Stabilized lignin nanoparticles for templated assembly of silver nanoparticles and covalent functionalization in dispersion state

Spherical lignin nanoparticles are emerging biobased nanomaterials, but instability and dissolution in organic solvents and aqueous alkali restricts their applicability. Here we report synthesis of hydroxymethylated lignin nanoparticles and their hydrothermal curing to stabilize the particles by internal crosslinking reactions. These colloidally stable particles contain a high bio-based content of 97% with a tunable particle size distribution and structural stability in aqueous media (pH 3 to 12) and organic solvents such as acetone, ethanol, dimethylformamide, and tetrahydrofuran. We demonstrate that the free phenolic hydroxyl groups that are preserved in the cured particles function as efficient reducing sites for silver ions, giving rise to hybrid lignin-silver nanoparticles that can be used for quick and facile sensing of hydrogen peroxide. The stabilized lignin particles can also be directly modified using base-catalyzed reactions such as the ring-opening of cationic epoxides that renders the particles with pH-dependent agglomeration and redispersion properties. Combining scalable synthesis, solvent-stability, and reusability these new class of lignin nanoparticles pave the way for a new era in circular bio-based nanomaterials.