In Situ Synthesis of Nitrogen-Enriched Activated Carbons from

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Environmental and Carbon Dioxide Issues

In Situ Synthesis of N-Enriched Activated Carbons from Procambarus Clarkii Shells with Enhanced CO2 Adsorption Performance Weiquan Cai, Shoute Zhang, Xin Hu, and Mietek Jaroniec Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02097 • Publication Date (Web): 14 Aug 2018 Downloaded from http://pubs.acs.org on August 15, 2018

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Energy & Fuels

In Situ Synthesis of N-Enriched Activated Carbons from Procambarus Clarkii Shells with Enhanced CO2 Adsorption Performance ‡

Weiquan Cai†, ,*, Shoute Zhang‡, Xin Hu§, Mietek Jaroniec∥,* †

School of Chemistry and Chemical Engineering, Guangzhou University, 230 GuangZhou University City Outer Ring Road, Guangzhou 510006, P. R. China ‡

School of Chemistry, Chemical Engineering & Life Sciences, Wuhan University of Technology, Luoshi Road 205#, Wuhan 430070, P. R. China

§

College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, P. R. China

∥

Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio, 44242, USA

ACS Paragon Plus Environment

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ABSTRACT Highly microporous N-enriched activated carbons were in situ synthesized by using K2C2O4·H2O as an activating agent and procambarus clarkii shells as carbon and nitrogen (N) source. The obtained samples exhibit good CO2 adsorption performance at 1 bar ranging from 4.99 to 6.48 mmol/g at 0 °C, and 2.55 to 4.51 mmol/g at 25 °C, respectively. In particular, high CO2 adsorption capacity of 4.51 mmol/g at 25 °C was achieved for the sample prepared by using the K2C2O4·H2O/precursor mass ratio of 3 and activated at 700 °C. The high CO2 uptake was achieved because of unique microporous structure and high N content. Furthermore, the CO2/N2 selectivity and CO2 adsorption heat of this carbon are as high as 52 and 33 kJ/mol, respectively. In addition, this carbon exhibits excellent reusable stability and high dynamic CO2 capture capacity of 0.79 mmol/g under conditions mimicking flue gas environment. The aforementioned advantages demonstrate that the obtained N-enriched activated carbon can be a potential alternative for capturing CO2.


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1. INTRODUCTION CO2 has drawn considerable attention in recent years because of its rising level in the atmosphere and the concern about global warming effect.1,2 Great efforts are directed towards developing new technologies for its capture and storage. Currently, chemical absorption is the most applicable technology for its capture in power plants. However, this method has the drawbacks of high energy consumption, difficult solvent regeneration, equipment corrosion and toxicity of organic amine.3,4 Therefore, a wide variety of porous adsorbents with high adsorption capacity and good regeneration stability have been explored for CO2 capture. Currently, these adsorbents include alkali metal nitrate-promoted MgO,5 mesoporous silica,6 porous carbon,7 zeolitic structures,8 metal-organic frameworks (MOFs),9 and mesoporous γ-Al2O3.10,11 Among them, porous carbons are advantageous because of low cost and simple preparation process, high thermochemical stability, adjustable pore structure, easy regeneration, and inert characteristic to water vapor.12 Some studies showed that incorporation of N atoms into the carbon skeleton can increase its CO2 adsorption capacity via base-acid interactions, quadrupole interactions or hydrogen bonds.13,14 Generally, N incorporation could be realized via either in situ pyrolysis of the N-containing precursor or post-processing of porous carbons.14 The former includes two methods: (i) the use of N containing organics through polymerization reaction (resorcinol-formaldehyde-melamine,15,16 sucrose and urea17) or available monomers (pyrrole,18,19 ionic liquids20 and polyaniline21) as the starting precursors in both hard-templating and soft-templating routes, which often need wasteful amounts of solvents and regents; (ii) the ingenious use of N-containing biomass and waste products as the starting precursors.22-24 The latter includes the post-treatment of carbons


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with ammonia12,25 and urea26 at elevated temperatures. Thus, this method is multi-step and time-consuming. Obviously, exploring the N-containing biomass as precursor and “appropriate” activator could simultaneously solve above issues.14 So far, Wei et al.22 prepared various N-enriched activated carbons from bean dreg by KOH activation, which showed good CO2 adsorption capacity of 4.24 mmol/g due to the hydrogen bonding interactions between hydrogen atoms from CH and NH on the carbon surface and CO2 molecules. Tao Chen et al.23 used crab shells to prepare N-enriched activated carbon by pre-carbonization followed by KOH activation, indicating the role of N-containing groups and micropores during CO2 adsorption process on activated carbons. All above examples demonstrate that N content plays an important role in promoting CO2 adsorption, especially at higher temperatures. However, it also indicates that a large amount of micropores smaller than 1.0 nm favors both CO2 adsorption capacity and selectivity.27 For example, Mokaya et al.28 proved that the presence of N has no favorable influence on CO2 adsorption. Rather, adsorption of CO2 on carbon at low pressure is mainly affected by the micropore size distribution up to 1 nm. Sevilla et al.29 reported analogous CO2 adsorption capacities for non-doped and N-doped activated carbons, and found that the N functionalities present in N-doped carbons have not effect on CO2 adsorption. Therefore, there is a long-standing debate regarding the effect of N species and micropore size distribution on CO2 adsorption. Although activation with KOH, H3PO4, ZnCl2 is often used to prepare activated carbons with high adsorption performance, these activators have the disadvantages of strong toxicity and corrosiveness.30 Therefore, milder activators would be more valuable for preparation of activated carbons.31 Recently, Chen et al.32 selected K2C2O4 as an activator for making kenaf


