Tunable Deep Eutectic Solvents for Biomass Fractionation: Physicochemical Insights and Toxicity

Deep eutectic solvents (DESs) have emerged as promising green solvents for lignocellulosic biomass pretreatment due to their tunable properties, low cost, and sustainability. Their unique hydrogen‐bonding networks, polarity, and ionic characteristics enable selective disruption of lignin–carbohydrate complexes. Despite these advantages, several challenges remain, including limited xylan recovery, an incomplete understanding of DES‐biomass interactions, and insufficient toxicity assessments. Toxicity is strongly influenced by DES composition, particularly the hydrogen bond donor (HBD), highlighting the need for systematic evaluation of environmental and biological impacts. Furthermore, the behavior of aqueous DES systems and their interactions with biomass components require further investigation. This review summarizes recent advances in DES‐based biomass pretreatment, emphasizing their physicochemical properties, mechanisms, and toxicity. By integrating current knowledge, it provides insights into DES behavior during biomass processing and offers guidance for the rational design of safer, more efficient solvents to support sustainable biorefinery development.