C Nanocomposite from Hierarchical

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Synthetic Architecture of MgO/C Nanocomposite from HierarchicalStructured Coordination Polymer towards Enhanced CO2 Capture Ping Li, Wen Liu, John S. Dennis, and Hua Chun Zeng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b14960 • Publication Date (Web): 01 Mar 2017 Downloaded from http://pubs.acs.org on March 5, 2017

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ACS Applied Materials & Interfaces

Synthetic Architecture of MgO/C Nanocomposite from Hierarchical-Structured Coordination Polymer towards Enhanced CO2 Capture Ping Li,a,b Wen Liu,b John S. Dennis,c and Hua Chun Zeng a,b,* a

Department of Chemical and Biomolecular Engineering, Faculty of Engineering, National

University of Singapore, 10 Kent Ridge Crescent, Singapore 119260. b

Cambridge Centre for Advanced Research in Energy Efficiency in Singapore, 1 Create Way,

Singapore 138602. c

Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke

Street, Cambridge, United Kingdom CB2 3RA KEYWORDS: MgO-based nanocomposite, carbon, hierarchical structure, coordination polymer, pyrolysis, CO2 capture

ABSTRACT: Highly efficient, durable and earth-abundant solid sorbents are of paramount importance for practical carbon capture, storage, and utilization. Here we report a novel and facile two-step strategy to synthesize a group of hierarchically structured porous MgO/C nanocomposites using flowerlike Mg-containing coordination polymer as a precursor. The new nanocomposites exhibit superb CO2 capture performance with sorption capacity up to 30.9 wt% (at 27 °C, 1 bar CO2), fast sorption kinetics and long cycling life. Importantly, the achieved

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capacity is > 14 times higher than that of commercial MgO, and favorably exceeds the highest value recorded to date for MgO-based sorbents under similar operating conditions. On the basis of the morphological and textural property analysis, together with CO2 sorption mechanism study using CO2-TPD and DRIFT techniques, the outstanding performance in CO2 uptake originates from unique features of this type of sorbent materials, which include hierarchical architecture, porous building blocks of nanosheets, high specific surface area (ca. 300 m2/g), evenly dispersed MgO nanocrystallites (ca. 3 nm) providing abundant active sites, and the in situ generated carbon matrix that acts as a stabilizer to prevent the growth and agglomeration of MgO crystallites. The nanocomposite system developed in this work shows good potential for future low-cost CO2 abatement and utilization.

1. Introduction It has been a world-wide consensus that the continuously rising concentration of atmospheric CO2 since the industrial revolution is anthropogenic, e.g., the combustion of fossil fuels, and will lead to catastrophic consequences.1-3 Accordingly, the carbon capture, storage, and utilization scheme (CCSU) has been proposed as a plausible solution to decarbonize the energy sector which still predominantly relies on fossil fuels.4,5 The most energy intensive step in CCSU is carbon capture.6 Therefore, development of new materials and technologies for the extraction of CO2 from combustion flue gases has attracted intensive research attention in the recent decades.7,8 One of the potential techniques for the CO2 removal is the application of regenerable solid sorbent materials.2,9-13 Compared with the conventional liquid amine-based scrubbing technology, the sorption processes using solid sorbents show promising advantages, such as economical, ease to operate, wide working temperature range, reduced energy for regeneration


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and environmentally friendly, etc. In recent years, a wide range of materials that include zeolites,14 carbonaceous materials,15,16 solid amine-based materials,17,18 organic polymers,19,20 metal-organic frameworks (MOFs),21-23 hydrotalcites (LDHs)24 and metal oxides/salts25-27 have been considered and employed for CO2 capture by absorption, adsorption, and/or separation. Among a wide variety of existing solid-state sorbents, MgO, a common alkaline earth metal oxide, is recognized as a promising candidate,3,25 and has attracted great research attention for its unique properties: (i) MgO possesses suitable basicity which can interact with the acidic CO2 and has a high theoretical uptake capacity (1.09 g of CO2 per gram of sorbent, 109 wt%); (ii) compared with other representative metal oxide based sorbents (e.g., CaO-based and Li4SiO4based materials), MgO can be regenerated under relatively low temperature and thus lower energy consumption for its regeneration;2,25 (iii) MgO-based materials are noncorrosive, ecofriendly, low-cost, and widely available in nature. Due to the above merit points, MgO-based materials hold great potential to treat CO2 and become the focus of intense investigations.28-34 Nevertheless, the CO2 capture performance of most MgO-based materials at the present time is far from satisfactory, as reflected in their uncompetitive sorption capacity and slow sorption kinetics. For instance, the capture capacity of CO2 by commercially available MgO powder is still fairly small (ca. 2.0 wt%).35,36 The low capture capacity is mainly attributed to its low surface area and the formation of a termination layer of CO2-impermeable MgCO3 at the gassolid interface which prevents any sub-surface or lattice MgO from reacting with CO2. In addition, the high-temperature regeneration process of MgO-based sorbents is always accompanied by a sintering process (i.e., agglomeration of MgO and thus resultant loss of surface area), leading to significant deteriorations in their CO2 capture capacity and recyclability for repeated sorption-desorption processes. All of these drawbacks greatly impede the practical


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application of MgO as an effective CO2 sorbent. Thus, development of MgO-based materials with high sorption capacity, rapid sorption rate, good stability and recyclability is highly desirable but particularly challenging for practical CCSU systems made with earth abundant elements. To this end, in the present work, a novel and simple strategy is developed to fabricate a class of hierarchical-structured 3D flowerlike porous MgO/C nanocomposites via thermal annealing of a Mg-containing coordination polymer obtained from polyol-mediated self-assembly process. Owing to their special structural features and physicochemical properties, the as-prepared MgO/C nanocomposites possess superb CO2 sorption capacities as high as 30.9 wt% (at 27 °C, 1 bar CO2), unmatched by all the previously reported MgO-based sorbents. Moreover, the MgO/C nanocomposites display fast sorption rate, wide working temperature range as well as excellent recyclability, and up to a total of 14 successive cycles of adsorption-desorption has been tested in this study. Besides, for better understanding the sorption features in MgO/C nanocomposites, the CO2 sorption mechanism are studied in detail through DRIFT and CO2-TPD techniques.

