Anion-regulated selective growth ultrafine copper templates in carbon nanosheets network toward highly efficient gas capture

Journal of Colloid and Interface Science 564 (2020) 296–302

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Anion-regulated selective growth ultrafine copper templates in carbon nanosheets network toward highly efficient gas capture Ning Fu a, Jing Yu a, Rui Liu a, Xiaodong Wang b, Zhenglong Yang a,⇑ a Department of Polymeric Materials, School of Materials Science and Engineering, Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Tongji University, Shanghai 201804, PR China b Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology & School of Physics Science and Engineering, Tongji University, Shanghai 200092, PR China

g r a p h i c a l a b s t r a c t

a r t i c l e

i n f o

Article history: Received 23 September 2019 Revised 25 December 2019 Accepted 28 December 2019 Available online 29 December 2019 Keywords: Copper templates Ultramicropore Porous carbon Light hydrocarbons CO2 adsorption

a b s t r a c t Controlling micropore size is the core for synthesizing highly efficient adsorbents for gas adsorption and separation engineering. Porous carbon prepared by traditional methods usually lacks competitiveness due to the random micropore size or complex process. Herein, we report a novel strategy for synthesizing nitrogen doped carbons nanosheets (Cu-NDPCs) with unimodal ultra-micropore based on the metalorganic covalency and the anion regulated in situ copper template. The thickness of single Cu-NDPCs is about 4.2 nm. In the presence of Cl
, the porosity of Cu-NDPCs can be tuned at 4.1–4.8 Å by adjusting the pyrolysis temperature. Among them, Cu-NDPC-800 has unique carbon nanosheets networks structure, ultrahigh surface area (2150 m2 g
1), large micropore volume (0.92 cm3 g
1) and abundant surface N doping (5.33%). As an adsorbent, it exhibits superhigh C2H2, C2H6, C3H8 and CO2 uptakes (6.7, 7.0, 11.4 and 4.4 mmol g
1) and corresponding x/CH4 or CO2/N2 IAST selectivities (12.9, 17.8, 468.6, 4.3 and 17.1) under ambient conditions. Meanwhile, the Cu-NDPC-800 possesses excellent cyclic stability. Ó 2019 Elsevier Inc. All rights reserved.

1. Introduction Environmental and energy issues are the most serious challenges that influence the sustainable development of mankind in this century Ma et al. [1–4]. Within those issues, global warming caused by CO2 emissions is a serve problem that cannot be neglected [5–7]. It is essential to prevent the increasing level of atmospheric CO2 [8,9]. In addition, the combustion of coal,

⇑ Corresponding author. E-mail address: [email protected] (Z. Yang). https://doi.org/10.1016/j.jcis.2019.12.127 0021-9797/Ó 2019 Elsevier Inc. All rights reserved.

petroleum and their derivatives simultaneously emit a large amount of tiny particulars, which is the main cause of heavy fog and smog. Therefore, looking for cleaner alternative energy resources has become a necessity for mankind survival and development. Natural gas, which mainly made up of methane, is a preferable option that meets the requirement. Methane, with high energy density, is one of the best alternative energy sources for traditional fuel vehicles [4]. However, natural gas also contains other impurities, such as C2H6, C3H8 and CO2 [10,11]. These impurities are chemical raw materials of vital significance. In addition, C2H2 is one of most important byproducts in the thermal cracking of natural gas, so those impurities need to be separated and stored. Physical