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core-based activated carbons. Garba et al.33 used K2C2O4 as an activator for preparation of activated carbon from prosopicafricana seed hulls as precursor and tested this carbon for removal of chlorophenols. Ludwinowicz et al.34 prepared highly microporous carbon spheres for CO2 adsorption via a somewhat modified one-pot Stӧber method in the presence of K2C2O4·H2O. However, the activation mechanism has not been well understood and needs to be further studied. To elucidate the effects of micropore size distribution and N doping, and develop a more sustainable approach for preparation of N-enriched carbon adsorbents, herein we report the synthesis of highly microporous N-enriched activated carbons by using K2C2O4·H2O as an activating agent and procambarus clarkii shells as both carbon and N source through simple physical mixing and direct carbonization. This method has the following advantages: firstly, the preparation process is quite simple without conventional two-step carbonization or impregnation process; secondly, high N content, high surface area and high volume of micropores can be simultaneously attained via in situ carbonization and activation; thirdly, K2C2O4·H2O is a milder activator than the conventional activators including KOH, H3PO4 and ZnCl2. More importantly, the as-prepared N-enriched activated carbon shows an enhanced CO2 adsorption capacity, good CO2/N2 selectivity, and can be easily reused with superior cyclic stability, indicating its great potential for CO2 capture. 2. EXPERIMENTAL SECTION 2.1 Pretreatment with HCl. Firstly, procambarus clarkii shells (a raw poultry market in Wuhan, Hubei Province) were washed, milled, and sieved into granules with the size of 100-120 mesh, and then impregnated in excess with 1 M HCl (Sinopharm Chemical Reagent


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Co., Ltd. AR ≥ 36.0-38.0 %) solution for 10 h to remove calcium carbonate, rinsed with distilled water and dried overnight in an oven at 110 °C. For simplicity, the pretreated procambarus clarkii shells were denoted as “P”. 2.2 Carbonization and K2C2O4·H2O Activation. In a typical experiment, firstly, 2 g P and 6 g K2C2O4·H2O (Sinopharm Chemical Reagent Co., Ltd. AR ≥ 99.8 %) were ground homogeneously using a grinding mill. Secondly, the resulting mixture was placed in a horizontal quartz pipe reactor, and activated at 700 °C for 2 h with an increasing rate of 5 °C/min in a N2 stream of 50 mL/min before cooling to the ambient temperature. The activated sample was rinsed with 1 M HCl solution and deionized water until the pH value of the post-washing water became neutral. Lastly, the resulting sample was dried at 110 °C for 12 h. The as-prepared sample was designated as PK-X-Y, where K represents K2C2O4·H2O, X represents the mass ratio of K to P, and Y represents the activation temperature. For example, the as-prepared sample was denoted as PK-3-700. In contrast, the samples obtained by direct carbonization of P and K were designated as P-Y and K-Y, respectively. Schematic diagram of the above preparation process is shown in Figure 1. 2.3. Characterizations. X-ray diffraction (XRD) measurements were performed on a D8 Adwance X-ray diffractometer with Cu Kα radiation (λ=0.1542 nm). Scanning electron microscopy (JSM-IT300) was used to study the morphology. X-ray photoelectron spectroscopy (XPS) was performed by an ESCALAB 250Xi device (Thermo Fisher Scientific Ltd., U.S.A) with Al Kα radiation. A Vario EL III Elemental Analyzer was used to obtain the elemental content of C, N, and H of a dry sample. A Nicolet 670 FT-IR spectrometer was applied to collect the Fourier transform infrared (FT-IR) spectra.


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Thermogravimetric analysis (TGA) data were recorded on a thermogravimetric/differential thermal analyzer in N2 flow from 25 °C to 800 °C with a heating rate of 5 °C/min. N2 adsorption-desorption isotherms were obtained at -196 °C on a Micromeritics ASAP 2020 analyzer (Micromeritics Instrument Corporation, U.S.A.). The samples were degassed for 12 h at 300 °C in a vacuum environment before measurement. The specific surface area (SBET) was obtained by the multi-point Brunauer-Emmett-Teller (BET) means at P/P0 values between 0.01 and 0.1. The total pore volume (V0) was estimated from the N2 adsorption amount at a relative pressure of 0.99, and the total micropore volume (Vt) was obtained by the t-plot analysis of N2 adsorption data. The pore size distribution (PSD) of the samples was determined by using a non-local density functional theory (NLDFT) method. The isotherms of CO2 adsorption were measured at 0 °C and 25 °C, respectively using a Micromeritics ASAP 3020 analyzer (Micromeritics Instrument Corporation, U.S.A.). All samples were degassed for 4 h at 150 °C before testing to remove guest molecules in the pores. The samples were evacuated by degassing at 150 °C for 4 h under vacuum to study their cyclic adsorption-desorption performance. Then, the CO2 adsorption isotherm was measured on the regenerated sample under the same conditions at 25 °C. To explore the selectivity of CO2 over N2, the N2 adsorption isotherms were tested at 25 °C under the same conditions. After drawing the adsorption curves of CO2 and N2 obtained for the same sample at 25 °C, the tangent slopes (denoted as KCO2 and KN2) of the two adsorption curves were evaluated respectively, and the selectivity was the ratios of KCO2 and KN2. The heat of adsorption was calculated from the CO2 adsorption isotherms measured at 25 °C and 0 °C, respectively via the Clausius−Clapeyron equation as follows:


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Qst = R[T1T2/(T2-T1)][ln(P1/P2)]v where Pi is the pressure for i-th isotherm, Ti is the temperature for i-th isotherm where i =1 and 2, and R is the universal gas constant 8.314 J/(mol·K). Note that both pressures P1 and P2 refer to the same amount adsorbed v. The dynamic CO2 capture capacity was measured on a fixed-bed adsorber with an internal diameter of 6 mm and a length of 100 mm at 25 °C and 1 bar (see Figure S1). The specific operation process was provided in Supplementary Information. The corresponding dynamic adsorption capacity was obtained by plotting and analyzing the breakthrough curves. 3. RESULTS AND DISCUSSION 3.1. Surface Morphology and Phase Structures. SEM was used to observe the morphology of P-700 and the N-enriched activated carbon (PK-3-700 as a representative sample). It was found that P-700 shows an enormous block structure with a smooth surface and the cell walls are dense (Figure 2a). While after activation with K2C2O4·H2O the resulting PK-3-700 sample shows the interconnected irregular and heterogeneous macropores with pore walls having sharp edges (Figure 2b). This change in the morphology proves that the K2C2O4·H2O activation is an effective strategy for preparation of activated carbons. Furthermore, the TEM image of PK-3-700 shows that its porosity is made up of randomly oriented worm-like micropores along with some mesopores (Figure 2c). The XRD pattern (Figure 2d) shows only two broad and weak diffraction peaks at around 23° and 43°, which match the (002) and (100) diffraction patterns of amorphous carbon, respectively.13 This amorphous nature is in good accordance with the TEM image. 3.2. Surface Properties of Carbon Samples. The elemental analysis data for the samples


