## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile as Fiber
A precipitation technique was used to make these nanoparticles utilizing potassium persulfate as an initiator, and then poly(styrene-acrylonitrile) poly(St-co-AN) was electrospun into nanofibers through an electrospinning method. The Langmuir adsorption isotherm was followed by poly(St-co-AN) nanofibers during the adsorption of methylene blue. Moreover, the rate of adsorption was well explained by a pseudo 2 nd order model. In another experiment, a chitosan immobilized polyacrylamide nanofibrous mat was prepared, as chitosan could easily bind to the nanofibers due to hydrogen bonding [95]. The mat was used to check the removal efficiency of acid blue-113 anionic dye. This adsorbent could be regenerated five times with almost similar efficiency to remove the adsorbate. The adsorption process was basically monolayer followed by the Langmuir adsorption isotherm. [PERSON] et al. (2020) synthesized electrospun porous polyacrylamide/polyvinylidene fluoride nanofibers to adsorb direct red 23 dyes [96]. The resultant nanofiber porosity and diameter could be increased by dissolving them in a solvent and then removing the solvent to enhance the fiber porosity. The adsorption phenomenon was well explained by intraparticle diffusion kinetics and the Langmuir isotherm. Polyacrylonitrile-coated graphene/carbon nanotube hybrid beads were prepared to absorb methylene blue dye [97]. During the synthesis of this adsorbent, the first step was the formation of a hydrogel through emulsification and self-assembly of graphene sheets and carbon nanotubes, and then immobilizing the polyacrylamide onto the hydrogel. In the second step, this polyacrylamide-coated hydrogel was activated through a potassium hydroxide carbonization technique. Through this whole procedure, extremely porous graphene/CNT hybrids were obtained with high mechanical strength and better physical properties. [PERSON] et al. (2018) synthesized core-shell nanofibers using a mixture of polyacrylic acid and dextran-polyaniline via electrospinning and in situ polymerization techniques, and used the formulated nanofibers to absorb Pb\({}^{2+}\) and Cu\({}^{2+}\) ions [98]. Polyacrylic acid and dextran were connected through crosslinking using a thermal treatment technique. Since dextran is a water-soluble polysaccharide and has many side chains, it can be easily chemically modified by aldehydes, methacrylate, thiol, phenol, maleimide, and vinyl sulfone moieties. Calcium carbonate was incorporated in various amounts into nanofibers of polyaniline to make the structure mesoporous. [PERSON], [PERSON], and [PERSON] (2020) prepared ethylenediamine-modified polyacrylonitrile fibers for the removal of mercury ions from aqueous systems [99]. The Freundlich, Langmuir, UT, Redlich-Peterson, and Temkin isotherm models were used to explain the equilibrium adsorption value of mercury ions by the above adsorbent. Box-Behnken designs in combination with response surface methodology were employed to explain the factors affecting the adsorption process, such as pH, equilibrium time, temperature, and initial concentration. A batch test as well as a column method were used to study the various parameters affecting the adsorption process. The Langmuir adsorption isotherm was found to explain the adsorption process well. [PERSON] et al. (2020) prepared a composite by impregnating zinc oxide nanoparticles onto polyacrylamide nanofibers ([PERSON] et al., 2020). The addition of hinokitiol to composite nanofibers was found to be effective in increasing nanofiber efficiency. It also improved antibacterial activity against bacteria such as _Escherichia coli_ and _Staphylococcus aureus_. Hinokitiol is related to terpenoid compounds obtained from the wood of trees in the family Cupressaceae. [PERSON] et al. (2019) fabricated a composite of graphene oxide/polyacrylamideonitrile/\(\beta\)-cyclodextrinn nanofibers by an electrospinninging method to study their efficacy for the removal of crystal violet ([PERSON] et al., 2020).