N. Fu et al. / Journal of Colloid and Interface Science 564 (2020) 296–302

adsorption separation has been widely concerned due to the energy-saving and easy regeneration [4,12,13]. Exploitation of highly efficient adsorbents is the core in gas adsorption separation engineering. The surface polarity and the size matching effect of gas molecule determine the capture capability of adsorbent He et al. [10,14,15]. To be more precise, the size matching effect is reflected in the pore size of adsorbent larger than that of the gas molecules (shown in Table S1) and less than 0.8 nm, which has the most significant contribution to the gas adsorption [16–18]. Among those adsorbents, porous coordination polymers (PCPs) and metalorganic frameworks (MOFs) exhibit excellent gas separation performance on light hydrocarbons and CO2/N2 due to its designed pore size, shape and functionalized pore surface [19–22]. However, the expensive, complex procedures of synthesis process and thermal instability restrict their practical applications. Porous carbon materials have been considered as one of the most promising adsorbents in gas separation because of their excellent thermal stability and low-cost property [23–25]. However, the characteristics of poreforming methods make the formation of suitable pore structures in carbon materials a very challenging task. Activation method is often used to form ultramicropores in carbon materials. However, the dispersed pore size of the activated porous carbon leads to a low utilization rate of pore structure, consequently in resulting the adsorption capacity and selectivity of carbonaceous adsorbents generally inferior to MOFs and PCPs. In addition, the most commonly used KOH activator is highly corrosive thus it can only be in the stage of published papers. Moreover, the activation poreforming method is at the cost of reducing the yield of carbon materials. For the template method, obtaining a suitable template with uniform grain size and high purity is the biggest obstacle towards its application in the synthesis of carbon adsorbents. Herein, we propose a novel strategy for preparing nitrogen doped carbon nanosheets (Cu-NDPCs) with unimodal ultramicropore based on the metal-organic covalency and the anion regulated in situ growth copper template. This strategy requires only three very simple process: mixing the carbon source with copper chloride in ethanol, carbonization, and etching by dilute hydrochloric acid. Carbon nanosheets are derived from the carbonizing of Cu2+ and poly(4-vinyipyridine) (P4VP) covalent complex. The appropriate in-situ template was obtained by adjusting the aggregation rate and the size of copper nanoclusters by anions. In the presence of Cl
, the formed ultrafine copper nanoclusters are uniformly dispersed in carbon nanosheets. The size of copper nanoclusters is controlled by temperature. After etching, the pore sizes are concentrated in the range of 4.1–4.8 Å, which is the optimum range for CH4, C2H2, C2H6, C3H8, CO2 and N2 adsorption and separation. 2. Experimental section 2.1. Synthesis of Cu-NDPCs Typically, 0.42 g Poly (4-vinylpyridine) (P4VP, Mn: 60000) and 3.41 g CuCl22H2O were mixed in 200 mL ethanol and stirred for 4 h. Then the coordination compound Cu-P4VP was obtained by vacuum distillation. The Cu-P4VP was carbonized at 800 °C for 5 h under N2 atmosphere to obtain Cu-NDC-800. The Cu-NDC800 was washed for 12 h with 200 mL HCl (1 M) to remove the Cu nanoclusters. Then washed it repeatedly with DI water, dried, and the Cu-NDPC-800 was obtained. The products at 600, 700, 900 and 1000 °C processed in the same way. 2.2. Characterization TGA curve was carried out with a STA 449C Thermogravimetric Analyzer. FT-IR measurements were performed using an EQUINOX

297

55 spectrometer. FESEM images were investigated on a Nova NanoSEM 450 microscope. AFM images were carried out with a Dimension Icon instrument. TEM iamges were performed using a JEOL-2100F microscope. Raman spectra were performed using a Senterra R200-L apparatus. XRD patterns were performed using a D/max 2550VB3+/PC. ICP-AES data were carried out with a iCAP6300 instrument. XPS data were obtained using an AXIS UltraDLD apparatus. N2 adsorption-desorption data were obtained using an Autosorb-iQ2 or 3H-2000PM2 instrument. BrunauerEmmett-Teller specific surface area (SBET) and total pore volume (Vtotal) were calculated from the amount of N2 adsorbed at P/P0 ~ 0.04–0.32 or P/P0 ~ 0.99. Micropore specific surface area (St-plot) was derived from the t-plot method. Pore size distributions (PSDs) were estimated by using slit pore model of density functional theory (DFT). 2.3. Gas adsorption measurements The gas static adsorption data at 273 and 298 K of CH4 (99.95%), C2H2 (99.95%), C2H6 (99.95%), C3H8 (99.95%), CO2 (99.999%) and N2 (99.999%) were carried out with an Autosorb-iQ2. Prior to experiment, all samples were outgassed at 523 K for 12 h. 2.4. Fitting of adsorption isotherms with single-site Langmuir-Freundlich model The single-component adsorption data were fitted with the single-site Langmuir-Freundlich model.

q ¼ qsat

bpv 1 þ bpv

with T-dependent parameter b

b ¼ b0 expð

E Þ RT

R = 8.314 J mol
1 K
1. 2.5. Gas selectivity calculation using the ideal adsorbed solution theory (IAST) The gas selectivity was calculated based on IAST according to the following equation:

