## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile as Fiber
The electrospinning method was utilized to make polyacrylamide nanofibers, which were then improvised through hexamethylenediamine to obtain the aminated polyacrylamide (APAN) nanofiber mats. The obtained nanofiber mat was utilized to extract three kinds of metal ions, namely, Pb\({}^{2+}\), Cu\({}^{2+}\), and Ni\({}^{2+}\) ions from aqueous solution. The maximum uptake values for Pb\({}^{2+}\), Cu\({}^{2+}\), and Ni\({}^{2+}\) metal ions on the APAN nanofiber mats were 175, 162.5, and 48.5 milligrams per gram of adsorbent, respectively. Another study examined the effectiveness of removing Cr\({}^{3+}\), Pb\({}^{2+}\), and Hg\({}^{2+}\) ions from industrial effluents using hydrolyzed/thioamidated polyacrylamide nanofibers [72]. The adsorption values for Cr\({}^{3+}\), Hg\({}^{2+}\), and Pb\({}^{2+}\) were found to be 0.73 mmol/g, 0.09 mmol/g, and 0.14 mmol/g (at pH 4.0), respectively. This adsorbent was very selective for the Cr\({}^{3+}\) ions compared with Pb\({}^{2+}\) and Hg\({}^{2+}\) ions. [PERSON], [PERSON], and [PERSON] (2011) synthesized polyacrylamide nanofibers by the electrospinning method and modified them by diethylenetriamine to form aminated polyacrylamide nanofibers [73]. These membranes were utilized to remove Cu\({}^{2+}\) ions from synthetic solutions. The percentage of amine loading on fibers was calculated by the gravimetric method. Atomic absorption spectroscopy (AAS) was utilized to determine the concentration of Cu\({}^{2+}\) ions in the aqueous solution after adsorption. The maximum adsorption value achieved through the Langmuir model for Cu\({}^{2+}\) ions was 116.522 mg/g. Atomic force microscopy was used to study the changes in morphology before and after the adsorption of copper ions, as shown in Figure 5.  
[PERSON] et al., 2013 produced polyacrylamide nanofibers through an electrospinning process and then functionalized them with-NH\({}_{2}\)OH to form chelating nanofibers [74]. These nanofibers were used to extract Fe\({}^{3+}\) and Cu\({}^{2+}\) ions. Amidoxime-containing polyacrylamide nanofibers (AOPAN) showed the highest uptake values of 320 mg/g and 380 mg/g for Cu\({}^{2+}\) ions and Fe\({}^{3+}\), respectively. The adsorption value of Fe\({}^{3+}\) by the adsorbent was found to be higher compared with Cu\({}^{2+}\) ions. Higher affinity for iron ions towards nanofibers could be explained on the basis of the hard-soft acid base theory. The maximum uptake value was dependent upon attractions between AOPAN and metal ions with similar initial concentrations. Another study reported the synthesis of activated carbons from polyacrylamide fibers and investigated their ability to remove toxic ions from wastewater [75]. Polyacrylonitrile fibers were oxidized in the presence of air in a temperature range of 463 K to 553 K for 3-4 days. Activated carbon was produced by treating the fibers at a higher temperature (553-573 K) and keeping them until the fibers converted to hard carbon deposits with the release of smoke. This carbon is then transformed into a powdery form before the activation. _Carbon dioxide_ and _steam are_ the most common _activating_ agents used for polyacrylamide oxidizing fibers (Figure 6). Two forms of commercially available activated carbon fibers, A-20 and W10-W, were used for comparable studies. It was found that the steam activation method produced a large surface area but low product of activated coke compared with carbon dioxide. In another study, the synthesis of polyacrylonitrile-polyamidoamine (PAMAM) composite nanofibers was done by an electrospinning scheme to investigate their dye removal ability [76]. Direct red 80 (DR80) and direct red 23 (DR23) with concentrations of 40 ppm were utilized to study the adsorption capacity of the resultant fibers. The factors such as adsorbent dose, initial dye concentration, and pH of the solution affected the dye removal process. Pseudo second-order kinetics and Langmuir isotherm were used to study the time taken to extract metal ions and the concentration of metal ions to be adsorbed.