Supplementary Figure 1: Schematic phase diagram of surfactant-water-oil systems showing a variety of self-assembled structures. (Adapted from ref.

Transcription

1 Supplementary Figure 1: Schematic phase diagram of surfactant-water-oil systems showing a variety of self-assembled structures. (Adapted from ref. [1].) 1

2 Supplementary Figure 2: SEM and TEM images of ultrathin 2D TiO 2 nanosheets. (a) Lowmagnification SEM image and (b) high-magnification SEM image of 2D ultrathin TiO 2 nanosheets; (c) low-magnification TEM image of the 2D TiO 2 nanosheets, with the corresponding selected area electron diffraction (SAED) pattern of the 2D TiO 2 nanosheets in the inset, demonstrating the presence of the anatase phase, and (d) high resolution TEM image of 2D TiO 2 nanosheets, where the lattice image of the anatase 2D TiO 2 nanosheets features an exposed surface of high-energy {010} facets, based on observation with the electron beam steered along the [010] direction. 2

3 Supplementary Figure 3: SEM and TEM images of ultrathin 2D ZnO nanosheets. (a) Lowmagnification SEM image and (b) high-magnification SEM image of 2D ultrathin ZnO nanosheets; (c) low-magnification TEM image of the 2D ZnO nanosheets; and (d) lattice image of the wurtzite 2D ZnO nanosheets with electron beam steered along the [001] direction, showing the exposed surface of {001} facets. 3

4 Supplementary Figure 4: SEM and TEM images of ultrathin 2D Co 3 O 4 nanosheets. (a) Lowmagnification SEM image and (b) high-magnification SEM image of 2D ultrathin Co 3 O 4 nanosheets; (c) low-magnification TEM image of the 2D Co 3 O 4 nanosheets; and (d) lattice image of the wurtzite 2D Co 3 O 4 nanosheets with the electron beam steered along the [001] direction, showing the exposed surface of {001} facets. 4

5 Supplementary Figure 5: SEM and TEM images of ultrathin 2D WO 3 nanosheets. (a) Lowmagnification SEM image and (b) high-magnification SEM image of 2D ultrathin WO 3 nanosheets; (c) low-magnification TEM image of WO 3 nanosheet edge, showing the curved nature of the ultrathin nanosheets; and (d) lattice image of WO 3 with the electron beam steered along the [100] direction, showing that the exposed surface consists of {100} facets. 5

6 Supplementary Figure 6: XRD patterns for 2D metal oxide nanosheets. (a) Anatase TiO 2 plus trace of rutile TiO 2, (b) wurtzite ZnO, (c) cubic Co 3 O 4, and (d) monoclinic WO 3. 6

7 Supplementary Figure 7: Electron microscope images of 2D Fe 3 O 4 nanosheets. (a) Lowmagnification SEM image and (b) high-magnification SEM image of 2D ultrathin Fe 3 O 4 nanosheets; (c) low-magnification TEM image of Fe 3 O 4 nanosheet edge, showing the curved nature of the ultrathin nanosheets; and (d) HRTEM lattice image of Fe 3 O 4 with the electron beam steered along the [11 ] direction, showing that the exposed surface consists of {11 } facets. 7

8 Supplementary Figure 8: Electron microscope images of 2D MnO 2 nanosheets. (a) Lowmagnification SEM image and (b) high-magnification SEM image of 2D ultrathin MnO 2 nanosheets; (c) low-magnification TEM image of MnO 2 nanosheet edge, showing the curved nature of the ultrathin nanosheets; and (d) HRTEM lattice image of MnO 2 with the electron beam steered along the [ 31] direction. 8

9 Supplementary Figure 9: XRD patterns for 2D tractional metal oxide nanosheets of (a) cubic Fe 3 O 4 and (b) tetragonal -MnO 2. 9

10 Supplementary Figure 10: Thickness of 2D TiO 2 nanosheets. (a) Edge configuration of 2D TiO 2 under the incident electronic beam, as observed by TEM, and (b) the intensity profile along the line L in (a), showing the 5-layer stacking of monolayers and the thickness of 0.62 nm for one monolayer in the ultrathin TiO 2 nanosheets; (c-e) AFM image (c) and profiles along line 1 (d) and line 2 (e) in (c), demonstrating thicknesses of the 2D TiO 2 nanosheets of 3.3 nm and 2.7 nm, which correspond to 5 layer and 4 layer stacking of TiO 2 monolayers. 10

11 Supplementary Figure 11: AFM images of the ultrathin 2D metal oxide nanosheets. (a-b) AFM image of ZnO nanosheets and the corresponding profile along the line in (a), indicating a thickness of around 3.35 nm; (c-d) AFM image of Co 3 O 4 nanosheets and the corresponding profile along the line in (c), indicating a thickness of around 1.65 nm; and (e-f) AFM image of WO 3 nanosheets and the corresponding profile along the line in (e), indicating a thickness of around nm. 11

