Wet-chemical synthesis and applications of non-layer structured two-dimensional nanomaterials

Abstract

Non-layer structured nanomaterials with single- or few-layer thickness have two-dimensional sheet-like structures and possess intriguing properties. Recent years have seen major advances in development of a host of non-layer structured ultrathin two-dimensional nanomaterials such as noble metals, metal oxides and metal chalcogenides. The wet-chemical synthesis has emerged as the most promising route towards high-yield and mass production of such nanomaterials. These nanomaterials are now finding increasing applications in a wide range of areas including catalysis, energy production and storage, sensor and nanotherapy, to name but a few.

Figure 1. 2D nanosheets synthesized using the 2D-templated synthesis method.

(a) TEM images of hcp AuSSs. Inset: crystallographic models for a typical AuSS with its basal plane along the [110]h zone axis, showing ABAB stacking along the [001]h direction. Adapted from ref. (b) TEM image of α-Fe₂O₃ nanosheets. Inset: HRTEM image and Tyndall effect of α-Fe₂O₃ nanosheets. Adapted, with permission, from ref. (copyright 2014 American Chemical Society). (c) Atomic force microscopy (AFM) image of α-Fe₂O₃ nanosheets. Adapted, with permission, from ref. . (Copyright 2014, American Chemical Society). (d) SEM and (e) TEM images of CuInS₂ nanosheets. Reproduced, with permission, from ref. (© 2014 John Wiley & Sons Inc). (f) TEM and (g) SEM images of CuSe and Cu_2−xSe nanosheets, respectively. Reproduced, with permission, from ref. (© 2014 John Wiley & Sons Inc).

Figure 2. 2D nanosheets synthesized using the hydro/solvothermal synthesis method.

(a,b) TEM image of the PVP-capped Rh nanosheets, and (c) AFM image of a bare Rh nanosheet. Adapted from ref. . (d) SEM images of 2D nanosheets of TiO₂, ZnO (e) and Co₃O₄ (f; scale bars, 200 nm). Adapted from ref. . (g) TEM image of ZnSe single layers (scale bar, 500 nm). Inset: the enlarged TEM image (scale bar, 100 nm) and Tyndall effect of ZnSe single layers. Adapted from ref. . (h) AFM image ZnSe single layers (scale bar, 500 nm). Adapted from ref. . (i) AFM image of ultrathin surface-pitted CeO₂ sheets (scale bars, 100 nm). Adapted from ref. .

Figure 3. 2D nanosheets synthesized using soft colloidal templated synthesis and other methods.

(a) SEM image of ultrathin CuS nanosheets. Inset: photograph of the colloid solution of CuS nanosheets. Adapted from ref. . TEM images of ultrathin CuS nanosheets with (b) lying flat and (c) standing on the TEM grids. Inset in b: scheme of an ultrathin CuS nanosheet. Adapted from ref. . (d) TEM and (e) AFM images of SnSe nanosheets. Adapted, with permission, from ref. (Copyright 2013 American Chemical Society). (f) TEM image of Pd nanosheets. Adapted from ref. .

Figure 4. Catalytic activities of Rh and CeO₂ nanosheets.

(a) Hydrogenation of phenol and (b) hydroformylation of 1-octene. Adapted from ref. . (c) The reaction temperature-dependent catalytic activities of CeO₂-based catalysts for CO oxidation (experimental error: ±3%), and (d) the corresponding Arrhenius plot for the three CeO₂-based samples (experimental error: ±3%). Adapted from ref. .

Figure 5. Performance of the β-Co(OH)₂ nanosheet-based supercapacitor.

(a) Cyclic voltammetry (CV) curves at various scan rates and (b) galvanostatic charge–discharge curves at different current densities (inset) and the corresponding calculated specific capacitances of the single-layer β-Co(OH)₂ nanosheet-based all-solid-state asymmetric supercapacitor. (c) Comparison of the electrochemical performance with previously reported asymmetric supercapacitors. (d) Cycling performance of the fabricated single-layer β-Co(OH)₂ nanosheet-based all-solid-state asymmetric supercapacitor measured at a scan rate of 20 mV s⁻¹. Inset: the corresponding CV curves. Reproduced, with permission, from ref. (© 2014 John Wiley & Sons Inc).

Figure 6. Performance of 2D nanosheet-based photodetectors.

(a) Current–voltage curves of PbS sheets in dark (red) and under illumination (blue) with a green laser. Inset: current–voltage curves on the logarithmic scale. From ref. . Reprinted from permission from AAAS. (b) Photograph of the flexibility demonstration of the fabricated electrode. Inset: SEM cross-section image of a typical photoelectrode. (c) I–V characteristics of photodetectors based on 2D nanosheets of TiO₂, ZnO, Co₃O₄ and WO₃, respectively. Inset: I–V characteristic of the dark photocurrent of 2D ZnO nanosheet photoanode. (d) The photoresponse behaviour of photodetectors under illumination with 325-nm ultraviolet light (67 mW cm⁻²) with ON/OFF interval of 10 s and bias of 0.5 V. Adapted from ref. .