Shrimp-derived chitosan/activated carbon composites for methylene blue removal: effect of glutaraldehyde crosslinking

Crosslinking in polymer-based adsorbents not only improves the chemical and mechanical properties of the adsorbent, but also affects its adsorption performance. In this study, shrimp-shell-derived chitosan was extracted through sequential demineralization, deproteinization, and deacetylation, and subsequently used for the preparation of chitosan/activated carbon composite beads via alkaline coagulation. Two types of shrimp-shell-derived chitosan/activated carbon composite beads were prepared, namely non-crosslinked beads (ChAc) and glutaraldehyde-crosslinked beads (ChAcG), and comparatively evaluated for methylene blue (MB) removal from water to elucidate the effect of glutaraldehyde crosslinking on adsorption behavior. N 2 adsorption, FTIR, TGA, and SEM analyses revealed the structural and physicochemical changes associated with glutaraldehyde crosslinking. The batch adsorption tests showed clear effects of pH, dosage, contact time, and temperature (298–318 K). Equilibrium uptake generally increased from 298 to 308 K, indicating an overall endothermic uptake in this range. The equilibrium adsorption data were well described by the Langmuir and Freundlich isotherm models. ChAc exhibited a high maximum adsorption capacity of 327.5 mg/g at 298 K, whereas crosslinking reduced the adsorption capacity to 115.2 mg/g, consistent with partial consumption of amine sites and network densification, which limits site accessibility and transport. The results showed that ChAc provides higher capacity, while ChAcG offers improved structural robustness at the expense of adsorption performance due to glutaraldehyde crosslinking.