Enhanced CO2 Adsorption Capacity and Hydrothermal Stability of

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Enhanced CO2 Adsorption Capacity and Hydrothermal Stability of HKUST‑1 via Introduction of Siliceous Mesocellular Foams (MCFs) Chunling Xin,†,‡ Xi Jiao,†,§ Yanlong Yin,†,§ Haijuan Zhan,†,§ Hongguang Li,†,§ Lei Li,† Ning Zhao,*,† Fukui Xiao,*,† and Wei Wei*,∥ †

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China Department of Chemistry and Chemical & Environmental Engineering, Weifang University, Weifang 261061, China § University of Chinese Academy of Sciences, Beijing 100049, China ∥ Center for Greenhouse Gas and Environmental Engineering, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China ‡

S Supporting Information *

ABSTRACT: New hierarchical composites containing micropores and mesopores were synthesized by assembling HKUST-1 (Cu3(BTC)2) on siliceous mesocellular foams (MCFs). The structure, morphology, and textural properties of as-prepared composites were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and N2 sorption isotherms, respectively. The results suggest that the coexistence of mesoporous silicas promotes the formation of nanosized MOFs, and the mesostructures of silicas are not destroyed by MOFs. Moreover, the micropore/mesopore volume ratio can be controlled by varying the amounts of MOFs. The CO2 adsorption capacities were calculated by breakthrough curves, which were tested in a fixed bed. The CO2 adsorption capacity of the composites reaches 1.40 mmol/g, which is higher than that of bulk HKUST-1. The structure and CO2 adsorption capacity of the composites after the hydrothermal treatment also have been evaluated. The results show that composite-2 has a larger CO2 adsorption capacity of 1.68 mmol/g after steam conditioning and that the structure of HKUST-1 in the composites remain stable.

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INTRODUCTION Metal−organic frameworks (MOFs) are a new class of materials composed of metallic sites and organic ligands (usually carboxylate, sulfate, or phosphate), which attract significant attention as adsorbents for separation of gases due to their ultrahigh surface area and tunable porosity.1−4 However, low thermal stability, poor mechanical strength, and slow gas diffusion rate limit the practical application of MOFs.5−7 Ligand extension is an easy approach to enlarge the pore size of MOFs.8,9 However, meso-structured MOFs tend to collapse upon guest removal. Qiu et al.10 employed a one-step templating method to synthesize hierarchical structured MOFs. However, it is really hard to precisely control the amounts of supra-molecular templates to obtain hierarchically micro- and mesoporous MOFs. Except for adjusting the pore structure, direct synthesis of composites adopting parental microporous and mesoporous materials is another good choice.11,12 Mesoporous silicas possess high surface area and thermal stability as well as mesosized pore distribution.13,14 For example, siliceous mesocellular foams (MCFs) consist of uniform spherical cells with diameters of 16−42 nm as well as uniform windows that create continuous 3D pore structures.15 MCFs possess the largest pore size among all mesoporous materials discovered during the last decades that can accommodate more microporous MOFs. Once the composites of MCFs and MOFs are © XXXX American Chemical Society

successfully synthesized, they would possess the advantages of two kinds of materials. For example, the mesopores will improve the gas mass transport, and the micropores will be favorable for gas separation. CO2 is the main component of greenhouse gases, so CO2 capture and separation are of great importance for human existence.16 Flue gases from fossil-fuel-burning power plants are one of the largest anthropogenic emission sources, accounting for approximate one-third of CO2 emissions.17,18 Compared to conventional methods including cryogenic distillation, solvent absorption, and membranes for CO2 separation, adsorption based on solid adsorbents is considered to be one of the most efficient approaches due to the low cost and facile operation.19,20 Most studies related to CO2 adsorption are focused on the MOFs adsorbents in the last two decades21−23 because of the higher CO2 adsorption capacities under high pressure due to the high specific surface area and developed porous structure. For example, the BET surface area of MOF210 reached 6240 m2/g with 16.9 mmol/g of CO2 adsorption Special Issue: International Conference on Carbon Dioxide Utilization 2015 Received: October 26, 2015 Revised: March 3, 2016 Accepted: March 16, 2016

