Physical and Chemical Characterization, Adsorption Kinetics, Thermodynamic Analysis, and the Mechanism Involved in the Removal of Methylene Blue Dye by a Biosorbent from Pecan Nutshells

) indicate that the adsorption process is spontaneous and endothermic, with an enthalpy change characteristic of weak to moderate interactions. Kinetic data were best described by the pseudo-second-order model, with equilibrium reached within approximately 180 min. Intraparticle diffusion analysis revealed a multistep adsorption involving an initial boundary-layer diffusion followed by a slower pore diffusion. Overall, the adsorption mechanism is interpreted as multifactorial, governed by hydrogen bonding, π-π stacking, and van der Waals forces, consistent with a physisorption-dominated process strengthened by structural heterogeneity. These results demonstrate that PNS combines high capacity with operational simplicity, representing a scalable and sustainable alternative for the treatment of dye-contaminated wastewater.