S¼

x1 y 1 = x2 y 2

where xi and yi are the molar fractions of component i (i = 1, 2) in the adsorbed phase and the bulk phase, respectively. 3. Results and discussion The synthesis process of Cu-NDPCs was illustrated in Fig. 1. Briefly, the P4VP reacted with CuCl22H2O in ethanol and then dried to form a coordination compound of Cu-P4VP. The Cu-P4VP was carbonized under N2 atmosphere to obtain Cu nanoclusters encapsulated nitrogen-doped carbon nanosheets (Cu-NDCs). The Cu-NDCs were etched by 1 M HCl to remove the Cu nanoclusters to obtain Cu-NDPCs. The FT-IR spectra indicated that when mixed with CuCl22H2O, the CAC and C@N characteristic absorption peaks of pyridine rings at 1418 and 1496 cm
1 were shifted to 1384 and 1500 cm
1, and the C@N peak at 1557 cm
1 disappeared (Figure S1), showing the formation of Cu–N coordination Groppo et al. [26,27]. TGA curves of P4VP and Cu-P4VP were shown in Figure S2a. For the P4VP, the weight loss reached 100% at 460 °C indicated the complete decomposition of P4VP. In contrast, the weight of Cu-P4VP remained at 36.9% until 1000 °C due to the residual copper and

298

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Fig. 1. Schematic illustration of the preparation process of Cu-NDPCs.

carbon. The result was directly carried out by Raman and TEM tests. Taking Cu-NDC-800 as an example, Raman spectra (Figure S2b) showed typical carbon peaks of D (1329 cm
1) and G (1590 cm
1) band [28,29]. TEM-EDS spectrum (Figure S3c) showed the existence of Cu and C elements, and the SAED pattern (Figure S3d) revealed that the weak crystallized structure of Cu, confirming the formation of carbon coated ultrafine Cu nanoclusters structure. The XRD patterns (Figure S4) further revealed the existence and phase structure of Cu (PDF #99-0034) in Cu-NDCs. The corresponding ICP-AES data revealed that the Cu content of Cu-NDCs was ranging from 77.46 to 91.71% (Table S2). The carbon yield of Cu-NDCs calculated from XRD and ICP-AES data was 27.5–88.7% (Figure S5). The results confirmed that CuCl22H2O could catalyze the carbonization of P4VP. Furthermore, under the same experimental conditions, CuCl22H2O was replaced by NaCl without carbon formation (Figure S6), indicating that Cl
had no catalytic effect on the carbonization of P4VP. It proved that Cu2+ was the real catalyst for the carbonization of P4VP. The effect of anions was reflected in the adjustment of aggregation rate and size of copper nanoclusters [30–31]. Influenced by saturated vapor pressure, CuCl22H2O tended to form amorphous or weak crystalline ultrafine nanoclusters (Figure S3a, b). Such nanoclusters were excellent template for the formation of ultramicropore. Under the same experimental conditions, CuCl22H2O was replaced by Cu(NO3)23H2O, and the sizes of formed nanoparticles were larger than 50 nm (Figure S7). The results demonstrated the importance of choosing Cl
. FESEM images (Figure S8) showed that Cu-P4VP had an obvious lamellar stacking structure, and its derived carbon materials inherited this structure perfectly (Figure S9a–e). Notably, the bulk density gradually decreased with the increasing carbonization temperature, indicating the excellent temperature-oriented property of Cu-NDPCs. Among them, the Cu-NDPC-800 showed a cross-linking carbon network structure (Fig. 2a, b), which was conducive to the rapid diffusion of gas molecules (Fig. 2c). AFM images further revealed that the carbon skeleton of Cu-NDPC-800 was formed by the stacking of multilayer carbon nanosheets, and the thickness of the monolayer was about 4.2 nm (Figure S10 and Fig. 2e). In addition, FESEM-mapping (Fig. 2d) showed the homogeneous distribution of N on the surface of Cu-NDPC-800. TEM images (Fig. 2f and g) revealed that the Cu-NDPC-800 had an obvious micropore structure. Such interconnected porous structure with N dopant provided fast gas molecular diffusion channels

