82 2.58 0.66 1.01 1.21

Table 2. CO2 uptake capacities of NFePC-x-A and NFePC-x at 0 and 25 °C CO2 uptake, mmol g−1 (wt%) Samples 0 °C 25 °C NFePC-5-A 4.1 (18.0) 1.9(8.4) NFePC-10-A 5.8 (25.5) 3.4 (15.0) NFePC-15-A 4.9 (21.6) 2.8 (12.3) NFePC-5 1.4 (6.2) 0.8(3.5) NFePC-10 2.3 (10.1) 1.4(6.2) NFePC-15 3.4 (15.0) 1.9(8.4)

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Figure 1.Schematic illustration of synthesis of NFePC-A.

Figure2. (a) FT-IR spectra of pure TA and TA-Fe-10, (b) TGA curves of TA and TA-Fe-10 under flowing nitrogen.

Figure 3. TEM (a and b) and SEM (c and d) images of NFePC-10-A.

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Energy & Fuels

Figure 4. N2 adsorption/desorption isotherms (a) and the corresponding DFT (b) and H-K (c) pore size distributions of NFePC-x-A and NFePC.

Figure 5. CO2 adsorption isotherms of NFePC-x-A and NFePCat (a) 0 and (b)25 °C.

Figure 6.(a) The effects of specific surface areas and micro-porosity of the derived adsorbents on CO2 adsorption capability at 0 and 25 °C. (b) IAST CO2/N2 selectivity of the adsorbents at 0 and 25 °C.

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Figure 7.(a) Isosteric heat of adsorption of NFePC-x-A and NFePC-x at different CO2 loadings.(b)CO2 adsorption capability of NFePC-10-A at 0 and 25 °C in four cycles after regeneration.

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Mechanochemical Synthesis of Tannic Acid-Fe Coordination

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