*3.1.2. Template synthesis*

**3.1. Wet chemical strategy**

10 Two-dimensional Materials - Synthesis, Characterization and Potential Applications

*3.1.1. Hydro/solvothermal synthesis*

dried under vacuum.

height profiles of a bare Rh NS [29].

Wet chemical method is promising for preparing all types of 2D materials owing to its highyield, low-cost and mass production. Wet chemical strategy is a big kind of synthesis method, which includes hydro/solvothermal synthesis and template synthesis. In this section, we introduce various types of wet-chemical synthesis strategies for preparing 2D nanomaterials.

Hydro/solvothermal method is a common strategy used for the synthesis of inorganic materials. Advantages of hydro/solvothermal method over other types of crystal growth include low temperature (generally in a temperature range of 100–240°C) and convenience of adjusting reaction conditions. Many factors play the key roles in the synthesis of ultrathin nanostructure, which include temperature, reaction time, reactant ratio and so on. Many 2D materials have been prepared by this method, just like MoS2, TiO2, ZnO, Co3O4, MnO2 and Rh [26–29]. In the following, we will take Li's work as an example to explain this strategy.

Ultrathin Rh nanosheets were synthesized successfully through solvothermal method by Li et al. recently [29]. For detailed steps, Rh(acac)3 and PVP are dissolved in solvent mixed by benzyl alcohol and formaldehyde. The mixture is stirred vigorously for 1 h and then transferred to a Teflon-lined stainless steel autoclave. The autoclave is sealed and maintained at 180°C for 8 h and then cooled to room temperature. The resulted black product is precipitated with acetone (10 mL), separated in a centrifuge and washed three times with ethanol (10 mL) and finally

**Figure 5.** (a) Low-magnification TEM image of PVP-capped Rh nanosheet, (b) high-magnification TEM image of PVPcapped Rh NSs, (c) aberration-corrected microscopy image of PVP-capped Rh NS (inset, the corresponding filtered im‐ age using crystallographic average method to improve signal-to-noise ratio), (d) AFM image and the corresponding

Detailed structure information for the synthesized atomically thick Rh nanosheets is indicated by TEM, HRTEM and AFM. TEM image clearly shows that ultrathin nanosheet has a dimen‐ sion lateral size of about 500 nm, while the near transparency of the sheets indicates the A typical procedure of template method includes complicating morphology of template by growing crystal confined in specific dimension and then removing template through high temperature or adjusting pH. By this way, nearly all types of nanostructure including quantum dot (0D), nanowire (1D) and nanosheets (2D) can be prepared. The suitable template and condition of removing template are important. Many nonlayered structure 2D nanomaterials can be synthesized using the as-prepared 2D nanomaterials as the template, such as Fe2O3, Au, CuInS2 and so on [30–32]. Herein, we take α-Fe2O3 as an example to illuminate this method.