and abundant adsorption active sites, which ensured excellent adsorption performance. All Cu-NDPCs demonstrated two broad XRD peaks 2h around 25° and 43° (Fig. 3a), which could be assigned to the N atom doping in carbon Yuan et al. [32]. In addition, no structure characteristics of metallic Cu were observed in the XRD patterns, indicating that the majority of Cu was removed during the etching process. The Cu content was less than 0.14% (Table 1). The results were in accordance with the TEM observations. The typical type-I N2 adsorption-desorption isotherms of Cu-NDPCs (Fig. 3b) indicated a steep adsorption in initial period (P/P0 < 0.1), showing the presence of abundant micropores. The St-plot and Vmicro of Cu-NDPC-X were 1398 (0.70), 1470 (0.74), 1841 (0.92), 1608 (0.82) and 1363 m2 g
1 (0.68 cm3 g
1), at temperature of 600, 700, 800, 900 and 1000 °C, respectively (Table 1). In addition, the SBET of Cu-NDPC-800 was up to 2150 m2 g
1, which was higher than the reported values for porous carbon prepared by activating method Fujiki and Yogo, [9,24,33–34]. Moreover, the DFT model revealed that the maximum in PSDs of Cu-NDPC-X were 4.8 (6 0 0), 4.6 (7 0 0), 4.2 (8 0 0), 4.1 (9 0 0) and 4.1 Å (1000), revealing that pore size could be tuned at sub-angstrom scale by adjusting the temperature. Such high specific surface area and suitable pore size were conducive to exposing more adsorption active sites and improving the utilization rate of pore structure. Notably, the Cu-NDCs exhibited very lower N2 capacities (Figure S11a), and thus had smaller SBET (823 m2 g
1) and Vmicro (0.31 cm3 g
1) (Table S2). The pore size distribution of Cu-NDCs was shown in Figure S11b. The pore structure of samples increased sharply only after one-step etching, suggesting the in-situ template poreforming effect of Cu nanoclusters coated in the carbon nanosheet. XPS spectra (Fig. 4a) indicated that Cu-NDPCs surface was enriched with N element, which was consistent with the above result of FESEM-mapping. The corresponding N content of CuNDPC-X were 4.53 (6 0 0), 3.24 (7 0 0), 5.33 (8 0 0), 4.73 (9 0 0) and 2.53 at% (1 0 0 0), respectively (Table 1). The asymmetric N 1 s XPS spectra (Fig. 4b-f) could be deconvoluted into three types of pyridinic N (398.4 ± 0.1 eV), pyrrolic N (400.0 ± 0.3 eV) and quaternary N (401.1 ± 0.1 eV) [35–38], exhibiting the content of quaternary N increased meanwhile pyridinic N and pyrrolic N decreased with increasing temperature (Table S3). The result was in accordance with previous reports [30,32,35]. The single-component gas (CH4, C2H6, C3H8, C2H2, CO2, N2) static adsorption of Cu-NDPCs was investigated at 273 and 298 K (Figure S12, Fig. 5, Table 2). All of samples could handily capture

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Fig. 2. Morphological characteristics of Cu-NDPC-800. (a, b) FESEM images, (c) schematic illustration of gas molecules diffusion, (d) FESEM elemental mapping, (e) AFM image, (f, g) TEM images.

Fig. 3. (a) XRD patterns, (b) N2 adsorption/desorption isotherms and (c) pore size distributions of Cu-NDPCs.

Table 1 Textural properties and chemical composition of Cu-NDPCs. Textural properties

a b

Chemical composition (%)

Sample

SBET (m2 g
1)

St-plot (m2 g
1)

Vmicro (cm3 g
1)

Vtot (cm3 g
1)

Na

Oa

Ca

Cub

Cu-NDPC-600 Cu-NDPC-700 Cu-NDPC-800 Cu-NDPC-900 Cu-NDPC-1000

1461 1633 2150 1960 1669

1398 1470 1841 1608 1363

0.70 0.74 0.92 0.82 0.68

0.81 1.02 1.31 1.45 1.17

4.53 3.24 5.33 4.73 2.53

13.81 14.59 12.04 7.00 16.06

81.36 81.83 82.32 87.96 81.16

0.065 0.104 0. 084 0.132 0.098

Surface chemical composition was characterized by XPS. Determination of Cu content by ICP-AES.