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studied are summarized in Table 1. The original P shows a high N content of 9.02 wt %; the N content in P-700 is also as high as 7.73 wt %, indicating that procambarus clarkii shells is a good precursor to prepare N-enriched activated carbons. The content of C and N is highly dependent on the activation conditions. When the mass ratio of K to P increases from 1 to 5, and the activation temperature increases from 650 °C to 750 °C, the C content increases. On the contrary, the corresponding H content decreases. Surprisingly, when the activation temperature reaches 750 °C, the H content is 0 wt %. However, N content always decreases with increasing activation temperature. These results indicate that more N species would be removed under severe activation conditions, which agrees with previous reports.24,35 The FT-IR spectra of P-700 and PK-3-700 are shown in Figure 3. As can be seen from this figure there are no obvious changes in spectra after introducing activation agent. The peaks at 3434 cm-1 and 1631 cm-1 attribute to the -OH groups, while 1631 cm-1 may also related to N-H in-plane bending vibration.36 The peaks at 2925 cm-1 and 2850 cm-1 are assigned to the -CH2groups corresponding to the antisymmetric vibration and symmetric vibration,32 respectively, which indicates incomplete decomposition of aliphatic compounds in raw materials after thermal treatment. The peak at 1575 cm-1 could be ascribed to the C=C bond in benzene ring, which may be due to the effective aromatization after high temperature treatment. In addition, the peaks at 1414 cm-1, 1123 cm-1 and 650 cm-1 can be attributed to the C-N stretching vibration, C-O-C bond and the deformation vibration of N-H, respectively.19,36,37 Hence, the FT-IR results verify the existence of N-H, C-O and C-N species in the samples, which is in accordance with the elemental analysis. The XPS spectra of PK-3-650, PK-3-700, PK-5-700 and PK-1-750 are shown in Figure S2 and analyzed to obtain information about N species


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present on the surface of the N-enriched samples. Figure 4 reveals the N 1s XPS spectra of the typical activated carbons, i.e., PK-3-650, PK-3-700, PK-5-700 and PK-1-750. For all of them, it was found that the XPS N 1s spectra can always be deconvoluted into three peaks, whose binding energies center at 398.3, 400.3 and 401.5 eV, respectively. The peak at 398.3 eV is classical representative of the pyridinic N (N-6), while the peaks at 401.5 and 400.3 eV attribute to the quaternary N (N-Q) and pyrrolic N (N-5), respectively.26 Quantitative studies imply that the amount of N in the form of N-6 and N-Q is less than that in the form of N-5. This is advantageous to CO2 adsorption, as it was reported that N-5 usually has a much larger influence onto CO2 adsorption than N-6 and N-Q.17,26 3.3. Porosity and Structural Properties. Figure 5 shows N2 adsorption isotherms and NLDFT PSDs of the N-enriched samples. As can be seen in Figure 5a, 5b and 5c, all the adsorption isotherms show type I in accordance with the IUPAC classification, which is the characteristic of microporous materials. The N2 isotherm shows a sharp knee in the order of 650 °C>700 °C >750 °C at low relative pressures, suggesting that the higher activation temperature

produces

samples

with

wider

PSDs.

Nevertheless,

a

tiny

closed

adsorption-desorption hysteresis loop at P/P0 values higher than 0.5 is visible indicating the presence of mesopores.38 This result is in a good agreement with the NLDFT PSDs shown in Figure 5d having three peaks at about 0.53, 0.85, and 1.18 nm. Figure 5e shows five peaks at about 0.53, 0.85, 1.18, 1.5 and 2.0 nm. Figure 5f shows six peaks at about 0.53, 0.58, 0.85, 1.18, 1.5 and 2.0 nm. The corresponding porous structure parameters are given in Table 1. These data indicate that with increasing K/P mass ratio and activation temperature, the SBET, V0 and Vt parameters increase from 1253 to 2995 m2/g, from 0.58 to 1.51 cm3/g and from 0.43


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to 1.01 cm3/g, respectively (with a minority exceptions), because severe activation conditions tend to consume more carbon atoms, and develop more pores. As compared to PK-3-750, the observed decrease in the surface area and the pore volume of PK-5-750 is probably due to the severe etching action by K2C2O4.H2O, which results in the partial collapse of porous structure. The above results indicate that highly developed narrow microporosity of these carbon materials is beneficial for CO2 capture via micropore filling mechanism.1,24 Furthermore, the existence of some mesopores can facilitate the diffusion of CO2 molecules, and consequently boost the rate of adsorption.22,39 3.4 Mechanism of Activation with K2C2O4·H2O. Although K2C2O4 has been proved as a promising activator for preparation of activated carbons, the detailed activation mechanism is not clear.32-34 Therefore, TGA in Figure 6 was performed to gain a further insight on this process, as well as the DTG in Figure S3. In the case of K, the initial mass loss below 125 °C is 9.79 % (calculated theoretical value is 9.78 %), which is equal to the amount of desorbed water (equation 1). The mass loss of the second step from 525 to 600 °C is about 16.01 % (calculated theoretical value is 16.86 %), indicating that K2CO3 forms and CO is released via K2C2O4 decomposition (equation 2). For P the second step from 196 to 381 °C and third step from 381 to 568 °C with mass losses of 61.73 % and 13.14 %, respectively, are mainly due to the decomposition of the cellulose, hemicellulose and lignin, respectively, resulting in some volatile gases like CO2 and CO. The last step could be ascribed to the residual carbon and formation of the basic skeleton of carbon. A comparison of P and K with different mass ratios shows that the mass loss curves from 525 to 600 °C are different from the former, and this could be attributed to the reaction between K2CO3 and the formed carbon (equation 3).31


