Harnessing Composition of Iron Oxide Nanoparticle: Impact of Solvent-Mediated Ligand–Ligand Interaction and Competition between Oxidation and Growth Kinetics

Abstract

The composition of metal oxide nanoparticles is of great importance for their applications because defects and/or deviation from stoechiometry strongly affect their physical properties. We report here on the crucial role of synthesis parameters such as solvent, ligand and iron precursors on the composition of spinel iron oxide nanoparticles synthesized by the thermal decomposition method. At first, the investigation of the thermal decomposition of iron stearates bearing either two or three stearate chains by thermogravimetric analysis, IR spectroscopy and Mössbauer spectrometry as a function of temperature and syntheses with only oleic acid and iron stearate confirmed that the composition of the first nuclei is wüstite Fe 1-x O. The synthesis of nanoparticles with high sizes requires the use of very high boiling point solvents to ensure an effective growth step. We observed that, when the grain growth and oxidation kinetics are similar, nanoparticles with a spinel composition and quite no defects are produced. An oxidation rate slower than the nuclei growth rate favours the formation of core-shell Fe 1-x O@Fe 3-x O 4 NPs. The oxidation kinetics is shown to be influenced by surfactant and solvent natures.Indeed, surfactants such as oleic acid form a dense monolayer at the nuclei surface which oxidation kinetics will depend on this monolayer permeability. Temperature, solvents with high surfactant affinity, deprotonated surfactants or decomposition products of solvents affect the monolayer stability and thus the nanoparticle composition. The solvents' nature and solvent mediated ligand-ligand interactions are thus evidenced to be important parameters to control the formation of defectsfree and stoechiometric oxide nanoparticles.

Orienting the Pore Morphology of Core-Shell Magnetic Mesoporous Silica with the Sol-Gel Temperature. Influence on MRI and Magnetic Hyperthermia Properties

“…Oleic acid-stabilized iron oxide nanospheres with a mean diameter around 18 nm have been synthesized by thermal decomposition following a recently reported procedure [ 53 ]. Briefly, iron stearate (III) was prepared by precipitation of sodium stearate and ferric chloride salts in an aqueous solution as described [ 54 ].…”

Assessing the parameters modulating optical losses of iron oxide nanoparticles under near infrared irradiation

“…45,46 On the other hand, a set of IONPs with comparable size (between 15 and 18 nm) and different shapes: spheres (S-IONP), cubes (C-IONP), platelets (P-IONP) and octopods (O-IONP) were synthesized at Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS) by a thermal decomposition method described elsewhere. [47][48][49][50] IONPs were transferred to aqueous media following a well-established protocol. 49,51,52 The resulting IONPs were coated with dendrons bearing phosphonic acid tweezers and three PEG chains for biocompatibility to ensure a strong coupling to the IONP surface.…”

Iron Stearate Structures: An Original Tool for Nanoparticles Design

“…For each stearate, Fe(III) species with mainly two different environments are noticed. From Mössbauer spectrometry detailed in reference 33 , the first "environment" (IS = 0.5 mm.s -1 , QS = 0.7 mm.s -1 with IS: isomer shift; QS: quadrupole splitting) is present in both precursors, and with a proportion larger than 50%. It is characteristic of HS (high spin) iron III in a distorted octahedral environment.…”

“…FTIR spectra are given in reference 33 but they are more in depth analysed here. Both FeSt2 and FeSt3 IR spectra exhibit main bands which can be attributed to alkyl chains (νs(CH2) = 2847 cm -1 ; νas(CH2) = 2915 cm -1 ) (Figure S5) and carboxylate bands (peaks between 1700 and 1300 cm -1 ) (Figure S6B, Table S1).…”