Herein, Fe3O4 core-TiO2/mesoSiO2 and Fe3O4 core-mesoSiO2/TiO2 double shell nanoparticles were prepared by first (R1) and second (R2) routes and applied for the removal of methylene blue. The reported adsorption capacities for R1-0.2, R1-0.4 and R2 samples were 128, 118 and 133 mg.g-1, respectively, which were obtained after 80 min as equilibrium contact time, and pH of 6 using a methylene blue concentration of 200 ppm. The adsorption of methylene blue using the prepared Fe3O4 core-meso SiO2/TiO2 double shell was analyzed by kinetic and isotherms models. In addition, thermodynamic investigations were applied to assess the spontaneous nature of the process. The obtained results confirmed that the pseudo-second order model is well fitted with the adsorption data and the Freundlich-isotherm assumption suggested a multilayer adsorption mechanism. In addition, results of the thermodynamic investigation indicated that ΔG° was in the range of -2.3 to -6.8 kJ/mol for R1-0.2, -2.8 to -6.3 kJ/mol for R1-0.4 and -2.0 to -5.2 kJ/mol for R2. In addition, the ΔH° and ΔS° values were found in the range of 26.4 to 36.19 kJ.mol-1 and 94.9 to 126.3 Jmol-1 K-1, respectively. These results confirm that the surfaces of Fe3O4 core-mesoSiO2/TiO2 and Fe3O4 core-TiO2/mesoSiO2 double shell exhibit a spontaneous tendency to adsorb methylene blue from the aqueous solutions. The achieved performance of Fe3O4 core-meso SiO2/TiO2 and Fe3O4 core-TiO2/meso SiO2 double shell as adsorbent for methylene blue removal will encourage future research investigations on the removal of a broad range of contaminants from wastewater.
Keywords: adsorption-modeling; coating; magnetic Fe3O4; methylene blue; nanotechnology; wastewater purification.