A

DOI: 10.1021/acs.iecr.5b04022 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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than that of pure HKUST-1 (∼15 μm) synthesized under the same conditions (Figure 2a). In addition, the high crystallinity of HKUST-1 in the composite can be observed with an increase in the precursor concentration of HKUST-1. The [111] direction is the preferential growth orientation of he bulk HKUST-1 crystals in this study. The diffraction peak of the (111) crystal plane disappears in the composites, which might be because the anisotropy disappears when the particle sizes decrease to nanoscale. As shown in Figure 2, the calcined MCFs present coral-type morphologies as have been report previously.28 Bulk HKUST-1 crystals show regular octahedral shapes with diameters of ∼15 μm. It is shown in Figure 2c−f that the morphology of MCFs in the composites remain unchanged, while the particle size of bulk HKUST-1 decreases to nanoscale, which is in accordance with the XRD results. It is shown in Figure 2 that MCFs are covered with nanosized HKUST-1 crystals. It is assumed that the generation of nanosized HKUST-1 may be caused by the action of apparent silicon hydroxyls of MCFs, which act as seed sites for HKUST-1 crystallization. The appearance of octahedral HKUST-1 crystals in composite-3 further confirm that the amounts of MCFs limit the formation of nanosized HKUST-1(Figure 2c). Bulk HKUST-1 crystals disappear with increasing amounts of MCFs. From the TEM image of composite-2 (Figure 3), a disordered array of silica struts are observed, which is a structural feature of MCFs, indicating that the structure of MCFs is not destroyed in the composites. However, the particle sizes of HKUST-1 decrease to nanoscale (Figure 3b and c). To the best of our knowledge, this is the minimum particle size of HKUST-1 without serious aggregation that has been reported.29,30 As shown in Figure 3b, the crystal particles are not aggregated due to the high surface energy, which indicates that the existence of MCFs could control the morphology and particle size of HKUST-1. For example, it is beneficial for the dispersion of nanosized HKUST-1. The composites overcome the surface energy of the nanosized particles and avoid aggregation of nanosized particles. Three stages of weight loss can be clearly observed from the TG curves (Figure 4). The first two weight loss peaks below 523 K can be ascribed to the removal of physisorbed water and organic solvents embedded in the frameworks, respectively. The third peak located in the temperature range of 583−643 K may be assigned to the decomposition of BTC, which is similar to that of bulk HKUST-1. However, the third weight loss peak in the composite has a slight hysteresis, which might be the result of the protected effect of MCFs.5,31,32 When the temperature exceeds 723 K, the composites show a slight weight loss, which suggests that MCFs hardly affect the thermostability of the composites. According to the weight loss between 473 and 723 K as well as the 100% yield of HKUST-1, the amounts of HKUST-1 in composite-1, composite-2, and composite-3 can be obtained as 24.1%, 33.5%, and 41.8%, respectively. The weight ratio of HKUST-1 to MCFs increases with an increasing concentration of the precursor of HKUST-1. The porous structures of all the samples are analyzed by N2 sorption at 77 K. The BET surface area and pore volume are calculated from N2 sorption isotherms, and the pore size distributions are determined by a desorption branch of the isotherms according to the BJH method. It is shown in Table 1 that bulk HKUST-1 has a BET surface area of 1748 m2/g, which is larger than many previous reports,27,33,34 while the BET surface area of the composites begins to decline with the

