Production of Full Biomass Photonic Materials from Lignin Extracted from Wood with High-Purity and Rich-Hydroxyl in Molten Salt Hydrate

Biomass-based photonic materials have broad application prospects due to their excellent biocompatibility. Lignin is the most abundant aromatic polymer in nature, and it can be transformed into monodispersed particles for photonic materials preparation. However, the heterogeneity of lignin often leads to nonuniform lignin particle formation. To address this issue, a novel separation method using citric acid-acidified molten salt hydrate (MSH) was proposed to dissolve cellulose and hemicellulose while partially depolymerizing lignin from pine wood. The removal of cellulose and hemicellulose significantly improved the purity of lignin to 97.11% and the selective cleavage of β-O-4 bonds minimized lignin condensation. Low-molecular-weight lignin with high hydroxyl groups of 8.06 mmol g–1 was obtained, exhibiting a narrow distribution of intermolecular forces. Monodispersed colloidal spheres can be readily prepared from the rich-hydroxyl lignin through antisolvent self-assembly, allowing precise control over particle size ranging from 150 to 250 nm and enabling tunable single-color coverage across the full spectrum of visible light. This green and sustainable extraction and modification method for lignin provides a simple and economical strategy for preparing biomass-based photonic materials in high yield with minimal chemical utilization.