Synthesis engineering of iron oxide raspberry-shaped nanostructures

Abstract

Magnetic porous nanostructures consisting of oriented aggregates of iron oxide nanocrystals display very interesting properties such as a lower oxidation state of magnetite, and enhanced saturation magnetization in comparison with individual nanoparticles of similar sizes and porosity. However, the formation mechanism of these promising nanostructures is not well understood, which hampers the fine tuning of their magnetic properties, for instance by doping them with other elements. Therefore the formation mechanism of porous raspberry shaped nanostructures (RSNs) synthesized by a one-pot polyol solvothermal method has been investigated in detail from the early stages by using a wide panel of characterization techniques, and especially by performing original in situ HR-TEM studies in temperature. A time-resolved study showed the intermediate formation of an amorphous iron alkoxide phase with a plate-like lamellar structure (PLS). Then, the fine investigation of PLS transformation upon heating up to 500 °C confirmed that the synthesis of RSNs involves two iron precursors: the starting one (hydrated iron chlorides) and the in situ formed iron alkoxide precursor which decomposes with time and heating and contributes to the growth step of nanostructures. Such an understanding of the formation mechanism of RSNs is necessary to envision efficient and rational enhancement of their magnetic properties.

First-Principles Study of Dissociation Processes for the Synthesis of Fe and Co Oxide Nanoparticles

“…This is however not a stable condition, and the H atom on the Fe center is spontaneously transferred back to the chain. These results are consistent with the experimental finding of regular iron oxide NPs synthesized from these stearates . Because of our choice of reaction coordinate, the long plateau of the free energy (Figure ) starting from d Fe–COO ∼ 4.00 Å indicates that the interaction of the iron with the hydrocarbon chain is terminated.…”

“…These results are consistent with the experimental finding of regular iron oxide NPs synthesized from these stearates. 18 Because of our choice of reaction coordinate, the long plateau of the free energy ( Figure 2) starting from d Fe−COO ∼ 4.00 Å indicates that the interaction of the iron with the hydrocarbon chain is terminated. An auxiliary BME simulation performed by using as a reaction coordinate the center of mass of the two oxygen atoms in the −COO group, instead of the central C atoms, has given an analogous result in terms of both free energy profile and dissociation mechanism.…”

“…Following the experimental suggestions, 17,18,24 and in view of the larger displacements of the ligands observed in the case of the Co-based stearates in comparison with the Fe-based counterparts, we repeated this same simulation by changing the pre-equilibration procedure and time. An initial geometry relaxation within a preconditioned conjugate gradient (PCG) procedure was done to optimize the system with the two H 2 O molecules in the octahedral position of Figure 1(c) to get rid of any residual forces.…”

“…Even small amounts of water impurities (0.02–0.1 mol/mol water:precursor) have been shown to impact negatively the NPs growth by limiting its size tunability . Indeed, the precursor chemistry and the rate of precursor conversion are important factors controlling NPs formation and growth, with possible unexpected influences on the NPs size and size distribution. , This makes the control of the NPs precursors a delicate issue, especially for small NPs below 20 nm, which are the major target for the applications mentioned above. − This, in turn, calls for special attention to the role of the ligand–NPs interactions starting from the NPs seed formation to the nucleation-to-growth process and to the postfunctionalization stages. All these subsequent steps are responsible for the final properties of the nano-object.…”

Facile synthesis of superparamagnetic iron oxide nanoparticles with tunable size: from individual nanoparticles to nanoclusters

“…1 c ) were obtained. TREG acted not only as the polar solvent with a high‐boiling point, but also as the reductive agent [21, 22]. During polyol process, ferric ions were partially reduced to ferrous ions by TREG and hydrolysed along with the resulting ferrous ions.…”