## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile as Fiber
This adsorbent showed the greatest sorption for chromium ions. Moreover, the thermal stability of calixarene immobilized polyacrylamide/polypyrrole nanofibers was found to be greater than that of polyacrylamide/polypyrrole. [PERSON] et al. (2016) synthesized polyacrylamide/polypyrrole nanofibers through an electrospinning method [83]. The surface of the fibers was modified with poly ethylenediaminetetraacetic acid (EDTAA) using ethylenediamine (EDA) as the cross-linker. The resultant fibers were used for the removal of Cd2+ and Cr4+ ions from aqueous solution. The utmost adsorption by modified fibers was 32.68 mg/g and 66.24 mg/g for Cd2+ and Cr4+ ions, respectively, at 298 K. Regeneration of nanofibers could be done through a 2M HCl solution. Another study reports activated carbon nanofibers (ACNFs) developed from precursor polyacrylamide/polypyrrole and manganese oxide (MnO2) through an electrospinning technique [84]. For the comparison of the extraction of Cd\({}^{2+}\) ions from the aqueous solution, ACNFs, composite ACNFs, and commercial powdered activated carbon were used to make a comparison. From the adsorption data, it was found that Cd\({}^{2+}\) ion extraction by activated carbon nanofibers/MnO\({}_{2}\) was maximum (97%), followed by activated carbon nanofibers (96%), and then followed by powdered activated carbon (74%). Silver-coated polyacrylamide mel membranes were also synthesized by an electrospinning technique [65]. The amidoxime moiety was attached to silver ions after polyacrylamide was modified with hydroxylamine and immersed in silver nitrate aqueous solution. This membrane was used for the complete removal of _E. coli_ with an efficient filtration rate of 8.0 mL/cm\({}^{2}\) min. Another paper reported the preparation of boehmite nanoparticles with polyacrylamide[85]. The boehmite nanoparticles were synthesized through the sol-gel method. Then, these boehmite nanoparticles were immobilized on polyacrylamide monofibers through the electrospinninging method. The synthesized nanofibers were more effective in the removal of _E. coli_ bacteria. Moreover, removal efficiency increased from 72.33% to 97.37% with an increase in boehmite nanoparticle concentration from 0 to 10% by weight. Maximum bacterial elimination was due to attractive forces among nanoparticles and bacteria, and due to the increased surface area of the nanoparticles. _E. coli_ bacterial extraction from the water bodies increased to 99.99% by repeating the filtration technique four times. The adsorption value of PAN/boehmite nanofibers for cadmium ions was found to be 0.23 mg/g for a 5 mL cadmium ion solution at pH 4.0. [PERSON] et al. (2020) investigated the various anionic groups of modified fibers [64] such as ethylsulfate-functionalized fibers, ethylsulfonic acid-functionalized fibers, benzoic acid-functionalized fibers, and phenol-functionalized fibers, all of which are promising adsorbents for cationic dyes. Brilliant cresyl blue, a hazardous cationic dye, was chosen to study the adsorption ability of the above modified fibers. It was found from the results that unmodified polyacrylamidefibers were not able to remove brilliant cresyl blue dye, while the phenolate immobilized fibers exhibited the strongest adsorption. Moreover, the adsorption values of the sorbents were decreased in the basic medium. [PERSON] et al. (2021) reported the triazine-modified dendrimer introduced into polyacrylamide fibrils fibers by a grafting technique and used them for the extraction of Hg\({}^{2+}\) ions from aqueous solution at adjusted pH 6 [86]. The equilibrium adsorption time was found to be 180 min. The extraction of mercury ions changed with the change in concentration from 0.1 g/L to 1.0 g/L, and adsorption did not increase beyond 1.0 g/L. Regeneration was partially achieved with 0.5 M HCl (37.22%) and 0.5 M HNO\({}_{3}\) (60.36%), while 0.5 M Na\({}_{2}\)S resulted in 80% desorption of the adsorbent.