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Based on the analysis of porosity two conclusions can be made: (i) wider PSDs are obtained for the carbons at higher activation temperature, which is related to the generation of CO2 and CO,40 (ii) the micropores and mesopores are formed during reaction between the activator and the carbon intermediate,41 and the unique micro-mesostructured pores would perhaps favor high CO2 adsorption capacity and fast adsorption/desorption dynamics.22 The above mechanism of activation with K2C2O4.H2O is different from that when KOH,30 KHCO341 and K2CO342 are used, respectively. However, the aforementioned activators have a common feature, the formation of K2CO3. Therefore, K2C2O4.H2O activation could be similar with the activation reaction resulted from K2CO3. However, in our study, due to the relatively lower activation temperature, K2CO3 decomposition does not occur. This was proved by the TGA analysis of K2C2O4.H2O. As compared to activation with K2CO3, the advantage of K2C2O4.H2O may be related to equation 2. The CO molecules released during the decomposition of K2C2O4.H2O act as carrier gas to help removal of pyrolysis volatiles from the char matrix to strengthen the activation degree as well as to reduce the pore widening progress and achieve better homogeneity of pores.32 3.5. CO2 Adsorption Properties. CO2 adsorption properties of the samples were investigated at 25 °C and 0 °C under 1 bar. Their corresponding adsorption isotherms are shown in Figure 7, and CO2 uptakes are collected in Table 1. All the samples exhibit good adsorption capacities ranging from 2.55 to 4.51 mmol/g at 25 °C and 4.99 to 6.48 mmol/g at 0 °C, and they are among the high values for N-enriched carbons8,18,22,26 and also higher than


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those for many MOFs,43 COFs.44 A comparison of the CO2 adsorption (25 °C and 1 bar) for biomass-derived N-enriched carbons is shown in Table S1. It is evident that the CO2 uptake on PK-3-700 is higher than those so far reported for the biomass-derived N-enriched carbon materials.12,22,24,35,45-47 The influence of activation temperature on the adsorption capacity is exploratory. When the mass ratio of the activator to the raw material is 1, the adsorption capacity of the carbon activated at high temperature (750 °C) is higher than those obtained for the carbons activated at lower temperatures (650 °C and 700 °C). However, the adsorption capacities of the carbons activated at 650 °C and 700 °C are higher than that on the carbon activated at 750 °C when the mass ratio is 3 or 5. With increasing the mass ratio, the active contact sites between the activator and carbon precursor increase, and the activation reaction is more efficient. Namely, the evolving gases such as CO make the activation of carbon matrix more effective. Therefore, both the control of activation temperature and the activator/raw material mass ratio affect the adsorption capacities of the resulting carbons. Furthermore, the CO2 uptakes at ambient pressure and temperature are affected by the porous structure parameters such as V0 and SBET, and the N content. The current data reveal that in addition to the aforementioned porous structure parameters, especially the volume of small micropores, the N species present on the surface of activated carbons may also enhance the CO2 uptake. Namely, PK-3-700 with lower SBET and V0 than those of PK-3-750 but much higher N content shows the highest CO2 uptake at the ambient conditions; in contrast, PK-3-750 with the highest SBET and V0, and the second lowest N content, shows the second lowest CO2 uptake. On the other hand, PK-3-650 with the highest N content, but the third lowest SBET and V0 values also shows lower CO2 uptake than that


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obtained for PK-3-700. Obviously, PK-5-750 shows the lowest adsorption capacity among all N-enriched carbons, which may be associated with its lowest N content. Namely, a comparison of the CO2 uptakes for N-enriched carbons shows that their adsorption capacities are determined by the microporous structure characteristics as well as N content. To evaluate application potentials of these carbons, the CO2 breakthrough curves were measured for PK-3-700 and PK-700 (Figure 8) to obtain the dynamic adsorption capacities in flowing CO2/N2 (10:90 v/v) mixed gas. Figure 8 shows that PK-3-700 exhibits higher adsorption capacity of 0.79 mmol/g than 0.35 mmol/g of P-700 with higher N content due to better microporous properties of the former (see Table 1). Furthermore, its dynamic CO2 capture capacity of 0.79 mmol/g is in a good agreement with the pure CO2 capture data at the partial pressure of 0.1 bar (see Figure 9), which shows its potential for capturing CO2 from flue gas.13 3.6. CO2/N2 Selectivity and Isosteric Heat of CO2 Adsorption. N2 adsorption capacity on PK-3-700 at 25 °C and 1 bar is low, 0.17 mmol/g (see Figure 9), indicating that this sorbent is potentially useful for selective CO2 capture from the combustion flue gas. The selectivity of CO2 over N2 was calculated using the initial slopes of CO2 and N2 adsorption isotherms12 in the Henry’s law region (see Figure S4). The estimated CO2/N2 selectivity is 52, which is in agreement with or better than those reported for N-enriched carbons,13,17,24 indicating its potential for industrial applications. To determine the interaction strength between the activated carbons and CO2, the isosteric heats of adsorption (Qst) for the selected N-enriched carbons was calculated using the Clausius-Clapeyron equation based on the CO2 sorption isotherms at 25 °C and 0 °C.12,13


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Figure 10 shows the Qst curves for PK-3-650, PK-3-700, PK-5-700 and PK-1-750. At the range of low CO2 uptakes (0 - 2.5 mmol/g) the isosteric heat Qst decreases rapidly from about 32-29 kJ/mol to about 25-22 kJ/mol for the carbons studied, and it is analogous or slightly higher than the values reported of carbonaceous sorbents.48 However, these values are still lower than those reported for the amine-functionalized sorbents in the range of 40-90 kJ/mol.49,50 Furthermore, Qst decreases with increasing CO2 uptake until it approaches a plateau level, indicating different binding energies of CO2 depending on the size of micropores and the presence of various surface sites such as N species. The reason for the relatively high initial Qst values is related to the presence of ultramicropores of different sizes and N species strongly interacting with CO2. It is noteworthy that the Qst values are in the range of 29-32 kJ/mol, which are typical for physisorption processes.51,52 At the same time, there is nearly no hysteresis between the CO2 adsorption and desorption curves for the carbon studied and CO2 uptake is lower at higher temperatures, which is characteristic for physical adsorption and beneficial for optimization of CO2 capture. 3.7 CO2 Adsorption/Desorption Measurements. Cyclic adsorption stability is an important indicator for evaluation of the adsorption performance of an adsorbent. As shown in Figure 11, the reusability of PK-3-700 and P-700 was measured by multiple adsorption/desorption cycling at 25 °C (the detailed CO2 adsorption isotherms for 15 cycles are shown in Figure S5). As can be seen from this figure, in comparison to the initial CO2 adsorption capacities of 4.51 mmol/g and 1.82 mmol/g, the CO2 uptakes recorded for PK-3-700 and P-700 after 15 adsorption/desorption cycles decreased to 3.48 mmol/g and 1.61 mmol/g, respectively. This excellent regeneration performance of PK-3-700 makes it a