capacity at 50 bar and 298 K.21 However, the CO2 adsorption capacity of MOFs decreases with a decrease in pressure. For example, the CO2 adsorption capacity of MOF-177 decreased from 13.8 mmol/g under 50 bar and 298 K to 1.5 mmol/g under 1 bar and 298 K.22 So, it is important to study the CO2 adsorption in MOFs under low pressure for CO2 separation from flue gases.24 Most efforts are devoted to enhancing the CO2 adsorption capacity of MOFs. Among these, amine grafting, introducing strongly polarizing functional groups, and open metal sites are the main methods that have been most intensively investigated.1,25,26 However, these three methods still cannot dissolve the limitation of mass transport and hydrothermal stability. Herein, HKUST-1 (Cu3(BTC)2) was chosen as the microporous material due to the facile synthesis process and specific adsorption sites known as open metal sites.27 The assynthesized samples were characterized, and the evaluation of their CO2 adsorption capacities were studied under low pressure. The X-ray diffraction (XRD) and N2 sorption isotherms results illustrate that the integration of micropores and mesopores of the composite material is realized. MCFs in the composites enhance the hydrothermal stability of the composites and relieve the mass transport limits. Among them, HKUST-1 provides open metal sites for CO2 adsorption. Moreover, the composites have a higher capacity for CO2 adsorption than bulk HKUST-1 under low pressure (0.1 bar).

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RESULTS AND DISCUSSION Figure 1 shows the XRD patterns of a series of HKUST-1/ MCFs composites, bulk HKUST-1, and MCFs. The character-

Figure 1. XRD patterns of the composites, MCFs, and bulk HKUST1.

istic peaks of HKUST-1 are similar to the pattern of HKUST-1 for all the composites, which indicates that the structure of HKUST-1 is not affected by the coexistence of mesoporous MCFs. However, a lower peak intensity of HKUST-1 is observed with an increase in MCFs content. A broad peak centered at 2θ of 23° in MCFs, which attributed to amorphous SiO2, disappears in the composite. The main reason should be that the peak intensity of MCFs is lower compared to that of HKUST-1. The addition of MCFs leads to broaden diffraction peaks of HKUST-1, which suggests the formation of smaller grain size of the HKUST-1 in the composites. It is far smaller B

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Figure 2. SEM images of (a) MCFs, (b) bulk HKUST-1, (c) composite-1, (d) composite-2, and (e, f) composite-3.

Figure 3. TEM images (a, b) and particle size distribution (c) of composite-2.

Figure 4. TG and DTG curves of bulk HKUST-1 (a), composite-1 (b), composite-2 (c), and composite-3 (d).

can be attributed to the interparticle cavity of nanosized HKUST-1 and the window sizes of MCFs, respectively.15,28 As shown in Figure 6, bulk HKUST-1 exhibits a type I isotherm, which is the character of the microporous materials. The N2 isotherms of composite-2 under low pressure keep the character of the micropore, which indicates that the introduction of MCFs does not affect the pore structure of

addition of MCFs. As shown in Figure 5a, all the composites have a large hysteresis loop at around P/P0 = 0.8−1.0, similar to that of MCFs, which indicates that the composites still contain large amounts of mesopores upon addition of HKUST-1. The hysteresis loop becomes small with an increase in the amount of HKUST-1. Two peaks centered at 4.0 and 15.5 nm in the pore size distribution curves are observed in Figure 5b, which C

DOI: 10.1021/acs.iecr.5b04022 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research Table 1. Textural Properties of Composites, MCFs, and Bulk HKUST-1 sample MCFs composite-1 composite-2 composite-3 bulk HKUST-1

SBET (m2/g)

total pore volume (cm3/g)

microporous volume (cm3/g)

microporous volume percentage (%)