2. Experimental Section 2.1. Materials and reagents. The following chemicals were used as received without any further purification: ethylene glycol (EG, 99.99%, Fluka, Sigma-Aldrich), Mg(CH3COO)2·4H2O (99+%, Sigma-Aldrich), polyvinylpyrrolidone (PVP, K30, 99%, Sigma-Aldrich), commercial MgO powder (99+%, Sigma-Aldrich) and ethanol (99.99%, Fisher). Deionized water was generated by the Elga Micromeg purified water system. 2.2. Preparation of flowerlike Mg-EG complex precursor. Flowerlike Mg-EG complex were

synthesized

using

a

previously

reported

solvothermal

approach

with

slight


4

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modification.37,38 In a typical synthesis, Mg(CH3COO)2·4H2O (0.428 g) and PVP (0.322 g) were dissolved in 20 mL of ethylene glycol (EG). Then the above solution was transferred into a Teflon-lined autoclave, sealed and heated at 180 oC for 4 h. The solid product was centrifuged, rinsed with deionized water and ethanol for several times, and dried in an oven at 60 oC for 12 h. 2.3.

Preparation

of

flowerlike

MgO/C

nanocomposite.

Flowerlike

MgO/C

nanocomposites were prepared by pyrolysing the above Mg-EG complex in an argon flow. The solid precursor was initially heated to 500, 550 or 600 oC at a rate of 10oC/min, followed by an isothermal pyrolysis for 4 h and cooling naturally to room temperature. The resultant black solids are denoted as MgO/C-500, MgO/C-550 and MgO/C-600, respectively, where the number represents the pyrolysis temperature of the sample. Note that when the pyrolysis temperature is too high (i.e., 700 or even 800 oC), the carbon species is burned out and the obtained product is in light gray or even white color. In other words, very high pyrolysis temperature will lead to the failure of the production of MgO/C nanocomposites with embedded MgO. 2.4. Preparation of flowerlike pure MgO sample. To obtain a carbon-free sorbent, the MgEG complex was directly calcined in air at 550 oC for 4 h, followed by natural cooling. A white powder sample, i.e., flowerlike pure MgO (in the form of spherical aggregates) was obtained afterward. 2.5. Preparation of the pure carbon sample. The pure carbon was obtained by treating the MgO/C-550 nanocomposite with 2 M HCl aqueous solution for 48 h to etch away the MgO phase. 2.6. CO2 capture performance test. The performance of the sorbent samples was investigated using a thermogravimetric analyser (TGA/DSC 2 STARe system, Mettler Toledo) at 1 bar. Dried pure CO2 (99.99%) or CO2 (15.00 vol%) in N2 was used for the sorption studies and


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ultrahigh purity N2 (99.9995%) was used as a purging gas for CO2 desorption and sorbent regeneration. In a typical experiment, approximately 10 mg of the sorbent was loaded into an alumina pan. The sorbent was firstly heated at 500oC in N2 flowing at 50 mL/min for 60 min to remove the moisture and CO2 adsorbed from the atmosphere during storage and transportation. Then the temperature was lowered to the sorption temperature, viz. 27, 50, 100, 150, or 200 oC in N2, which was then switched to pure CO2 or a mixture of 15 vol% CO2 in N2; the total flow rate of the reactive gas was 50 mL/min in both cases. The sorbent was kept at the test temperature for 120 min for the sorption study. The measurement was repeated 4 times for each sample, and an average value was then obtained. The CO2 capture capacity of the sorbent in wt% was calculated from the weight gain of the sample in the sorption process. For the kinetic analysis of CO2 capture, the temperature was fixed at 27 oC under a pressure of 1 bar CO2 (50 mL/min) for 2 h, and the weight variation of MgO/C nanocomposite with the capture time was recorded. For comparison, CO2 capture performances of the flowerlike pure MgO spheres and commercially available MgO powder were also measured under identical conditions. In CO2 sorption-desorption recyclability tests, the sample was held at 27 oC under a CO2 flow (50 mL/min) for 120 min to take up CO2, then the sample was heated at 400 oC in a N2 flow (50 mL/min) for 30 min to desorb CO2. Such an adsorption-desorption cycle was repeated 14 times and the weight variation of the sample with the time was recorded. 2.7. Materials characterization. The microscopic features of the samples were characterized by scanning electron microscopy (SEM, JEOL-6700F) equipped with an energy-dispersive X-ray (EDX) analyser (Oxford INCA), transmission electron microscopy (TEM, JEOL JEM-2010, 200 kV), and high resolution transmission electron microscopy (HRTEM, JEOL JEM-2100F, 200


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kV). The elemental mapping was done by energy-dispersive X-ray spectroscopy (EDX, Oxford Instruments, model 7426). The wide-angle X-ray (Cu Kα radiation) diffraction patterns were taken using Bruker D8 Advance system. Nitrogen adsorption–desorption isotherms were obtained on Quantachrome NOVA-3000 system at 77 K. Prior to BET measurements, the samples were degassed at 200 oC for 15 h with a N2 flow. The surface area of the samples was measured by the Brunauer–Emmet–Teller (BET) method. The pore size distribution curve was obtained using the NLDFT method and the pore volume was calculated at P/P0 = 0.9754. CHN elemental analysis (EA) was also performed on the elemental analyser (Elementar vario MICRO cube). TGA measurement was carried out under a N2 stream (50 mL/min) at a heating rate of 5 o

C/min using Shimadzu TGA-50 instrument. Fourier transform infrared spectroscopy (FTIR,

Bio-Rad FTS-135) was used to obtain chemical bonding information of samples using the potassium bromide (KBr) pellet technique. To monitor the thermal decomposition of Mg-EG precursor, approximately 10 mg of the solid sample was heated in a quartz tube from room temperature to 600 oC at a rate of 10 oC/min with an argon flow (50 mL/min). The gaseous products were detected by a mass spectrometer (MS). The diffuse reflectance infrared Fourier transformed spectroscopy (DRIFT) experiment was carried out on Bruker TENSOR II FT-IR spectrometer equipped with a MCT detector. The sample was loaded into the DRIFT cell, pretreated at 400 oC for 1 h under a N2 flow (50 mL/min), then cooled to 27 oC and exposed to a stream of CO2 (50 mL/min) for 1 h, followed by N2 purging for 30 min to remove the physically adsorbed CO2. Afterwards, the sample was heated from 27 to 400 oC in the same N2 flow and the FT-IR spectra were recorded at the given temperature (prestabilized at this temperature for 10 min before scanning the spectrum).


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Temperature-programmed desorption (TPD) of CO2 was performed in a quartz tube using HIDEN analytical CATLAB instrument. The solid sample was pretreated at 400 oC for 1 h under a N2 flow (50 mL/min). Then the sample was cooled to 50 oC and exposed to a stream of CO2 (50 mL/min) for 2 h, followed by N2 purging for 30 min to remove the physically adsorbed CO2. Then the TPD of CO2 was performed at 10 oC/min in N2 (50 mL/min), and the desorbed CO2 was detected by a mass spectrometer (MS).

