Extraction of chitosan from shrimp-shell biowaste and its integration into a high-performance hydrogel for energy storage applications and sustainable wastewater treatment.

Multifunctional hydrogels capable of integrating mechanical robustness, excellent electrochemical performance, and environmental remediation are highly desirable but remain challenging to develop from sustainable biomass resources. In this study, a multifunctional chitosan/polyacrylamide/Ni (CS/PAAm/Ni) hydrogel was successfully synthesized from shrimp shell-derived chitosan via a simple one-pot method without the use of additional chemical crosslinkers. Structural characterization by FTIR and XPS confirmed the formation of a crosslinked polymer network with nickel incorporated as both Ni2+ and Ni3+ species. The resulting hydrogel exhibited excellent mechanical properties, including a tensile stress of 597 kPa at approximately 912% elongation and a compressive stress of 1.26 MPa, together with a high swelling ratio (508%) and excellent water retention (97.07% after 15 days). Owing to its highly hydrated and conductive network, the hydrogel achieved an ionic conductivity of 4.11 S·m-1 and outstanding electrochemical performance, delivering a specific capacitance of 435 F·g-1, an energy density of 38.67 Wh·kg-1, and a power density of 5200 W·kg-1. As a preliminary demonstration of its multifunctionality, the hydrogel was also evaluated for the removal of the carcinogenic textile dye Reactive Black 5, achieving 87.30% removal efficiency with a maximum adsorption capacity of 54.82 mg·g-1. The adsorption equilibrium was better described by the Freundlich isotherm, indicating heterogeneous adsorption. These findings demonstrate that the developed CS/PAAm/Ni hydrogel is a high-performance material for flexible energy-storage applications while also exhibiting promising dye-removal capability, highlighting its potential as a sustainable multifunctional hydrogel derived from shrimp-shell biowaste.