468 943 1057 1464 1748

2.62 1.48 1.17 0.98 0.63

0.01 0.26 0.32 0.42 0.53

0.38 17.57 27.35 42.86 84.13

HKUST-1, and the mesoporous character of MCFs is also reserved. The nanosized particles of HKUST-1 produce more interparticle cavities, leading to an increase in the adsorbed volume of N2. The total pore volume of the composites seems to increase with an increase in MCFs (Table 1). Meanwhile, the BET surface area, microporous volume, and micropore percentage increase with a decrease in the amount of MCFs, indicating that the micropores of HKUST-1 are accessible. The BET surface area of the composites is larger than that of MCFs. In addition, the surface area of composite-3 is 28% lower compared to that of bulk HKUST-1. To examine the CO2 adsorption capacities of the composites in the subatmosphere pressure, a breakthrough experiment was carried out in a fixed-bed reactor with a binary gas (CO2:N2 = 1:9) at 303 K. After activation at 473 K, all the weight of HKUST-1 and composites samples were reduced due to the removal of the organic solvents and water adsorbed in the frameworks. The breakthrough curves of all the composites and parent materials are shown in Figure S1. The CO2 adsorption capacities of all the samples are calculated according to the breakthrough curves, and the results are listed in Table 2. The composites show a remarkable increase in CO2 adsorption capacity compared to the parent materials. When the HKUST-1 loading amount reaches 33.5%, the maximum adsorption capacity is obtained. By further increasing the amount of HKUST-1, the adsorption capacity decreases to 1.13 mmol/g. According to the HKUST-1 loading in the composites based on the TG results, the theoretical CO2 adsorption capacity can be calculated as eq 1: qtheoretical = qCuBTC × wt%CuBTC + qMCFs × wt%MCFs

Figure 6. N2 sorption isotherms for bulk HKUST-1 and composite-2.

Table 2. CO2 Adsorption Capacities for All Samples before and after Hydrothermal Treatment CO2 adsorption capacity (mmol/g) sample

initial

conditioned

MCFs composite-1 composite-2 composite-3 bulk HKUST-1

0.45 1.17 1.40 1.13 0.96

0.64 1.12 1.68 1.46 0.97

where, qHKUST‑1 and qMCFs are the CO2 adsorption capacity of HKUST-1 and MCFs, respectively; wt %HKUST‑1 and wt %MCFs are the mass percent of HKUST-1 and MCFs, respectively. It is noteworthy that the measured values of the composites are higher than that of theoretical value. The increment of adsorption capacity in the composites compared to the mixture of bulk HKUST-1 and MCFs is a remarkable characteristic of the composite. The incorporation of MCFs leads to the formation of well-dispersed nanosized HKUST-1 as confirmed by the TEM images. Minimizing MOFs particle size is beneficial for CO2 adsorption due to the remarkably decreased diffusion length of the gas molecules.35 Furthermore, decreasing HKUST-1 crystal size provides additional pore space for improving CO2 adsorption capacity.36

(1)

Figure 5. N2 sorption isotherms (a) and pore size distributions (b) of all the samples. D

DOI: 10.1021/acs.iecr.5b04022 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research On the basis of the above-mentioned results, the adsorption kinetics of composite-2 was investigated by comparing with that of bulk HKUST-1 due to the largest CO2 adsorption capacity. Figure 7 shows the CO2 adsorption kinetics profiles of

Figure 8. XRD patterns of bulk HKUST-1 and composites after steam conditioning.

Figure 7. CO2 adsorption kinetics profiles on bulk HKUST-1 and composite-2 at 298 K.