C2H6, C3H8, C2H2 and CO2 at a low relative pressure (P/P0 < 0.1). Furthermore, the adsorption equilibrium was not reached until 1 bar, suggesting that Cu-NDPCs could adsorb more adsorbates at higher pressure. Notably, The C2H2, C2H6 and C3H8 capacities of

Cu-NDPC-800 were as high as 6.7, 7.0, 11.4 mmol g
1 at 298 K and 1 bar. For all we know, the results were significantly better than that of Co-P4VP based porous carbon Co-NDPC-700 [30] (5.8, 5.2 and 7.4 mmol g
1) (Table S7). In addition, its CO2 uptakes

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Fig. 4. (a) XPS spectra and (b-f) corresponding N 1s XPS spectra of Cu-NDPCs.

Fig. 5. (a–e) Gas adsorption isotherms of Cu-NDPCs at 298 K. (f) 5 cycles experiments of Cu-NDPC-800 for C3H8 at 298 K and 1 bar.

Table 2 Gas uptakes of Cu-NDPCs at 273, 298 K and 1 bar. CH4 (mmol g
1)

C2H2 (mmol g
1)

C2H6 (mmol g
1)

C3H8 (mmol g
1)

CO2 (mmol g
1)

N2 (mmol g
1)

sample

273 K

298 K

273 K

298 K

273 K

298 K

273 K

298 K

273 K

298 K

298 K

Cu-NDPC-600 Cu-NDPC-700 Cu-NDPC-800 Cu-NDPC-900 Cu-NDPC-1000

1.6 2.2 2.5 2.2 1.5

1.1 1.1 1.6 1.2 1.1

7.3 8.0 10.2 9.1 5.5

5.0 5.5 6.7 6.1 3.7

6.3 7.3 9.6 8.7 4.8

4.7 5.4 7.0 6.2 3.7

8.6 10.0 12.9 11.7 11.6

7.9 9.1 11.4 10.6 10.4

5.2 6.0 7.1 6.7 4.2

3.5 4.0 4.4 4.2 2.8

0.21 0.32 0.55 0.54 0.39

N. Fu et al. / Journal of Colloid and Interface Science 564 (2020) 296–302

301

Fig. 6. (a–e) x/CH4 (50/50, v/v) and (f) CO2/N2 (10/90, v/v) IAST selectivities of Cu-NDPCs at 298 K.

also reached 4.4 mmol g
1 at 298 K, which was larger than that of Fe-P4VP based porous carbon NDPC-2-600 [39] (4.3 mmol g
1) (Table S8). The results were also superior than the reported activated porous carbons (such as NAC 700 [33], FCP-1-KC [24], SUMAC-600 [25], GPC-A [40] and MOFs/PCPs (such as FJI-C1 [41], JLU-Liu18 [42], PCP-33 [43]. Especially, the C2H2 uptake of CuNDPC-800 (6.7 mmol g
1) was higher than the highest reported capacity of porous carbon NAC 700 (6.39 mmol g
1) (Table S7 and Table S8). The gas separation selectivity of Cu-NDPCs were predicted using IAST (Table S4). The x/CH4 (x: C2H2, C2H6, C3H8 and CO2; 50/50, v/v) and CO2/N2 (10/90, v/v) selectivity of Cu-NDPC-800 were up to 12.9, 17.8, 468.6, 4.3 and 17.1 respectively (Fig. 6, Table S5 and Table S6), which were higher than that of other adsorbents (Table S7 and Table S8). In addition, the IAST selectivity generally decreased with the increasing CH4 or N2 mole fraction in the gas phase (Figure S13). Isosteric adsorption heats (Qst) of CH4, C2H2, C2H6, and CO2 on Cu-NDPCs were calculated using Clausius-Clapeyron equation [30] (Figure S14). The general order of Qst values was C3H8 > C2H6 > CO2 > CH4. The cyclic adsorption experiment was exemplified by Cu-NDPC-800 and C3H8 (Fig. 5f). The adsorption capacity had a little change after 5 cycles and proved its excellent cyclic stability, consequently showing that gas capture processes were physisorption.

comparable to the optimum carbon-based adsorbents reported in the previous work while avoiding a series of defects in traditional pore-forming methods. In addition, this approach may provide an avenue for the development of high-performance porous materials for other diffusion-controlled applications. CRediT authorship contribution statement Ning Fu: Investigation, Methodology, Data curation, Writing original draft. Jing Yu: Validation, Formal analysis. Rui Liu: Supervision, Formal analysis. Xiaodong Wang: Data curation, Validation. Zhenglong Yang: Conceptualization, Methodology, Writing review & editing, Supervision. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was supported by National Key Research and Development Program of China (2017YFA0204600).

