## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile as Fiber
The  
Figure 5: Three-dimensional AFM images of (**a**) animated PAN-NF before adsorption and (**b**) after copper adsorption. Adapted with permission from reference [73]. Figure 6: Activated carbon derived from PAN fibers. maximum uptake value of dyes by PAN/PAMAM composite nanofibers was 1666.66 mg/g and 2000 mg/g for DR80 and DR23, respectively. The preparation of polyacrylamide/polypyrrole (PAN/PPy) core-shell structure nanofibers was carried out through an in situ chemical oxidative polymerization technique to extract Cr6+ from wastewater [77]. The pH was found to be an important parameter to affect the adsorption of Cr6+ ions; adsorption of Cr6+ ions was enhanced with a decrease in the pH of the solution. The time taken to reach equilibrium was 30 min and 90 min, with the change in initial concentration from 100 ppm to 200 ppm. The results agreed with the pseudo-second-order model. [PERSON] et al. (2012) contemplated a method to synthesize polyacrylamide/polypyrrole by an electrospinning method for the removal of radioactive uranium particles from aqueous systems via column adsorption under continuous flow [78]. These fibers were functionalized with NH2 OH.HCl to convert nitrile moieties into amidoxime moieties. Amidoximated polyacrylamide/polypyrrole is used repeatedly, however, their adsorption tendency decreased regularly. [PERSON] et al. (2009) investigated functionalized polyacrylamide/polypyrrole fiber by reacting it with diethylenetriamine and chloroacetic acid to form a reusable chelating fiber containing polyamino-polyacrylamide/acid ligands [79]. The immobilization of amine and carboxymethyl into polyacrylamide/polypyrrole fibers was determined through X-ray diffraction, SEM, and FT-IR. These chelating fibers decreased the Cd2+ ions concentration in sewage water by up to 0.001 ppm, although the highest adsorption value of Cd2+ ions was 1.34 mmol/g. In addition, the resultant adsorbent was highly efficient for treating other metal ions such as Cu2+, Ca2+, Zn2+, Mg2+, Pb2+, Ni2+, Ag+, and Hg2+ ions. Another study reports acrylic fibers synthesized and improved by diethylenetriamine to produce modified chelating fibers [80]. This functionalized resin was utilized to remove Pb2+, Cu2+, and Ce4+ ions from water. It was found that the mechanical strength of modified resin was low compared with unmodified resin. In other research, activated carbon nanofibers (ACNFs) were synthesized from the precursor polyacrylamide/polypyrrole and magnesium oxide through an electrospinning process [81]. Adsorption of cadmium ions was investigated using different adsorbents such as polyacrylamide/polypyrrole-based activated carbon nanofibers/magnesium oxide, pristine, activated carbon nanofibers, and granular-activated carbon. A batch adsorption study showed that polyacrylamide/polypyrrole-based activated carbon nanofibers/magnesium oxide and activated carbon nanofibers were best in the extraction of cadmium compared with granular activated carbon. The polyacrylamide/magnetic nanofibers were prepared via an electrospinning process followed by chemical precipitation by magnetite (Fe3O4) [82]. It was a two-step process. Iron nanoparticles tend to accumulate and settle down at the bottom, making them less effective in the removal process. Therefore, iron nanoparticles were loaded onto polyacrylamide/polypyrrole to enhance their efficiency in the extraction of metal ions. A batch method was used for the extraction of lead ions using polyacrylamide/magnetic nanofibers. An equilibrium time study was conducted with a 50 mg/L solution for different time intervals. It was observed that maximum adsorption capacity for lead ions was obtained within 80 min. Afterwards, there was no change in the adsorption capacity. The polyacrylamide/polypyrrole-based calixarene nanofibrous sorbents were synthesized by an electrospinning process for the extraction of Cr6+ ions [31]. Calixarene molecules having piperidine groups at the lower or upper ends of their calix structure were used as water-resistant composite nanofiber adsorbents.