Walnut xylem-derived activated carbon with microtubule bundle architectures for highly efficient and rapid treatment of methylene blue

Hierarchical porous activated carbon (WXAC) was synthesized from walnut xylem. Precarbonization first preserved the vascular bundle structure, followed by controlled KOH activation-etching to precisely develop the porous architecture. Systematic characterization (BET, XRD, SEM, XPS, FTIR) confirmed a 3D interconnected microtubular structure with ultrahigh surface area (3116 m 2 /g) and pore volume (1.69 cm 3 /g). This hierarchical architecture combines microporous dominance with meso/macropore synergism, while oxygen enrichment (11.6 %) and abundant functional groups enhance methylene blue (MB) adsorption. WXAC achieves exceptional adsorption capacity (1015.29 mg/g) with rapid initial kinetics (125.8 mg/(g·min) within 5 min. Over 75 % removal efficiency persists through three regeneration cycles. Mechanistic investigations identified synergistic adsorption pathways combining hydrogen bonding, electrostatic interactions, π-π stacking, and pore confinement. Furthermore, the adsorption process follows pseudo-second-order kinetic and Redlich-Peterson isotherm models, suggesting the coexistence of monolayer and multilayer adsorption mechanisms. Thermodynamic parameters confirm spontaneous endothermic behavior. This work transforms agroforestry waste into high-performance adsorbents through controlled pore engineering.