Stabilization of Layered Double Oxide in Hybrid Matrix of Graphene

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Stabilization of Layered Double Oxide in Hybrid Matrix of Graphene and Layered Metal Oxide Nanosheets: An Effective Way to Explore Efficient CO Adsorbent 2

Haslinda Binti Mohd Sidek, Yun Kyung Jo, In Young Kim, and Seong-Ju Hwang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b08065 • Publication Date (Web): 30 Sep 2016 Downloaded from http://pubs.acs.org on October 4, 2016

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The Journal of Physical Chemistry

Revised to Journal of Physical Chemistry C as a regular article (Sep. 30, 2016) (MS. No.: jp-2016-080656)

Stabilization of Layered Double Oxide in Hybrid Matrix of Graphene and Layered Metal Oxide Nanosheets: An Effective Way to Explore Efficient CO2 Adsorbent Haslinda Binti Mohd Sidek, Yun Kyung Jo, In Young Kim, and Seong-Ju Hwang* Department of Chemistry and Nanoscience, College of Natural Sciences, Ewha Womans University, Seoul 03760, Korea

* To whom all correspondances are addressed. Tel: +82-2-3277-4370 Fax: +82-2-3277-3419 E-mail: [email protected]

ACS Paragon Plus Environment

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ABSTRACT A novel methodology to explore efficient CO2 adsorbent is developed by the stabilization of layered double oxide (LDO) in the hybrid matrix of reduced graphene oxide (rG-O) and layered titanate nanosheets. The electrostatically-derived self-assembly between cationic Mg-Al-layered double hydroxide (LDH) nanosheet and anionic graphene oxide (GO)/layered titanate nanosheets followed by heat-treatment at high temperature leads to the cohybridization of LDO (MgO/MgAl2O4) nanocrystals with exfoliated rG-O and layered titanate nanosheets. The incorporation of LDO into the hybrid matrix of rG-O and layered titanate nanosheets is highly effective in increasing its surface area through the formation of mesoporous stacking structure. Of prime importance is that, even at very low concentration of titanate (0.3wt%), an addition of layered titanate nanosheet induces a remarkable surface area expansion of LDO−rG-O nanocomposite from 178 to 330 m2 g−1.

This result is

attributable to the depression of the self-aggregation of rG-O nanosheets due to the incorporation of layered titanate nanosheet.

The resulting LDO−rG-O−layered titanate

nanocomposite shows promising CO2 adsorption capability of 1.71 mmol g−1 at 273 K, which is much greater than those of LDO (0.79 mmol g−1) and LDO−rG-O nanocomposites (1.19 mmol g−1), highlighting the remarkable advantage of titanate addition to improve the CO2 adsorptivity of LDO. The present study clearly proves that the restacked assembly of rG-O nanosheet and layered metal oxide one has potential applications as an efficient hybrid matrix for exploring high performance gas adsorbent.


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1. Introduction The deepening crisis of climate change evokes a great deal of research effort to develop diverse technologies to mitigate the atmospheric concentration of greenhouse gas like CO2.1−4 One of the most effective options to decrease the amount of CO2 emission is the development of efficient gas adsorbents.5 The basic nature of layered double hydroxide (LDH) renders this material a promising CO2 adsorbent. The CO2 adsorption capability of LDH can be further improved by calcination at elevated temperature, leading to the formation of layered double oxide (LDO) nanocomposite with high concentration of surface basic sites.6−9 To further enhance the CO2 adsorption functionality of LDO material, several strategies such as incorporation of alkali metal ions, hybridization with nanostructured material, intercalation of organic/inorganic species into the precursor LDH are developed.4,6,9,10 In one instance, the hybrid materials of exfoliated LDH and graphene nanosheets derived from the electrostatic self-assembly method is effective in forming highly porous materials with house-of-cardstype stacking structure of these nanosheets.11,12

The resulting LDH−graphene

nanocomposites can be effective precursors for synthesizing efficient LDO-based CO2 adsorbents by calcination at elevated temperature. However, a strong tendency of graphene for self-agglomeration prevents from optimizing the porosity and gas adsorption function of the calcined LDO−graphene nanocomposite. Taking into consideration the absence of the π electrons of layered metal oxide nanosheets, the intervention of these inorganic nanosheets can enhance the porous structure of restacked graphene nanosheets.12 As the exfoliated layered metal oxide nanosheet shows similar negative surface charge and hydrophilic surface nature to graphene oxide (G-O) nanosheet, both of these nanosheets can form homogeneous colloidal mixture.13,14 Judging from their common negative surface charge, they can be easily hybridized with positively-charged LDH nanosheet, leading to the formation of homogeneously-mixed LDH−G-O−layered metal oxide nanocomposite.15 The heat-treatment