3. Results and Discussion 3.1. Synthetic strategy for the flowerlike MgO/C nanocomposites.

Scheme 1. Synthesis procedure for flowerlike MgO/C nanocomposites. In Mg-EG complex (i.e., coordination polymer), for illustrative purpose, Mg2+ ion is located inside octahedrons formed by six oxygen atoms of EG ligands, and the edges of octahedron then connect into metal-oxygen sheets.


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The typical strategy to fabricate hierarchical-structured flowerlike MgO/C nanocomposites is schematically depicted in Scheme 1. Firstly, the Mg-containing coordination polymer, Mg-EG complex intermediate, was prepared via ethylene glycol (EG)-mediated self-assembly process. EG is a good cross-linking reagent and has strong chelating ability with metal ions.39 EGmediated solvothermal method has been successfully utilized to prepare various noble metal nanocrystallites,40

metal

alkoxides

and

the

corresponding

derived

metal

oxide

nanomaterials.37,39,41-47 In the present work, by treating Mg salt in the presence of EG under solvothermal condition, Mg-EG complex with hierarchical 3D flowerlike morphology can be obtained through the coordination of EG with Mg ions and the subsequent oligomerization. In the second step, the Mg-EG complex intermediate, which served as both sacrificial template and precursor, was subjected to a high-temperature pyrolysis process under an inert gas atmosphere. During the thermolysis, the inorganic Mg species incorporated in the coordination polymer was converted to MgO nanocrystallites, and at the same time the organic ligands were transformed into carbon species via chemical decomposition. In this way, the carbon can be embedded in situ among the newly formed MgO nanocrystallites, restricting the latter from further growing or aggregating. Besides, the thermolysis was accompanied by decomposition of organic moieties as well as the release of gaseous products and moisture, leaving behind numerous nanopores and interstitials, thus generating highly porous structures with unchanged 3D flowerlike morphology comprising MgO and carbon. 3.2. Formation and characterization of Mg-EG complex precursor. SEM (Figure S1) and TEM investigations (Figure 1) show that the as-synthesized Mg-EG complex precursor is uniform flowerlike spheres formed by a large number of twisted thin nanosheets connecting with each other. The average diameter of these spheres is approximately


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500 nm. The EDX analysis (Figure S2a) demonstrates the Mg-EG complex is composed of magnesium, carbon and oxygen, a chemical composition that agrees well with chemical composition of magnesium glycolate.

Figure 1. (a, b) TEM images of flowerlike spheres of Mg-EG complex precursor. The FTIR spectrum of Mg-EG complex in Figure S2b affirms the presence of the coordination interaction between EG ligand and the centre Mg ions. The powder X-ray diffraction (XRD) pattern (Figure S2c) shows a strong low-angle reflection at around 10.1°, which is characteristic of stacked metal-oxygen sheets separated by the bonded alcoholate anions (Scheme 1) commonly observed in layered metal-EG coordination polymers.37,48,49 On the basis of the lowangle diffraction peak, the interlayer distance of Mg-EG complex is calculated to be 0.87 nm. The TGA curve of Mg-EG complex (Figure S2d) exhibits an obvious weight loss step in the temperatures ranging from 300 to 500 oC, which can be ascribed to the thermal decomposition of the organic ligands in the Mg-EG complex precursor. Besides, mass spectrometry (MS) technique was applied to monitor this thermal decomposition process of Mg-EG complex. According to the mass ion detection (Figure S3), the gaseous products released during carbonization include H2O (m/z = 17), CO2 (m/z = 16), ethanol (m/z = 46), methanol (m/z = 32), and acetaldehyde (m/z = 26).


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3.3. Fabrication and characterization of MgO/C nanocomposites.

Figure 2. XRD patterns of spherical flowerlike MgO/C nanocomposites prepared from different pyrolysis temperatures.


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Figure 3. (a) SEM, (b-e) TEM, (f) HRTEM images and (g) EDX elemental mapping of flowerlike MgO/C-550 nanocomposite. Based on the TGA result, we chose three different temperatures (500, 550 and 600 oC) to pyrolyze Mg-EG complex precursor. The pyrolysis of Mg-EG complex was performed at the designed temperature by heating with a ramping rate of 10 oC/min in an argon flow. After maintaining at final temperature for 4 h, the original white precursor was converted into a black powder due to the formation of carbon phase (Scheme 1). The XRD patterns of the pyrolysis products (Figure 2) display the characteristic diffractions which can be indexed to the cubic symmetry of MgO phase (JCPDS card no. 75-0447). Due to small-sized MgO crystallites, the diffraction peaks are rather broad. The Debye-Scherrer equation was applied to estimate the crystalline size of MgO by using the (200) diffraction peak and the crystalline sizes of MgO in the MgO/C-500, MgO/C-550 and MgO/C-600 were calculated to be 3.0, 3.3 and 3.4 nm, respectively. The TEM images (Figure 3, S4 and S5) show that all the thermolyzed products successfully retain their flowerlike hierarchical architecture of the original Mg-EG complex precursor. The petal-like building blocks are highly porous ultrathin nanosheets with thickness below 5 nm and are constructed from numerous MgO crystallites. From the TEM images in high magnification (Figure 3d, 3e, S4d and S5d), the particle size of MgO crystallites is indeed in the range of only 2−3 nm, consisting wit h the XRD results. A representative HRTEM image taken from the nanosheet (Figure 3f) shows a clear lattice fringe spacing of 0.21 nm, which corresponds to the spacing of the (200) planes of MgO, confirming the presence of nanosized MgO in the MgO/C product. The EDX elemental mapping of flowerlike MgO/C nanocomposites (Figure 3g and S6) indicate the chemical composition of magnesium, oxygen and carbon for all the samples. And all


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of these elements are uniformly dispersed throughout the sample, verifying the coexistence and homogeneous distribution of MgO nanocrystallites and carbon species. Besides, the carbon contents in the MgO/C nanocomposites were estimated using CHN elemental analysis. As listed in Table 1, the carbon content continuously decreases with increasing pyrolysis temperature (10.58, 10.21 and 9.66 wt% for MgO/C-500, MgO/C-550 and MgO/C-600, respectively) All these analytical results demonstrate the successful synthesis of flowerlike MgO/C nanocomposites through this pyrolysis process.

Figure 4. Nitrogen adsorption–desorption isotherms of MgO/C nanocomposites prepared from different pyrolysis temperatures.