4. Conclusion

Appendix A. Supplementary material

In conclusion, the Cu-NDPCs with ultrahigh specific surface area (up to 2150 m2 g
1), centralized ultramicropore and suitable surface functionalities have been synthesized based on metalorganic covalency and the anion regulatory. In this strategy, the carbon nanosheets are synthesized by pyrolyzing of metal organic covalent compounds (Cu-P4VP), the ultramicropore originates from in situ ultrafine copper nanoclusters regulated by chloride ion. Moreover, the pore size could be tuned in the range of 4.1–4.8 Å by adjusting the pyrolysis temperature. As adsorbents, the Cu-NDPCs display excellent C2H2, C2H6, C3H8 and CO2 uptakes and corresponding x/CH4 or CO2/N2 IAST selectivities, which are

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jcis.2019.12.127. References [1] L.T. Ma, H.Q. Fan, J. Wang, Y.W. Zhao, H.L. Tian, G.Z. Dong, Water-assisted ions in situ intercalation for porous polymeric graphitic carbon nitride nanosheets with superior photocatalytic hydrogen evolution performance, Appl. Catal. BEnviron. 190 (2016) 93–102. [2] J.W. Ma, H.Q. Fan, X.H. Ren, C. Wang, H.L. Tian, G.Z. Dong, et al., A Simple absorbent cotton biotemplate to fabricate SnO2 porous microtubules and their gas-sensing properties for chlorine, ACS Sustainable Chem. Eng. 7 (2019) 147– 155.

