Fabrication and Mechanistic Study of Aerogels Directly from Whole Biomass

Lignocellulosic aerogels were prepared directly from whole biomass Douglas fir wood without prior removal of hemicellulose and lignin using lithium bromide (LiBr) molten salt hydrate (lithium bromide trihydrate, LBTH) as a cellulose solvent via a procedure of cellulose dissolution, gelation, and regeneration. The fabricated aerogels had a homogeneous and continuous porous structure, extremely high porosity, large surface area, and very low density. The lignin-excluding aerogel had a density as low as 4.6 mg/cm3 and a porosity larger than 99%, while the lignin-including whole biomass aerogel retained almost all lignin and more than 90% of the starting biomass and had 24.9 mg/cm3 density and 98.3% porosity. A mechanistic study revealed that different from that in other cellulose solvent systems, cellulose gelation and regeneration occurred in two independent steps in the LBTH system. The weak cross-linking through a coordination effect between a cellulose hydroxyl group and Li+ cation when cooling the cellulose solution in the LBTH led to gelation, while cellulose regeneration via precipitation/aggregation due to the exchange of solvent LBTH with nonsolvent water during washing resulted in the formation of a 3D fibrous network of cellulose skeleton.