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potential adsorbent for CO2 capture. 4. CONCLUSIONS A series of highly microporous N-enriched activated carbons was synthesized using procambarus clarkii shells as the carbon source, and K2C2O4·H2O as an activator. The synergistic effect of the unique microstructure and rich N content of PK-3-700 resulted in the high adsorption capacity of 4.51 mmol/g for CO2 at 25 °C and 1 bar. The activation mechanism of K2C2O4·H2O was also further explored, indicating that this compound is an effective activator for preparation of microporous carbons with enhanced CO2 adsorption performance. Moreover, PK-3-700 shows good CO2/N2 selectivity, high initial CO2 adsorption heat, stable cyclic behavior, and better dynamic adsorption capacity under flue gas conditions. Therefore, the obtained N-enriched activated carbon from procambarus clarkii shells can be a prospective candidate for CO2 adsorption and separation. ■ ASSOCIATED CONTENT Supporting Information Schematic diagram of the fixed-bed flow experimental apparatus. Comparison of the CO2 adsorption (25 °C and 1 bar) for biomass-derived carbon sorbents. XPS survey spectra of PK-3-650, PK-3-700, PK-5-700 and PK-1-750. Determination of the initial slopes from CO2 and N2 adsorption isotherms at 25°C for PK-3-700. CO2 adsorption isotherms recorded for PK-3-700 (a) and P-700 (b) after 15 cycles. These information is available free of charge via the internet at http://pubs.acs.org. ■ AUTHOR INFORMATION Corresponding Author


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*Phone: +86-20-39366905. E-mail: [email protected]; Tel.: +1 (330) 672-2032. Fax: +1 (330) 672-3816. E-mail: [email protected]. Author Contributions W.Q. Cai and S.T. Zhang contributed equally to this work. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ■ ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (51272201 and 21476179), one hundred talents project of Guangzhou University and 2016 Wuhan Yellow Crane Talents (Science) Program. ■ REFERENCES (1) Yue, L.; Rao, L.; Wang, L.; Sun, Y.; Wu, Z.; DaCosta, H.; Hu, X. Enhanced CO2 adsorption on nitrogen-doped porous carbons derived from commercial phenolic resin. Energ. Fuel. 2018, 32 (2), 2081−2088. (2) Gholidoust, A.; Atkinson, J. D.; Hashisho, Z. Enhancing CO2 adsorption via amine-impregnated activated carbon from oil sands coke. Energ. Fuel. 2017, 31 (2), 1756−1763. (3) Yuan, S.; Yang, Z.; Ji X.; Chen Y.; Sun Y.; Lu X. CO2 absorption in mixed aqueous solution of MDEA and cholinium glycinate. Energ. Fuel. 2017, 31 (7), 7325−7333. (4) Veawab, A.; Tontiwachwuthikul, P.; Chakma, A. Corrosion behavior of carbon steel in the CO2 absorption process using aqueous amine solutions. Ind. Eng. Chem. Res. 1999, 38


Energy & Fuels 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

(10), 3917−3924. (5) Jin, S.; Ho, K.; Vu, A-T.; Lee, C-H. Salt-composition-controlled precipitation of triple-salt-promoted MgO with enhanced CO2 sorption rate and working capacity. Energ. Fuel. 2017, 31 (9), 9725–9735. (6) Heydari-Gorji, A.; Belmabkhout, Y.; Sayari, A. Polyethylenimine-impregnated mesoporous silica: effect of amine loading and surface alkyl chains on CO2 adsorption. Langmuir 2011, 27 (20), 12411−12416. (7) Fu, N.; Wei, H. M.; Lin, H. L.; Li, L.; Ji, C. H.; Yu, N. B.; Chen, H. J.; Han, S.; Xiao, G. Y. Iron nanoclusters as template/activator for the synthesis of nitrogen doped porous carbon and Its CO2 adsorption application. ACS Appl. Mater. Interfaces 2017, 9 (11), 9955−9963. (8) Liu, X.; Sun, Y.; Liu, J J.; Sun, C G.; Liu, H.; Xue, Q.; Smith, E.; Snape, C. Potassium and zeolitic structure modified ultra-microporous adsorbent materials from a renewable feedstock with favorable surface chemistry for CO2 capture. ACS Appl. Mater. Interfaces 2017, 9 (32), 26826−26839. (9) Salehi, S.; Anbia, M. High CO2 adsorption capacity and CO2/CH4 selectivity by nanocomposites of MOF-199. Energ. Fuel. 2017, 31 (5), 5376–5384. (10) Zhang, S.; Cai, W.; Yu, J.; Ji, C.; Zhao, N. A facile one-pot cation-anion double hydrolysis approach to the synthesis of supported MgO/γ-Al2O3 with enhanced adsorption performance towards CO2. Chem. Eng. J. 2017, 310, 216−225. (11) Cai, W.; Tan, L.; Yu, J.; Jaroniec, M.; Liu, X.; Cheng, B.; Verpoort, F. Synthesis of amino-functionalized mesoporous alumina with enhanced affinity towards Cr(VI) and CO2. Chem. Eng. J. 2014, 239, 207−215.


