Core-Shell Fe@SiO₂ Nanoparticles Synthesized via Modified Stober Method for High Activity in Cr(VI) Reduction

In this paper, Fe@SiO2 nanoparticles (α-Fe nanoparticles coated with SiO2 shell) were synthesized at room temperature using the modified Stöber method combined with potassium borohydride (KBH4) reduction process. The present study depicts the facile synthesis of Fe@SiO2 without the presence of surfactants and stabilizers. In this experiment, KBH4 acted both as a reducing agent for iron salt and a catalyst for hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The Fe@SiO2 nanoparticles were characterized using X-ray diffraction method, specific surface area (BET) technique, transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimal mass ratio of Fe in the form of anhydrous ferric chloride (FeCl3) and SiO2) in the form of TEOS was 4:1. α-Fe-Fe nanoparticles (size of about 45 nm) were coated with approximately 10 nm thick SiO2 shells. Moreover, Fe/SiO2 (Fe0 nanoparticles supported by silica nanoparticles) was synthesized to compare the results. Due to the silica shells, Fe cores cannot be oxidized when dipped in the concentrated sulfuric acid, and hence, the removal of Cr(VI) was not weakened in the acidic environment.