**4. Perspective and conclusions**

With the advantages of very high surface-to-volume ratios and special electronic properties in two-dimensional materials, ultrathin nanosheets are very promising in catalysis, supercapa‐ citors, photoconductive materials, batteries and magneto-optical components. Therefore, it is imperative to exploit more technologically advanced synthesis strategies to obtain high quality, large size, ultrathin two-dimensional materials. At present, thinner, larger size, high productive and quality nanosheets are still the chief purpose for scientists. Usually, the thinner nanosheets give a higher catalytic performance and other special properties. Besides these, controllable thickness, architectures assembled by nanosheets and composite nanostructure, such as quantum-dot/nanosheets, sandwich structure and modification on two-dimensional nanosheets, also provide new opportunities for material science.

In summary, synthetic strategies, such as top-down and bottom-up method, have been employed for synthesizing two-dimensional crystals. The top-down strategy includes micro‐ mechanical exfoliation, ultrasonic exfoliation, lithium-intercalated and exfoliation and ionchange exfoliation. Using top-down strategies, one is able to obtain high-quality and large-size two-dimensional crystal conveniently. Even so, this method is only appropriate for those materials whose bulk crystals are layered. Comparatively, bottom-up strategy could overcome this shortage. Bottom-up strategy is composed of wet chemical method, microwave-assisted chemical, topological conversion strategy and chemical vapor deposition method. All these strategies may present different features and questions for preparing two-dimensional materials. In the future, scientists should take more and more efforts to develop new synthetic technologies for high-quality 2D material and the relevant applications.
