Preparation of highly porous β-chitin structure through nonsolvent–solvent exchange-induced phase separation and supercritical CO2 drying

A highly open, porous, three-dimensional β-chitin network structure with meso- and macropores was successfully fabricated by exploiting nonsolvent–solvent exchange-induced phase separation and supercritical CO2 drying processes. It was revealed that a formation of the highly porous structure, consisting of interconnected micro-scale mesoporous chitin particles and nano-scale fibrils, was favored by repeating the freeze–thaw cycle of the chitin–formic acid solution. The sodium hydroxide (NaOH) solution was used to remove the residual formic acid in the chitin gel network during the neutralization step. Nitrogen adsorption was used to characterize the properties of the mesopores, which were found to be in the range of 5–25 nm. The crystalline structure was also investigated by X-ray diffraction, which revealed a conversion of β-chitin to α-chitin during the fabrication and drying processes.