12 Supplementary Figure 12: UV-Visible (UV-Vis) spectra of ultrathin 2D metal oxide nanosheets. UV-Vis spectra of the TiO 2, ZnO, Co 3 O 4, and WO 3 ultrathin 2D nanosheets, which show ev blue-shift compared to their corresponding bulk materials. [2-4] 12

13 Without EG Without P123 With 300 wt% H2O With 700 wt% H2O a TiO 2 b ZnO c d e f g h Supplementary Figure 13: Roles of the addition of P123, EG, and water in the synthesis of the ultrathin 2D nanosheets. (a-b) Morphology of the products of TiO 2 (a) and ZnO (b) synthesized from the solutions without P123, presenting the obtained large agglomorates; (c-d) morphology of the products of TiO 2 (c) and ZnO (d) synthesized from the solutions without the addtion of EG; (e-f) morphology of the products of TiO 2 (c) and ZnO (d) synthesized from the solutions with the addtion of 300 wt% water; and (g-h) morphology of the products of TiO 2 (c) and ZnO (d) synthesized from the solutions with the addtion of 700 wt% water. The results show that all of the added P123, EG, and water are crucial for the formation of ultrathin 2D metal oxide nanosheets, and the amount of the additions can only be allowed to vary to a very small extent. 13

14 Supplementary Figure 14: Specific surface areas of 2D metal oxide nanosheets. Specific surface areas of the 2D metal oxide nanosheets (individual symbols with error bars) together with the reported specific surface areas (individual bars with numbers) of the conventional metal oxide nanoparticles [5-8]. 14

15 Supplementary Table 1. Thickness and corresponding monolayer numbers of the synthesizes nanosheets Materials Monolayer thickness Thickness in present work Layer numbers TiO nm ~3.3 nm 5 ZnO 0.68 nm [9] ~3.4 nm 5 Co 3 O 4 ~0.8 nm [10] ~1.6 nm 2 WO nm [11] nm 3-7 Supplementary Table 2. Core levels of Ti 2p, Zn 2p, Co 2p, and W 4f for ultrathin 2D TiO 2, ZnO, Co 3 O 4, and WO 3 nanosheets measured by XPS, and the binding energy differences between the standard reference and the measured values. Chemical states Binding energy (ev) FWHM (ev) References [12-15] (ev) Binding energy difference (Ref - Measured) (ev) Ti 2p Anatase Rutile Ti 3+ Ti 2p 1/ / 2.11 Ti 2p 3/ Zn 2p Zn 2p 1/ Zn 2p 3/ Co 2p Co 2p 3/ W 4f W 4f 5/ W 4f 7/

16 Supplementary Methods Materials The chemical reagents used for the synthesis of 2D metal oxide nanosheets were commercially available reagents. Titanium isopropoxide (TTIP), zinc acetate dihydrate (Zn(Ac) 2 2H 2 O), cobalt acetate tetrahydrate (Co(Ac) 2 4H 2 O), tungsten hexachlorate (WCl 6 ), iron nitrate nonahydrate (Fe(NO 3 ) 3 9H 2 O), copper acetate mono hydrate (Cu(Ac) 2 H 2 O), hexamethylenetetramine (HMTA), hydrochloric acid (HCl), ethylene glycol (EG), absolute ethanol (EtOH) and polyethylene oxide - polypropylene oxide - polyethylene oxide (PEO 20 - PPO 70 -PEO 20, P123) were purchased from Sigma-Aldrich. All the chemicals were used as received without further purification. Synthesis of 2D ultrathin Fe 3 O 4 nanosheets 0.2 g Pluronic P123 was added into 3 g EtOH to form a clear solution with stirring for 15 min, and then 0.2 g Fe(NO 3 ) 3 9H 2 O and 0.07 g HMTA were added into the ethanol solution. After stirring for around 15 min, a clear solution was obtained. Then, 13 ml EG was put into the ethanol solution. After stirring for 30 min, a transparent solution was obtained. The obtained EtOH + EG precursor solution was statically aged for 2 days. After aging, the transparent precursor solution was transferred into a 45 ml autoclave and heated at 150 o C for 15 h. The products of the solvothermal reaction were washed with distilled water and ethanol 3 times, and the dark powders were collected after washing/centrifugation and drying at o C for 2-10 h. Some powders were redispersed in ethanol by ultrasonication for further characterization. Synthesis of 2D ultrathin MnO 2 nanosheets 0.2 g Pluronic P123 was added into 3 g EtOH with 1 g H 2 O to form a clear solution with stirring for 15 min, and then 0.12 g Mn(Ac) 2 2H 2 O was added into the ethanol solution. After stirring for around 15 min, a clear solution was obtained. Then, 13 ml EG was put into the ethanol solution. After stirring for 30 min, a transparent solution was obtained. The obtained EtOH + EG precursor solution was statically aged for 0-3 days. After aging, the transparent precursor solution was transferred into a 45 ml autoclave and heated at 170 o C for 5 h. The products of the solvothermal reaction were washed with distilled water and ethanol 3 times, and the dark powders were collected after washing/centrifugation and drying at o C for 2-10 h. Some powders were redispersed in ethanol by ultrasonication for further characterization. 16

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