Modified expanded graphite/Fe₃O₄ composite as an adsorbent of methylene blue: Adsorption kinetics and isotherms

A magnetic expanded graphite (MEG) composite was synthesized by the explosive combustion method using black powder. Successful expanded graphite coating of iron oxide nanoparticles (Fe₃O₄) was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The expanded volume and specific surface area (S_BET) of the expanded graphite were 300.0 mL/g and 34.8 m²/g, respectively, and the crystalline particle sizes of Fe₃O₄ were around 100–400 nm. In addition, the Fe₃O₄ and MEG exhibited magnetic properties, with a magnetic saturation of 72.1 and 17.5 emu/g, respectively. The adsorption kinetics of methylene blue (MB) dye were consistent with a pseudo-second-order model (R² = 0.9999). The data obtained fit the Langmuir (R² = 0.99906) and Redlich–Peterson (R² = 0.99998) isotherm models, with a maximum MB adsorption capacity of 78.06 mg/g. The Redlich–Peterson isotherm equation best fit the adsorption experiment datasets examined in this study.