composite-2 and bulk HKUST-1 at 298 K, in which the coordinate axis is ln(1 − Mt/Me) and the abscissa axis is time (s). Here, Mt is the CO2 adsorption capacity at time t, and Me is the CO2 adsorption capacity at equilibrium. It can be found that the adsorption rate of composite-2 is higher than that of bulk HKUST-1. The adsorption kinetics may be enhanced due to an increase in molecular diffusivity in the nanoparticles as well as the mesopores in the composites. For practical application, CO2 adsorbents should not only have high CO2 adsorption capacity but also possess a stable performance for multiple adsorption−desorption cycles. Therefore, the stability of composite-2 was measured in the fixed-bed reactor. The adsorption−desorption cycles were operated at 303 K and 10 vol % CO2. The results are shown in Figure S2. The CO2 adsorption capacity of composite-2 almost remains unchanged after 10 cycles, which reveals the stable performance of the sample. Because the flue gases usually contain 8−17 vol % water vapor in practical conditions, the structure and CO2 adsorption capacity of adsorbents were also investigated after hydrothermal treatments. From the XRD pattern of the composites and bulk HKUST-1 after hydrothermal treatment (Figure 8), it can be found that the structure of the composites are not destroyed after hydrothermal treatment. However, compared with the XRD patterns of the untreated samples, the full width at half-maximum (fwhm) of the conditioned samples becomes narrow, which suggests the enlarged particle sizes in the composites after treatment. As shown in Figure 9, the crystal surface of bulk HKUST-1 is slightly damaged without a morphology change. However, the nanosized HKUST-1 crystals aggregate obviously for the composites after steam conditioning. This may lead to a decrease in the specific surface area of the composites. The conclusion is verified by the results of the N2 sorption isotherms. The textural properties of the composites and bulk HKUST1 after hydrothermal treatment are listed in the Table 3. It can be found that the BET surface area of conditioned MCFs is almost the same with untreated MCFs, while the total pore

Figure 9. SEM images of bulk HKUST-1 and composites after hydrothermal treatment: (a) bulk HKUST-1, (b) composite-1, (c) composite-2, and (d) composite-3.

Table 3. Textural Properties of Composites, MCFs, and Bulk HKUST-1 after Hydrothermal Treatment sample MCFs composite-1 composite-2 composite-3 bulk HKUST-1

SBET (m2/g)

total pore volume (cm3/g)

microporous volume (cm3/g)

microporous volume percentage (%)

479 271 550 584 1088

1.29 0.42 0.29 0.54 0.75

0.02 0.06 0.19 0.17 0.34

1.55 14.28 65.52 31.48 45.33

volume decreases from 2.62 to 1.29 cm3/g, which may result from the incorporation of water molecules filling in the pore channel of MCFs. In addition, the BET surface area, total pore volume, and microporous volume of the composites decrease obviously after hydrothermal conditioning. The dynamic adsorption property of the composites after conditioning was also measured in a fixed bed. As shown in Table 2, the CO2 adsorption capacities of composite-2 and composite-3 increase by 20% and 29% after conditioning, respectively. Among them, the CO2 adsorption capacity of E

DOI: 10.1021/acs.iecr.5b04022 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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However, further increasing the loading of HKUST-1 decreases the CO2 adsorption capacity of the composites. After hydrothermal treatment, the CO2 adsorption capacity of the composites is improved. XRD and SEM results suggest that the structure of HKUST-1 is well preserved after conditioning. For composite-2, the CO2 adsorption capacity reaches 1.68 mmol/g. This method can also be applied to other composites composed of different types of mesoporous materials and MOFs.

