## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile in Ion Exchange Resins
These chelating resins were utilized to extract Pb\({}^{2+}\), Cd\({}^{2+}\), and Zn\({}^{2+}\) from wastewater through batch and column methods. The amount of metal ions adsorbed by resin was studied through Freundlich and Langmuir isotherm models. It was found from the results that chelating resins adsorbed the ions in single metal systems in the order Cd\({}^{2+}\) > Pb\({}^{2+}\) > Zn\({}^{2+}\). Monodispersed poly(acrylonitrile) was synthesized through a surfactant-free emulsion polymerization technique and the nitrile moiety was transformed into amidoxime on reaction with hydroxylamine hydrochloride in water ([PERSON] et al., 2016). The synthesized resin was used as an adsorbent in the extraction of three types of contaminants; methylene blue (MB) and rhodamine 6G (R6G), a heavy metal ion Cd\({}^{2+}\), and the herbicide paraquat. The various factors that influenced the adsorption rate were amidoxime concentration, pH of contaminated water, adsorbent dose, and initial metal ion concentration. Amidoximated poly(acrylonitrile) polymer extraction ability was increased to 87 mg/g, 91 mg/g, 74 mg/g, and 91 mg/g from 5 mg/g, 1.54 mg/g, 1.06 mg/g, and 1.22 mg/g for Cd\({}^{2+}\), methylene blue, rhodamine 6G, and herbicide paraquat, respectively. [PERSON] et al. (2014) reported polyacrylonitrile embedded on the surface of a wheat straw matrix (WSM) via single-electron transfer-living radical polymerization (SET-LRP) ([PERSON] et al., 2014). Wheat straw matrix grafted polyacrylamide was converted into wheat straw matrix grafted-amidoxime group by reacting with hydroxylamine hydrochloride. Wheat straw matrix grafted-amidoxime was used to extract mercury metal ions with the utmost adsorption ability of 4.7 mmol/g. It was found that in the binary system of metal ions Hg\({}^{2+}\)- Pb\({}^{2+}\), Hg\({}^{2+}\)- Ni\({}^{2+}\), Hg\({}^{2+}\)-Zn\({}^{2+}\), Hg\({}^{2+}\)- Ag\({}^{+}\), and Hg\({}^{2+}\)- Cu\({}^{2+}\), the above adsorbent showed high selectivity for mercury ions. As per the acid-base theory, mercury ions form stable complexes with the ligands containing nitrogen and sulfur atoms. [PERSON] et al. explained the preparation of polyacrylamidetonitrile containing carbon materials (PPC-0.6-600, PPC-0.8-600, PPC-0.6-800, and PPC-0.8-800) [59]. These materials were synthesized by heating carbon with potassium hydroxide at 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C for the extraction of chromium ions from aquatic systems. The adsorption value of chromium ion on PPC-0.8-800 was more than other carbon materials, and the greatest adsorption capacity was found to be 374.90 mg/g at pH 2.0. This resin could be reused even after five cycles. This adsorption process was due to the electrostatic force between polyacrylamidetonitrile-based porous carbon materials and hydrogen chromate (HCrO\({}_{4}\)\({}^{-1}\)) ions. For the extraction of Pb\({}^{2+}\) ions, an ethyleneamine functionalized crosslinked poly(acrylonitrile-ethylene glycoldimethacrylate) chelating resin was synthesized [60]. This resin was modified with different amine groups such as ethylenediamine, triethylenetetraamine, and tetraethyleneptamine. The maximum extraction value for toxic metal lead ions was obtained at pH 4.6 in the pH range of 1-4.6 studied for all copolymers. The adsorption of Pb\({}^{2+}\) ions was conducted with an artificial metal ion solution having a concentration of 0.483-2.4154 mmol/L at pH 4.6. Maximum uptake values of lead ions were 1.73 mmol/g, 1.68 mmol/g, and 1.62 mmol/g, respectively. In another experiment, an adsorbent was prepared by graft polymerization of polyacrylamidetonitrile with arabic gum (PAN-g-AG) by using potassium permanganate or nitric acid as a redox initiator for the extraction of lead, cadmium, and copper ions from their solutions [61]. The grafted copolymer was modified with hydrazine and then hydrolyzed with sodium hydroxide. The batch adsorption method was used for the extraction of the metal ions from a solution having an initial concentration of 100 ppm by using 50 mg of improved PAN-g-AG for four hours.