A sustainable approach to water quality improvement of aquatic ecosystems using low-cost chitosan from discarded crustacean exoskeletons as an adsorbent for heavy metal removal

Heavy metals are considered hazardous chemicals in the environment and, under certain conditions, become toxic to plants, animals and humans. Heavy metal contamination in water resources poses a significant environmental challenge. Chitosan, a biopolymer derived from chitin, has emerged as a promising adsorbent for heavy metal removal. This review firstly focuses on the extraction of chitosan from discarded crustacean exoskeletons and secondly on the application of Isothermal Titration Calorimetry (ITC) to investigate the thermodynamics of metal ion binding to chitosan. ITC provides crucial insights into the binding mechanisms, including the number of binding sites, binding affinities, and the driving forces behind the interactions. Additionally, this review synthesizes findings from studies employing ITC to understand the potential of chitosan for heavy metal remediation. Magnesium (II) is found to exhibit the strongest affinity toward chitosan. Zinc (II) is the next strongest cation, while calcium (II) is found to show the weakest measurable affinity for chitosan chelation. Binding of all these cations to chitosan takes place with negative free energy values. Based on the results, ITC method clearly demonstrates that chitosan is a versatile bio polymer that can effectively bind the three metals studied minimizing the impact of these elements on the aquatic ecosystem.