composite-2 reaches 1.68 mmol/g. As far as we know, this is the largest dynamic CO2 adsorption capacity for HKUST-1 under such low pressure.37 At the same time, the CO2 adsorption capacity of hydrated bulk HKUST-1 changes slightly. Consequently, MCFs play an important roles in increasing the CO2 adsorption capacity in the composites. Among them, the CO2 adsorption capacity of MCFs after hydrothermal treatment increases from 0.45 to 0.64 mmol/g, which may be due to the CO2 molecules dissolving in the water in the frameworks of MCFs after treatment. On the other hand, a certain number of hydroxyl groups of MCFs, which had disappeared in the calculation process, have reformed during the hydrothermal treatment. A previous report implied that a small amount of H2O would increase the CO2 capacity of HKUST-137 due to the Columbic interactions between water and CO2. As shown in Figure S3b, the electrostatic interaction derived from the quadruple moment of CO2 interacting with the electric field gradient of the sorbent increases when water occupies the copper open metal sites.38 Our experiments results also suggest that the CO2 capacity of bulk HKUST-1 maintains a high value after hydrothermal treatment for 5 h. The increments of CO2 adsorption capacity for composite-2 and composite-3 are larger than the calculated value according to eq 1. It seems that the textural properties of the composites do not play important roles in the improvement of CO2 adsorption capacity after hydrothermal treatment. Interestingly, the microporous volume and microporous volume percentage become the largest among all the composite materials, which suggest that the CO2 adsorption capacity of conditioned composites is related to the microporous volume percentage in the composites. According to the above-mentioned results, the increment of CO2 adsorption capacity in the composites is mainly due to three aspects. First, the recovery of the hydroxyl group in MCFs increases the amounts of the hydroxyl group. Water adsorbed in the pore channel of MCFs increases the CO2 adsorption capacity. Second, the adsorbed water occupying the open site of HKUST-1 interacts with CO2 molecules through electrostatic interaction. Finally, the reserved structures of the composites after conditioning ensure the hierarchical structures that promote the adsorption and mass transportation of the CO2 molecules in the composites.

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EXPERIMENTAL SECTION 2.1. Synthesis of Mesoporous Silica. The synthesis of mesocellular foams (MCFs) was based on the previous report with a little modification.28 Four grams of P123 was initially dissolved in 125 mL of deionized water, and then, 25 g of concentrated HCl (36−38 wt %) was added to the solution while stirring at 313 K for 1 h. Afterward, 3 g of trimethylbenzene (TMB) was added to the mixture and stirred for another 1 h followed by dropwise addition of 8.5 g of tetraethyl orthosilicate (TEOS) under stirring. After the mixture was stirred for 24 h at 313 K, 46 mg of NH4F was added to the mixture, and then, the mixture was aged for 24 h at 393 K. The obtained solids were calcined at 773 K for 6 h to remove the template. 2.2. Synthesis of HKUST-1/MCFs Composites. HKUST1/MCFs composites were synthesized as follows: 0.25−1.0 g of benzenetricarboxylic acid (H3BTC) and 0.57−2.28 g of Cu(NO3)2·3H2O were dissolved in 12 mL of DMF/EtOH/ H2O (1:1:1), denoted as solution A and B, respectively. Then, 0.5 g of MCFs was added to solution A and stirred for 1 h, and solution B was added into the mixture, stirring at room temperature for another 6 h. The mixture was crystallized at 353 K for 24 h. The obtained blue powder was filtered and washed two times with 25 mL of DMF and then dried at 373 K overnight. The as-prepared materials were denoted as composite-1, composite-2, and composite-3. 2.3. Hydrothermal Conditioning. To evaluate the hydrothermal stability of the adsorbents at high temperature and humidity, all the samples were placed on filter paper and suspended above a beaker filled with boiling water. The samples were held at 358 K in saturated water vapor for 5 h. After treatment, they were dried at room temperature. 2.4. CO2 Dynamic Breakthrough Experiments. CO2 adsorption and desorption processes were conducted in a fixedbed reactor. Moderate adsorbents were added in a U type quartz tube with an inner diameter of 8 mm and plugged by quartz wool in the side of the gas outlet. The HKUST-1 powder was pressed into a disk under 5 MPa for 3 min. Then, the disk was broken to particles, and the particles were sieved for 20−40 mesh particles. The sorbents were heated at 473 K for 6 h in an argon atmosphere with a flow of 50 mL/min and then cooled to adsorption temperature under an argon atmosphere. The simulated flue gases (CO2 10 vol %, N2 90 vol %) were introduced into the reactor with a flow of 60 mL/ min. The CO2 concentration of the outlet gas of the quartz tube was determined by a gas analyzer (Vaisala, Finland) for every 10 s. The CO2 absorption quantity of HKUST-1 can be determined from the breakthrough curves as reported in a previous report.39 2.3. Characterization. Powder X-ray diffraction (PXRD) patterns were collected with a D8 Advanced diffractometer operated at 40 kV and 40 mA with monochromatic Cu Kα radiation (λ = 1.5406 Å) and with a scan speed of 3°/min.

