## 3 Polymer Nanocomposites as Adsorbent
### Adsorbent from Nanocomposites Polymer for the Elimination of Metals Ions
[PERSON] and [PERSON] also presented a study on the absorptive characteristics of polyaniline prepared in 50/50 volume ratio of water and acetonitrile [113]. The prepared polyaniline powder was utilized as an adsorbent for the elimination of noxious hexavalent chromium from aqueous solutions. The optimal pH for the total removal of chromium was 7 (neutral condition) and pH of 3 (acidic condition) offered a maximum removal of hexavalent chromium. The maximum estimated adsorption of chromium was 36.1 mg/g for polyaniline [113]. Despite the successful use of polyaniline for adsorption, polyaniline is subjected to crucial shortcomings, which include inseparability, very low solubility when used in most obtainable solvents, shoddy conductivity when likened to metals, poor technology effectiveness, moisture absorbing, and unstable structure. With the purpose of improving the properties of polyaniline, different sorts of polyaniline composites have been synthesized with metals, metal oxides, diverse nanotubes, etc. A study has confirmed that polyaniline nanocomposites demonstrated value-added physical and physiochemical properties [108]. Scholars have employed polyaniline/polyaniline composites as adsorbents for inorganic and organic pollutants [114; 115]. [PERSON] et al. [116] prepared polyaniline nanoparticles and 1-D nanostructures by means of a facile sono-assisted chemical oxidation technique in protonic acids such as hydrochloric acid, surfulamic acid, citric acid, taurine, and deionized water for the elimination of aqueous Cr(VI) [116]. Their result revealed that all nanocomposite adsorbents demonstrated effectual adsorption for Cr(VI). Nonetheless, the extent of their adsorption efficacies is dependent on the protonic acids and the resultant molecular structures of polyaniline. In all, the polyaniline-hydrochloric acid synthesized in strong hydrochloric acid showcased maximum adsorption capacity, followed by polyaniline-surfulamic acid, polyaniline-citric acid, polyaniline-taurine, and polyaniline-deionized water. The capacity of the adsorption was equivalent with oxidation state and the extent of polyaniline protonation. Polypyrrole adsorbents also have a substantial role in the elimination of metal ions owing to their simplicity and high flexibility in synthesis, high conductivity, biocompatibility, stability, good mechanical properties, and redox properties [117]. As much as adsorption efficiency is mostly influenced by the preparation conditions of polypyrrole, some attempts have been carried out to eliminate metal ions by means of polypyrrole conducting polymers made via chemical oxidative polymerization of pyrrole in the company of several oxidants at various conditions [109; 118; 119]. [PERSON] et al. [120] reported polypyrrole-based adsorbents synthesized by means of doping polypyrrole with chloride, polypyrrole with dodecyl sulfate, or polypyrrole with octadecyl sulfate and by aminating polypyrrole with aminopropyl-triethoxy-silane [120]. A huge quantity of bovine serum albumin was adsorbed on polypyrrole with chloride adsorbent at roughly pH of 5; however, nearly no lysozyme was adsorbed at the same pH. Contrastingly, a substantial quantity of lysozyme was adsorbed on polypyrrole with dodecyl sulfate or polypyrrole with octadecyl sulfate adsorbent at roughly pH of 10; however, nearly no bovine serum albumin was adsorbed by these two types of adsorbents at the same pH. Nonetheless, polypyrrole with aminopropyl-triethoxy-silane adsorbent exhibited a dissatisfactory selectivity for bovine serum albumin or lysozyme adsorption in the pH range of < 5 \(\leq\) 9. [PERSON] et al. [121] presented a study on the adsorption of uranium (VI) ions on the polypyrrole adsorbent [121]. The investigation was done to examine the impact of a number of surfactants on the prepared polymers and their performance as the uranium adsorbent. The results revealed that the adsorption capacity peak of polypyrrole for uranium (VI) was determined to be 87.72 mg g\({}^{-1}\).