**2.3. Layered systems**

Lamellar materials are solids with two-dimensional structures possessing atoms firmly linked together in two directions of space forming foil (planes), and they are weakly linked in the perpendicular direction among them. The region of weak interaction between the sheets is normally known as interlamellar region or gallery [21]. Many kinds of solid lamellar blades have electric charge due to substitutions of isomorphic ions of different network load. To reach the electrical neutrality of the structure, ions of opposite charge, normally solvated by water or other polar molecules, occupying the interlamellar region, are known as compensation ions. Layered solids have high surface areas between 100 and 1000 m2 /g. In many cases, the interlamellar surface is accessible only to water and other small polar molecules that are capable of solvated ions of compensation.

The elimination of molecules of solvation by degassing at elevated temperatures results in a collapse of the interlamellar region, especially if interspersed compensating charge ions are small in relation to the occupied space; on the other hand, if the compensating charge ions are relatively large, they can have the role of pillars and prevent the collapse of the interlamellar regions when the middle of solvation is eliminated, resulting in solids called solid lamellar pillars. Figure 2 presents a system that shows some characteristics of layered solids.

**Figure 2.** Representation of a layered solid pillared, wherein pores are defined by the height of the interlamellar space (d2) and the lateral spacing (d1) between the guest molecules or pillars (P). R denotes the interlamellar region.

Laminar solid pillars can be described as sandwich compounds serving three important criteria:


Lamellar surface area presented by solids (between 100 and 1000 m2 /g) makes these materials an object of study important above all in the area of nanoscience and nanotechnology because they have been shown to generate opportunities in different fields of application, such as biomedical electronics, applications in the area of storage and energy conversion, and catalysis [22].