Page 18 of 33

Page 19 of 33 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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(12) Arami-niya, A.; Rufford, T. E.; Zhu, Z. Nitrogen-doped carbon foams synthesized from banana peel and zinc complex template for adsorption of CO2, CH4, and N2. Energy Fuels 2016, 30, 7298−7309. (13) Yang, M.; Guo, L.; Hu, G.; Hu, X.; Chen, J.; Shen, S.; Dai, W.; Fan, M. Adsorption of CO2 by Petroleum coke nitrogen-doped porous carbons synthesized by combining ammoxidation with KOH activation. Ind. Eng. Chem. Res.2016, 55 (3), 757−765. (14) Zhang, S.; Mandai, T.; Ueno, K.; Dokko, K.; Watanabe, M. Hydrogen-bonding supramolecular protic salt as an “all-in-one” precursor for nitrogen-doped mesoporous carbons for CO2 adsorption. Nano Energy 2015, 13, 376−386. (15) Feng, S.; Li, W.; Shi, Q.; Li, Y.; Chen, J.; Ling, Y.; Asiri, A. M.; Zhao, D. Synthesis of nitrogen-doped hollow carbon nanospheres for CO2 capture. Chem. Commun. 2014, 50 (3), 329−331. (16) Yu, J.; Guo, M.; Muhammad, F.; Wang, A.; Yu, G.; Ma, H.; Zhu, G. Simple fabrication of an ordered nitrogen-doped mesoporous carbon with resorcinol-melamine-formaldehyde resin. Micro. Meso. Mater. 2014, 190, 117−127. (17) Sivadas, D. L.; Vijayan, S.; Rajeev, R.; Ninan, K. N.; Prabhakaran, K. Nitrogen-enriched microporous carbon derived from sucrose and urea with superior CO2 capture performance. Carbon 2016, 109, 7−18. (18)Yang, Q.-S.; Sui, Z.-Y.; Liu, Y.-W.; Han, B.-H. Porous nitrogen-doped carbon nanoribbons for high-performance gas adsorbents and lithium ion batteries. Ind. Eng. Chem. Res. 2016, 55 (22), 6384−6390. (19) Li, Y.; Zou, B.; Hu, C.; Cao, M. Nitrogen-doped porous carbon nanofiber webs for


Energy & Fuels 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

efficient CO2 capture and conversion. Carbon 2016, 99, 79−89. (20) Lee, J. S.; Wang X.; Luo H.; Baker, G. A.; Dai, S. Facile ionothermal synthesis of microporous and mesoporous carbons from task specific ionic liquids. J. Am. Chem. Soc. 2009, 131 (13), 4596−4597. (21) Lin, D.; Zhang, X.; Cui, X.; Chen, W. Highly porous carbons with superior performance for CO2 capture through hydrogen-bonding interactions. RSC Adv. 2014, 4 (52), 27414. (22) Xing, W.; Liu, C.; Zhou, Z.; Zhang, L.; Zhou, J.; Zhuo, S.; Yan, Z.; Gao, H.; Wang, G.; Qiao, S. Z. Superior CO2 uptake of N-doped activated carbon through hydrogen-bonding interaction. Energy Environ. Sci. 2012, 5 (6), 7323. (23) Fujiki, J.; Yogo, K. The increased CO2 adsorption performance of chitosan-derived activated carbons with nitrogen-doping. Chem. Commun. 2016, 52 (1), 186−189. (24) Chen, T.; Deng, S.; Wang, B.; Huang, J.; Wang, Y.; Yu, G. CO2 adsorption on crab shell derived activated carbons: contribution of micropores and nitrogen-containing groups. RSC Adv. 2015, 5 (60), 48323−48330. (25) Zhang, C.; Song, W.; Ma, Q.; Xie, L.; Zhang, X.; Guo, H. Enhancement of CO2 capture on biomass-based carbon from black locust by KOH activation and ammonia modification. Energy Fuels 2016, 30 (5), 4181−4190. (26) Bai, R.; Yang, M.; Hu, G.; Xu, L.; Hu, X.; Li, Z.; Wang, S.; Dai, W.; Fan, M. A new nanoporous nitrogen-doped highly-efficient carbonaceous CO2 sorbent synthesized with inexpensive urea and petroleum coke. Carbon 2015, 81, 465−473. (27) Sevilla, M.; Fuertes, A. B. Sustainable porous carbons with a superior performance for


Page 20 of 33

Page 21 of 33 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

Energy & Fuels

CO2 capture. Energy Environ. Sci. 2011, 4 (5), 1765. (28) Adeniran, B.; Mokaya, R. Is N-doping in porous carbons beneficial for CO2 storage? Experimental demonstration of the relative effects of pore size and N-doping. Chem. Mater. 2016, 28 (3), 994−1001. (29) Sevilla, M.; Parra, J. B.; Fuertes, A. B. Assessment of the role of micropore size and N-doping in CO2 capture by porous carbons. ACS Appl Mater. Interfaces 2013, 5 (13), 6360−8. (30) Wang, J.; Kaskel, S. KOH activation of carbon-based materials for energy storage. J. Mater. Chem. 2012, 22 (45), 23710. (31) Sevilla, M.; Ferrero, G. A.; Fuertes, A. B. Beyond KOH activation for the synthesis of superactivated carbons from hydrochar. Carbon 2017, 114, 50−58. (32) Chen, Y.-D.; Chen, W.-Q.; Huang, B.; Huang, M.-J. Process optimization of K2C2O4-activated carbon from kenaf core using box-behnken design. Chem. Eng. Res. Des. 2013, 91 (9), 1783−1789. (33) Garba, Z. N.; Rahim, A. A. Process optimization of K2C2O4-activated carbon from Prosopis africana seed hulls using response surface methodology. J. Anal. Appl. Pyrolysis 2014, 107, 306−312. (34) Ludwinowicz, J.; Jaroniec, M. Potassium salt-assisted synthesis of highly microporous carbon spheres for CO2 adsorption. Carbon 2015, 82, 297−303. (35) Huang, B.; Shao, H.; Liu, N.; Xu, Z. J.; Huang, Y. From fish scales to highly porous N-doped carbon: a low cost material solution for CO2 capture. RSC Adv. 2015, 5 (107), 88171−88175.


