Cubic Silica-Coated and Amine-Functionalized FeCo Nanoparticles with High Saturation Magnetization

Abstract

By systematically varying the reaction parameters in a liquid-phase reduction reaction, large FeCo nanocubes with tunable body diagonal lengths of 175, 350, and 450 nm were synthesized. The nanocubes were initially stabilized with poly(vinyl pyrrolidone) (PVP) and then coated with a relatively thin layer of silica (~55 nm thick), which allowed them to retain their cubic shape. The magnetization curves showed that the PVP-stabilized nanocubes exhibited a high saturation magnetization of 167 ± 4 emu/g. The saturation magnetization, however, decreased upon coating with silica to 146 ± 13 emu/g for the particles with 350 and 450 nm FeCo cores and 48 ± 1 emu/g for the particles with 175 nm FeCo cores. The silica-coated FeCo nanocubes were then functionalized with 3-(aminopropyl)-trimethoxysilane (APTMS), and a layer of surface-bound nanoparticle was generated by exposing the resultant amine-functionalized nanocubes to self-assembled monolayers (SAMs) on gold terminated with carboxylic-acid groups.

Facile Synthesis of FeCo/Fe3O4 Nanocomposite with High Wave-Absorbing Properties

“…Figure 3 shows similar curves and confirms the presence of Fe, Co and O elemental signatures for all samples [23–25]. The result further confirms the formation of FeCo/Fe 3 O 4 nanocomposite.…”

Silica Encapsulation of Ferrimagnetic Zinc Ferrite Nanocubes Enabled by Layer-by-Layer Polyelectrolyte Deposition

“…8, 9 However, one of the shortcomings of high m MNPs is their tendency to spontaneously aggregate. Approaches to prevent MNP aggregation include creating a shell around the MNPs, 10 fabricating synthetic antiferromagnetic nanoparticles, 3, 11 or decreasing the MNP size until superparamagnetic behavior is observed. 12 Superparamagnetism (at 298 K) occurs in single-domain ferro- and ferrimagnetic nanoparticles of sufficiently small size that their magnetic dipole undergoes random thermal fluctuations in the absence of an external magnetic field ( H ); this situation results in the absence of an observable moment.…”

Fe3O4/SiO2 Core/Shell Nanocubes: Novel Coating Approach with Tunable Silica Thickness and Enhancement in Stability and Biocompatibility

“…Furthermore, the surface to volume ratio (S/V) of nanomaterial plays a significant role on the biomolecules immobilization for various bioapplications. Particularly, the geometries other than spherical are, however, preferred for applications involving magnetic-based biosensing devices, where a larger contact area can lead to more-robust binding to a sensor platform [10,11]. Thus, nanocubes could be the good candidate comparing with other shapes for the bio-application because of its high surface to volume ratio which can increase the density of biomolecules on the surface [12].…”

“…Therefore, integration of the cubic structure of magnetic NPs in the form of magnetite and thereafter functionalization with silica as a shell would obviously enhance its performance and thus becomes a promising material for these applications. The uniform coating of silica on magnetite nanocubes with controlled thickness being a challenging task for researchers because of the high tendency of nanocubes towards the aggregation and problem with retention of cubic shape after silica coating [11]. However, recently Kolhatkar et al have reported 55 nm silica coated FeCo nanocubes using Stober method with long synthesis times [11].…”

“…The uniform coating of silica on magnetite nanocubes with controlled thickness being a challenging task for researchers because of the high tendency of nanocubes towards the aggregation and problem with retention of cubic shape after silica coating [11]. However, recently Kolhatkar et al have reported 55 nm silica coated FeCo nanocubes using Stober method with long synthesis times [11]. Even though they succeeded in the coating process of silica onto nanocube shape, their data do not provide adequate information about the silica shell thickness and also on the mechanism of controlling the shell thickness.…”