## 3 Polymer Nanocomposites as Adsorbent
### Polymer Nanocomposites as Adsorbent for Dye Removal
#### 3.2.2 Adsorbent Made from Polymer Carbon Nanotube for Dye Removal  
Several researchers have presented reports on improved adsorbents for the elimination of dyes from wastewater with the utilization of the modifications of carbon nanotubes with excellent functional groups. This type of functionalization method has resulted in a reduction in aggregation and hydrophobicity. This increases its capacity for adsorption, offers a very good distribution in aqueous solutions, and provides selectivity and affinity in the direction of the contaminants in the wastewater [160; 161]. Carbon nanotubes probably comprise of functional groups, contingent on the preparation and purification process [7]. The functional groups of carbon nanotubes have made its usage possible with amalgamation with other materials to form composites for dye removal. Nonetheless, studies on polymer carbon nanotube composite, as adsorbent for the removal of dye is quite rare in comparison to polymer nanoparticle composite for the same purpose. [PERSON] et al. [162] removed Congo red from aqueous solution using a multiwalled carbon nanotube oxidized and treated with HNO\({}_{3}\). Excellent adsorption capacity of 357.14 mg g\({}^{-1}\) was attained and it points to the efficiency and suitability of the nanotube for the attainment of a safe and clean environment. In a study by [PERSON] et al., [163], the zeolitic imidazolate framework was used as a metal-organic structure, based on graphene oxide, and carbon nanotubes; its hybrid nanocomposites were prepared by the facile approach at the surrounding temperature. The fabricated nanomaterials were employed as adsorbents for malachite green removal. The optimum adsorption capacities were 1667, 2034, and 3300 mg g\({}^{-1}\) for zeolitic imidazolate framework, zeolitic imidazolate framework-carbon nanotubes and zeolitic imidazolate framework-graphene oxide, respectively, at 20 \({}^{\circ}\)C. The hybrid nanocomposites showed steady and extensive reusability of more than four cycles. Although carbon nanotubes have been broadly employed as adsorbents for dye removal due to their small size, large surface areas, and exceptional chemical structure, the impact of unmodified carbon nanotubes on adsorption application is not quite satisfactory as a result of their agglomeration and being devoid of active adsorption sites [164]. Hence, the modification of carbon nanotubes that precedes the adsorption process is of significant interest owing to the efficiency of the modified composites. With the intention of enhancing the adsorption performance of carbon nanotubes for methylene blue removal, [PERSON] and [PERSON] [165] improved carbon nanotubes wrapped with poly (sodium 4-styrene sulfonate) to attain carbon nanotubes/poly (sodium 4-styrenesulfonate). Their results proposed that carbon nanotubes wrapped with poly (sodium 4-styrenesulfonate) with the aid of \(\pi\)-\(\pi\) electron-donor-acceptor interactions and \(-SO_{\overline{3}}\) groups can have the ability to accept the \(\pi\) -electrons from the conjugated system of carbon nanotubes. Hence, carbon nanotubes in the hybrid did not only adsorb methylene blue only via \(\pi\)-\(\pi\) interactions but also aided the electrostatic attraction amid \(-SO_{\overline{3}}\) groups of poly (sodium 4-styrene sulfonate) and dimethylamino groups of methylene blue. [PERSON] et al. [166] examined the prospect of utilizing improved multi-walled carbon nanotubes as an effectual adsorbent for several cationic dyes' removal. The fabrication of the magnetic carbon nanotube composites were done by means of surface reversible addition fragmentation transfer of chain co-polymerization of acrylic acid and \(N\)-isopropyl acrylamide in the presence of magnetite nanoparticles. The composite adsorbent demonstrated high adsorption capacities. It is reusable and offers easy recovery, making it a good choice in the treatment of wastewater [166]. [PERSON] et al.