Preparation of lignocellulose aerogels from cotton stalks in the ionic liquid-based co-solvent system

Abstract

Ionic liquid-based lignocellulose aerogel systems have attracted significant focus in advanced material research due to their intrinsic environment-friendly properties. Use of co-solvent is deemed useful in improving these systems efficiency without affecting reaction dynamics. Herein, a green synthesis strategy is reported to produce highly porous, physically cross-linked lignocellulose aerogel by dissolving lignocellulose biomass obtained from the cotton stalk in 1-allyl-3-methylimidazolium chloride/dimethyl sulfoxide (AmimCl/DMSO) co-solvent system. Samples with different concentrations were treated under both cyclic conventional freezing-thawing conditions (−20 °C to 20 °C) and liquid nitrogen freezing-thawing conditions (−196 °C to 20 °C) followed by solvent exchange and freeze drying. Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis of these lignocellulose samples showed that conventional freezing-thawing treated samples exhibit hierarchical 3D open porous “web-like” structure with a low specific surface area and larger dominant pore diameter. On the other hand, use of liquid nitrogen freezing-thawing treatment resulted in the creation of “film-like” porous structure with a higher specific surface area and relatively smaller dominant pore diameter. Quantitative analysis through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermo-gravimetric analysis (TGA) verified that cyclic freezing-thawing treatment has potential to fix all major components of lignocellulose in a matrix. The proposed strategy is not only environmentally benign but also the cost-effective making an ionic liquid-based system more commercially viable.