Scavenger-controlled activation of lignin in microwave-assisted deep eutectic solvents for antioxidant nanoparticles

Lignin holds promise as a renewable feedstock for functional materials, but its conversion into well-defined nanomaterials is constrained by the heterogeneity of conventional activation. While phenolic scavengers have been employed to suppress undesired recondensation, their role has traditionally been regarded as static. Herein, we report a scavenger- controlled strategy for converting alkali lignin (AL) into antioxidant lignin nanoparticles (LNPs) via microwave‑assisted deep eutectic solvent (DES) treatment combined with in‑situ scavenger addition. The function of ferulic acid (FA) is critically modulated by the DES matrix. In lactic acid-based DES, FA functions primarily as a covalent stabilizer within an acid-catalyzed degradation environment, forming unique adducts that preserve lignin linkages under aggressive conditions. Conversely, in glycerol-based DES, FA transitions to a dynamically catalytic stabilizer that directs a highly selective activation pathway while suppressing over-oxidation and side reactions. This solvent-tuned adaptive mechanism offers a promising strategy to overcome the longstanding trade-off between depolymerization depth and product homogeneity. The synergistic Gly-DES/FA system yields chemically uniform, phenolic-rich lignin fragments that self-assemble into LNPs exhibiting the narrowest particle size distribution, highest total phenolic hydroxyl content (3.42 mmol g^-1), and superior radical scavenging activity. This work establishes a new principle of environment-dependent pathway control in lignin valorization, demonstrating that engineering of the reaction microenvironment can direct molecularly function to enable the green synthesis of high-performance, uniform nanomaterials from agricultural waste.