Selectivity of acid-base extraction routes and their effects on the structure, physicochemical properties, and adsorption performance of shrimp-shell-derived chitosan.

Chitosan, obtained from crustacean shells, has broad applications for environmental, agricultural, and pharmaceutical industries. In this study, we synthesized several chitosan samples from shrimp shell waste by applying different combinations of acid and alkali treatments during the demineralization, deproteinization, and deacetylation steps. The degree of deacetylation (DD), determined via titration and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), ranged from 70% to 92%. The physicochemical and structural properties of the extracted chitosan were systematically compared with commercial chitosan (CS-Com) by using X-ray diffraction (XRD), ATR-FTIR, field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FESEM-EDX), thermogravimetric and differential scanning calorimetry (TGA-DSC), asymmetrical flow field-flow fractionation (AF4), dynamic light scattering (DLS), and Brunauer-Emmett-Teller (BET) surface area analysis. Differences were observed in crystallinity, surface morphology, elemental composition (N/C ratio), porosity, thermal stability, water and fat-binding capacities, solubility, and wettability. Among the samples, CS-2 and CS-5 showed properties most similar to CS-Com. Adsorption studies using chloride and nickel ions as model ions indicated a close relationship between adsorption efficiency and the physicochemical characteristics of chitosan. The acid-base treatment conditions have a major impact on chitosan's solubility, degree of deacetylation, crystallinity, thermal stability, and adsorption performance. The findings provide insights for optimizing chitosan extraction and tailoring the material's properties for biomedical, food, and environmental applications.