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Table 1. The texture features and elemental compositions of the solid samples. BET surface

Pore volume a

Crystallite size

area (m /g)

(cm /g)

of MgO (nm)

Carbon (wt%) c

MgO/C-500

290.4

0.79

3.0

10.58

MgO/C-550

294.6

0.94

3.3

10.21

MgO/C-600

333.4

0.96

3.4

9.66

Flowerlike pure MgO

64.5

0.19

13.2

-

Sample

a

2

3

b

The pore volume was calculated at P/P0 = 0.9754. b The crystal size of MgO was calculated

from the (200) diffraction peak of XRD patterns using the Scherrer equation. c Carbon content was determined by CHN elemental analysis. In order to assess textural properties of the MgO/C nanocomposites obtained at different pyrolysis temperatures, nitrogen adsorption−desorption measurement was carried out. As shown in Figure 4, all three MgO/C samples display type IV isotherms with an H3 type hysteresis loop, suggesting the presence of the slit-shaped mesoporous structure. As summarized in Table 1, all the MgO/C samples have large BET surface areas and total pore volumes (294.6 m2/g and 0.79 cm3/g for MgO/C-500, 290.4 m2/g and 0.94 cm3/g for MgO/C-550, 333.4 m2/g and 0.96 cm3/g for MgO/C-600, respectively). In addition, the pore size distribution was further analysed using the NLDFT method. As displayed in Figure S7, all the MgO/C nanocomposites possess pores with wide size distribution, ranging from micropores to mesopores. It is anticipated that the excellent textural properties in the flowerlike MgO/C nanocomposite spheres would greatly facilitate the mass transportation and diffusion processes, concerning their CO2 capture application.


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3.4. CO2 capture performance of MgO/C nanocomposites.

Figure 5. CO2 sorption capacities of solid sorbents studied in this work at (a) 27 oC, 1 bar CO2 and at (b) 27 oC, 0.15 bar CO2. The CO2 capture kinetics of three representative MgO/C nanocomposites (MgO/C-500, MgO/C-550 and MgO/C-600) at (c) 27 oC, 1 bar CO2 and at (d) 27 oC, 0.15 bar CO2. As

revealed

above,

the

biphasic

MgO/C

nanocomposites

hold

many appealing

physicochemical features and they may serve as a promising candidate for CO2 capture. To test our hypothesis, the MgO/C nanocomposites were first exposed to 1 bar CO2 at 27 oC. As reported in Figure 5a, indeed, all three MgO/C samples give superior CO2 capture performance (27.6−30.9 wt%). Remarkably, MgO/C-550 shows the highest sorption capacity up to 30.9 wt%, which is about 15-fold higher than that of the commercial MgO powder (whose sorption capacity


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is only 2.0 wt%). To the best of our knowledge, the sorption capacity of MgO/C-550 is the highest recorded value reported to date among all the MgO-based sorbents under similar operating conditions.3,25,32,36,50 For a closer comparison, other MgO-based sorbents reported in the literature are also listed in Table S1. Furthermore, it is worth mentioning that our MgO/C nanocomposite is even comparable to the state-of-the-art MOFs-based adsorbent, Mg-MOF-74 (also known as CPO-27-Mg or Mg/DOBDC).22,51,52 Besides, it is found that when the pyrolysis temperature for Mg-EG is too high (e.g., 700 and 800 oC), the carbon phase is almost burned out, and the obtained products show much inferior CO2 uptake performances (14.90 wt% and 11.70 wt% at 700 and 800 oC, respectively). Furthermore, to investigate their feasibility in practical application, the CO2 trapping experiments were also carried out by exposing the above MgO/C to 15 vol% CO2 in N2 at 1 bar and 27 oC, which mimics dry flue gas from the power plant. As displayed in Figure 5b, the MgO/C nanocomposites are still remarkably efficient −21.0 (19.1 wt%) even under the dilute CO2 condition. The highest CO2 uptake was again attained for MgO/C-550 (21.0 wt%), which is about 18 times higher than that of commercial MgO (1.1 wt%) and significantly surpass the previously reported high-performance MgO-based sorbents under similar measuring conditions (See Table S1 for a detailed comparison).3,30,53,54 The CO2 sorption kinetics of MgO/C nanocomposites at 27 oC under 1 bar CO2 as well as under conditions mimicking flue gas (27 oC, 0.15 bar CO2) were also investigated. As reported in Figure 5c and d, the adsorption consists of two stages: an initial fast stage where the uptake rises rapidly to > 10 wt%, followed by a slow stage, which continues beyond t > 2 h. Such a two-stage behavior is typical for CO2 uptake experiments using TGA technique.55 Here, the fast stage corresponds to rapid surface reactions, the rate of which is often limited by external mass transfer whereas the transition into the slow phase represents a point where the resistance to the diffusion


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of CO2 through the partially spent sorbent becomes substantial. In fact, the extent of the fast phase is governed by factors such as surface area, meso- or micro-porosity, and the availability of surface active sites. The CO2 uptake by our MgO/C nanocomposites during the first stage is significantly higher other MgO-based sorbents reported in the literature.28 Therefore, we can deduce that there are much more active sites for CO2 sorption in our MgO/C samples from these kinetic data.

Figure 6. TEM images (a, b) of flowerlike phase pure MgO sample (in the form of spherical aggregates). It is noteworthy that the in situ generated carbon species in the MgO/C nanocomposites plays a crucial role in their extraordinary performance for CO2 uptake. To elucidate this point further, a series of control experiments were conducted. For example, we also prepared a pure phase MgO sample in similar 3D flowerlike hierarchical structure, while without any carbon inclusion, and studied its CO2 uptake property. The pure MgO sample was synthesized by directly calcining the Mg-EG complex precursor under air atmosphere instead of an argon flow. The resultant product has a white color, different from the black color of MgO/C nanocomposites. The MgO product was also systematically characterized with TEM, XRD and nitrogen sorption measurement. As


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shown in Figure 6 and S8, the sample also retains the flowerlike morphology, but the petal-like building blocks are constructed with highly crystalline interconnected MgO nanocrystallites with an average particle size of around 14 nm. Note that owing to the heat treatment in air atmosphere, the particle size of the MgO nanocrystallites is much larger (compared to about 3 nm in inert gas; Figure 3e, S4d and S5d). The XRD diffraction peaks of this sample can be indexed solely to MgO phase (Figure S9a). According to the Debye-Scherrer equation, the average crystalline size of MgO is estimated to be 13.2 nm, which agrees well with direct TEM observation. Furthermore, nitrogen sorption measurement (Figure S9b and S9c) reveals that the BET surface area and pore volume of the flowerlike MgO (64.5 m2/g and 0.19 cm3/g, respectively) are much lower than those of MgO/C nanocomposites. The CO2 uptake by the pure MgO is 7.48 wt% at 27 oC, 1 bar CO2 and 3.30 wt% at 27 oC, 0.15 bar CO2 (Figure 5a and b), respectively. Although its uptake values are higher than those of commercial MgO powder, the capture performance of this pure MgO sample is incomparable to those of the MgO/C nanocomposites (i.e., 27.6−30.9 wt% and 19.1−21.0 wt% in 1 bar and 0. 15 bar CO2, respectively; see Figure 5a and b). To further investigate the contribution of carbon to the excellent CO2 sorption performance of MgO/C nanocomposite, the pure carbon phase was obtained by acid treatment of MgO/C-550 in order to etch away MgO. From the TEM images (Figure S10), the flowerlike morphology collapses completely, as the small mass fraction of carbon hardly sustain the overall structure after MgO dissolution. The as-obtained pure carbon sample could only uptake CO2 with as low as 2.80 wt% of capacity at 27 oC, 1 bar CO2, indicating the carbon phase alone was unable to adsorb such large amount of CO2. It appears that the outstanding performance of MgO/C nanocomposites originates from their unique structural features. In particular, the benefit of nanosized MgO and the role of embedded


