Hermetically Coated Superparamagnetic Fe₂O₃ Particles with SiO₂ Nanofilms

Abstract

Magnetic nanoparticles are frequently coated with SiO 2 to improve their functionality and biocompatibility in a range of biomedical and polymer nanocomposite applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coated with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis of iron acetylacetonate in xylene/acetonitrile solutions and the resulting aerosol was in situ coated with silicon dioxide by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe 2 O 3 (maghemite) particle properties and the thickness of their silica coating film. This ensures that the nonmagnetic SiO 2 layer can be closely controlled and minimized. The optimal SiO 2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe 2 O 3 coated with about 2 nm thin SiO 2 layers was nearly identical to that of uncoated, pure Fe 2 O 3 nanoparticles.

Formation of Magnetic FexOy/Silica Core-Shell Particles in a One-Step Flame Aerosol Process

“…The core-shell particles and the non-core-shell particles appar- ently had different magnetic domain sizes, and hence different temperature-dependence of the magnetic properties (Tartaj et al 2002). The main magnetic properties of the core-shell particles and the non-core-shell nanoparticles are shown in Table 4, in comparison with magnetic properties of iron oxide silica core-shell nanoparticles generated in other aerosol processes (Li et al 2006;Teleki et al 2009). The core-shell particles in this study exhibited very soft room-temperature magnetization behaviors (low coercivity and remanence) in comparison to particles from the other studies.…”

“…Most recently, a twostep approach based on a flame reactor was reported for the synthesis of Fe 2 O 3 /SiO 2 core-shell nanoparticles (Teleki et al 2009). Teleki et al used a flame spray pyrolysis (FSP) reactor to generate Fe 2 O 3 nanoparticles; by introducing hexamethyldisiloxane vapor in the post-flame region, they were able to encapsulate the Fe 2 O 3 nanoparticles with a very thin silica coating.…”

Synthesis of TiO2 nanoparticles containing Fe, Si, and V using multiple diffusion flames and catalytic oxidation capability of carbon-coated nanoparticles

“…TiO2 can also be used in a number of applications related to coatings, UV filters, and lenses, where the photocatalytic effects of TiO2 are harmful (Nie et al 2009). To overcome this challenge, TiO2 can be coated with SiO2 to limit the photocatalytic activity of the nanoparticles (Teleki 2009). Teleki et al, (Teleki et al 2005) synthesized silica-titania composites and studied the evolution of composite particle morphology from ramified agglomerates to spot-or fully coated particles.…”

A photopatternable superparamagnetic nanocomposite: Material characterization and fabrication of microstructures

“…A presence of maghemite can lower magnetization. Maghemite nanoparticles produced with flame aerosol technology with similar diameters (14 ± 0.8 nm) show a magnetization of 34 emu g −1 [31]. In Fig.…”