Heavy metal is released from many industries into water. Before the industrial wastewater is discharged, the contamination level should be reduced to meet the recommended level as prescribed by the local laws of a country. They may be poisonous or cancerous in origin. Their presence does not only damage people, but also animals and vegetation because of their mobility, toxicity, and non-biodegradability into aquatic ecosystems. The review comprehensively discusses the progress made by various adsorbents such as natural materials, synthetic, agricultural, biopolymers, and commercial for extraction of the metal ions such as Ni²⁺, Cu²⁺, Pb²⁺, Cd²⁺, As²⁺ and Zn²⁺ along with their adsorption mechanisms. The adsorption isotherm indicates the relation between the amount adsorbed by the adsorbent and the concentration. The Freundlich isotherm explains the effective physical adsorption of the solute particle from the solution on the adsorbent and Langmuir isotherm gives an idea about the effect of various factors on the adsorption process. The adsorption kinetics data provide valuable insights into the reaction pathways, the mechanism of the sorption reaction, and solute uptake. The pseudo-first-order and pseudo-second-order models were applied to describe the sorption kinetics. The presented information can be used for the development of bio-based water treatment strategies.

Water gets polluted due to the dumping of untreated industrial waste into bodies of water, particularly those containing heavy metals and dyes. Industrial water contains both inorganic and organic wastes. Numerous adsorbents that are inexpensive and easily available can be used to address the issue of water deterioration. This review report is focused on polyacrylonitrile as an efficient constituent of adsorbents to extract toxic ions and dyes. It discusses the various formulations of polyacrylonitrile, such as ion exchange resins, chelating resins, fibers, membranes, and hydrogels, synthesized through different polymerization methods, such as suspension polymerization, electrospinning, grafting, redox, and emulsion polymerization. Moreover, regeneration of adsorbent and heavy metal ions makes the adsorption process more cost-effective and efficient. The literature reporting successful regeneration of the adsorbent is included. The factors affecting the performance and outcomes of the adsorption process are also discussed.

Removal of lead ions was investigated by ethylenediamine, triethylenetetramine and tetraethylenepentamine functionalized polymeric adsorbent. Macroporous acrylonitrile-ethylene glycol-dimethacrylate copolymer beads were synthesized by suspension polymerization as already reported.^[17] The adsorbent was prepared by amination of copolymer synthesized from acrylonitrile-ethylene glycol-dimethacrylate. The adsorption study for removal of lead ions using functionalized poly(AN-EGDMA) copolymer as an adsorbent was carried out at room temperature at various solution concentrations of 0.483–2.4154 mmol/l at pH 4.6. Functionalized polymers were studied by Fourier transform infrared spectroscopy (FTIR). Scanning electron microscope-X-ray energy dispersive spectrometer (SEM-EDAX) was utilized to study an increase in nitrogen content of functionalized polymers.