Adsorption of Methylene Blue Using Pinecone Residue

Abstract

This study explores the adsorption of methylene blue (MB) from wastewater using pinecone residue, a low-cost and abundant biosorbent. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and particle size distribution were used to characterize the material. Particle size strongly influenced both the removal efficiency and the equilibrium capacity. The adsorption performance was optimized using response surface methodology and decision tree regression. Optimal conditions included a contact time > 45 min, an initial dye concentration > 37.5 mg L⁻¹, and a biosorbent dosage of 40–75 mg. Under these conditions, the equilibrium adsorption performance showed a significant improvement over previous studies. Kinetic modeling revealed that the Elovich model best represented the adsorption process, whereas the equilibrium data were most accurately described by the Langmuir isotherm, yielding a maximum monolayer adsorption capacity of 148.54 mg g⁻¹. Additionally, thermodynamic parameters confirmed the spontaneous, exothermic nature of the adsorption, although regeneration studies demonstrated the material's reusability, with increased adsorptive capacity after acid desorption cycles. The findings demonstrate the strong adsorption potential of pinecone residue, emphasizing its efficiency and sustainability for wastewater treatment applications.