**3.2 Template synthesis (sol-gel technology)**

An aqueous solution or a gel containing material and silicate block has been utilized during this process. During nucleation processing, the inorganic host crystals grow and are adsorbed within the layered surface. The sol-gel method can enhance the elimination between silicate layers through the single-step process in the absence of important oniumions, with some disadvantages. First, in the composition of clay compounds, the clay mineral requires high amounts of heat energy, which decomposes polymers matrix. Also, the negative tendency has been found while merging during silicate growth. Sol-gel process has commonly been employed for the generation of dual-layer nanocomposites, but with very little variation in concentrated silicates [2]. The natural features of the matrix structure have allowed it to be the most widely used synthetic material.

The main advantages of the method are as follows:


*Recent Progress and Overview of Nanocomposites DOI: http://dx.doi.org/10.5772/intechopen.102469*

The drawback with metal-metal nanocomposites is agglomeration and nonhomogeneous composition. The preparation of high-quality polymer nanocomposite materials using appropriate processing methods is essential to achieve high NC performance. Unique processing methods have been designed for the preparation of polymer nanocomposites. One universal method of preparation for all nanocomposites is not possible due to the structural and chemical differences of NCs and the different types of materials used. Each process requires specific processing conditions depending on the synthesis method, the type of nanoscale filler, and the required structures. In general, processing different technologies does not produce the same results.

#### **3.3 Layered filled/nanocomposites (LFNCs)**

Since silicate clay is hydrophilic, it is not suitable for mixing and blending with many compounds. In addition, the electrostatic forces cause the solid accumulation of platelets of clay. The neighboring platelets can share counter-ions, resulting in stacked platelets. It does not work with untreated clay to form nanocomposites because most of the clay matter is trapped internally and shows an interaction with layered nanocomposites. So, the clay must be processed well, before it can be utilized to prepare a nanocomposite material. The ion-exchange method is commonly used to obtain molded clays which make it more compatible with organic nanocomposites. After that, the clay can be mixed with different materials to get the desired product. Toyota has begun extensive research on nanocomposites molding and done a lot of work on loaded nanocomposites. There are four main processes that are used for the synthesis of polymer composites. These processes are as follows:


The silicate layers are hardened and the polymer is melted to further processing stages. The concentrated silicate is swollen in a solvent, for example, chloroform, toluene, or water. Thereafter, the surface silicate and polymer solutions are mixed, the polymer chains bind and the solution inside the silicate layers evaporates. The composite structure remains the same during solvent removal, resulting in nanocomposite being deposited between the moving layers. Because of their excellent properties, that often used in materials, that are embedded in many nanocomposites. For example, amino acids convert montmorillonite (MMT) which is degraded by caprolactam monomer at 100 degrees centigrade and initiate its ring opening to detect MMT/nylon-6 nanocomposites. Ammonium cation of amino acids prefers the separation of caprolactam. The number of carbon atoms in the amino acid moiety greatly affects the flammability, which indicates that the concentration of caprolactam monomer is higher.

In the second process, embedded silicate begins to swell in an aqueous monomer mixture to form a polymer solution between the coated clay layers. Although the methods of interlamellar polymerization are best known for using concentrated

silicates. Polymer nanocomposites are receiving a lot of attention due to the nanocomposite activity of MMT/nylon-6. In addition, two-step *in situ* polymerization was used to prepare MMT/polymer nanocomposite. These two steps include the preparation of the treated MMT solution and the mixing of polymers, respectively.

In the third process, melt intercalation occurs directly and composite silicates are combined with molten state NPs without the requirement of solvent. The polymer mixture is drawn by cutting over the softening area of the polymer suspension. The expanded chains of the polymer penetrate the intermediate layers of silicate from the melting of the polymer mass during the shrinkage. Fourthly, the process enforces as polymer suspension behaves as a template to form layered clay material. Siliconbased polymer materials are made from *in situ* hydrothermal crystallization, where a colloidal matrix of polymer gel and silicon-based NCs are being synthesized. This technique is being radially used to assemble nanocomposites with a double layer where silicates are formed in a solid solution consisting of building blocks of silicate and polymer precursor. This process is most suitable for water-soluble polymers, such as hydroxypropylmethylcellulose (HPMC), poly (dimethyldi-allylammonium) (PDDA), poly (vinyl-pyrrolidone) (PVPyr), and poly (aniline) (PANI)).

