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 Cu ²⁺ 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 Cu ²⁺ concentrations, the prepared lignin nanoparticles showed controllable Cu ²⁺ ‐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.