Benign-Salt/DES Processing of Papyrus to Ultralight Nanocellulose Sponges for Organic-Solvent Removal

Hydrophobic organic solvents in pharmaceutical operations are difficult to remove due to phase immiscibility and volatility, prompting the use of biodegradable sorbents with rapid absorption and clean regeneration. This study produces papyrus ( Cyperus papyrus L.) into nanocellulose (NC) and then creates lightweight, freeze-dried sponges for solvent capture. The objective was to establish an eco-efficient, scalable pathway and evaluate sorption performance under controlled conditions while clarifying structure–performance relationships. Papyrus was processed using sodium chloride (NaCl)-assisted hydrothermal processing (HTP), alkaline pulping, and deep eutectic solvent extraction (DES), subsequently being formed into sponges through freeze-drying. Sorption was evaluated in neat toluene as a model hydrophobic solvent utilizing sealed containers and an evaporation-adjusted mass balance. The unmodified with 1% nanocellulose sponge (NC_1.0) exhibited the highest capacity (18.22 g/g) and maintained 16.31 and 16.21 g/g in cycles 2–3 (<10% loss) under simple thermal regeneration, indicating practical reusability. Iron oxide nanoparticles (Fe₃O₄) and methyltrimethoxysilane (MTMS)-modified (NC_1.0_S) exhibited reduced capacity (8.39 g/g), consistent with Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) evidence of partial pore occlusion and densification after silanization. Notably, the best-performing sponge requires no hydrophobization, supporting a low-additive, low-footprint design suitable for circular wastewater management.