**5. Future outlook**

One of the major problems with 2D nanostructures is to achieve a large-scale synthesis method for producing high quality, large surface area, high crystallinity, and free from any impurity nanosheets. Different methods have been reported to synthesize these nanosheets so far, which generally suffer from problems such as impurities, low crystallinity, low lateral dimension, and little yield, which limit the use of these 2D nanosheets in the industry. At present, many studies focus on improving the synthesis methods of these nanosheets.