302

N. Fu et al. / Journal of Colloid and Interface Science 564 (2020) 296–302

[3] H.J. Peng, H.Q. Fan, L. Ning, W.J. Wang, J.N. Sui, Templated manganese oxide by pyrolysis route as a promising candidate cathode for asymmetric supercapacitors, J. Electroanal. Chem. 843 (2019) 54–60. [4] K.V. Kumar, K. Preuss, M.M. Titirici, F. Rodríguez-Reinoso, Nanoporous materials for the onboard storage of natural gas, Chem. Rev. 117 (3) (2017) 1796–1825. [5] A. Aijaz, N. Fujiwara, Q. Xu, From metal-organic framework to nitrogendecorated nanoporous carbons: high CO2 uptake and efficient catalytic oxygen reduction, J. Am. Chem. Soc. 136 (19) (2014) 6790–6793. [6] N. Ali, A.A. Babar, Y.F. Zhang, N. Iqbal, X.F. Wang, J.Y. Yu, et al., Porous, flexible, and core-shell structured carbon nanofibers hybridized by tin oxide nanoparticles for efficient carbon dioxide capture, J. Colloid. Interf. Sci. 560 (2020) 379–387. [7] L. Legrand, Q. Shu, M. Tedesco, J.E. Dykstra, H.V.M. Hamelers, Role of ion exchange membranes and capacitive electrodes in membrane capacitive deionization (MCDI) for CO2 capture. J. Colloid. Interf. Sci. https://doi.org/ 10.1016/j.jcis.2019.12.039. [8] X.Y. Shi, H. Xiao, H. Azarabadi, J.Z. Song, X.L. Wu, X. Chen, et al., Sorbents for direct capture of CO2 from ambient air, Angew. Chem. Int. Ed. 10.1002/ anie.201906756. [9] J. Fujiki, K. Yogo, The increased CO2 adsorption performance of chitosanderived activated carbons with nitrogen-doping, Chem. Commun. 52 (1) (2016) 186–189. [10] Y.B. He, R. Krishna, B.L. Chen, Metal-organic frameworks with potential for energy-efficient adsorptive separation of light hydrocarbons, Energy Environ. Sci. 5 (10) (2012) 9107–9120. [11] C. Altintas, S. Keskin, Computational screening of MOFs for C2H6/C2H4 and C2H6/CH4 separations, Chem. Eng. Sci. 139 (2016) 49–60. [12] J. Wang, L. Huang, R. Yang, Z. Zhang, J. Wu, Y. Gao, et al., Recent advances in solid sorbents for CO2 capture and new development trends, Energy Environ. Sci. 7 (11) (2014) 3478–3518. [13] K. Adil, Y. Belmabkhout, R.S. Pillai, A. Cadiau, P.M. Bhatt, A.H. Assen, et al., Gas/vapour separation using ultra-microporous metal-organic frameworks: insights into the structure/separation relationship, Chem. Soc. Rev. 46 (11) (2017) 3402–3430. [14] F.Q. Liu, L. Wang, Z.G. Huang, C.Q. Li, W. Li, R.X. Li, et al., Amine-tethered adsorbents based on three-dimensional macroporous silica for CO2 capture from simulated flue gas and air, ACS Appl. Mater. Interfaces 6 (6) (2014) 4371– 4381. [15] F. Zheng, L.D. Guo, B.X. Gao, L.Y. Li, Z.G. Zhang, Q.W. Yang, et al., Engineering the pore size of pillared-layer coordination polymers enables highly efficient adsorption separation of acetylene from ethylene, ACS Appl. Mater. Interfaces 11 (2019) 28197–28204. [16] V. Presser, J. McDonough, S.-H. Yeon, Y. Gogotsi, Effect of pore size on carbon dioxide sorption by carbide derived carbon, Energy Environ. Sci. 4 (8) (2011) 3059–3066. [17] G.-P. Hao, Z.-Y. Jin, Q. Sun, X.-Q. Zhang, J.-T. Zhang, A.-H. Lu, Porous carbon nanosheets with precisely tunable thickness and selective CO2 adsorption properties, Energy Environ. Sci. 6 (12) (2013) 3740–3747. [18] J. Marszewska, M. Jaroniec, Tailoring porosity in carbon spheres for fast carbon dioxide adsorption, J. Colloid. Interf. Sci. 487 (2017) 162–174. [19] B. Li, H.-M. Wen, W. Zhou, B. Chen, Porous metal-organic frameworks for gas storage and separation: what, how, and why?, J. Phys. Chem. Lett. 5 (20) (2014) 3468–3479. [20] J. Duan, M. Higuchi, S. Horike, M.L. Foo, K.P. Rao, Y. Inubushi, et al., High CO2/ CH4 and C2 hydrocarbons/CH4 selectivity in a chemically robust porous coordination polymer, Adv. Funct. Mater. 23 (28) (2013) 3525–3530. [21] P.-Q. Liao, W.-X. Zhang, J.-P. Zhang, X.-M. Chen, Efficient purification of ethene by an ethane-trapping metal-organic framework, Nature Commun. 6 (2015) 8697. [22] J.-R. Li, J. Yu, W. Lu, L.-B. Sun, J. Sculley, P.B. Balbuena, et al., Porous materials with pre-designed single-molecule traps for CO2 selective adsorption, Nat. Commun. 4 (2013) 1538. [23] G. Srinivas, V. Krungleviciute, Z.-X. Guo, T. Yildirim, Exceptional CO2 capture in a hierarchically porous carbon with simultaneous high surface area and pore volume, Energy Environ. Sci. 7 (1) (2014) 335–342.

