## 3 Types of Adsorbents Made from Polyacrylonitrile
### Polyacrylonitrile in Membranes  
The extraction of the pollutants using different membranes is a significant approach in the field of chemistry. Among these different membranes, ion exchange membranes are mostly used in fields such as dialysis, reverse osmosis, food industries, wastewater remediation, pharmaceutical industries, etc. Polyacrylonitrile, when used as a membrane for various processes, showed outstanding features, including heat resistance, and tolerance towards solvents, microorganisms, and radiation ([PERSON] et al., 2020). [PERSON] and [PERSON] (2012) reported an anion-exchange membrane of polyacrylamide/silica gel prepared through the solution casting method by taking various concentrations of polyacrylamide and silica gel ([PERSON] et al., 2020). The maximum anion exchange value was obtained with an equal ratio of polyacrylamide and silica gel. The above membrane was used to manufacture an arsenic selective electrode to determine the different concentrations of arsenic in solutions. The useful pH of the electrode was 5.0-10.0. In addition, the electrode demonstrated good selectivity for As\({}^{5+}\) over interfering anions. In another study, highly porous polyacrylamide/nicnoflurous membranes were successfully fabricated using a hot water bath as an extractor from a polyacrylamide/nicnoflure and poly(vinyl pyrrolidone) (PVP) blended solution, and then aminated with diethylene triamine (DETA). The obtained aminated nanofibrous mats (APAN) showed unique micro/nano structures and possessed an extra-high extraction capability for the removal of lead ions (Pb\({}^{2+}\)) from aqueous solution (maximum uptake capacity of Pb\({}^{2+}\) was up to 1520.0 mg/g) and could maintain over 90% of its extraction capacity at the sixth cycle of extraction-dissociation ([PERSON] et al., 2020). Adsorptive ultrafiltration membranes were formulated from synthesized polyvinyletrazo-co-polyacrylamideonitrile (PVT-co-PAN) by nonsolvent-induced phase separation ([PERSON] et al., 2020). PVT-co-PAN with varied degree of functionalization was explored to prepare adsorptive membranes. It was found that PVT segments could alter the pore size, charge, and hydrophilic behavior of the membranes; the membranes became more negatively charged and hydrophilic after the addition of PVT. The PVT segments also served as the primary binding sites for Cu\({}^{2+}\) ion adsorption from aqueous solution. At pH = 5, the maximum adsorption of Cu\({}^{2+}\) ions in a continuous ultrafiltration solution of 10 ppm were achieved. The Freundlich isotherm model accurately described the aqueous solution Cu\({}^{2+}\) ion adsorption on membranes. The adsorption capacity obtained from the Freundlichisotherm model was 44.3 mg/g, which is higher than others. [PERSON] et al. (2020) produced bilayer nanofiber membranes with enhanced adsorption and mechanical properties by functionalizing a layer of polyacrylonitrile with metal oxides (ZnO or TiO\({}_{2}\)) and chitosan via consecutive electrospinning [107]. The incorporation of a chitosan layer into nanofibers increased lead adsorption capacity by 102% and cadmium adsorption capacity by 405%. Chitosan also enhanced the tensile strength of the membrane by approximately 68%, owing to the strong interaction between the fibers at the interface of the two layers. [PERSON] et al. (2018) prepared a polyacrylonitrile/polyaniline (PANI)-nylon core-shell nanofiber membrane as a filtration-adsorption membrane and modified its surface with diethylenetriamine (DETA) for separating Pb\({}^{2+}\) and Cd\({}^{2+}\) ions from aqueous solutions [20]. The modification resulted in an increase in the hydrophilicity and permeability of the membrane. The anti-fouling of the membrane was tested by bovine serum albumin filtration. The results revealed a rejection efficiency of 89.11% for BSA and a flux recovery ratio of 91.85%, which can be owed to the hydrophilic nature of nanofibers.