Molecular Structural and Copper(II)-Dependency in the Formation of Lignin Nanoparticles

As one of the most abundant natural polyphenols, lignin possesses numerous hydroxyl and carboxyl groups that endow it with exceptional metal-ion coordination capabilities. Metal-phenolic complexes derived from lignin have exhibited promising potential in catalysis, environmental remediation, and biomedicine. However, the inherent heterogeneity and polydispersity of lignin often lead to unpredictable metal-ion loading performance, and it is even more challenging to achieve precise morphological regulation. Herein, we proposed a lignin fractionation‒metal complexation strategy, where lignin fractions with different molecular structural characteristics were co-assembled with Cu²⁺ via a facile, one-step antisolvent precipitation method to fabricate metal-loaded lignin nanoparticles. By systematically tuning the molecular structure of lignin fractions and the Cu²⁺ concentrations, the prepared lignin nanoparticles showed controllable Cu²⁺-immobilization efficiency (93.63%-95.73%) and sizes (278.4-423.3 nm) with narrow distributions. This work provides actionable insights for the design of advanced nanomaterials from abundant renewable feedstocks.