## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile as Fiber
Another author has discussed the synthesis of polyacrylamide nanofiber mat by an electrospinning technique and embedded \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) into nanofibers through a hydrothermal process [87]. This \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)/polyacrylamideonitrile nanofiber mat could effectively extract lead ions from the mixture of nickel and copper ions at pH 4.8. A pseudo-second-order model better explained the kinetics of adsorption. Moreover, the Langmuir adsorption isotherm better explained the adsorption process than the Freundlich isotherm. [PERSON] and [PERSON] (2019) reported the incorporation of various quantities of zinc oxide into polyacrylamide-lonitrile nanofibers and utilized them for the extraction of Pb\({}^{2+}\) and Cd\({}^{2+}\) ions [88]. A field emission scanning electron microscope (FESEM) was used to study the surface morphology of polyacrylamide nanofibers as well as zinc oxide immobilized polyacrylamide-l on nanofibers. The addition of zinc oxide on the surface of the nanofibers increased the mean diameter from 135 nm to 240 nm. [PERSON] et al. (2018) fabricated TiO\({}_{2}\).Ag\({}_{3}\)VO\({}_{4}\) polyacrylamide-l on nanofibers through an electrospinninging process and used them to remove methylene blue [89]. The extraction of dyes increased within the pH range of 3-8 and further, there was no change in removal efficiency with an increase in pH. The adsorption process was also affected by temperature, contact time, and adsorption dose. [PERSON] et al. (2018) reported effective ion-selective polyacrylamide-l nanofibers that were chemically modified in two steps: first, hydrolysis, and then reaction with ethylenediamine (EDA), ethylenedi-col (EG), or diethylenetriamine (DTA). These chemically modified nanofibers were used to extract Cu\({}^{2+}\), Pb\({}^{2+}\), and Zn\({}^{2+}\) ions from aqueous solutions [90]. The anions such as Cl\({}^{-}\)NO3\({}^{2-}\), SO4\({}^{2-}\), and PO4\({}^{3-}\)present in water were found to affect the adsorption process by competing with the metal ions and hence lowering the adsorption ability towards the adsorbent. In another study, the authors used an electrospinning technique to create a different amine-modified polyacrylonitrile nanofiber to extract anionic Congo red dye from aqueous solution [91]. Since Congo red dye is an anionic dye, it could be easily attracted by cationic species (-NH3\({}^{+}\)) present on the surface of the adsorbent in acidic conditions. [PERSON] and [PERSON] (2020) reported polyacrylonitrile anion exchange fibers immobilized with polyethyleneimine [92]. Alkylation of amine moieties present in polyethylenimine-functionalized polyacrylamide was carried out to synthesize three anion exchange fibers (PAN-PEI-3C, PAN-PEI-5C, and PAN-PEI-8C). These three adsorbents were studied for the removal of nitrate ions. It was found from the results that the uptake values of all adsorbents were the same, but PAN-PEI-5C showed more attraction towards the nitrate ions. [PERSON] et al. (2017) reported polyacrylonitrile fibers synthesized through an electrospinning process and covered with carbon matter via an aqueous carbonization method utilizing diethylenetriamine and glucose as the forerunner [93]. Here, toxic metal ions, chromium (Cr6\({}^{+}\)), and herbicide 2, 4-dichlorophenoxyayacetic acid were removed through the obtained resin. Chromium was removed in two steps: (1) Cr6\({}^{+}\) diffused in the form of HCrO4\({}^{-}\) and Cr2O7\({}^{2-}\), which were attracted by the -NH3\({}^{+}\) moiety of amine-containing hydrothermal carbon-coated polyacrylamide fiber (PAN@NC) and (2) Cr6\({}^{+}\) was reduced to Cr3\({}^{+}\) ions by gaining electrons from the -NH3, -OH, and -COOH moieties. [PERSON] et al. (2019) synthesized carbon nanotubes and graphite impregnated poly(styrene-acrylonitrile) nanofibers to adsorb methylene blue dye [94].