Polymerization techniques are well known for using concentrated silicates. Polymer nanocomposites are receiving high admiration due to nanocomposite induction. The *in situ* polymerization process could also be used to prepare nanocomposites loaded with graphene oxide. Natural graphite flakes are efficient and wearable structures with a carbon axis at the normal lattice. Because there are no active ionic groups of natural graphite flakes present, it is difficult to combine monomers onto graphite components to form graphite/polymer NCs with ion-exchange interactions. However, the dispersion of graphite has many holes with a diameter of 2–10 μm. Firstly, the graphitic dispersion starts interacting with a polymer solution with the help of the sonication technique and then polymers get embedded in the dispersed graphite holes and the solvent is released, thereafter. Graphene and composites are then obtained through heat transfer or immersion process. In addition, an electrostatic bonding process has been reported for the preparation of graphene/polymer nanocomposites [29]. First, polystyrene (PS) latex was synthesized using hexadecyl trimethyl ammonium bromide (cationic surfactant), creating favorable conditions in the areas of PS micelles. In addition, CNT/polymer resin (such as epoxy) nanocomposites could be prepared by means of thermal compression. The thin layer of the nanotube network is first detected by multiple nanotube dispersing steps and suspension filters, the large CNT sheets are then processed as a permeable resin. These large sheets are assembled to form solid nanocomposites for thermal mechanics.

#### **3.4 Synthesis of chitosan nanocomposites (Ch-NCs)**

To date, there have been several reported studies on the integration of Ch-NCs using a variety of integrated approaches. Researchers have developed several novel methods for the synthesis of Ch-NCs. Such methods include emulsion droplet coalescence, micellar modification, ionic gelation, precipitation, sieving, and spray drying. These methods have been used in the integration of chitosan-based materials which are used for drug delivery and other biomedical applications. However, the use of nanocomposites for agro-applications is still very limited. This can only happen if nanocomposite sources are economical and consistent. To ascertain the desirable characteristics, chitosan has been used for nanocomposite synthesis. As per the literature, ionic gelation methods and spray suspension methods have been considered as the most suitable synthetic methods for the production of large Ch-NCs.

*Recent Progress and Overview of Nanocomposites DOI: http://dx.doi.org/10.5772/intechopen.102469*

The mechanism of ionic gelation has been discussed. In this system, well-charged amino groups are combined with the less well-gelled tripolyphosphate (TPP). TPP is an anionic cross-linker that binds to the chitosan molecule and converts it into nanoparticles. TPP is nontoxic, so it is used in the production of chitosan-based nanomaterials (ChNMs). The plant response to nanocomposites used depends on a number of factors, including particle size, size distribution index, higher zeta capacity, and component nature. Nanocomposites and their activities with naturally occurring materials have introduced the environmentally friendly pollution-free method to deal with many challenges. Manufactured nanocomposites can be used as a foliar application, seed growth, and in soil mixing.

Chitosan-based nanomaterials are very extensively tested on plants to identify various factors, such as antimicrobial, adhesive, antioxidant. Chitosan can be used as a single ingredient or combined with other substances, such as copper (Cu), zinc (Zn), and silver (Ag), to synthesize the material of interest. Chitosan exhibits a strong metal bonding due to the availability of free amine groups throughout the polymeric spine of chitosan. The Zn+ 2 and Cu+ 2 have an important role in plant growth and germination; therefore, researchers have focused more on these two metal ions, by combining them with chitosan substrate.

#### **3.5 Chitosan-Zn nanocomposites (Ch-ZnNCs)**

The researchers have incorporated a variety of plant micronutrients onto NCs, including zinc. Zinc (Zn) was named as an integral part of the plant micronutrient in 1869. The addition of Zn to plants was intended to ensure its continued availability and increased efficiency. Zinc also protects plants from different environmental hazards (sun, water, etc.). Interactions between Zn-chitosan molecules have been demonstrated by using analytical methods, such as FT-IR and X-ray diffraction. The amino moiety in chitosan has shown two different styles, which are as follows:


In 2018, Ch-Zn nanocomposite was prepared by the incorporation of lowmolecularized chitosan molecules by iron-containing organosol. In a standard test, Zn granules (0.5 g), toluene (120 ml), and chitosan (4 g) were used. The synthesized NC was also tested for the physicochemical parameters by using different analytical methods, such as; SEM, TEM, and XRF. The nanocomposite, when combined with iron, has shown excellent antifungal activity against *Rhizoctonia solani.* Du, Niu, in 2009, loaded Zn2+ granules into chitosan solution to improve antibacterial activity [48]. In summary, ZnSO4 solution was obtained by adding 0.3%, w/v Zn-granules to chitosan-solution (dissolved in 1% (v/v) acetic acid and TPP (1% w/v). The results of the study showed that the increased concentration of Zn2+ significantly improved the potential zeta of nanocomposite which led to an increase in the combined antibacterial activity. Chitosan zinc oxide nanocomposites (Ch-ZnO) were also tested for antifungal activity against Fusarium wilt (created by Fusarium oxysporum F.sp. Ciceri in chickpea). In addition to reducing recorded disease ~40% after using Ch-ZnO; and contributed to the increased growth of chickpeas.
