## 3 Polymer Nanocomposites as Adsorbent
### Adsorbent from Nanocomposites Polymer for the Elimination of Metals Ions  
Wastewaters from the industries comprising of metal ions are indirectly or directly released into streams, lakes, and rivers [101]. Usually, heavy metals cannot be decomposed or biodegradable; hence, they are stable environmental contaminants. In recent time, metal ion pollution in wastewater is globally the main ecological challenge that is dangerous to human life because of the mobility of contaminants in natural water bodies and their noxiousness [102]. Numerous approaches such as ion-exchange, membrane filtration, and electrochemical and adsorption technologies are employed for the elimination of several metal ions from wastewater [103]. Adsorption is most widely used among them as a result of low capital cost of the technology, simple strategy, ease of working principles, and insensitivity to toxic pollutants [104]. Furthermore, adsorption does not lead to the creation of destructive substances [105]. Factors such as solution pH, adsorbent dosage, contact time, concentration of initial metal ions, and temperature impact the adsorption of metal ions [106]. In the last decade, polymeric adsorbents have become apparent as prospective substitutes to conventional adsorbents with respect to their enormous surface area, modifiable surface chemistry, excellent mechanical stiffness, sizes of pores and distribution, and practicable reinforcement under minor conditions [107]. Conductive polymers consist of molecules, which are organic in nature, and have the capacity to conduct electricity and mimic metals through the possession of mobile electrons as charge carriers. Such polymers could display semi-conductivity. Generally, conductive polymers are in nature non-thermoplastic and have its place in the class of organic material [108]. Basically, there has been extensive study on conducting organic polymers such as polyaniline, polypyrrole, and polythiophene over the last two decades as a result of their excellent electrical conductivity, and good environmental stability [109]. These conductive polymer based-adsorbents and their composites have stimulated substantial consideration as a result of their possible utilization as adsorbents for metal ions such as iron, manganese, magnesium, arsenic, cobalt, nickel, etc., from wastewater [102; 103]. Polyaniline and its derivatives have shown good adsorption ability because of their large quantity of amine and amine functional groups in polymer chains. Hence, they are employed as adsorbents to eliminate metal ions from wastewater. Researchers have recently investigated polyaniline and its derivatives as effectual nanoadsorbents for the elimination of metal ions [99]. Polyaniline particles have been assessed for the removal of mercury ions from aqueous solutions [110]. It was discovered from the study that the capacity of the adsorption of polyaniline particles was 600 mg g\({}^{-1}\) for mercury ions [110]. Additionally, pH of 5.5 was suitable for the adsorption capacity of mercury ions owing to all the nitrogen-comprising functional groups on the polymer matrix, which might be responsible for mercury adsorption. Another metal ion of interest is chromium ion. There is an increasing attention on hexavalent chromium Cr(VI) due to its noxious and carcinogenic impacts on human health and its wide-ranging utilizations in industries like mining and electroplating [111]. [PERSON] et al. presented a study on the adsorption of Cr(VI) ions in aqueous solutions by polyaniline particles [112]. These authors established that the kind of solvent utilized for the production of polyaniline had a distinct influence on the polyaniline morphology and its capacity to eliminate Cr(VI) from the aqueous solution. Furthermore, the elimination efficiency peak of Cr(VI) (more than 90%) was attained using the produced polyaniline. In accordance with these studies, it was finalized that the mechanism of polyaniline responsible for the removal was the amalgamation of surface adsorption.