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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

The thickness and dimension of exfoliated 2D nanosheets.(a–d) The dispersions of graphene, MoS2, WS2, and BN nanosheets and their AFM images respectively. Inset: thickness profiles along the white lines shown in the AFM images (a–d), respectively.
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f3: The thickness and dimension of exfoliated 2D nanosheets.(a–d) The dispersions of graphene, MoS2, WS2, and BN nanosheets and their AFM images respectively. Inset: thickness profiles along the white lines shown in the AFM images (a–d), respectively.

Mentions: Further examination of the nature of the nanosheets was performed by atomic force microscopy (AFM) measurement (Fig. 3), which presents the thickness of exfoliated 2D materials. The MoS2 nanosheets have different thicknesses with the majority in the range of 2–5 nm. Since the thicknesses of the single-layer MoS2 nanosheets were determined to be in the range of 0.9–1.2 nm23, AFM measurement confirms that the exfoliated MoS2 nanosheets consist of 2–4 monolayers. Similarly, the thicknesses of graphene (3–5 nm), WS2 (1–3 nm), and BN (2–6 nm) nanosheets indicate that they also exist as few-layer nanosheets in dispersions. The absorption spectra of exfoliated 2D nanosheets dispersions is illustrated in Supplementary Fig. S5. These characteristic absorption curves ranging from 300 to 900 nm coincide with the general features of exfoliated 2D layered materials2122. The Raman spectra of the exfoliated MoS2 nanosheets were recorded using a 514 nm excitation line. As shown in Supplementary Fig. S6, the smaller frequency difference (Δ) between E12g and A1g modes for the few-layer MoS2 (Δ = 24.7 cm−1) in comparison with that of the bulk MoS2 (Δ = 26.9 cm−1) manifests the significant reduction of the sheets thicknesses from the bulk MoS2 to the exfoliated samples44. According to the “Δ-thickness relation” established by previous works based on exfoliated samples, the thicknesses of exfoliated 2D MoS2 nanosheets are mostly less than 5 monolayers (<4 nm). From XPS analysis, the exfoliated MoS2 nanosheets show Mo 3d peaks with peak position and width characteristic of the 2 H phase45 (Supplementary Fig. S7).


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)

The thickness and dimension of exfoliated 2D nanosheets.(a–d) The dispersions of graphene, MoS2, WS2, and BN nanosheets and their AFM images respectively. Inset: thickness profiles along the white lines shown in the AFM images (a–d), respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4645177&req=5

f3: The thickness and dimension of exfoliated 2D nanosheets.(a–d) The dispersions of graphene, MoS2, WS2, and BN nanosheets and their AFM images respectively. Inset: thickness profiles along the white lines shown in the AFM images (a–d), respectively.
Mentions: Further examination of the nature of the nanosheets was performed by atomic force microscopy (AFM) measurement (Fig. 3), which presents the thickness of exfoliated 2D materials. The MoS2 nanosheets have different thicknesses with the majority in the range of 2–5 nm. Since the thicknesses of the single-layer MoS2 nanosheets were determined to be in the range of 0.9–1.2 nm23, AFM measurement confirms that the exfoliated MoS2 nanosheets consist of 2–4 monolayers. Similarly, the thicknesses of graphene (3–5 nm), WS2 (1–3 nm), and BN (2–6 nm) nanosheets indicate that they also exist as few-layer nanosheets in dispersions. The absorption spectra of exfoliated 2D nanosheets dispersions is illustrated in Supplementary Fig. S5. These characteristic absorption curves ranging from 300 to 900 nm coincide with the general features of exfoliated 2D layered materials2122. The Raman spectra of the exfoliated MoS2 nanosheets were recorded using a 514 nm excitation line. As shown in Supplementary Fig. S6, the smaller frequency difference (Δ) between E12g and A1g modes for the few-layer MoS2 (Δ = 24.7 cm−1) in comparison with that of the bulk MoS2 (Δ = 26.9 cm−1) manifests the significant reduction of the sheets thicknesses from the bulk MoS2 to the exfoliated samples44. According to the “Δ-thickness relation” established by previous works based on exfoliated samples, the thicknesses of exfoliated 2D MoS2 nanosheets are mostly less than 5 monolayers (<4 nm). From XPS analysis, the exfoliated MoS2 nanosheets show Mo 3d peaks with peak position and width characteristic of the 2 H phase45 (Supplementary Fig. S7).

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