Sonochemical Approach to the Synthesis of Fe₃O₄@SiO₂ Core−Shell Nanoparticles with Tunable Properties

Abstract

In this study, we report a rapid sonochemical synthesis of monodisperse nonaggregated Fe(3)O(4)@SiO(2) magnetic nanoparticles (NPs). We found that coprecipitation of Fe(II) and Fe(III) in aqueous solutions under the effect of power ultrasound yields smaller Fe(3)O(4) NPs with a narrow size distribution (4-8 nm) compared to the silent reaction. Moreover, the coating of Fe(3)O(4) NPs with silica using an alkaline hydrolysis of tetraethyl orthosilicate in ethanol-water mixture is accelerated many-fold in the presence of a 20 kHz ultrasonic field. The thickness of the silica shell can be easily controlled in the range of several nanometers during sonication. Mossbauer spectra revealed that nonsuperparamagnetic behavior of obtained core-shell NPs is mostly related to the dipole-dipole interactions of magnetic cores and not to the particle size effect. Core-shell Fe(3)O(4)@SiO(2) NPs prepared with sonochemistry exhibit a higher magnetization value than that for NPs obtained under silent conditions owing to better control of the deposited silica quantities as well as to the high speed of sonochemical coating, which prevents the magnetite from oxidizing.

Applications of Ultrasound to the Synthesis of Nanostructured Materials

“…A recent report by Nikitenko et al describes sonochemical coating of silica over Fe 3 O 4 nanoparticles. [108] In this work, ultrasonic irradiation significantly promotes the homogeneity of the hydrolysis of tetraethyl orthosilicate (TEOS) and prevents agglomeration of silica sols by improving the mass transport of silica sols to Fe 3 O 4 nanoparticle surfaces, which results in homogeneously coated core-shell nanoparticles. Not only is the sol-gel reaction time significantly reduced, but also the thickness of silica coating over Fe 3 O 4 nanoparticles can be easily manipulated by sonication time in this synthetic route.…”

Protein-Directed Synthesis of γ-Fe2O3Nanoparticles and Their Magnetic Properties Investigation

“…In the Fe2p high-resolution XPS spectrum (magnified region), the binding energies around 710 and 723 eV are related to Fe (2p 3/2 ) and Fe (2p 1/2 ), respectively, which are very close to the values of Fe 3 O 4 published in the literature. 21,22 It is remarkable that no charge transfer satellite of Fe (2p 3/2 ) at about 720 eV is detected, indicating the formation of mixed oxides of Fe (II) and Fe (III), such as Fe 3 O 4 .…”

Monodisperse Water-Stable Sio2- Coated Fluoride Upconversion Nanoparticles with Tunable Shell Thickness

“…Several approaches has been attempted toward this regard, including SiO 2 coating, wrapping by small molecular surfactant, amphiphilic polymer, oxidizing oleic acid ligands with the Lemieuxvon Rudolf reagent, and ligand exchange [11,[15][16][17][18][19][20][21][22][23][24][25]. In particular, SiO 2 -coating are of particular interest, due to its high biocompatibility, easy surface modifi cation through silicon-enriched chemistry, and easy control of interparticle interactions [26][27][28][29]. However, there lacks a facile way to perform silica coating of UCNPs with a controlled thickness.…”