## 3 Polymer Nanocomposites as Adsorbent
### Polymer Nanocomposites as Adsorbent for Dye Removal  
In the past three decades, the movement and dispersal of dyes in water have been extensively studied on the account of their toxic effects to human beings, plants, animals, and aquatic entities. Discharging dyes to the water source reduces the quality of water. Dyes, textile, cosmetics, rubber, paper, leather, foodstuff, and plastic industries utilize massive amount of synthetic dyes for the purpose of giving colour to their products; and they consume substantial volumes of water, which generates a large substantial quantity of coloured wastewater [127]. The colours in wastewater are classify by their high oxygen demand, inconsistent pH, imperishable, and dependability to several oxidizing agents. On the account of complex constructions and their pronounced struggle to dilapidation, several wastewater effluents have turned out to be a challenge for decolourization and demineralization [128]. In textile industries, close to 25% dye is discharged in the course of dyeing process and 2-21% is the discharge into several ecological constituents through a direct process. Aquatic life finds it difficult to get enough sunlight because of the colour of dyes [129]. The noxious effects of dyes have gotten to an extreme push on the account of their high half-life period. Devoid of any acceptable treatment process, dyes continue to linger in the milieu for an extended period. The extremely multifaceted structure and synthetic foundation of dyes makes their removal relatively problematic [129]. Furthermore, as a result of dyes' chemical structure, they behave as resistant to numerous chemicals, oxidizing agents, and heat that are biologically non-degradable. Hence, it is not quite easy to decolorize the effluents as soon as they are released into the aquatic environment. From several available methods employed for eliminating noxious waste from wastewater, the most vital methods are ion exchange, reverse osmosis, precipitation, and adsorption. Amongst these methods, adsorption technique is the most versatile approach extensively used for the removal of dyes [130; 131]. Currently, natural polymeric materials as adsorbents are attaining more interest for the treatment of wastewater due to their non-toxic and biodegradable nature [132]. Availability and low cost of polymer nanocomposites as adsorbent have encouraged their use for several commercial purposes, which includes the removal of dye from wastewater. Furthermore, polymer nanocomposites have also taken an important place when used as adsorbentsbecause they possess excellent granulometric properties, a high surface area, boosted active sites, and are chemically and thermally stable. Functionalized polymer nanocomposites have captivated noteworthy attention on account of their chemical and physical features, simplicity of separation, and diverse reactive groups on the backbone chain [133]. In addition, due to the development in adsorbent synthesis and functionalization, there has been a solid prediction to ensure that adsorbents are prepared in an enhanced condition with an improved demonstration of the preferred qualities of an extremely competitive adsorbent [134]. This functionalization allows the adsorbents to be further responsive to binding with large dye molecules. Furthermore, it gives room for the behavior of adsorption and its subjection to a performance test in binary systems [135] and ternary dye systems [136]. Usually, raw adsorbent materials possess very low adsorption capacities; hence, the need to functionalize them preceding their utilizations [135; 137]. There are different methods of functionalizing adsorbent materials; they could be grouped into three main classes (chemical, physical, and biological modifications), as shown in Figure 4. The mechanism of covalent functionalization comprises of the formation of covalent connection amid the carbon \(\pi\)-bond that is not saturated and other functional groups.