Fabrication of Fe 3 O 4 core-TiO 2 /mesoSiO 2 and Fe 3 O 4 core-mesoSiO 2 /TiO 2 Double Shell Nanoparticles for Methylene Blue Adsorption: Kinetic, Isotherms and Thermodynamic Characterization.

Herein, Fe 3 O 4 core-TiO 2 /mesoSiO 2 and Fe 3 O 4 core-mesoSiO 2 /TiO 2 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 Fe 3 O 4 core-meso SiO 2 /TiO 2 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 Fe 3 O 4 core-mesoSiO 2 /TiO 2 and Fe 3 O 4 core-TiO 2 /mesoSiO 2 double shell exhibit a spontaneous tendency to adsorb methylene blue from the aqueous solutions. The achieved performance of Fe 3 O 4 core-meso SiO 2 /TiO 2 and Fe 3 O 4 core-TiO 2 /meso SiO 2 double shell as adsorbent for methylene blue removal will encourage future research investigations on the removal of a broad range of contaminants from wastewater.