Microwave-assisted extraction of Camellia oleifera shell lignin via dual-acidic deep eutectic solvent and its...

Lignin represents a promising biomass resource for functional materials; however, its intricate structure poses significant challenges for efficient extraction. Herein, a novel dual-acidic deep eutectic solvent (DADES) composed of ZnCl₂ and lactic acid (1:8 molar ratio) was developed, and which applied to facilitate the rapid extraction of lignin from waste Camellia oleifera shells (WCOS). Notably, this extraction process was significantly enhanced by microwave irradiation. This tailored DADES exhibits optimal performance, enabling the extraction of lignin with an impressive yield of 97.1 %, purity of 91.2 %, and low dispersity (1.49) within just 10 min at 70 W microwave power. The extracted lignin is identified as guaiacyl-syringyl (GS) type. Density functional theory (DFT) calculations highlight the pivotal role of extensive hydrogen bonding interactions between the dual-acidic DES and lignin in facilitating the efficient extraction process. This work presents an efficient DADES-based extraction technique, synergistically boosted by microwave irradiation, for the selective fractionation and recovery of lignin from WCOS. Furthermore, the combined features of solvent recyclability and generation of a valorizable cellulose-rich residue highlight a promising pathway toward a sustainable biorefinery.