Energy & Fuels 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

(36) Wan, L.; Wang, J.; Feng, C.; Sun, Y.; Li, K. Synthesis of polybenzoxazine based nitrogen-rich porous carbons for carbon dioxide capture. Nanoscale 2015, 7 (15), 6534-6544. (37) 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. (38) Falco, C.; Marco-Lozar, J. P.; Salinas-Torres, D.; Morallón, E.; Cazorla-Amorós, D.; Titirici, M. M.; Lozano-Castelló, D. Tailoring the porosity of chemically activated hydrothermal carbons: influence of the precursor and hydrothermal carbonization temperature. Carbon 2013, 62, 346−355. (39) Yuan, B.; Wang, J.; Chen, Y.; Wu, X.; Luo, H.; Deng, S. Unprecedented performance of N-doped activated hydrothermal carbon towards C2H6/CH4, CO2/CH4, and CO2/H2 separation. J. Mater. Chem. A 2016, 4 (6), 2263−2276. (40) Coromina, H. M.; Walsh, D. A.; Mokaya, R. Biomass-derived activated carbon with simultaneously enhanced CO2 uptake for both pre and post combustion capture applications. J. Mater. Chem. A 2016, 4 (1), 280−289. (41) Deng, J.; Xiong, T.; Xu, F.; Li, M.; Han, C.; Gong, Y.; Wang, H.; Wang, Y. Inspired by bread leavening: one-pot synthesis of hierarchically porous carbon for supercapacitors. Green Chem.2015, 17 (7), 4053−4060. (42) Tzvetkov, G.; Mihaylova, S.; Stoitchkova, K.; Tzvetkov, P.; Spassov, T. Mechanochemical and chemical activation of lignocellulosic material to prepare powdered activated carbons for adsorption applications. Powder Technol. 2016, 299, 41−50. (43) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T. H.; Long, J. R. Carbon dioxide capture in metal-organic frameworks. Chem Rev. 2012,


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Energy & Fuels

112 (2), 724−81. (44) Furukawa, H.; Yaghi, O. M. Storage of hydrogen, methane, and carbon dioxide in highly porous covalent organic frameworks for clean energy applications. J. Am. Chem. Soc. 2009, 131 (25), 8875−8883. (45) Guo, L.; Yang, J.; Hu, G.; Hu, X.; Wang, L.; Dong, Y.; DaCosta, H.; Fan, M. Role of hydrogen peroxide preoxidizing on CO2 adsorption of nitrogen-doped carbons produced from coconut shell. ACS Sustainable Chem. Eng. 2016, 4 (5), 2806−2813. (46) Xu, L.; Guo, L.; Hu, G.; Chen, J.; Hu, X.; Wang, S.; Dai, W.; Fan, M. Nitrogen-doped porous carbon spheres derived from d-glucose as highly-efficient CO2 sorbents. RSC Adv.2015, 5 (48), 37964−37969. (47) Luo, H.; Zhu, C. C.; Tan, Z. C.; Bao, L. W.; Wang, J. J.; Miao, G.; Kong, L. Z.; Sun, Y. H. Preparation of N-doped activated carbons with high CO2 capture performance from microalgae (Chlorococcum sp.). RSC Adv. 2016, 6 (45), 38724−38730. (48) Sevilla, M.; Falco, C.; Titirici, M.-M.; Fuertes, A. B. High-performance CO2 sorbents from algae. RSC Adv. 2012, 2 (33), 12792. (49) Arstad, B.; Fjellvåg, H.; Kongshaug, K. O.; Swang, O.; Blom, R. Amine functionalised metal organic frameworks (MOFs) as adsorbents for carbon dioxide. Adsorption 2008, 14 (6), 755−762. (50) Mello, M. R.; Phanon, D.; Silveira, G. Q.; Llewellyn, P. L.; Ronconi, C. M. Amine-modified MCM-41 mesoporous silica for carbon dioxide capture. Micro. Meso. Mater. 2011, 143 (1), 174−179. (51) Sun, L. B.; Kang, Y. H.; Shi, Y. Q.; Jiang, Y.; Liu, X. Q. Highly selective capture of


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the greenhouse gas CO2 in polymers. ACS Sustainable Chem. Eng. 2015, 3 (12), 3077−3085. (52) Sun, L. B.; Li, A. G.; Liu, X. D.; Liu, X. Q.; Feng, D.; Lu, W.; Yuan, D.; Zhou, H. C. Facile fabrication of cost-effective porous polymer networks for highly selective CO2 capture. J. Mater. Chem. A 2015, 3 (7), 3252−3256.


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Table 1. Porous texture parameters, elemental composition, and CO2 uptakes for sorbents derived from procambarus clarkii shells under different conditions CO2 uptake SBETa Vob Vt c N C H (mmol/g) Sample (m2/g) (cm3/g) (cm3/g) (wt %) (wt %) (wt %) 25 °C 0 °C d P 9.02 46.57 5.75 P-700 4.9 0.003 0.002 7.73 76.82 0.36 1.82 1.91 PK-1-650 1253 0.58 0.43 6.99 70.14 1.44 3.64 5.49 PK-3-650 1403 0.65 0.49 6.38 73.34 0.96 4.09 5.29 PK-5-650 1558 0.74 0.55 6.45 72.24 0.57 3.91 5.75 PK-1-700 2255 1.20 0.56 4.86 72.76 0.18 3.44 4.99 PK-3-700 2022 1.00 0.71 3.48 79.54 1.12 4.51 6.48 PK-5-700 2534 1.37 0.57 3.36 82.24 0.26 3.65 5.10 PK-1-750 2790 1.49 0.83 1.39 88.87 0 3.88 5.83 PK-3-750 2995 1.51 1.01 1.25 88.61 0 2.62 5.72 PK-5-750 2135 1.09 0.66 1.02 88.50 0 2.55 5.27 a

Surface area was calculated using the BET method using adsorption data at P/P0=0.01-0.1.

b

Single-point total pore volume at P/P0=0.995. cMicropore volume was evaluated by the

t-plot method. dNo detected.


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Figure captions Figure 1. Schematic diagram of the preparation process of N-enriched activated carbons. Figure 2. SEM images of P-700 (a) and PK-3-700 (b), TEM image (c) and XRD pattern (d) of PK-3-700. Figure 3. FT-IR spectra of P-700 and PK-3-700. Figure 4. N 1s XPS spectra of the samples: (a) PK-3-650, (b) PK-3-700, (c) PK-5-700, and (d) PK-1-750. Figure 5. N2 adsorption isotherms measured for the samples prepared at different conditions (a) 650 °C, (b) 700 °C, and (c) 750 °C (Filled and empty symbols represent adsorption and desorption branches, respectively) and NLDFT PSDs for the samples prepared at different conditions (d) 650 °C, (e) 700 °C, and (f) 750 °C. Figure 6. TGA curves measured for P-800, K-800, PK-1-800, PK-3-800 and PK-5-800. Figure 7. CO2 adsorption isotherms at 25 °C (empty symbols) and 0°C (filled symbols) for N-enriched activated carbons prepared under different conditions (a) 650 °C, (b) 700 °C and (c) 750 °C. Figure 8. Breakthrough curves for PK-3-700 and PK-700. Figure 9. CO2 and N2 adsorption isotherms for PK-3-700 at 25 °C. Figure 10. Isosteric heat of CO2 adsorption for PK-3-650, PK-3-700, PK-5-700, and PK-1-750 calculated from the adsorption isotherms at 0 °C and 25 °C. Figure 11. CO2 adsorption-desorption cycles for PK-3-700 and P-700 at 25 °C and 1 bar.


