AbstractMagnetite (Fe3O4) is the most important iron oxide species that has received considerable attention by many researchers because of its strong magnetic susceptibility, lack of a remanent field, coercivity, and absence of a hysteresis loop. In this study, Fe3O4 was prepared by three different techniques: coprecipitation, hydrothermal, and sonochemical. The samples prepared by coprecipitation, sonochemical, and hydrothermal methods possessed magnetic saturation values of 60, 52, and 27 emu/g (A·m2/kg), respectively. Therefore, the coprecipitated sample was functionalized by mono- and diamino silane coupling agents (ASCs). The loading of ASCs onto the Fe3O4 surface was carried out in different solvents, such as toluene, ethanol, and water. The functionalized surfaces were characterized by using different techniques, namely, X-ray powder diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, vibrating-sample magnetometry, thermogravimetric analysis, scanning electron microscopy, energy-dispersive X-ray analysis, transmission electron microscopy, and Brunauer–Emmett–Teller analysis. The adsorption of eosin-Y (EY) dye onto the Fe3O4-APTS surface was affirmed by fitting in the Langmuir isotherm model. Besides, the qmax value (38.32 mg/g) obtained from the Langmuir isotherm model was matched with the theoretical qecal value calculated from the pseudosecond-order (PSO) model. Furthermore, the adsorption mechanism of EY onto the functionalized Fe3O4 surface was by physisorption, according to the lower free energy values (ΔG°) obtained. In addition, the adsorption process is endothermic in nature. However, adsorption kinetics was best described by the PSO model.