Synthesis of Chitosan-Based Nanocomposites from Crab Shells for Optimized Cadmium (II) Removal in Aqueous Solution

Heavy metal pollution especially that of cadmium (II), poses serious threats to the environment and human health because of its toxicity and endurance. The synthesis of chitosan from crab shells, a fisheries waste, and its effectiveness as a biosorbent for the removal of Cd2+ from aqueous solutions are the subjects of this work. Crab shells were demineralised, deproteinised, and deacetylated to create chitosan, which was then characterised using FTIR to verify the functional groups (-NH₂, -OH) in charge of metal binding. The effects of pH, adsorbent dosage, beginning Cd2+ concentration, and contact time with adsorption behavior analyzed using Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, alongside kinetic and thermodynamic studies. The chitosan exhibited a maximum adsorption capacity of 714.3 mg/g at pH 8, with 92.5% removal efficiency, as described by the Langmuir isotherm model (R² = 0.99). Pseudo-second-order kinetics (R² = 0.9995) confirmed chemisorption as the dominant mechanism. Thermodynamic studies revealed an endothermic (ΔH° = 14.8 kJ/mol) and spontaneous (ΔG° = -6.1 to -8.2 kJ/mol) process, with efficiency increasing from 85.3% to 94.7% at 303–333 K. Compared to commercial chitosan, the crab shell-derived chitosan offers a cost-effective, sustainable alternative, aligning with circular economy principles. These results demonstrate its potential for large-scale wastewater treatment in areas affected by heavy metal contamination, and further study is advised to improve chitosan regeneration and modification for industrial use.