Fabrication of lignin-derived microspheres via catalytic depolymerization for high-efficiency rubidium adsorption

The valorization of lignin into high-value functional materials remains challenging due to its recalcitrant structure. This study presents an integrated strategy that couples efficient catalytic depolymerization of lignin with the synthesis of functional microspheres for selective rubidium (Rb⁺) recovery, advancing sustainable biorefinery and resource recycling. A Ru/MoS₂ nanoflower catalyst was synthesized via hydrothermal and high-temperature hydrogen reduction, exhibiting high thermal stability and mesoporous structure. Under mild conditions (200 °C, 1 atm H₂, 6 h, methanol solvent), 90.7% of delignification and 27.4 wt% yield of monomers were achieved during the depolymerization of eucalyptus. The resulting lignin oil, rich in preserved phenolic hydroxyl groups, was successfully valorized into uniform microspheres via self-assembly. These lignin-derived microspheres exhibited a high Rb⁺ adsorption capacity of 170.3 mg/g under optimal conditions (pH=9, 25 °C), with a theoretical maximum adsorption capacity of 292.7 mg/g based on Langmuir isotherm modeling. Adsorption followed Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer chemisorption, and was spontaneous and exothermic as confirmed by thermodynamic analysis. This work not only demonstrates an efficient catalyst for lignin depolymerization but also establishes a full-chain pathway for converting lignin into a high-performance adsorbent for strategic metal recovery, offering a novel and sustainable alternative to conventional adsorbents such as activated carbon or metal oxides.