Iranian Journal of Materials Science and Engineering

---

Modification of MnFe₂O₄@SiO₂ core-shell nanoparticles with (3-aminopropyl) triethoxysilane (APTES) was investigated. The magnetite MnFe₂O₄ nanoparticles with an average size of ~33 nm were synthesized through a simple co-precipitation method followed by coating with silica shell using tetraethoxysilane (TEOS); that has resulted in a high density of hydroxyl groups loaded on nanoparticles. The prepared MnFe₂O₄@SiO₂ nanoparticles were further functionalized with APTES via silanization reaction. For having suitable surface coverage of APTES, controlled hydrodynamic size of nanoparticles with a high density of amine groups on the outer surface, the APTES silanization reaction was investigated under different reaction temperatures and reaction times. Based on dynamic light scattering (DLS) and zeta potential results, the best conditions for the formation of APTES-functionalized MnFe₂O₄@SiO₂ nanoparticles were defined at a reaction temperature of 70 °C and the reaction time of 90 min. The effectiveness of our surface modification was established by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). The prepared magnetite nanostructure can be utilized as precursors for synthesizing multilayered core-shell nanocomposite particles for numerous applications such as medical diagnostics, drug, and enzyme immobilization, as well as molecular and cell separation.

---

Fe₃O₄ nanoparticles (NPs) with a continuous and mesoporous silica (m-SiO₂) shell were synthesized using a one-step method, sourcing silica from rice husk ash (RHA). The rice husk was thermally treated to obtain ash, from which silica was extracted as sodium silicate and precipitated by pH reduction. This silica powder, combined with iron chloride salts, facilitated the synthesis of the core-shell NPs. Mint extract acted as a capping agent to prevent agglomeration, and CTAB (cetyltrimethylammonium bromide) was used to create the porous SiO₂ shell. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) characterization investigated the structure, size, and shell formation. Coating integrity and suspension stability were assessed through Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS). DLS analysis showed a relatively narrow particle size distribution with an average hydrodynamic size of 72.6 nm. Small-angle X-ray scattering (SAXS) provided insights into the meso- and nanoscale structure, while BET and nitrogen adsorption-desorption isotherms confirmed the mesoporous nature of the silica shell. Magnetization measurements showed superparamagnetic behavior, with specific magnetization values of 57.9 emu/g for Fe₃O₄ and 27.5 emu/g for Fe₃O₄@m-SiO₂. These results confirm the successful synthesis of superparamagnetic magnetite NPs with a mesoporous silica coating from RHA.