**Abstract**

Two-dimensional (2D) nanomaterials are composed of thin layers that may have a thickness of at least one atomic layer. Contrary to bulk materials, these nanomaterials have a high aspect ratio (surface-area-to-volume ratio) and therefore have many atoms on their surface. These atoms have a different function than internal atoms, and so the increase in the number of surface atoms leads to a change in the behavior of 2D nanomaterials. Graphene, as one of the most widely used and most important 2D materials, has unique properties that result in its widespread use in various industries. After successful performance of graphene in many applications and industry, it is expected that other two-dimensional materials will also have this capability. However, the use of other two-dimensional materials requires more time and effort.

**Keywords:** two-dimensional, nanomaterial, graphene, hexagonal boron nitride, chalcogenide

## **1. Introduction**

Dimensional classification is one of the methods for classifying nanomaterials: the same chemical compounds can exhibit extraordinary different properties when they are configured in a zero (0D)-, one (1D)-, two (2D)-, and three (3D)-dimensional crystal structure [1]. In spite of the fact that there have been plenty of scientific reports on 0D [2], 1D [3–5] and, of course, 3D [6, 7], however, a limited number of researches on 2D nanomaterials are published.

2D nanomaterials are considered to be the thinnest nanomaterials due to their thickness and dimensions on macroscale/nanoscale. These nanomaterials have a layered structure with strong in-plane bonds and weak van der Waals (vdW) between layers. These ultrathin nanomaterials can be produced from laminated precursors described in the following sections. Although the ideal state is a single layer, but often these nanosheets are composed of few layers (less than ten layers). In recent years, 2D nanomaterials such as graphene, hexagonal boron nitride (hBN), and metal dichalcogenides (MX2) have attracted a lot of attention due to their satisfactory properties and widespread uses in the electronics, optoelectronics, catalysts, energy storage facilities, sensors, solar cells, lithium batteries, composites, etc.

The schematic structure of graphene, boron nitride nanosheets, and tungsten diselenide (WSe2) as a dichalcogenide has been illustrated in **Figure 1**. As shown, these compounds are configured in honeycomb structure, but the arrangement of the neighboring atoms in the upper and lower layers of 2D nanomaterials is

**Figure 1.**

*The structure of (a) single layer of graphene with a lattice of carbon atoms, (b) boron nitride nanosheets with B in blue and N in pink, and (c) tungsten diselenide (WSe2) with W in blue and Se in yellow [8].*

different. In graphene, each carbon atom is next to another carbon atom in its upper and lower layers, while in the structure of BNNSs, each atom is located in the center of the benzene ring on the upper and lower layers. In the structure of dichalcogenides, each atomic layer of metal is sandwiched between two atomic layers of X.

In this chapter, the recent developments in the synthesis, properties of 2D nanomaterials especially graphene, and boron nitride nanosheets (BNNSs) are discussed. A comprehensive understanding of the properties and physics of these materials can be very effective in finding their application in the industry that is discussed in this chapter. The reported virtues and novelties of these nanomaterials are highlighted, and the current problems in their developing process are clarified.
