Insights into lignocellulosic waste fractionation for lignin nanospheres fabrication using acidic/alkaline deep eutectic solvents.

Facile fractionation of lignocellulosic waste into useable forms is essential to achieve a multi-product treatment process especially when the resulting lignin streams are expected for high-value materials valorization. Despite acidic/alkaline deep eutectic solvents (DESs) are promising solvents for lignocellulosic waste fractionation, there is little information about their differences in the fractionation and lignin extraction profiles. In this work, four DESs that were cataloged to acidic types (formic acid-choline chloride, lactic acid-choline chloride) and alkaline types (monoethanolamine-choline chloride, glycerol-K2CO3) were investigated to compare their abilities of bamboo waste fractionation. Physicochemical properties of these resulting cellulose, lignin and derived lignin nanospheres (LNPs) were also assessed. Results showed that DESs could selectively extract lignin via cleaving lignin-carbohydrate linkages and lignin ether bonds. Acidic DESs pretreatments were more effective in biomass delignification (~95.0 %), while alkaline DESs showed better polysaccharide retention. Glycerol-K2CO3 LNPs exhibited much smaller sphere size (50-100 nm) while acidic DESs LNPs showed higher thermal stability due to higher extent of lignin condensation. In addition, MEA-ChCl could introduce amine groups onto lignin hydroxyl. This work provided insightful information for tailoring technique routes to selective lignocellulosic waste fractionation, while facilitating the downstream applications of the obtained cellulose/lignin.

Honeycomb-structured carbon aerogels from nanocellulose and skin secretion of Andrias davidianus for highly compressible binder-free supercapacitors.

Nanocellulose-derived carbon is a promising material in energy storage because of its sustainability, low environmental impact, and large specific surface area. Herein, the skin secretion of Andrias davidianus (SSAD) is applied for the first time as the bio-nitrogen source to dope carbon aerogels from nanocellulose. Cellulose nanocrystal (CNC) is discovered to be very effective to address the dispersion problem of SSAD in water. After being homogeneously mixed with cellulose nanofiber (CNF), honeycomb-structured nanofibrous carbon aerogels are obtained via unidirectional freeze-drying of the SSAD/CNC/CNF mixture followed by high-temperature carbonization. Impressively, unlike those fragile carbon aerogels in many early works, the present ones exhibit outstanding elasticity in repeated compression and release tests. Moreover, a symmetric binder-free supercapacitor is assembled from the carbon aerogels, which exhibits improved electrochemical capacitive properties and cycling stability. And even after 500 compression and release cycles, the supercapacitor can still maintain high capacitive performance, indicating its superiorities in durability and electrochemical stability.