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Figure 1. Schematic diagram of the preparation process of N-enriched activated carbons.

d

(100)

(002)

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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Intensity

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10

20

30

40

50

60

70

80

2 Theta

Figure 2. SEM images of P-700 (a) and PK-3-700 (b), TEM image (c) and XRD pattern (d) of PK-3-700.


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PK-3-700 P-700

IR absorbance (a.u.)

2850

2925 1123 1631 1414

650

1575

3434

4000 3500 3000 2500 2000 1500 1000

500

Wavenumber (cm-1) Figure 3. FT-IR spectra of P-700 and PK-3-700.

b

N-5

Intensity (a.u.)

Intensity (a.u.)

a N-6

N-Q

N-Q

394 396 398 400 402 404 406 408 410 412

Binding energy (eV)

Binding energy (eV)

N-5

c N-6

N-5

N-6

394 396 398 400 402 404 406 408 410 412

d

N-Q N-5

N-Q

Intensity (a.u.)

Intensity (a.u.)

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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394 396 398 400 402 404 406 408 410 412

N-6

394 396 398 400 402 404 406 408 410

Binding energy (eV)

Binding energy (eV)

Figure 4. N 1s XPS spectra of the samples: (a) PK-3-650, (b) PK-3-700, (c) PK-5-700, and (d) PK-1-750.


Volume adsorbed (cm3/g, STP)

a

500 400 300 200

PK-1-650 PK-3-650 PK-5-650

100 0 0.0

0.2

0.4

0.6

0.8

1000

b 800 600 400 PK-1-700 PK-3-700 PK-5-700

200 0 0.0

1.0

0.2

800 600 400

PK-1-750 PK-3-750 PK-5-750

200 0 0.0

0.2

0.4

0.6

0.8

d

1.0

8 6 4 2 0 1

10

Pore width (nm)

1.0

6 4 2 0 1

100

10

100

Pore width (nm)

10

f

3

dv/d(log w) pore volume (cm /g)

3

e

PK-1-700 PK-3-700 PK-5-700

0.8

PK-1-650 PK-3-650 PK-5-650

8

Relative pressure (P/P0) 10

0.6

10

3



c

1000

0.4

Relative pressure (P/P0)

Relative pressure (P/P0)


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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PK-1-750 PK-3-750 PK-5-750

8 6 4 2 0 1

10

Pore width (nm)

100

Figure 5. N2 adsorption isotherms measured for the samples prepared at different conditions (a) 650 °C, (b) 700 °C, and (c) 750 °C (Filled and empty symbols represent adsorption and desorption branches, respectively) and NLDFT PSDs for the samples prepared at different conditions (d) 650 °C, (e) 700 °C, and (f) 750 °C; v denotes the volume adsorbed in cm3/g at -196 oC and w denotes the pore width.


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100

125~525

525~600

Mass (%)

80

P-800 K-800 PK-1-800 PK-3-800 PK-5-800

60 40

196~381 381~568

20

568~800

100 200 300 400 500 600 700 800

Temperature (°C) Figure 6. TGA profiles measured for P-800, K-800, PK-1-800, PK-3-800 and PK-5-800. 6 5

6

a

CO2 uptake (mmol/g)

CO2 uptake (mmol/g)

4 3 2

PK-1-650 PK-3-650 PK-5-650

1

b

5 4 3 2

PK-1-700 PK-3-700 PK-5-700

1 0

0 0.0

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0.4

0.6

0.8

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Pressure (bar) 6

CO2 uptake (mmol/g)

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5

c PK-1-750 PK-3-750 PK-5-750

4 3 2 1 0 0.0

0.2

0.4

0.6

0.8

1.0

Pressure (bar) Figure 7. CO2 adsorption isotherms at 25 °C (empty symbols) and 0°C (filled symbols) for N-enriched activated carbons prepared under different conditions: (a) 650 °C, (b) 700 °C and (c) 750 °C.


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1.0

C/C0

0.8 0.6 0.4 0.2

PK-700 PK-3-700

0.0 0

10

20

30

40

Time (min)

5

5

4

4

3

3

2

2

(0.1, 0.79)

1

1

0

N2 uptake (mmol/g)

CO2 uptake (mmol/g)

Figure 8. Breakthrough curves for PK-3-700 and PK-700.

0 0.0

0.2

0.4

0.6

0.8

1.0

Pressure (bar)

Figure 9. CO2 and N2 adsorption isotherms for PK-3-700 at 25 °C. 32

PK-3-650 PK-3-700 PK-5-700 PK-1-750

30

Qst (kJ/mol)

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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28 26 24 22 0

1

2

3

4

5

Adsorbed CO2 amount (mmol/g)

Figure 10. Isosteric heat of CO2 adsorption for PK-3-650, PK-3-700, PK-5-700, and PK-1-750 calculated from the adsorption isotherms at 0 °C and 25 °C.


Energy & Fuels

5.0

CO2 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

4.5 4.0 3.5

PK-3-700 P-700

3.0 2.5 2.0 1.5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Cycle (time)

Figure 11. CO2 adsorption-desorption cycles for PK-3-700 and P-700 at 25 °C and 1 bar.


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Energy & Fuels

TOC Graphic

A series of highly microporous N-enriched activated carbons with enhanced CO2 adsorption performance were synthesized by using K2C2O4·H2O as an activating agent and procambarus clarkia shells as both carbon and N source.


In Situ Synthesis of Nitrogen-Enriched Activated Carbons from

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