Reconstruction of biorefinery lignin into nanoparticles with controlled morphology and structure

Lignin nanoparticles (LNPs) exhibit application potential in fields such as ultraviolet (UV) shielding, antioxidant materials, and water purification owing to their versatile chemical structure. However effective, nontoxic solvent-based strategies to synthesize LNPs with diverse morphologies have not been reported. This study presents a continuous biorefinery method to produce monodisperse LNPs with diverse morphologies from isopropanol-solubilized lignin (IPA-lignin). IPA-lignin, which is rich in hydroxyl and carboxyl groups, was extracted from sweet sorghum bagasse via disc refining. The recovered IPA was reused with IPA-lignin to generate LNPs with hollow to dense structures at various temperatures. Morphology control was achieved by modulating the interaction between IPA and distilled water (DIW), an antisolvent. The interplay between IPA and DIW, coupled with the self-assembly kinetics of the lignin molecules, affected the encapsulated DIW content of the final materials, resulting in particles with different densities. The resulting LNPs exhibited varied surface chemistries, leading to diverse UV protection (maximum absorbance wavelength = 361 nm), antioxidant (half-maximal inhibitory concentration = 0.48 mg/mL), and selective cationic dye adsorption (over 90 %) properties. The correlation between the properties of the LNPs and their applications was then assessed to offer valuable insights into their functional optimization.