Green Synthesis of Stable Lignin Nanoparticles with Reversible Swelling Behavior and Enhanced Multifunctional Features

Lignin nanoparticles (LNPs) are biobased multifunctional nanomaterials that are able to manage lignin complexity and add value as sustainable substitutes for conventional organic materials, usually obtained from fossil fuels. However, lack of stability of LNPs in organic solvents, poor scalability, and yield of production methods significantly limit their widespread application. This study proposes a straightforward, high-yield green route for synthesizing LNPs. It utilizes a hybrid approach based on the combination of the antisolvent (AS) and ultrasonication (US) procedures. The rationale behind this combination is to improve the LNP yield and enable better control of size morphology, distribution, as well as stability. The obtained nanostructures were investigated using SEM, FTIR, TGA, XRD, DLS, AFM, NMR, and UV-vis analyses, as well as chemical degradation experiments. The results were compared with those of particles obtained from conventional syntheses. The synthesized nanoparticles showed relevant stability in organic solvents, such as acetone, ethanol, and acetonitrile, as well as in alkaline solutions at pH 10 with reversible swelling features when switching the dispersant medium, allowing for their use in a wide range of applications. Moreover, LNPs exhibited higher antioxidant and antimicrobial activities than neat lignin and those obtained using the other approaches. This method paves the way for large-scale production of LNPs with excellent functional properties, enabling high-value use of lignin derivatives in a number of applications, including bionanocomposites, drug release, and adsorbents.