The Impact of Drying Method on the Hierarchical Structure and Porosity of Cellulose Beads Regenerated from Superbase Ionic Liquids

Superbase ionic liquids (SBILs), such as 1,5-diazabicyclo[4.3.0]non-5-enium acetate, [DBNH][OAc], dissolve cellulose under mild dissolution conditions and low dope viscosities, enabling shape-controlled regeneration. We prepared regenerated cellulose beads from cellulose/[DBNH][OAc]/DMSO solution via drop-wise addition into water, and subsequently dried the obtained hydrogels by ambient evaporation (xerogel), freeze-drying from HO or tert-butanol (cryogels), or supercritical CO (aerogel). It was shown that dring methods, that avoid capillary forces and ice templating, best preserve the hydrogel nanostructure formed during regeneration. Accordingly, aerogels exhibited high specific surface area (SSA 450 m g) and mesopore volume (1.98 cm g), exceeding those values for tBuOH cryogels (123 m g; 0.45 cm g) and for HO cryogels (29 m g; 0.06 cm g) by factors of ~ 4 and ~ 16 in SSA, respectively, while xerogels were essentially non-porous (0.04 m g) and practically transparent. SEM revealed regeneration-derived spherical substructures in aerogels that progressively consolidated through cryogels and vanished in xerogels. SAXS identified characteristic length scales near 30 and 63 nm and Porod exponents consistent with increasingly smooth interfaces upon consolidation, confirming systematic shifts in morphology with the drying severity. These results link regeneration pathway and drying route to hierarchical morphology in SBIL-derived cellulose, providing design rules for tailoring porosity for adsorption and related applications.