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CONCLUSION A series of composites with different micropore/mesopore ratios were prepared by combination of MCFs and HKUST-1. The ratio of the micropore/mesopore volumes can be tuned by controlling the amount of HKUST-1. The presence of mesoporous silica promotes the formation of nanosized HKUST-1, which results from the seed sites provided by the surface hydroxyl group of silica. Therefore, the existence of MCFs is beneficial for the increase in the CO2 adsorption capacity for the composites. The results in this study imply a new method for the synthesis of nanosized MOFs and provide a new functional composite containing micropores and mesopores. The adsorption kinetics results also confirm that the adsorption rate of the composites is higher than that of bulk HKUST-1. The CO2 dynamic adsorption experiments results suggest that the MOFs and MCFs composites have improved CO2 adsorption capacity compared with the two parent materials. The CO2 adsorption capacity of the composites increases with the amount of HKUST-1 in the composites. F

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(6) Pachfule, P.; Balan, B. K.; Kurungot, S.; Banerjee, R. Onedimensional Confinement of a Nanosized Metal Organic Framework in Carbon Nanofibers for Improved Gas Adsorption. Chem. Commun. 2012, 48, 2009. (7) Qian, D.; Lei, C.; Hao, G. P.; Li, W. C.; Lu, A. H. Synthesis of Hierarchical Porous Carbon Monoliths with Incorporated Metalorganic Frameworks for Enhancing Volumetric Based CO2 Capture Capability. ACS Appl. Mater. Interfaces 2012, 4, 6125. (8) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. The Chemistry and Applications of Metal-organic Frameworks. Science 2013, 341, 1230444. (9) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi, E.; Yazaydin, A. O.; Snurr, R. Q.; O’Keeffe, M.; Kim, J.; Yaghi, O. M. Ultrahigh Porosity in Metal-organic Frameworks. Science 2010, 329, 424. (10) Qiu, L.-G.; Xu, T.; Li, Z.-Q.; Wang, W.; Wu, Y.; Jiang, X.; Tian, X.-Y.; Zhang, L.-D. Hierarchically Micro- and Mesoporous MetalOrganic Frameworks with Tunable Porosity. Angew. Chem., Int. Ed. 2008, 47, 9487. (11) Yang, J. H.; Yang, D.; Li, Y. M. Graphene Supported Chromium Carbide Material Synthesized from Cr-based MOF/graphene Oxide Composites. Mater. Lett. 2014, 130, 111. (12) Petit, C.; Bandosz, T. J. Synthesis, Characterization, and Ammonia Adsorption Properties of Mesoporous Metal-Organic Framework (MIL(Fe))-Graphite Oxide Composites: Exploring the Limits of Materials Fabrication. Adv. Funct. Mater. 2011, 21, 2108. (13) Huo, Q.; Margolese, D. I.; Stucky, G. D. Surfactant Control of Phases in the Synthesis of Mesoporous Silica-Based Materials. Chem. Mater. 1996, 8, 1147. (14) Zhao, D.; Huo, Q.; Feng, J.; Chmelka, B. F.; Stucky, G. D. Nonionic Triblock and Star Diblock Copolymer and Oligomeric Surfactant Syntheses of Highly Ordered, Hydrothermally Stable, Mesoporous Silica Structures. J. Am. Chem. Soc. 1998, 120, 6024. (15) Lukens, W. W.; Schmidt-Winkel, P.; Zhao, D.; Feng, J.; Stucky, G. D. Evaluating Pore Sizes in Mesoporous Materials: A Simplified Standard Adsorption Method and a Simplified Broekhoff−de Boer Method. Langmuir 1999, 15, 5403. (16) Wang, Q.; Luo, J.; Zhong, Z.; Borgna, A. CO2 Capture by Solid Adsorbents and Their Applications: Current Status and New Trends. Energy Environ. Sci. 2011, 4, 42. (17) Choi, S.; Drese, J. H.; Jones, C. W. Adsorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources. ChemSusChem 2009, 2, 796. (18) Hallenbeck, A. P.; Kitchin, J. R. Effects of O2 and SO2 on the Capture Capacity of a Primary-Amine Based Polymeric CO2 Sorbent. Ind. Eng. Chem. Res. 2013, 52, 10788. (19) Hao, G.-P.; Li, W.-C.; Lu, A.-H. Novel Porous Solids for Carbon Dioxide Capture. J. Mater. Chem. 2011, 21, 6447. (20) Samanta, A.; Zhao, A.; Shimizu, G. K. H.; Sarkar, P.; Gupta, R. Post-Combustion CO2 Capture Using Solid Sorbents: A Review. Ind. Eng. Chem. Res. 2012, 51, 1438. (21) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi, E.; Yazaydin, A. Ö .; Snurr, R. Q.; O’Keeffe, M.; Kim, J.; Yaghi, O. M. Ultrahigh Porosity in Metal-Organic Frameworks. Science 2010, 329, 424. (22) Farha, O. K.; Ö zgür Yazaydın, A.; Eryazici, I.; Malliakas, C. D.; Hauser, B. G.; Kanatzidis, M. G.; Nguyen, S. T.; Snurr, R. Q.; Hupp, J. T. De novo Synthesis of a Metal−organic Framework Material Featuring Ultrahigh Surface Area and Gas Storage Capacities. Nat. Chem. 2010, 2, 944. (23) Dietzel, P. D. C.; Besikiotis, V.; Blom, R. Application of Metalorganic Frameworks with Coordinatively Unsaturated Metal Sites in Storage and Separation of Methane and Carbon Dioxide. J. Mater. Chem. 2009, 19, 7362. (24) Zhang, Z.; Zhao, Y.; Gong, Q.; Li, Z.; Li, J. 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, 653.