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for the obtained nanocomposite can induce simultaneous transformations from LDH to LDO and from G-O to reduced graphene oxide (rG-O), yielding metal oxide nanosheetincorporated LDO−rG-O nanocomposite. At the moment of the submission of this study, we are however unaware of other work regarding to the immobilization of LDO in the hybrid matrix of exfoliated rG-O and metal oxide nanosheets, and the application of the obtained nanocomposite for CO2 adsorbent.

Figure 1. Schematic diagram for the stabilization of LDO crystallites in the hybrid matrix of exfoliated rG-O and layered titanate nanosheets. In the present study, an efficient method to enhance the gas adsorption functionality of LDO material is developed by the co-hybridization with exfoliated layered metal oxide and rG-O nanosheets, see Figure 1. The effects of the incorporation of layered titanate nanosheet on the composite structures, crystal structures, and chemical bonding natures of the restacked Mg-Al-LDH−G-O nanocomposites and their calcined derivatives are systematically investigated. The calcined nanocomposites of LDO−rG-O−layered titanate are applied as CO2 adsorbents. To examine the impact of the content of layered titanate nanosheet on the physicochemical characteristics of the obtaining nanocomposite, several LDO−rG-O−layered


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titanate nanocomposites are synthesized with variable contents of layered titanate nanosheet (0, 0.1, 0.3, and 0.5wt%).

The resulting materials are denoted as MAGT0, MAGT1,

MAGT3, and MAGT5, respectively.

2. Experimental 2.1. Synthesis. The colloidal suspension of G-O was obtained by modified Hummer’s method16,17 and that of lepidocrocite-type layered titanate nanosheet was prepared via tetrabutylammonium (TBA+) intercalation into the protonated derivative of layered Cs0.67Ti1.83O4.18 A mixing of the colloidal suspensions of layered titanate and G-O yielded the homogeneous colloidal mixtures of these nanosheets, which is attributable to their common negatively charged surfaces and similar surface natures (see Figure S1 of Supporting Information).

Another precursor of exfoliated Mg-Al-LDH nanosheet was

formed by dispersing the pristine Mg-Al-LDH material in formamide.3,19

The Mg-Al-

LDH−G-O−layered titanate nanocomposites were prepared by the addition of the colloidal suspension of Mg-Al-LDH nanosheets (0.15wt% ; 100 mL) into the colloidal mixtures of GO (0.05wt% ; 21 mL) and layered titanate nanosheets (0.25wt%; 0.10, 0.25, and 0.41 mL), which was then heated at 333 K for 24 h. After the synthesis of this order is completed, the obtaining nanocomposites were centrifuged, washed with formamide and absolute ethanol, and then vacuum-dried. The obtained transparent supernatant solution, demonstrating that the incorporation of colloidal nanosheets into the resulting nanocomposites was completely occurred. The phase transformation of the as-prepared Mg-Al-LDH−G-O−layered titanate nanocomposites into the MAGT nanocomposites was achieved by calcination at 673 K for 4 h under N2 flow. The mass contents of MgO/MgAl2O4:rG-O:layered titanate were estimated to 2.3:1:0 for MAGT0, 2.3:1:0.01 for MAGT1, 2.3:1:0.03 for MAGT3, and 2.3:1:0.05 for MAGT5, respectively.

As a reference, the rG-O/titanate nanosheet-free LDO material


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(MgO/MgAl2O4) was prepared by the heat-treatment of Mg-Al-LDH precursor at 673 K for 4 h under N2 flow. 2.2. Characterization. The crystal structures of the MAGT nanocomposites were probed with powder X-ray diffraction (XRD) analysis using Rigaku D/Max-2000/PC diffractometer (Cu Kα radiation, 298 K).

The chemical compositions of the present materials were

determined using inductively coupled plasma−mass spectrometry (ICP−MS, Agilent 7900). For this chemical analysis, all the materials were digested using the mixed solution of nitric acid (HNO3), hydrogen peroxide (H2O2), and hydrofluoric acid (HF).

