Microwave-assisted fast co-production of fermentable sugar and nanocellulose via tunable zinc acetate based deep eutectic solvents treatments

Deep eutectic solvent (DES) treatment has been considered as a promising approach to lignocellulose deconstruction and valorization. Nevertheless, some aspects such as high energy consumption and cellulose residue loss limited bioconversion efficiency. Herein, neutral DESs based on choline chloride (ChCl) and zinc acetate (ZAC) in different molar ratios were designed for ultra-fast treatment on bamboo holocellulose with the assistance of microwave radiation for the first time. ZAC/ChCl-1 promoted the glucose conversion yield to 67.3%, due to more hydrophobic sites exposed on crystallite surfaces caused by fibrils swelling and enlarged gaps between adjacent glucan chains after the treatment. Furthermore, the proposed DES also displayed the ability to exfoliate cellulose nanofibrils with high aspect ratios from microfibrils at high treatment temperature (120 °C). With a large amount of negative charge on surface, the nanocellulose maintained satisfying dispersion stability and homogeneity, which achieved the full use and tunable dual conversion of bamboo cellulose. Thus, the present study provides a deeper understanding of novel DES pretreatment for biomass conversion and widens the scope of high-efficiency biorefinery.