Valorization of Pineapple Leaf Waste for Methylene Blue Adsorption: A Comparative Study of Natural and Modified Adsorbents

Synthetic dyes like methylene blue (MB) are widely used in textiles and pharmaceuticals but pose environmental risks when discharged into wastewater. This study evaluates pineapple leaf biomass as a low-cost, biodegradable adsorbent for MB removal. Four materials─raw fiber (PALF), nonfibrous material (NFM), alkali-treated microfibers (PALMF), and ultrasonically treated PALMF (Ultra_PALMF)─were prepared and characterized. PALF achieved the highest adsorption capacity (53.93 mg g^–1), while NFM showed excellent reusability, retaining >96% efficiency after three cycles. Nonlinear kinetic analysis indicated that adsorption generally followed the pseudo-second-order model, though PALF was better described by the pseudo-first-order model. Equilibrium data were best represented by the Sips model, confirming the heterogeneous nature of the adsorption sites. Thermodynamic analysis confirmed a spontaneous, exothermic process. These findings highlight pineapple leaf waste as a sustainable alternative for dye removal, with NFM offering strong potential for practical reuse.