## 3 Polymer Nanocomposites as Adsorbent
### Polymer Nanocomposites as Adsorbent for Dye Removal
#### 3.2.1 Polymer Nanoparticle as Adsorbent for Dye Removal  
There has been increasing attention on research in the advancement and applications of nanomaterials (nanoparticles, nanotubes, nanofibers, and nanowires) in science and engineering [139]. The cost and properties (particle size, shape, even distribution of particle size, structure of crystal, composition distribution, purity, aggregation control, and stabilization) of nanoparticles, made them appropriate for dye removal in wastewater. The large porosity of organic or inorganic nanoparticles and their small size and huge surface area take full advantage of their interface with the dye molecules via their several contaminant bindings sites, hence, their adsorption efficacy. From a kinetic perspective, the adsorption process facilitated via the nanoparticles is fast [140]. Hence, the utilizations of nanoparticles in the wastewater treatment process offer a novel channel of nanoparticles applications. Figure 4: Classes of functionalization (covalent and non-covalent) approaches for adsorbent materials. Chemical modifications permit enhancement of their chemical and physical properties. The physical modifications are grouped into thermal treatment techniques and deionized water treatment techniques. Biological modifications involve the bioadsorbtion treatment method. Researchers have studied polymer nano adsorbents in water purification and dyes sorption using diverse kind of nanoparticles [141]. Nanoparticles such as iron oxides/hydroxides, zero-valent iron, iron oxide nanoparticles (such as magnetite, maghemite), titanium oxide, zinc oxide, and aluminium oxide nanoparticles together with their composites have been utilized as an adsorbent for the removal of dye from wastewater. In addition, there is consideration on the employment of polymer-based nanoparticles for the removal of dyes. Polymer-based nanoparticles possess abundant dormant usages like optical activity, increased catalytic, conductivity, toughness, and chemical selectivity [128]. However, nanoparticles of zero-valent metals, magnetic oxides, biopolymers, metallic oxides, and single-enzyme nanoparticles are usually employed for dye removal. Magnetic nanoparticles have proven to be significant nano-adsorbents because they have the capability of easy separation. The adsorption process using this nanoparticle is done through the utilization of an external magnetic field, circumventing the monotonous and expensive separation technique of nano-adsorbents from aqueous solutions [142]. Furthermore, preferred functional groups can be hosted onto the surfaces of magnetic nanoparticles via several types of surface modification approaches, in order to channel the nanoparticles for precise utilizations [143; 144]. From the investigation conducted by [PERSON] et al., [145], chitosan-coated octadecyl-functionalized magnetic nanoparticle was prepared for the elimination of perfluorinated compounds. The coating advances the dispersibility of magnetic nanoparticles in aqueous solution and improves the non-intrusion ability of the adsorbent to natural organic macromolecules in multifaceted samples. [PERSON] et al. [146] directly prepared ultrafine well-dispersed Fe\({}_{3}\)O\({}_{4}\)-poly(acrylamide-co-sodium acrylate) core-shell magnetic nanogels in an aqueous solution using the controlled co-precipitation method. The composite was prepared for methylene blue removal from aqueous solutions. Their study revealed that for methylene blue removal, the adsorbents demonstrated high sorption capacities. [PERSON] et al. [147] formulated a facile and eco-friendly route to synthesize magnetic nano-adsorbent for the elimination of pollutants from the environment. Founded on mussel-inspired polymerization, amino-coated magnetic nanoparticles were synthesized via immersion of magnetic nanoparticles into an aqueous solution of catechol and hexanediamine at a constant temperature, for the elimination of Congo red.