Cross‐Linked Chitosan Composites for Lead and Mercury Ions Removal: A Review

ABSTRACT Heavy metal ions such as lead (Pb (II)) and mercury (Hg (II)) in water bodies are a critical global concern due to their extremely poisonous effects, strong bioaccumulation potential, and resistance to natural degradation. Chitosan is a bio‐based material with many amino and hydroxyl groups, making it a favorable adsorbent for heavy metal adsorption. However, its low chemical and mechanical stability in acidic environments significantly limits its practical applications. To overcome these problems, extensive efforts have been directed toward incorporating various crosslinkers and functional nanomaterials to develop new cross‐linked chitosan‐based composites. These new composites exhibit pronounced adsorption efficiency due to improved structural integrity. This review discusses how cross‐linked chitosan composites have been used to remove Pb (II) and Hg (II) from aqueous systems (2020‐2025), with particular emphasis on adsorption mechanisms elucidated through density functional theory (DFT), adsorption kinetics, and isotherm models. Furthermore, identifies key research gaps and proposes new strategic avenues, including the design of multifunctional adsorbents capable of multiple recyclable strategies and performance evaluation under real‐water conditions.