A Confinement‐Driven Nucleation Mechanism of Metal Oxide Nanoparticles Obtained via Thermal Decomposition in Organic Media

Abstract

Thermal decomposition is a very efficient synthesis strategy to obtain nanosized metal oxides with controlled structures and properties. For the iron oxide nanoparticle synthesis, it allows an easy tuning of the nanoparticle's size, shape, and composition, which is often explained by the LaMer theory involving a clear separation between nucleation and growth steps. Here, the events before the nucleation of iron oxide nanocrystals are investigated by combining different complementary in situ characterization techniques. These characterizations are carried out not only on powdered iron stearate precursors but also on a preheated liquid reaction mixture. They reveal a new nucleation mechanism for the thermal decomposition method: instead of a homogeneous nucleation, the nucleation occurs within vesicle‐like‐nanoreactors confining the reactants. The different steps are: 1) the melting and coalescence of iron stearate particles, leading to “droplet‐shaped nanostructures” acting as nanoreactors; 2) the formation of a hitherto unobserved iron stearate crystalline phase within the nucleation temperature range, simultaneously with stearate chains loss and Fe(III) to Fe(II) reduction; 3) the formation of iron oxide nuclei inside the nanoreactors, which are then ejected from them. This mechanism paves the way toward a better mastering of the metal oxide nanoparticles synthesis and the control of their properties.

In situ liquid transmission electron microscopy reveals self-assembly-driven nucleation in radiolytic synthesis of iron oxide nanoparticles in organic media

“…Ex situ and cryo-electron microscopy experiments have recently confirmed the presence of iron in similar structures. 60 These observations point to a two-step pre-nucleation/ nucleation process 61 taking place for the radiolytically induced formation of iron oxide in organic media. Mechanisms involving self-assembly prior to nucleation have been enlisted to explain the crystallization of proteins, some organic molecules 62,63 and a few minerals and metallic nano- particles.…”

“…Such inverse vesicles-like structures had been intuited from in situ x-ray absorption and mass spectrometry studies that have shown evidence of poly-oxo-iron bridges at the pre-nucleation stage in a heating-up synthesis. 60 The fact that we directly observe this phenomenon from radiolytic synthesis shows that at least the prenucleation and nucleation stages are similar, whatever the stimulus used for the decomposition of iron precursors.…”

Hope for bone regeneration: The versatility of iron oxide nanoparticles

“…Magnetism is the most important property of IONPs. SPION can sparingly deliver drugs to specific areas under the action of an external magnetic field and can undergo magnetothermal transformation to kill tumour cells which ultimately treats (Mengesha et al, 2022); (C) IONPs obtained by thermal decomposition (Cotin et al, 2022); (D) Preparation of IONPs by co-precipitation method in microchannel reactor (Lin et al, 2017); (E) Preparation of high saturation magnetic IO nanomaterials (Bhavani et al, 2017).…”

“…At present, the preparation of IONPs primarily consists of dry and wet methods ( Yu et al, 2016 ; Huang et al, 2018 ) ( Figure 3 ). The wet methods are more commonly used and include thermal decomposition, chemical co-precipitation, sol-gel, ball milling and atomic layer deposition ( Cotin et al, 2022 ; Kiyani et al, 2022 ). The co-precipitation method is more commonly used in the synthesis of MNPs and allows for better control of the size and magnetic properties of the material, but the MNPs have a tendency to aggregate due to the small particle size ( Lin et al, 2017 ).…”

“… Methods for the preparation of IONPs. (A) Wet method preparation process of CTS-g-PTMAAC/SC-Fe 3 O 4 composite magnetic nanoparticles ( Chen et al, 2016 ); (B) Images of IONPs prepared by immunoprecipitation technique under scanning electron microscope (SEM), (a) 5 nm, (b) 20 nm ( Mengesha et al, 2022 ); (C) IONPs obtained by thermal decomposition ( Cotin et al, 2022 ); (D) Preparation of IONPs by co-precipitation method in microchannel reactor ( Lin et al, 2017 ); (E) Preparation of high saturation magnetic IO nanomaterials ( Bhavani et al, 2017 ). …”