Kinetics and thermodynamics of methylene blue adsorption on the Fe-oxide nanoparticles embedded in the mesoporous SiO₂

Fe-oxide nanoparticles with a diameter of ~10 nm embedded into the porous structure of mesoporous SiO₂ particles using temperature regulated chemical vapor deposition and a subsequent annealing process. The kinetics and thermodynamics of MB adsorption on bare SiO₂ and Fe-oxide/SiO₂ particles were investigated. MB adsorption kinetics of both SiO₂ particles can be described by pseudo first order and intra particle diffusion plot. Thermodynamic parameters were calculated based on the modified Langmuir isotherm model. Equilibrium constant and spontaneity of MB adsorption was increased with the presence of Fe-oxide nanoparticles inside the SiO₂ pores_, which can be ascribed to the more negative values of ΔH of Fe-oxide/SiO₂ particles compared to bare SiO₂. A higher affinity of Fe-oxide nanoparticles for MB adsorption facilitated the intra particle diffusion of MB molecules at a longer time of MB adsorption and improve the maximum MB adsorption capacities of Fe-oxide/SiO₂ compared to bare SiO₂. The maximum MB adsorption capacities of bare SiO₂ and Fe-oxide/SiO₂ particles reduced as the initial pH of MB solution increased, however, Fe-oxide/SiO₂ particles always exhibited the higher capacity of MB adsorption than bare SiO₂.