## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile in Ion Exchange Resins  
Ion exchange resins are high-molecular-weight crosslinked polymers used to exchange the ions present in the wastewater with the ions present in the resin. Ion exchange resins are insoluble in water as well as in organic solutions, and these crosslinked polymers are connected through covalent bonds [32]. Ion exchange resins are of two types, namely, cation exchangers and anion exchangers. There are several research papers available on ion exchange resins that are used to extract toxic ions and dyes. In an initial experiment, the anion exchange resin was obtained by the reaction of highly permeable acrylonitrile-DVB copolymers with hydrazines, ethylene diamine, diethylene triamine, and triethylene tetramine, and their complexing properties towards copper and cobalt ions were explored [33]. The complexation values were found to be 13-53 mg/g for copper and 27-60 mg/g for cobalt. In another study, a redox technique was used to prepare poly(acrylonitrile-co-acrylamide) poly(AN-co- AM) by utilizing sodium bisulfite and potassium persulfate as the initiators [34]. The resultant copolymers were then modified by chemical treatment with hydroxylamine hydrochloride to introduce amidoxine functional moieties into the polyacrylonitrile (PAN) framework. The function of the amidoxime moiety was to develop a chelating ion-exchange resin formed through acrylonitrile for the extraction of toxic metal waste in water. Inductively coupled plasma was used to investigate the sorption behavior of poly(AN-co-AM) for Cu\({}^{2+}\) ions. The adsorption capacity of Cuincreased with an increase in pH until optimum adsorption of Cu\({}^{2+}\) (52.63 mg/g) at pH 5. The adsorption of Cu\({}^{2+}\) onto poly(AN-_co_-AM) correlates well with the Langmuir equation. A kinetic study showed that the adsorption of Cu\({}^{2+}\) follows the pseudo-second-order model. The adsorption capacity of Cu\({}^{2+}\) onto amidoximed poly(AN-co-AM) decreased as the adsorbent amount increased. [PERSON] et al. (1994) reported the -COOH moiety containing hydrazine immobilized polyacrylonitrile fibers ([PERSON] et al., 2015). The highest uptake values of functionalized polyacrylonitrile fiber for the heavy metal ions Cu\({}^{2+}\), Cd\({}^{2+}\), Zn\({}^{2+}\), Co\({}^{2+}\), Pb\({}^{2+}\), Cr\({}^{3+}\), Ni\({}^{2+}\), and Hg\({}^{2+}\) were found to be 1.33 mmol/g, 1.30 mmol/g, 1.03 mmol/g, 1.02 mmol/g, 0.98 mmol/g, 0.96 mmol/g, 0.95 mmol/g, and 0.63 mmol/g, respectively. This cation exchanger was selective for different metal ions and was arranged according to their distribution coefficient values as follows: Cu\({}^{2+}\)\(>\) Zn\({}^{2+}\)\(>\) Cr\({}^{3+}\)\(>\) Hg\({}^{2+}\)\(>\) Cd\({}^{2+}\)\(>\) Pb\({}^{2+}\)\(>\) Ni\({}^{2+}\)\(>\) Co\({}^{2+}\). The product could be regenerated and reused after recovery with diluted nitric acid. A polyacrylonitrile-based adsorbent was synthesized for the separation of cesium and cobalt ions from radioactive waste ([PERSON] et al., 2015). Inorganic-organic adsorbent was formed by inorganic ion exchangers modified by polyacrylamide having larger size particles with higher granular strength. Potassium nickel hexacyanoferrate (KCNFPAN) was used as an inorganic ion exchanger and polyacrylamideonitrile as a binding matrix to produce a composite adsorbent. Three different complexing agents based on granular hexacyanoferrate were utilized to extract Cs\({}^{+}\) and Co\({}^{2+}\) ions from aqueous solution. The ion exchange ability of the adsorbent was also dependent on the drying temperature of samples; the sorption value of adsorbent KCNFPAN was increased as the temperature reached 110 \({}^{\circ}\)C. The highest adsorption values were obtained to be 2.85 mmol/g and 2.15 mmol/g for cesium and cobalt ions, respectively. [PERSON] et al. (2005) synthesized polyacrylonitrile fiber by using various strong and weak base moieties to produce an anion exchange fiber ([PERSON] et al., 2015).