Ultrasmall, Low-Molecular-Weight Lignin Nanoparticles via Effective Suppression of Lignin Condensation by Strong Nucleophilic Interaction

The formation of low molecular weight lignin nanoparticles (LMW-LNPs) remains challenging due to their severe self-aggregation effect as well as thermal instability, hindering their scalability and functional applications. This study develops a novel γ-valerolactone (GVL)/deep eutectic solvent (DES) biphasic system incorporating polyol-based hydrogen bond donors (HBDs) to systematically modulate the hydrogen bond acidity of DES, enabling selective depolymerization of industrial lignin in acid lithium bromide hydrate (ALBTH) while effectively suppressing lignin condensation. The optimized system achieved a low lignin molecular weight of 1213 g/mol with minimal condensation, yielding monodisperse low-molecular-weight lignin nanoparticles (LMW-LNPs) with an average diameter of 92.3 nm. Mechanistic investigations using the veratrylglycerol-β-guaiacyl ether (VG) model compound revealed that lignin aryl ether bonds are cleaved via hydrogen transfer from the DES-HBD component, which disrupts the condensation pathway through competitive hydrogen bonding. The LMW-LNPs which maintain structural integrity while achieving depolymerization during the preparation of lignin-based materials exhibit efficient photothermal conversion and dye adsorption properties. They offer a transformative approach for the sustainable production of functional lignin nanomaterials with customized properties, addressing key challenges in the value-added utilization of lignin and promoting advanced applications of lignin-based materials.