The dawn of aqueous deep eutectic solvents for lignin extraction

Lignin, the most abundant renewable aromatic compound, finds diverse applications across various sectors, including environmental, energy, catalytic, and pharmaceutical industries. The application of aqueous deep eutectic solvents (ADESs) for lignin valorization has garnered significant attention in recent years. However, a comprehensive review addressing lignin extraction using ADESs is currently unavailable, and the implementation of these processes at an industrial scale is still ongoing. This review aims to fill the research gap by presenting recent advancements in lignin valorization using ADESs, with a specific focus on the impact of water on DES properties, such as viscosity, polarity, and nanostructure. The major influencing factors and mechanisms of lignin extraction using ADESs are also highlighted, particularly in optimizing the water content for achieving efficient extraction. Moreover, this review examines the structural features of lignin generated from ADESs and explores its potential valorization. Additionally, an evaluation of the economic and environmental sustainability of lignin extraction using ADESs is provided, highlighting the potential feasibility toward the coming industrial-scale applications. Finally, insights into future perspectives for lignin extraction with ADESs are proposed, reinforcing the status of ADESs as the most promising green solvents for lignin valorization in the coming years.