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carbon should be considered. During the thermal conversion of Mg-EG complex precursor in inert gas atmosphere, the in situ generated carbon could restrict the growth of coexisting MgO nanocrystallites and thus limit their particle size in the nanoscale (at about 3 nm in size), as evidenced in the TEM and XRD studies. Compared with the large-sized MgO particles, the ultrafine nanocrystallites possess much more surface active sorption sites for CO2 capture, leading to high efficient utilization of MgO phase. Meanwhile, the in situ generated carbon species, which homogeneously distributes in the hybrids, can serve as a protectant to separate and prevent MgO nanocrystallites from agglomeration. More importantly, owing to the optimal trade-off balance among the conversion of Mg ions to crystalline MgO, the pyrolysis of organic ligands to carbon and the evaporation of the organic moieties to generate porous nanostructure, the transformation of the Mg-EG precursor into the MgO/C product under the inert gas atmosphere can successfully retain the 3D flowerlike architecture (of the original Mg-EG complex precursor) with large surface area and rich nanopores, which greatly facilitate gas diffusion and enhance CO2 uptake ability. The CO2 capture capacity of MgO/C nanocomposites at different operating temperatures was also investigated. As observed in Figure S11, the capacity of MgO/C-550 decreases with increasing sorption temperature (27, 50, 100, 150, and 200

o

C). This phenomenon is

understandable since it has been known that both physical adsorption and chemical adsorption of CO2 are exothermic processes. Despite the decrease in sorption, the MgO/C-550 nanocomposite still maintains a reasonably high CO2 uptake capacity even at 200 oC (8.33 wt%), which is also much higher than those of the pure MgO (Figure S12), demonstrating the versatility of MgO/C550 for application. Similar trends are also observed for other two samples (MgO/C-500 and


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MgO/C-600; Figure S11). Thus, these MgO/C nanocomposites can be considered as effective sorbents for CO2 capture over a broad range of working temperature. In addition to high CO2 capturing capacity, rapid CO2 uptake and wide working temperature range, long-term stability and recyclability of CO2 trappers are also key criteria for their application, as any useable sorbents must be able to withstand long-term cyclic operation. Herein, we selected the MgO/C-550 as a testing sample. As presented in Figure 7a, the capture capacity of this sample only slightly drops over 14 consecutive cycles. Of note, although the presence of loss of capacity in the cycling test, the stability of our MgO/C-550 is still favorably comparable to those of the state-of-the-art MgO-based sorbents under similar testing conditions,3,25,30,31 elucidating its reasonably good recyclability for practical application. Besides, TEM images of the used MgO/C-550 (Figure 7b and c) reveal that the flowerlike morphology and the porous structure of the sample remain largely intact even after 14 repeated tests, further affirming the chemical and structural stability of the MgO/C nanocomposite.


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Figure 7. (a) CO2 sorption-desorption cyclic performance of MgO/C-550 nanocomposite. Testing condition: 27 oC, 1 bar CO2 for 2 h of sorption. (b, c) TEM images of the spent MgO/C-550 nanocomposite after 14 cycles of adsorption-desorption operations. 3.5. CO2 capture mechanism of MgO/C nanocomposites.


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Figure 8. Three different types of CO2 adsorption modes on MgO: bicarbonate, unidentate carbonate, and bidentate carbonate species.

Figure 9. The DRIFT spectra of CO2 adsorbed on (a, c) MgO/C-550 composite and (b, d) pure MgO control upon desorption under N2 purge at increasing temperature. With the encouragingly high-performance MgO/C composites in hand, we further carried out the in-situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFT) studies to identify the nature of the active basic sites available and CO2 adsorption modes on the solid sorbents. All the sorbents were preadsorbed CO2 at room temperature and then desorbed at


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increasing temperature under N2 flowing, during which DRIFT spectra were recorded. From the spectra and combined with the previous reported accounts,36,53,56,57 it is revealed that at least three different CO2 adsorption modes are present in the sample (Figure 8): bicarbonate, unidentate carbonate, and bidentate carbonate. Specifically, the peaks at around 1221 and 1665 cm−1 can be assigned to bicarbonate species, the formation of which involves the interaction with surface hydroxyl groups on the sorbent. Moreover, the bands identified in the broad range of 1380−1570 cm−1 could be attributed to the unidentate carbonate species. The formation of unidentate carbonate requires surface isolated O2− ions, i.e., low-coordination edge- and cornerlocated basic O2− on the crystallites. In addition, the peaks at around 1315 and 1648 cm−1 can be ascribed to the bidentate carbonate species, and its formation involves the participation of Lewis acid-Brønsted base pair (i.e., Mg2+-O2− pair site) on the sample. As for the DRIFT spectra of MgO/C nanocomposites, apart from the bands corresponding to the carbonate species, other peaks are also detected: peaks at around 2800−3100, 1594 and 1246 cm

−1

are assigned to C−H,

C=C (or C=O) and −O C stretching vibrations of the amorphous carbon component in the composite, respectively. From the DRIFT spectra recorded with elevated temperature (from 27 to 400 oC), obvious evolution of peaks is demonstrated. In the case of pure MgO control (Figure 9b and d), the peaks (ca. 1221 and 1665 cm−1) assigned to bicarbonate species disappear while the peak (ca. 3745 cm−1) attributed to hydroxyl groups emerges as the temperature increases to 400 o

C, indicating the bicarbonate species was relatively unstable, resulting to easily desorption from

surface hydroxyl groups. In contrast, the bands of unidentate and bidentate carbonate species are still remained, although their amounts dramatically declined upon the successive thermal treatment. In the cases of MgO/C nanocomposites (Figure 9a, 9c and S13), the bands attributed to the amorphous carbon component retained well, demonstrating the relative stability of carbon


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phase. For the peaks assigned to carbonate group species, similar trends with pure MgO control are observed (Figure 9c, S13c and S13d), further revealing the more labile property of bicarbonate, which can be destroyed at relatively low temperatures, and the more stability of both unidentate and bidentate carbonate species although along with slowly breakdown at an increasing temperature.

