All‐Lignin Microspheres with Controllable Surface Charges Fabricated from Water‐Soluble Quaternized Lignin

ABSTRACT Technical lignin offers a renewable aromatic platform for functional materials. However, its direct transformation into well‐defined particulate adsorbents remains challenging owing to its poor aqueous processability and uncontrolled interfacial properties. In this study, kraft lignin (KL) is quaternized by introducing permanent quaternary ammonium groups, yielding a water‐processable quaternized lignin (QL) with tunable cationic characteristics. Polymer matrix‐free lignin microspheres are then fabricated by water‐in‐oil emulsion crosslinking using KL and QL as lignin building blocks. Compared with KL‐based microspheres (KLM), QL‐containing microspheres (QLM) show improved structural stability, reduced lignin leakage, and enhanced affinity for anionic methyl orange (MO). QLM achieves a Langmuir maximum adsorption capacity of 651.4 mg g −1 , far exceeding that of KLM, primarily through the electrostatic attraction between quaternary ammonium groups and MO sulfonate groups, with additional contributions from π–π interactions, hydrogen bonding, and network‐assisted diffusion. QLM retains high adsorption performance over multiple reuse cycles and enables continuous‐flow MO removal in a packed‐bed system. These results demonstrate a charge‐engineering strategy for converting technical lignin into processable high‐performance microsphere adsorbents for sustainable water purification.