Evaluation of hyper-cross-linked polymers performances in the removal of hazardous heavy metal ions: A review

Heavy metal ions, especially in water sources, are a critical issue for human health and the ecosystem. Generally, industrial effluents are the most critical origins in the contamination of water sources, typically rivers and lakes. Thus, rectification of contaminated water from heavy metal ions before discharging into the environment is the primary concern for researches. Variant procedures have been suggested, such as membrane technologies, biological separations, electrochemical techniques, chemical sedimentation, and adsorption for elimination of heavy metal ions. Among them, adsorption is a promising technique due to free or less generation of toxic substances, high efficiency, economy, and without secondary pollution. Several adsorbents, including activated carbon, zeolite, biomass, agricultural wastes and, hyper-cross-linked polymers (HCPs), are studied. Among the adsorbents, HCPs are efficient and functional choices. HCPs are a subset of the microporous category initially discovered by Davankov. In the current investigations, HCPs have attracted extreme attention due to the distinct exclusive privileges such as various synthesis techniques, simple utilization, high surface area, inexpensive required material and, medium operating conditions. In this work, different types of polymers, cross-linkers, and chemical reagents that are effective in the structure and efficiency of cross-linked adsorbents are explained. Various parameters such as synthesis method, adsorbent price, adsorbent reversibility, eco-friendly, and adsorption capacity of the adsorbents have been investigated for evaluating the appropriate resin. Thermal stability, morphology, and surface area are studied in some of the adsorbents for analyzing the mechanical properties of the adsorbents. Among the polymers, sodium alginate and hydroxyl terephtalic acid are preferred owing to their high adsorption capacity, biodegradable, and recyclability. Besides, loading the chitosan with the polystyrene reduce the equilibrium time to 10 min, which prove the energy consumption. Finally, alumina was an excellent additive, because of having the highest adsorption capacity, which was 315.15 mg/g after 40 min, and desire recovery which was observed 90% after the five cycles.