Dual-functional thiosulfate activators enable high-capacity sulfur-doped lignin porous carbon for water purification

Complex side reactions between the activating agent and dopant atoms during chemical activation complicate pore structure development and mechanistic understanding in porous carbons. This study introduces thiosulfate-based activators (K₂S₂O₃, K₂S₂O₅, K₂S₂O₈) that simultaneously create hierarchical pores and tune surface functionalities. Lignin activated with these agents yielded sulfur-doped porous carbons with high surface areas, demonstrating exceptional adsorption potential. The K₂S₂O₃-derived adsorbent achieved surface area of 3300 m² g^-1, pore volume of 2.33 cm³ g^-1, and optimal sulfur-group concentration. Pore evolution involves three stages: (1) macropore formation via K₂S₂O₃ decomposition gases (honeycomb network), (2) micropore generation by K₂SO₄ self-activation, and (3) mesopore creation through K-mediated micropore etching. Exhibiting a Langmuir MB adsorption capacity of 1120 mg g^-1 and excellent reusability, the material relies on adsorption mechanisms including electrostatic interactions, hydrogen bonding, pore filling, and π-π stacking. This multifunctional activation strategy for sulfur-doped porous carbons presented here significantly advances adsorbent applications.