Figure 10. CO2-TPD profiles of the three representative MgO/C nanocomposites (MgO/C500, MgO/C-550 and MgO/C-600). Furthermore, surface basic properties of MgO/C nanocomposites were also probed by using CO2-TPD technique. Combined with the DRIFT characterization results, the TPD profiles of the four samples in Figure 10 can be roughly deconvoluted into three desorption peaks: a low temperature peak at around 90 oC ascribed to the bicarbonates desorbed from surface hydroxyl groups, a middle-temperature peak at around 135 oC originated from unidentate carbonates


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released from surface low-coordination O2− sites, and a high-temperature peak at 238 oC attributed to bidentate carbonates released from Mg2+-O2− pair sites.53,57,58 More interestingly, it is noted that the MgO/C from different pyrolysis temperatures during thermal conversion of MgEG precursor can exhibit pronouncedly different TPD profiles: the intensity of low temperature peak decreases while that of high-temperature peak increases with elevating of the pyrolysis temperature. This result can be interpreted as that pyrolyzing of Mg-EG precursor at relatively low temperature (i.e., 500 oC) is beneficial to generate MgO with abundant surface hydroxyl groups and crystalline defects (that is, surface low-coordination O2− sites). While the increase of pyrolysis temperature would lead to the removal of surface hydroxyl groups as well as the defect sites, and instead, produce a more thermally stable structure possessing higher concentration of strong-strength Mg2+-O2− pair sites. In other words, the surface basic property of MgO/C nanocomposite can be finely engineered through regulating the annealing preparation temperature, and thus leading to the modification of their corresponding CO2 sorption performance, like MgO/C-T (T = 500, 550 and 600 oC) nanocomposites reported in this study. Overall, based on all our experimental results here, MgO/C composite is a type of excellent sorbent with exceptionally high capacity and stability. The outstanding performance of the MgO/C nanocomposites in the capture of CO2 can be attributed to the following factors: (i) the flowerlike morphology, porous nanosheets, large surface area and pore volume are conducive to the facile mass transfer and diffusion of CO2; (ii) highly dispersed nanoscale MgO crystallites (about 3 nm in size) provide more surface adsorption sites including surface hydroxyl groups, low-coordination edge-/corner-located basic O2−, and Mg2+-O2− pair sites to efficiently interact with CO2; and (iii) more importantly, the carbon matrix which is in situ generated during pyrolysis process, albeit in a small mass fraction, acts as spatial protectant to separate and


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prevent MgO nanocrystallites from growth as well as agglomeration, further enhancing the full exposure of adsorption active sites of MgO nanocrystallites on the one hand and improving the durability of the sorbent on the other hand.

4. Conclusions In summary, we have developed a novel approach to synthesize 3D hierarchical-structured porous MgO/C nanocomposites using flowerlike Mg-containing coordination polymer as a solid precursor via a combination of polyol-mediated self-assembly process with subsequent pyrolysis treatment. The optimized MgO/C nanocomposite exhibits remarkable CO2 capture capacities up to 30.9 wt% (at 27 oC, 1 bar CO2) and 21.0 wt% under the simulated flue gas; a superior performance has been achieved, which is the best among all the MgO-based sorbents reported to date and even comparable to the state-of-the-art MOFs-based adsorbents. In addition to the facile synthetic procedure, high capture capacity and fast sorption rate, the as-obtained MgO/C nanocomposites are effective and retain their high performance over a wide range of working temperature (27−200

o

C). Furthermore, they are highly durable, showing good stability in

successive cycles. The excellent performance can be attributed to the special physicochemical features of MgO/C, such as flowerlike hierarchical architecture, thin nanosheets (below 5 nm in thickness) with rich porous structure, large specific surface area, highly distributed ultrafine MgO nanocrystallites, along with the in situ generated carbon species which can serve as protectant to separate and prevent nano-crystalline MgO from agglomeration. Considering a wide range of choices on metal glycolate precursors, this synthetic strategy can be further extended to other metal oxide/carbon systems with targeted nanostructures and compositions for


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a multitude of applications at low-cost including CO2 capture and utilization, heterogeneous catalysis and energy conversion/storage.

ASSOCIATED CONTENT Supporting Information. Additional SEM images, TEM images, EDX patterns, XRD patterns, DRIFT spectra, nitrogen adsorption/desorption isotherms of the samples. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The authors gratefully acknowledge the financial support provided by the Ministry of Education, Singapore, NUS, and GSK Singapore. This project is also partially funded by the National Research Foundation (NRF), Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program.

REFERENCES (1) Mikkelsen, M.; Jorgensen, M.; Krebs, F. C. The Teraton Challenge. A Review of Fixation and Transformation of Carbon Dioxide. Energy Environ. Sci. 2010, 3, 43-81.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(2) Wang, J.; Huang, L.; Yang, R.; Zhang, Z.; Wu, J.; Gao, Y.; Wang, Q.; O'Hare, D.; Zhong, Z. Recent Advances in Solid Sorbents for CO2 Capture and New Development trends. Energy Environ. Sci. 2014, 7, 3478-3518. (3) Vitillo, J. G. Magnesium-Based Systems for Carbon Dioxide Capture, Storage and Recycling: from Leaves to Synthetic Nanostructured Materials. RSC Adv. 2015, 5, 36192-36239. (4) Haszeldine, R. S. Carbon Capture and Storage: How Green Can Black Be? Science 2009, 325, 1647-1652. (5) Boot-Handford, M. E.; Abanades, J. C.; Anthony, E. J.; Blunt, M. J.; Brandani, S.; Mac Dowell, N.; Fernandez, J. R.; Ferrari, M.-C.; Gross, R.; Hallett, J. P.; Haszeldine, R. S.; Heptonstall, P.; Lyngfelt, A.; Makuch, Z.; Mangano, E.; Porter, R. T. J.; Pourkashanian, M.; Rochelle, G. T.; Shah, N.; Yao, J. G.; Fennell, P. S. Carbon Capture and Storage Update. Energy Environ. Sci. 2014, 7, 130-189. (6) Kenarsari, S. D.; Yang, D.; Jiang, G.; Zhang, S.; Wang, J.; Russell, A. G.; Wei, Q.; Fan, M. Review of Recent Advances in Carbon Dioxide Separation and Capture. RSC Adv. 2013, 3, 22739-22773. (7) Li, L.; Zhao, N.; Wei, W.; Sun, Y. A Review of Research Progress on CO2 Capture, Storage, and Utilization in Chinese Academy of Sciences. Fuel 2013, 108, 112-130. (8) Li, B.; Duan, Y.; Luebke, D.; Morreale, B. Advances in CO2 Capture Technology: A Patent Review. Appl. Energy 2013, 102, 1439-1447. (9) Choi, S.; Drese, J. H.; Jones, C. W. Adsorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources. ChemSusChem 2009, 2, 796-854. (10) D'Alessandro, D. M.; Smit, B.; Long, J. R. Carbon Dioxide Capture: Prospects for New Materials. Angew. Chem. Int. Ed. 2010, 49, 6058-6082.