[24] L.-H. Zhang, W.-C. Li, H. Liu, Q.-G. Wang, L. Tang, Q.-T. Hu, et al., Thermoregulated phase-transition synthesis of two-dimensional carbon nanoplates rich in sp2 carbon and unimodal ultramicropores for kinetic gas separation, Angew. Chem. Int. Ed. 57 (6) (2018) 1632–1635. [25] J.W. To, J. He, J. Mei, R. Haghpanah, Z. Chen, T. Kurosawa, et al., Hierarchical Ndoped carbon as CO2 adsorbent with high CO2 selectivity from rationally designed polypyrrole precursor, J. Am. Chem. Soc. 138 (3) (2016) 1001–1009. [26] E. Groppo, M.J. Uddin, S. Bordiga, A. Zecchina, C. Lamberti, Structure and redox activity of copper sites isolated in a nanoporous P4VP polymeric matrix, Angew. Chem. Int. Ed. 47 (48) (2008) 9269–9273. [27] B. Gao, D. Kong, Y. Zhang, Preparation and catalytic activity of P4VP-Cu(II) complex supported on silica gel, J. Mol. Catal. A-Chem. 286 (2008) 143– 148. [28] L. Miao, X. Qian, D. Zhu, T. Chen, G. Ping, Y. Lv, et al., From interpenetrating polymer networks to hierarchical porous carbons for advanced supercapacitor electrodes, Chinese Chem. Lett. 30 (7) (2019) 1445–1449. [29] D. Xue, D. Zhu, W. Xiong, T. Cao, Z. Wang, Y. Lv, et al., Template-free, self-doped approach to porous carbon spheres with high N/O contents for highperformance supercapacitors, ACS Sustain. Chem. Eng. 7 (7) (2019) 7024– 7034. [30] N. Fu, J. Yu, J. Zhao, R. Liu, F. Li, Y. Du, et al., In-situ preparation of nitrogendoped unimodal ultramicropore carbon nanosheets with ultrahigh gas selectivity, Carbon 149 (2019) 538–545. [31] G. Wan, C. Yang, W. Zhao, Q. Li, N. Wang, T. Li, et al., Anion-regulated selective generation of cobalt sites in carbon: toward superior bifunctional electrocatalysis, Adv. Mater. 29 (47) (2017) 1703436. [32] K. Yuan, C. Lu, S. Sfaelou, X. Liao, X. Zhuang, Y. Chen, et al., In situ nanoarchitecturing and active-site engineering toward highly efficient carbonaceous electrocatalysts, Nano Energy 59 (2019) 207–215. [33] J. Wang, R. Krishna, T. Yang, S. Deng, Nitrogen-rich microporous carbons for highly selective separation of light hydrocarbons, J. Mater. Chem. A 4 (36) (2016) 13957–13966. [34] X. Ren, H. Li, J. Chen, L. Wei, A. Modak, H. Yang, et al., N-doped porous carbons with exceptionally high CO2 selectivity for CO2 capture, Carbon 114 (2017) 473–481. [35] M. Sevilla, P. Valle-Vigón, A.B. Fuertes, N-doped polypyrrole-based porous carbons for CO2 capture, Adv. Funct. Mater. 21 (14) (2011) 2781–2787. [36] M. C. Wu, B. K. Guo, A. M. Nie, R. Liu, Tailored architectures of FeNi alloy embedded in N-doped carbon as bifunctional oxygen electrocatalyst for rechargeable zinc-air battery, J. Colloid. Interf. Sci., https://doi.org/10.1016/j. jcis.2019.11.033. [37] Q. Sun, B. Xi, J.-Y. Li, H. Mao, X. Ma, J. Liang, et al., Nitrogen-doped graphenesupported mixed transition-metal oxide porous particles to confine polysulfides for lithium-sulfur batteries, Adv. Energy Mater. (2018) 1800595. [38] A. Zhu, L. Qiao, P. Tan, W. Zeng, Y. Ma, R. Dong, et al., Boosted electrocatalytic activity of nitrogen-doped porous carbon triggered by oxygen functional groups, J. Colloid. Interf. Sci. 541 (2019) 133–142. [39] N. Fu, H.-M. Wei, H.-L. Lin, L. Li, C.-H. Ji, N.-B. Yu, et al., Iron nanoclusters as template/activator for the synthesis of nitrogen doped porous carbon and its CO2 adsorption application, ACS Appl. Mater. Interfaces 9 (11) (2017) 9955– 9963. [40] Y. Wang, J. Wang, C. Ma, W. Qiao, L. Ling, Fabrication of hierarchical carbon nanosheet-based networks for physical and chemical adsorption of CO2, J. Colloid. Interf. Sci. 534 (2019) 72–80. [41] Y. Huang, Z. Lin, H. Fu, F. Wang, M. Shen, X. Wang, et al., Porous anionic indium-organic framework with enhanced gas and vapor adsorption and separation ability, ChemSusChem 7 (9) (2014) 2647–2653. [42] S. Yao, D. Wang, Y. Cao, G. Li, Q. Huo, Y. Liu, Two stable 3D porous metalorganic frameworks with high performance for gas adsorption and separation, J. Mater. Chem. A 3 (32) (2015) 16627–16632. [43] J. Duan, W. Jin, R. Krishna, Natural gas purification using a porous coordination polymer with water and chemical stability, Inorg. Chem. 54 (9) (2015) 4279– 4284.