## 2 Zeolites
### Physical Properties
Layer thickness ranges from 1 to 1.5-unit cells, and layers isolated by exfoliation have a thickness of 3.5 nm or 1.5 unit cells. Some structures may be produced by bifunctional MFI templates, multilayered and monolayered, i.e., reaching the ideal increasing of interlayer spaces and accessibility [64]. One of the advantages in physical modification of layered zeolites in comparison to conventional unmodified zeolites is the accessibility of bulky molecules in micropores. In this way, the 2D structures increase the selectivity and reduce coke formation, making the access of reagents to active sites easier. These materials are hierarchical, i.e., they combine the microporosity with intracrystalline mesoporous of pillared, self-pillared, and delaminated exfoliated forms. A parameter that quantifies the volume of micropores versus the surface area of mesopores is the hierarchical factor (HF), and 2D layer structures have large HF values, meaning mesopore surfaces are large and do not affect micropore volume [65]. The absence of Na\({}^{+}\) causes the formation of unilamellar nanosheets [66]. The delamination of a pillared structure allows it to incorporate different active sites and separate them at a controlled distance, leading to material with hydrothermal stability, typical of inorganic solids. The disordered characteristics of these materials do not mean that its structure is amorphous [67]. The profile of adsorption of 2D zeolites is more complex than 3D zeolites, and only fragments of adsorbate are incorporated with micropores [68]. Among the physical properties of great importance is adsorption. The adsorption process involves the fixation by a physical or chemical interaction of a solute in an interface of different natures. However, in zeolites, the process occurs between liquid-solid or gas-solid interfaces. In this process, the solute is selectively dispersed in the zeolitic material. The amount of solute capable of adsorbing on zeolite is small and in general demands high internal area per unit volume. Two types of adsorption phenomena are known, physical adsorption or physisorption, which involves van der Waals forces, and delaying chemisorption, which involves chemical bond formation. Exploration of these phenomena has shown great applicability in the processes of removal of pollutants from aqueous effluents or gases present in the atmosphere [69]. The textural properties are important in evaluating the capacity to undertake the adsorption process, and several methods may be used to determine the textural properties of zeolites, such as pore volume, surface area, and pore size. The ability of molecules to penetrate the pores at a certain speed helps in determining the pore size of the structure. To obtain a precise value, it is important that the measurement temperature is close to the reaction process temperature [69]. The molecules must be inert during the process, so the use of unsaturated molecules such as olefins, which can isomerize or oligomerize on the surface of acidic zeolites, must be avoided. For interpretation of pore openings, Lennard-Jones kinetic diameters are usually used [69]. The presence of impurities in zeolite is one of the causes of decreased performance in terms of textural properties, allowing better adsorption. Postsynthesis base, acid, and hydrothermal treatments are performed to remove impurities. Some of these treatments use acids and remove the Al content, varying the acidity of material. Others uses a basic treatment to remove Si by hydrolysis in the presence of OH ions, altering specific surface area and pore size and generating mesoporous for easy access of molecules and improving the adsorption capacity [70]. Al content may influence textural properties directly. The BET surface area and the micropore volume are parameters that translate this relationship. In some cases, the higher the Al content, the better the textural features that are reached, improving the performance of adsorbents.