28

Page 29 of 35

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


(11) Hedin, N.; Chen, L.; Laaksonen, A. Sorbents for CO2 Capture from Flue Gas-Aspects from Materials and Theoretical Chemistry. Nanoscale 2010, 2, 1819-1841. (12) 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, 1438-1463. (13) Sreenivasulu, B.; Sreedhar, I.; Suresh, P.; Raghavan, K. V. Development Trends in Porous Adsorbents for Carbon Capture. Environ. Sci. Technol. 2015, 49, 12641-12661. (14) Merel, J.; Clausse, M.; Meunier, F. Experimental Investigation on CO2 Post−Combustion Capture by Indirect Thermal Swing Adsorption Using 13X and 5A Zeolites. Ind. Eng. Chem. Res. 2008, 47, 209-215. (15) Zhong, M.; Natesakhawat, S.; Baltrus, J. P.; Luebke, D.; Nulwala, H.; Matyjaszewski, K.; Kowalewski, T. Copolymer-Templated Nitrogen-Enriched Porous Nanocarbons for CO2 Capture. Chem. Commun. 2012, 48, 11516-11518. (16) Marco-Lozar, J. P.; Kunowsky, M.; Suárez-García, F.; Linares-Solano, A. Sorbent Design for CO2 Capture under Different Flue Gas Conditions. Carbon 2014, 72, 125-134. (17) Bollini, P.; Didas, S. A.; Jones, C. W. Amine-Oxide Hybrid Materials for Acid Gas Separations. J. Mater. Chem. 2011, 21, 15100-15120. (18) Qi, G.; Fu, L.; Giannelis, E. P. Sponges with Covalently Tethered Amines for HighEfficiency Carbon Capture. Nat Commun 2014, 5, 5796-5802. (19) Du, N.; Park, H. B.; Robertson, G. P.; Dal-Cin, M. M.; Visser, T.; Scoles, L.; Guiver, M. D. Polymer Nanosieve Membranes for CO2-Capture Applications. Nat Mater 2011, 10, 372-375. (20) Gao, X.; Zou, X.; Ma, H.; Meng, S.; Zhu, G. Highly Selective and Permeable Porous Organic Framework Membrane for CO2 Capture. Adv. Mater. 2014, 26, 3644-3648.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 35

(21) Britt, D.; Furukawa, H.; Wang, B.; Glover, T. G.; Yaghi, O. M. Highly Efficient Separation of Carbon Dioxide by a Metal-Organic Framework Replete with Open Metal Sites. PNAS 2009, 106, 20637-20640. (22) 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, 112, 724-781. (23) Li, B.; Wang, H.; Chen, B. Microporous Metal–Organic Frameworks for Gas Separation. Chem. Asian J. 2014, 9, 1474-1498. (24) Song, Q.; Liu, W.; Bohn, C. D.; Harper, R. N.; Sivaniah, E.; Scott, S. A.; Dennis, J. S. A High Performance Oxygen Storage Material for Chemical Looping Processes with CO2 Capture. Energy Environ. Sci. 2013, 6, 288-298. (25) Wang, S.; Yan, S.; Ma, X.; Gong, J. Recent Advances in Capture of Carbon Dioxide Using Alkali-Metal-Based Oxides. Energy Environ. Sci. 2011, 4, 3805-3819. (26) Kierzkowska, A. M.; Pacciani, R.; Müller, C. R. CaO-Based CO2 Sorbents: From Fundamentals to the Development of New, Highly Effective Materials. ChemSusChem 2013, 6, 1130-1148. (27) Sanna, A.; Uibu, M.; Caramanna, G.; Kuusik, R.; Maroto-Valer, M. M. A Review of Mineral Carbonation Technologies to Sequester CO2. Chem. Soc. Rev. 2014, 43, 8049-8080. (28) Lee, S. C.; Chae, H. J.; Lee, S. J.; Choi, B. Y.; Yi, C. K.; Lee, J. B.; Ryu, C. K.; Kim, J. C. Development of Regenerable MgO-Based Sorbent Promoted with K2CO3 for CO2 Capture at Low Temperatures. Environ. Sci. Technol. 2008, 42, 2736-2741.


30

Page 31 of 35

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


(29) Bian, S.-W.; Baltrusaitis, J.; Galhotra, P.; Grassian, V. H. A Template-free, Thermal Decomposition Method to Synthesize Mesoporous MgO with A Nanocrystalline Framework and Its Application in Carbon Dioxide Adsorption. J. Mater. Chem. 2010, 20, 8705-8710. (30) Kim, T. K.; Lee, K. J.; Cheon, J. Y.; Lee, J. H.; Joo, S. H.; Moon, H. R. Nanoporous Metal Oxides with Tunable and Nanocrystalline Frameworks via Conversion of Metal–Organic Frameworks. J. Am. Chem. Soc. 2013, 135, 8940-8946. (31) Liu, W.-J.; Jiang, H.; Tian, K.; Ding, Y.-W.; Yu, H.-Q. Mesoporous Carbon Stabilized MgO Nanoparticles Synthesized by Pyrolysis of MgCl2 Preloaded Waste Biomass for Highly Efficient CO2 Capture. Environ. Sci. Technol. 2013, 47, 9397-9403. (32) Han, K. K.; Zhou, Y.; Lin, W. G.; Zhu, J. H. One-Pot Synthesis of Foam-like Magnesia and its Performance in CO2 Adsorption. Microporous Mesoporous Mater. 2013, 169, 112-119. (33) Liu, M.; Vogt, C.; Chaffee, A. L.; Chang, S. L. Y. Nanoscale Structural Investigation of Cs2CO3-Doped MgO Sorbent for CO2 Capture at Moderate Temperature. J. Phys. Chem. C 2013, 117, 17514-17520. (34) Harada, T.; Simeon, F.; Hamad, E. Z.; Hatton, T. A. Alkali Metal Nitrate-Promoted HighCapacity MgO Adsorbents for Regenerable CO2 Capture at Moderate Temperatures. Chem. Mater. 2015, 27, 1943-1949. (35) Bhagiyalakshmi, M.; Lee, J. Y.; Jang, H. T. Synthesis of Mesoporous Magnesium Oxide: Its Application to CO2 Chemisorption. Int. J. Greenhouse Gas Control 2010, 4, 51-56. (36) Ding, Y.-D.; Song, G.; Zhu, X.; Chen, R.; Liao, Q. Synthesizing MgO with a High Specific Surface for Carbon Dioxide Adsorption. RSC Adv. 2015, 5, 30929-30935.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 35