Micro raman

spectroscopy (JY LabRam HR spectrometer, 632.8 nm of Ar+ ion laser) was used to characterize the natures of the chemical bonding of the MAGT nanocomposites. The oxidation states of the component ions in the present nanocomposites were studied with Xray photoelectron spectroscopy (XPS, Thermo VG, UK, Al Kα). All the obtained XPS data were energy-referenced based on the adventitious C 1s peak at 284.8 eV to eliminate charging effect. The electronic and local geometric structures of layered titanate nanosheet in the present nanocomposites were examined with X-ray absorption near-edge structure (XANES) spectroscopy at Ti K-edge. The present XANES spectra were collected at the beam line 10C of the Pohang Accelerator Laboratory (PAL) in Korea. The crystal shapes of the present materials were determined with field emission-scanning electron microscopy (FESEM, JEOL JSM-6700F). The composite structures and local atomic arrangements of the present materials were tested with high resolution-transmission electron microscopy/selected area electron diffraction (HR-TEM/SAED, Jeol JEM-2100F, an accelerating voltage of 200 kV). The measurements of N2 adsorption−desorption isotherms of the present materials were performed with BET machine (Micromeritics ASAP 2020, 77 K) to probe the surface areas and pore structures of the obtained materials. Prior to the measurement, the pore structures of the present materials were activated at 423 K for 3 h under vacuum condition.

The


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functionalities of the present nanocomposites as CO2 adsorbents were investigated by measuring CO2 adsorption isotherms at 273 and 573 K.

3. Results and Discussion 3.1. Powder XRD analysis. Figure 2 presents the powder XRD patterns of the asprepared Mg-Al-LDH−G-O−layered titanate nanocomposites and their calcined MAGT derivatives. Like the pristine Mg-Al-LDH, all the as-prepared Mg-Al-LDH−G-O−layered titanate nanocomposites display typical Bragg reflections of Mg-Al-LDH phase. There are no notable dependences of the positions of the LDH-related XRD peaks on the contents of the layered titanate and rG-O nanosheets, indicating negligible modification of the unit cell volume of LDH upon the composite formation (see Table S1 of Supporting Information). In opposition to the LDH-related peaks, no Bragg reflections of layered titanate and rG-O phases are discernible in the present XRD patterns.

Since the XRD peaks of layered

materials become observable only in the case of well-ordered stacking of nanosheets, no detection of these peaks strongly suggests that these incorporated nanosheets are homogeneously dispersed in the present nanocomposites without any segregation of rG-O and layered titanate phases. Also, the absence of superlattice XRD peaks related to the heterolayered lattice of interstratified component nanosheets indicates that the incorporated titanate nanosheets are randomly distributed in the LDH−rG-O matrix without the formation of well-ordered heterolayered structure.20 As can be observed in the right panel of Figure 2, all the calcined MAGT nanocomposites show broad XRD peaks of MgO phase (JCPDS no. 45-946) with complete disappearance of the LDH-related reflections. This result underscores the complete phase transformation from LDH to LDO upon the heat-treatment. Although the phase transition of Mg-Al-LDH into MgO and MgAl2O4 is well-reported,21,22 the poor crystallinity of generated MgAl2O4 phase hinders from observing the XRD peaks of this


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phase. Similarly to the as-prepared nanocomposites, there is no notable displacement of Bragg reflections depending on the contents of titanate and rG-O, indicating negligible variations of lattice parameters upon the composite formation (see Table S1 of Supporting Information). In contrast to the peak position, the peak width displays notable broadening due to the incorporation of layered titanate nanosheet, implying the decrease of the particle sizes of LDO. According to Scherrer equation, the particle size of the MgO component is calculated

to

be

~5.2−5.8

nm

for

the

titanate

nanosheet-incorporated

MAGT

nanocomposites, which is somewhat smaller than that of the titanate-free MAGT0 nanocomposite (~6.3 nm). This result highlights the notable influence of layered titanate nanosheet on the crystal growth of LDO material.

Figure 2. Powder XRD patterns of (left) (a) the pristine Mg-Al-LDH and the asprepared Mg-Al-LDH−G-O−layered titanate nanocomposites with the titanate contents of (b) 0, (c) 0.1, (d) 0.3, and (e) 0.5wt%, and (right) the corresponding calcined derivatives of (a) LDO, (b) MAGT0, (c) MAGT1, (d) MAGT3, and (e) MAGT5. According to ICP−MS analysis, all the titanate-incorporated MAGT nanocomposites show the presence of Ti element and a gradual increase of Ti content with increasing the amount of


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titanate nanosheet in the precursors, confirming the effective incorporation of titanate nanosheet into the present MAGT nanocomposites (see Table S2 of Supporting Information). 3.2. Micro-Raman spectroscopic analysis. Figure 3 plots micro-Raman spectra of the present MAGT nanocomposites and the following lepidocrocite-type titanate, G-O, and rG-O as the references. Like the precursor G-O, all the MAGT nanocomposites display two typical graphene-related Raman peaks D and G at 1350 and 1580 cm−1, respectively.23,24 The observation of these graphene-related peaks clearly demonstrates the incorporation of graphene species into the present nanocomposites, although no graphene-related Bragg reflections are distinguishable in the corresponding XRD patterns. According to the peak convolution analysis, the intensity ratio of D/G peaks is determined to be 1.20 for MAGT1, 1.11 for MAGT3, and 1.14 for MAGT5, which is smaller than that of MAGT0 (1.25) but greater than that of G-O (1.12). Since the degree of the structural disorder of graphene species is proportional to the intensity ratio of D/G peaks,23 the observed depression of D/G ratio due to the incorporation of titanate nanosheet strongly suggests the enhanced structural order of graphene species in the titanate-incorporated MAGT nanocomposites. D

G (g)

Intensity (a.u.)

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(f) (e) (d) (c) (b) (a) 500

1000 1500 2000 -1

Wavenumber (cm )

Figure 3. Micro-Raman spectra of (a) lepidocrocite-type layered titanate, (b) MAGT0, (c) MAGT1, (d) MAGT3, (e) MAGT5, (f) G-O, and (g) rG-O.


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In the lower region of wavenumber ( 0.4, all the obtaining materials display distinct hysteresis, reflecting the presence of mesopores. The left panel of Figure 7 shows that the LDO material indicates distinct H1-type hysteresis at high pressure region of ppo−1 < 0.5, confirming the agglomeration of spherical nanoparticles.29

All

the

MAGT

nanocomposites

commonly

exhibit

Brunauer−Deming−Deming−Teller (BDDT)-type-IV shaped isotherm with H3-type weak hysteresis based on the IUPAC classification. This kind of isotherm behavior typically occurs for the agglomerates of plate-like particles with slit-shaped mesopores.15,30 Although the incorporation of layered titanate nanosheets does not cause notable modification in the isotherm shape of the present MAGT nanocomposites, the amount of N2 adsorption becomes greater due to the incorporation of layered titanate nanosheet, indicating the improvement of the porosity of the LDO−rG-O nanocomposite. On the basis of Brunauer−Emmett−Teller (BET) equation, the surface areas of the obtaining nanocomposites are calculated to be 64 m2g−1 for LDO, 178 m2g−1 for MAGT0, 233 m2g−1 for MAGT1, 330 m2g−1 for MAGT3, and 191 m2g−1 for MAGT5, respectively. The present results provide clear evidence for the surface area increment of the LDO−rG-O nanocomposite even by the addition of very small amount of layered titanate nanosheets. The remarkable surface area expansion because of the incorporation of layered titanate nanosheet can be due to the depression of π−π interaction between rG-O nanosheets by the intervention of metal oxide nanosheets, and the resulting


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prevention of tight packing of rG-O nanosheets.31 The observed high efficiency of surface expansion is attributable to the homogeneous mixing between layered titanate and rG-O nanosheets due to their similar crystal dimension and surface charge.32 Beyond the optimal titanate content of 0.3wt%, a further addition of titanate nanosheets contributes towards the depression of the surface area of MAGT nanocomposite. This can be ascribed to the increase of the mass of unit formula of nanocomposite due to the addition of heavier titanate nanosheet.

Figure 7. (Left) N2 adsorption−desorption isotherms of (a) LDO, (b) MAGT0, (c) MAGT1, (d) MAGT3, and (e) MAGT5. (Right) Pore size distribution curves of the present materials determined by BJH method. The size distribution curves of mesopores are evaluated on the basis of Barrett−Joyner−Halenda (BJH) equation. As presented in the right panel of Figure 7, all the obtaining nanocomposites usually exhibits mesopores with the average size of ~3.5 nm resulted from the house-of-cards-type stacking structure of nanosheets. This type of mesopore with similar pore size is frequently reported for the exfoliated metal oxide nanosheets with the stacking structure.17,29 In comparison with the MAGT


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nanocomposites, the LDO material displays much greater pore size of ~6.5 nm, which is attributable to the formation of mesopores by the agglomeration of spherical nanoparticles. 3.7. CO2 adsorption test.

The left panel of Figure 8 presents the CO2 adsorption

isotherms of the MAGT nanocomposites recorded at 273 K and 101.325 kPa (standard temperature and pressure, STP). All the present MAGT nanocomposites display efficient adsorption of CO2 gas, indicating their promising functionalities as CO2 adsorbents. The CO2 adsorption capacities of the present nanocomposites are much greater than that of LDO (0.79 mmol g−1 at STP), indicating the beneficial role of hybridized 2D nanosheets in enhancing the gas adsorption property of LDO material. At the optimal titanate content of 0.3wt%, the incorporation of layered titanate nanosheets contributes to the significant enhancement of CO2 adsorption ability, underscoring the useful role of layered titanate nanosheet as an additive for improving CO2 adsorption functionality of LDO−rG-O nanocomposite.

0.8

1.5

Vads (mmol g-1)

Vads (mmol g-1)

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


1.0

0.5

0.0 0

20

40

60

80

100

0.6

0.4

0.2

0.0 0

20

P (kPa)

40

60

80

100

P (kPa)

Figure 8. (Left) CO2 adsorption isotherms at 273 K of LDO (crosses), MAGT0 (circles), MAGT1 (triangles), MAGT3 (squares), and MAGT5 (diamonds). (Right)


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High temperature CO2 adsorption isotherms at 573 K of LDO (crosses), MAGT0 (circles), and MAGT3 (squares). The beneficial influence of the incorporation of layered titanate nanosheet on the CO2 adsorption capacity of LDO−rG-O material can be likely due to the surface expansion of the nanocomposite providing more active sites for CO2 adsorption. The remarkable enhancement of the surface area of MAGT nanocomposite is attributable to the depression of the selfstacking trend of rG-O nanosheets by the intervention of layered titanate nanosheets.12 The obtaining outcomes evidently indicate that the stabilization of LDO in hybrid matrix of graphene and layered metal oxide nanosheets can provide a new effective way to enhance the CO2 adsorption capacity of LDO. For the MAGT3 nanocomposite showing the best CO2 adsorption performance at 273 K, CO2 adsorption isotherm at higher temperature of 573 K is also measured, together with those of the titanate-free MAGT0 nanocomposite and LDO. As can be observed in the right panel of Figure 8, both the MAGT0 and MAGT3 nanocomposites show promising CO2 adsorptivities (0.74 mmol g−1 for MAGT0 and 0.78 mmol g−1 for MAGT3), which are superior to or compatible with that of the LDO material (0.58 mmol g−1). This finding clearly indicates the usefulness of the rG-O and titanate nanosheets as immobilization matrix in improving the high temperature CO2 adsorptivity of LDO. However, the improvement of the CO2 adsorptivity of LDO upon the formation of the composite with these nanosheets is less prominent for the higher temperature of 573 K than at the lower temperature of 273 K.

This finding can be due to the physisorption and

chemisorption of CO2 molecule. That is, the expanded surface area upon the combination with nanosheets provides many surface sites for the physisorption of CO2 playing an important role at low temperature. Conversely, the accompanying decrease of the basic LDO content leads to the decrease of the chemisorption site of CO2, leading to a weakening of the beneficial influence of composite formation in increasing the CO2 adsorptivity of LDO at


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high temperature.

Additionally, the durability of the CO2 adsorptivity of the present

nanocomposite is examined by carrying out four consecutive cycling test of CO2 adsorption for the most efficient MAGT3 nanocomposite (see Figure S3 of Supporting Information). Even though this material experiences notable degrading of CO2 adsorptivity after the first cycling, its CO2 adsorption capacity becomes stabilized after the second cycle, indicating the recyclability of the CO2 adsorption performance of the present nanocomposites. 3.8. Powder XRD and FE-SEM analyses for tested MAGT nanocomposites. The transformations of the crystal structures and morphologies of the present MAGT nanocomposite are characterized with XRD and FE-SEM techniques. As plotted in the left panel of Figure 9, there is no prominent modification of the XRD features of MAGT3 nanocomposite upon the gas adsorption test, reflecting negligible structural modification caused by the gas adsorption test. As presented in the right panel of Figure 9, the porous stacking morphology of the present MAGT nanocomposite retains after the gas adsorption test even with a slight degrading of porous stacking structure, indicating the high morphological stability of the present nanocomposite material.

Figure 9. (Left) Powder XRD patterns and (right) FE-SEM images for the MAGT3 nanocomposite (a) before and (b) after the test of CO2 adsorption.


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To verify the superiority of the LDH and metal oxide nanosheets as promising building blocks for discovering effective CO2 adsorbent, the CO2 adsorption performance of the present MAGT nanocomposite is compared with the previously reported data of related materials. As shown in Table 1, the CO2 adsorptivity of the present titanate nanosheetincorporated LDH−graphene nanocomposite is superior or comparable to those of other materials. This result strongly confirms the superiority of the composite formation with LDH nanosheet in synthesizing efficient nanocomposite-type CO2 adsorbent. Taking into account the effectiveness of the addition of K2CO3 or organic molecule in improving the CO2 adsorptivity of LDH-based material, the CO2 adsorption performance of the present nanocomposite would be further optimized by the additional coupling with K2CO3 or organic molecule. This comparative investigation clearly indicates that the exfoliated LDH and metal oxide nanosheets are beneficial as powerful building blocks for exploring efficient CO2 adsorbent.

Table 1. CO2 adsorption capacities of Mg-Al-LDH-based materials from the previous reports and the current work. Adsorbent material

Tads (K)

Ptotal (bar)

Capacity (mmol g-1)

Ref

Calcined Mg3-Al1-CO3-LDHs at 400 °C

573

1

0.25

33

Calcined Mg2-Al1-CO3-LDHsGO (7wt%) at 400 °C

573

0.2

0.45

11

Mg2-Al1-CO3-LDHs-MWCNT

573

0.2

0.40

4

Mg3-Al1-CO3-LDHs-stearate

573

1

1.30

10

Mg3-Al1-CO3-LDHs-K2CO3 20wt%

473

1

1.21

34

Coal-derived graphitic materialsupported (5wt%) K-promoted Mg-Al-LDH

573

1

1.10

35


20

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Calcined Mg3-Al1-CO3-LDHsTiO2 Ti27 at% at 400 °C

423

0.2

0.75

36

Calcined Mg3-Al1-CO3-LDHsGO 6.5wt%-K2CO3 4wt% at 400 °C

473

1

0.60

37

Mg-Al-LDH-G-O-layered titanate nanocomposites

273 573

1 1

1.71 0.78

This work This work

4. Conclusion In the present work, we are able to establish a novel synthetic strategy for exploring efficient CO2 adsorbent via the stabilization of LDO in the hybrid matrix of rG-O and metal oxide nanosheets. Even at very small titanate content of 0.3wt%, the incorporation of layered titanate nanosheets contributes to the remarkable surface expansion of the LDO−rG-O nanocomposites with the increase of micropore volume. This is ascribable to the depression of the self-stacking of rG-O caused by the intervention of layered titanate nanosheet. As a consequence of enhanced porosity, the incorporation of exfoliated layered titanate nanosheet as well as rG-O nanosheet significantly enhances the CO2 adsorption capacity of LDO material. The resulting MAGT nanocomposite is a promising CO2 adsorbent, which is superior to the nanosheet-free LDO material and the LDO−rG-O nanocomposite.

The

present study highlights the beneficial role of the hybrid matrix of rG-O and layered titanate nanosheets as an effective substrate for optimizing the gas adsorption capacity of LDO material. The resulting MAGT nanocomposites boast good thermal and chemical stability of their porous structures, which renders them promising CO2 adsorbents. We are currently working across the combination of the present synthetic approach with previously-reported methods such as the incorporation of alkali metal salt, the intercalation of organic molecules into the LDH precursor for developing efficient CO2 adsorbents.

Supporting Information.


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Lattice parameters of the present nanocomposites, the zeta potential profiles of the colloidal suspensions of exfoliated layered titanate nanosheet and G-O, and their mixture, and powder XRD and FE-SEM data of calcined titanate nanosheet. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *[email protected], phone: +82-2-3277-4370, fax: +82-2-3277-3419

ACKNOWLEDGMENT This research is supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (NRF-2010-C1AAA001-2010-0029065). The experiments at PAL were supported by MOST & POSTECH.

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