<p>Toxic heavy metal contamination in aquatic environments poses serious threats to human health and ecosystems due to their non-biodegradable and bio-accumulative nature. The increased awareness of sustainable development goals (SDGs) of good health and well-being (3), responsible consumption and production (12), protecting life below water (14), and life on earth (15) has triggered intensive studies focused on heavy metal ions removal from water. Chitosan, a natural biopolymer derived from chitin, has emerged as a promising biosorbent owing to its amine (-NH₂) and hydroxyl (-OH) groups, which possess high affinity toward metal ions, environmental friendliness, and structural tunability. This review explores the potency and recent advancements in the rational design of chitosan-based adsorbents. Outlines of the challenges in practical applications were presented to emphasize the importance of modification in chitosan-based adsorbents to achieve efficient removal of heavy metal ions. Key strategies such as grafting of selective functional groups, crosslinking for mechanical improvement, and morphological engineering into different forms of chitosan-based adsorbents are discussed in detail. Mini case studies on Pb²⁺ adsorption are provided to highlight the effectiveness of different design approaches.</p> Graphical abstract <p></p>