(37) Bain, S.-W.; Ma, Z.; Cui, Z.-M.; Zhang, L.-S.; Niu, F.; Song, W.-G. Synthesis of Micrometer-Sized Nanostructured Magnesium Oxide and Its High Catalytic Activity in the Claisen−Schmidt Condensation Reaction. J. Phys. Chem. C 2008, 112, 11340-11344. (38) Yang, S.; Huang, P.; Peng, L.; Cao, C.; Zhu, Y.; Wei, F.; Sun, Y.; Song, W. Hierarchical Flowerlike Magnesium Oxide Hollow Spheres with Extremely High Surface Area for Adsorption and Catalysis. J. Mater. Chem. A 2016, 4, 400-406. (39) Jiang, X.; Wang, Y.; Herricks, T.; Xia, Y. Ethylene Glycol-Mediated Synthesis of Metal Oxide Nanowires. J. Mater. Chem. 2004, 14, 695-703. (40) Sun, Y.; Xia, Y. Shape-Controlled Synthesis of Gold and Silver Nanoparticles. Science 2002, 298, 2176-2179. (41) Zhong, L. S.; Hu, J. S.; Liang, H. P.; Cao, A. M.; Song, W. G.; Wan, L. J. Self-Assembled 3D Flowerlike Iron Oxide Nanostructures and Their Application in Water Treatment. Adv. Mater. 2006, 18, 2426-2431. (42) Zhong, L.-S.; Hu, J.-S.; Cao, A.-M.; Liu, Q.; Song, W.-G.; Wan, L.-J. 3D Flowerlike Ceria Micro/Nanocomposite Structure and Its Application for Water Treatment and CO Removal. Chem. Mater. 2007, 19, 1648-1655. (43) Zhu, T.; Chen, J. S.; Lou, X. W. Highly Efficient Removal of Organic Dyes from Waste Water Using Hierarchical NiO Spheres with High Surface Area. J. Phys. Chem. C 2012, 116, 6873-6878. (44) Zhao, J.; Liu, Y.; Fan, M.; Yuan, L.; Zou, X. From Solid-state Metal Alkoxides to Nanostructured Oxides: A Precursor-Directed Synthetic Route to Functional Inorganic Nanomaterials. Inorg. Chem. Front. 2015, 2, 198-212.


32

Page 33 of 35

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


(45) Su, D. W.; Dou, S. X.; Wang, G. X. Hierarchical Orthorhombic V2O5 Hollow Nanospheres as High Performance Cathode Materials for Sodium-ion Batteries. J. Mater. Chem. A 2014, 2, 11185-11194. (46) Zhang, G.; Lou, X. W. General Synthesis of Multi-Shelled Mixed Metal Oxide Hollow Spheres with Superior Lithium Storage Properties. Angew. Chem. Int. Ed. 2014, 53, 9041-9044. (47) Guan, B. Y.; Yu, L.; Wang, X.; Song, S.; Lou, X. W. Formation of Onion-Like NiCo2S4 Particles via Sequential Ion-Exchange for Hybrid Supercapacitors. Adv. Mater. 2017, 29, 1605051-n/a. (48) Larcher, D.; Sudant, G.; Patrice, R.; Tarascon, J. M. Some Insights on the Use of PolyolsBased Metal Alkoxides Powders as Precursors for Tailored Metal-Oxides Particles. Chem. Mater. 2003, 15, 3543-3551. (49) Cao, A.-M.; Hu, J.-S.; Liang, H.-P.; Wan, L.-J. Self-Assembled Vanadium Pentoxide (V2O5) Hollow Microspheres from Nanorods and Their Application in Lithium-Ion Batteries. Angew. Chem. Int. Ed. 2005, 44, 4391-4395. (50) Bhagiyalakshmi, M.; Hemalatha, P.; Ganesh, M.; Mei, P. M.; Jang, H. T. A Direct Synthesis of Mesoporous Carbon Supported MgO Sorbent for CO2 Capture. Fuel 2011, 90, 1662-1667. (51) Caskey, S. R.; Wong-Foy, A. G.; Matzger, A. J. Dramatic Tuning of Carbon Dioxide Uptake via Metal Substitution in a Coordination Polymer with Cylindrical Pores. J. Am. Chem. Soc. 2008, 130, 10870-10871. (52) Zhang, Z.; Yao, Z.-Z.; Xiang, S.; Chen, B. Perspective of Microporous Metal-Organic Frameworks for CO2 Capture and Separation. Energy Environ. Sci. 2014, 7, 2868-2899. (53) Jiao, X.; Li, L.; Zhao, N.; Xiao, F.; Wei, W. Synthesis and Low-Temperature CO2 Capture Properties of a Novel Mg–Zr Solid Sorbent. Energy & Fuels 2013, 27, 5407-5415.


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(54) Ruminski, A. M.; Jeon, K.-J.; Urban, J. J. Size-Dependent CO2 Capture in Chemically Synthesized Magnesium Oxide Nanocrystals. J. Mater. Chem. 2011, 21, 11486-11491. (55) Liu, W.; González, B.; Dunstan, M. T.; Saquib Sultan, D.; Pavan, A.; Ling, C. D.; Grey, C. P.; Dennis, J. S. Structural Evolution in Synthetic, Ca-based Sorbents for Carbon Capture. Chem. Eng. Sci. 2016, 139, 15-26. (56) Li, Y. Y.; Wan, M. M.; Lin, W. G.; Wang, Y.; Zhu, J. H. A Novel Porous MgO Sorbent Fabricated Through Carbon Insertion. J. Mater. Chem. A 2014, 2, 12014-12022. (57) Cornu, D.; Guesmi, H.; Krafft, J.-M.; Lauron-Pernot, H. Lewis Acido-Basic Interactions between CO2 and MgO Surface: DFT and DRIFT Approaches. J. Phys. Chem. C 2012, 116, 6645-6654. (58) Li, Y. Y.; Han, K. K.; Lin, W. G.; Wan, M. M.; Wang, Y.; Zhu, J. H. Fabrication of a New MgO/C Sorbent for CO2 Capture at Elevated Temperature. J. Mater. Chem. A 2013, 1, 1291912925.


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C Nanocomposite from Hierarchical

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