Nitrogen sorption isotherms were measured at 77 K on a Micrometric ASAP 2020 system. The samples were outgassed at 473 K overnight before the measurement. Scanning electron microscopy (SEM) images were obtained on a JEOL at 10 kV. Transmission electron microscopy (TEM) investigations were performed with a JEM-2100F (operated at 200 kV). Thermal gravimetric analysis (TGA) was performed on a Rigaku TG thermal gravimetric analyzer in the temperature range of 293− 1173 K under nitrogen atmosphere at a heating rate of 10 K/ min.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b04022. Breakthrough curves before and after hydrothermal conditioning, regeneration capacity of composite-2, and crystal structure images of HKUST-1. (PDF)

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AUTHOR INFORMATION

Corresponding Authors

* Tel.: +86 351 4049612. Fax: +86 351 4041153. E-mail: [email protected] (Ning Zhao). * Tel.: +86 351 4049612. Fax: +86 351 4041153. E-mail: [email protected] (Fukui Xiao). * Tel.: +86 351 4049612. Fax: +86 351 4041153. E-mail: [email protected] (Wei Wei). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge supports from the National Natural Science Foundation of China (21306217); ‘‘Strategic Priority Research Program-Climate Change: Carbon Budget and Related Issues’’ of the Chinese Academy of Sciences (XDA05010109, 05010110); Instrument Developing Project of the Chinese Academy of Sciences (YZ201139); Chinese Academy of Sciences, Strategic Pilot Science and Technology Projects−Carbon Dioxide Capture, Use, and Storage, Key Technology and Engineering Demonstration (XDA070401); and Key Science and Technology Program of Shanxi Province, China (MD2014-09).

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DOI: 10.1021/acs.iecr.5b04022 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX