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High-efficiency exfoliation of layered materials into 2D nanosheets in switchable CO2/Surfactant/H2O system.

Wang N, Xu Q, Xu S, Qi Y, Chen M, Li H, Han B - Sci Rep (2015)

Bottom Line: Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis.Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2).The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated.

View Article: PubMed Central - PubMed

Affiliation: College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450052, China.

ABSTRACT
Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis. However, fully exploiting the outstanding properties will require a method for their efficient exfoliation. Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2). The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated. Moreover, we demonstrate that the exfoliated 2D nanosheets have their worthwhile applications, for example, graphene can be used to prepare conductive paper, MoS2 can be used as fluorescent label to perform cellular labelling, and BN can effectively reinforce polymers leading to the promising mechanical properties.

No MeSH data available.


Related in: MedlinePlus

Mophology of exfoliated 2D nanosheets and their atomic structure.(a–d) Low-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (e–h) High-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (i–l) High-resolution TEM (HRTEM) images of flakes of graphene, MoS2, WS2, and BN nanosheets, respectively. (Insets) Top: Fast Fourier transforms of the images; Bottom: Schematic drawing of the atomic structure of graphene, MoS2, WS2, and BN, respectively.
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f2: Mophology of exfoliated 2D nanosheets and their atomic structure.(a–d) Low-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (e–h) High-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (i–l) High-resolution TEM (HRTEM) images of flakes of graphene, MoS2, WS2, and BN nanosheets, respectively. (Insets) Top: Fast Fourier transforms of the images; Bottom: Schematic drawing of the atomic structure of graphene, MoS2, WS2, and BN, respectively.

Mentions: We exfoliated a series of layer materials of graphene, MoS2, WS2, and BN in the emulsions microenvironment of the CO2/PVP/H2O system (Supplementary Fig. S1). Transmission electron microscopy (TEM) examination of materials deposited from the dispersions shows the existence of large quantities of ultrathin 2D sheets (Fig. 2a–d). The ranges of lateral size of graphene, MoS2, WS2, and BN are different possibly due to the different size of their bulk materials. Figures 2e–h show that these 2D nanosheets turn slightly transparent to the electron beam due to their ultrathin structure. The diffraction patterns in Fig. 2e–h illustrate typical six-fold symmetry of highly crystalline structure. Additional TEM micrographs of these nanosheets are shown in Supplementary Fig. S3. Figure 2i–l are high-resolution TEM micrographs (HRTEM) of graphene, MoS2, WS2, and BN, providing more detailed structural information. The integrity and uniformity of the lattice structure of these nanosheets suggest that defects and deformation were not introduced in the fabrication process. These images reveal graphene lattice spacing of 2.4 Å, MoS2 and WS2 lattice spacing of 2.7 Å, and BN lattice spacing of 2.2 Å. Addtionally, the analysis of HRTEM intensity profiles suggests the presence of monolayer in the dispersions2143. A near perfect planar structure of monolayer 2 H-MoS2 without defects and deformation is shown in Supplementary Fig. S4. A significant variation in intensity between neighboring atom peaks can be observed from the intensity profile across the red dashed line in Supplementary Fig. S4c. For ABAB stacking order of the 2 H-MoS2, there is no difference in the micrograph intensity between neighboring atom peaks if the nanosheets are more than two layers43. Therefore, the significant variation in intensity suggests the exfoliated MoS2 nanosheet to be the planar 2D structure with monolayer.


High-efficiency exfoliation of layered materials into 2D nanosheets in switchable CO2/Surfactant/H2O system.

Wang N, Xu Q, Xu S, Qi Y, Chen M, Li H, Han B - Sci Rep (2015)

Mophology of exfoliated 2D nanosheets and their atomic structure.(a–d) Low-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (e–h) High-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (i–l) High-resolution TEM (HRTEM) images of flakes of graphene, MoS2, WS2, and BN nanosheets, respectively. (Insets) Top: Fast Fourier transforms of the images; Bottom: Schematic drawing of the atomic structure of graphene, MoS2, WS2, and BN, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645177&req=5

f2: Mophology of exfoliated 2D nanosheets and their atomic structure.(a–d) Low-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (e–h) High-magnification TEM images of flakes of graphene, MoS2, WS2, and BN, respectively. (i–l) High-resolution TEM (HRTEM) images of flakes of graphene, MoS2, WS2, and BN nanosheets, respectively. (Insets) Top: Fast Fourier transforms of the images; Bottom: Schematic drawing of the atomic structure of graphene, MoS2, WS2, and BN, respectively.
Mentions: We exfoliated a series of layer materials of graphene, MoS2, WS2, and BN in the emulsions microenvironment of the CO2/PVP/H2O system (Supplementary Fig. S1). Transmission electron microscopy (TEM) examination of materials deposited from the dispersions shows the existence of large quantities of ultrathin 2D sheets (Fig. 2a–d). The ranges of lateral size of graphene, MoS2, WS2, and BN are different possibly due to the different size of their bulk materials. Figures 2e–h show that these 2D nanosheets turn slightly transparent to the electron beam due to their ultrathin structure. The diffraction patterns in Fig. 2e–h illustrate typical six-fold symmetry of highly crystalline structure. Additional TEM micrographs of these nanosheets are shown in Supplementary Fig. S3. Figure 2i–l are high-resolution TEM micrographs (HRTEM) of graphene, MoS2, WS2, and BN, providing more detailed structural information. The integrity and uniformity of the lattice structure of these nanosheets suggest that defects and deformation were not introduced in the fabrication process. These images reveal graphene lattice spacing of 2.4 Å, MoS2 and WS2 lattice spacing of 2.7 Å, and BN lattice spacing of 2.2 Å. Addtionally, the analysis of HRTEM intensity profiles suggests the presence of monolayer in the dispersions2143. A near perfect planar structure of monolayer 2 H-MoS2 without defects and deformation is shown in Supplementary Fig. S4. A significant variation in intensity between neighboring atom peaks can be observed from the intensity profile across the red dashed line in Supplementary Fig. S4c. For ABAB stacking order of the 2 H-MoS2, there is no difference in the micrograph intensity between neighboring atom peaks if the nanosheets are more than two layers43. Therefore, the significant variation in intensity suggests the exfoliated MoS2 nanosheet to be the planar 2D structure with monolayer.

Bottom Line: Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis.Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2).The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated.

View Article: PubMed Central - PubMed

Affiliation: College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450052, China.

ABSTRACT
Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis. However, fully exploiting the outstanding properties will require a method for their efficient exfoliation. Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2). The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated. Moreover, we demonstrate that the exfoliated 2D nanosheets have their worthwhile applications, for example, graphene can be used to prepare conductive paper, MoS2 can be used as fluorescent label to perform cellular labelling, and BN can effectively reinforce polymers leading to the promising mechanical properties.

No MeSH data available.


Related in: MedlinePlus