Preparation of nanochitin hydrogels via ice templated chemical/physical crosslinking for microplastic removal.

Formaldehyde (FO) and nanochitin suspension (DEChN) were combined to synthesize stable hydrogels via ice-templated chemical/physical crosslinking. The synthesis process involved the mixing of formaldehyde and nanochitin, followed by ammonia-induced gas phase coagulation to achieve dual crosslinking, thereby enhancing the mechanical properties of the hydrogels. The chemically crosslinked hydrogel exhibited a storage modulus of 680.05 Pa, whereas the demonstrated an approximately 5-times increase in storage modulus of 3110.34 Pa for DEChN(5)/FO(1), along with a reduced surface area and improved structural stability. Filtration experiments revealed that the dual-crosslinked hydrogel achieved nearly complete removal of microplastics (∼3 μm in diameter), with a flux of 8.22 mL cm-2 h-1, outperforming both the chemically (5.05 mL cm-2 h-1) and physically (3.01 mL cm-2 h-1) crosslinked samples. This enhanced performance was attributed to the larger pore size and robust channel structure in dual crosslinked hydrogels. The nanochitin hydrogels offered a more straightforward fabrication process, superior filtration efficiency, and cost-effectiveness, highlighting their scalability for practical water purification systems.