Surface engineering of Fe3O4@SiO2 Core-Shell nanoparticles: Role of CTAB/TEOS ratio

Core- shell Fe3O4@SiO2 nanoparticles with tunable SiO2 shell thickness and porosity were successfully synthesized using cetyltrimethylammonium bromide (CTAB) as the crosslinking agent and tetraethyl orthosilicate (TEOS) as the silica precursor. The increase in the O-H stretching peak intensity observed in the Fe3O4/CTAB and Fe3O4/CTAB/SiO2 nanoparticles was attributable to the increased number of hydroxyl groups resulting from hydrogen bonding between the head of CTAB and water molecules and the increased exposure of the SiO2 surface owing to CTAB dissolution. The shell thickness and porosity of the nanoparticles were controlled by adjusting the TEOS/CTAB ratio. Increasing the CTAB content while maintaining a fixed amount of TEOS resulted in a constant shell thickness but increased porosity. Conversely, increasing the TEOS content while fixing the amount of CTAB led to the formation of a double-shell structure with a new dense silica layer on top of the existing shell at concentrations exceeding a certain threshold. These findings provide valuable insights into the design and application of SiO2-coated nanoparticles tailored for various applications.