Synthesis Of Iron Oxide Nanocrystals Research Articles

Tailored Synthesis of Iron Oxide Nanocrystals for Formation of Cuboid Mesocrystals.

In this work, we systematically studied the shape- and size-controlled monodisperse synthesis of iron oxide nanocrystals (IONCs) for their use as building blocks in the formation of mesocrystals. For this aim, on understanding the influence of the oleic acid concentration, iron-oleate concentration, and heating rate on the synthesis of robust and reproducible IONCs with desired sizes and shapes, we synthesized highly monodisperse ∼11 nm sized nanocubes and nanospheres. Magnetic measurements of both cubic and spherical IONCs revealed the presence of mixed paramagnetic and superparamagnetic phases in these nanocrystals. Moreover, we observed that the magnetic moments of the nanocubes are more substantial compared to their spherical counterparts. We then demonstrated a simple magnetic-field-assisted assembly of nanocubes into three-dimensional (3D) cuboid mesocrystals while nanospheres did not form any mesocrystals. These findings indicate that small cubic nanocrystals hold great promise as potential building blocks of 3D magnetic hierarchical structures with their superior magnetic properties and mesocrystal assembly capability, which may have high relevance in various fields ranging from high-density data storage to biomedical applications.

Size-tunable synthesis of iron oxide nanocrystals by continuous seed-mediated growth: role of alkylamine species in the stepwise thermal decomposition of iron(II) oxalate.

The properties of inorganic nanoparticles (NPs) are governed by their size. Therefore, tuning the size of NPs is a fundamental technique in nanoscience. However, the size-tunable synthesis of inorganic NPs is generally carried out in a dilute solution, which produces large quantities of waste. Herein, we report the predictable size-tunable synthesis of Fe3O4 NPs by the stepwise thermal decomposition of iron(II) oxalate (Fe(ox)). Monodisperse Fe3O4 seed crystals were synthesized by the thermal decomposition of oleylamine-coordinated iron oxalate (Fe(ox)-OAm) in a small amount of oleylamine, followed by continuous seed-mediated growth of Fe3O4 NPs. The thermal decomposition behavior of Fe(ox) in oleylamine with and without N,N-diethyl-1,3-diaminopropane (dedap) revealed the important role of dedap in the stepwise thermal decomposition of Fe(ox). The size of the Fe3O4 NPs was easily tuned via the stepwise thermal decomposition of Fe(ox) by controlling the amount of decomposed Fe(ox) in a small amount of an alkylamine mixture. The particle diameter was predicted from the size of the Fe3O4 seed crystals and the amount of decomposed Fe(ox). Finally, the size dependency of magnetic properties of the synthesized Fe3O4 NPs was studied. This continuous seed-mediated growth method based on the stepwise thermal decomposition of metal oxalate can be applied to control the size of a variety of metal and metal oxide NPs.

Role of aliphatic ligands and solvent composition in the solvothermal synthesis of iron oxide nanocrystals

This paper describes a new method for controlling nanocrystal size and crystal phase in solvothermal syntheses of iron oxide nanocrystals by altering the carbon chain length of aliphatic iron(III) carboxylate precursors and reaction solvent composition, respectively. Hematite (α-Fe2O3) nanocrystals were synthesized from iron(III) carboxylate precursors in a 2:1 water:ethanol mixture in the presence of free aliphatic carboxylic acids or aliphatic primary amine ligands. In the presence of amine, increasing the length of the carbon chain of the iron(III) carboxylate precursor from two to eighteen carbons produced pseudocubic nanocrystals with size dispersities of ∼10% and diameters that decreased from 65 nm to 25 nm. Changing the chain length of the amine does not affect the size of the nanocrystals. In contrast, free carboxylic acid ligands produce polydisperse, polycrystalline hematite nanoparticles. The crystal structure of the iron oxide nanocrystals synthesized by this method depends on the mole-fraction of water (xwater) in the water/ethanol solvent mixture: xwater = 0 produces maghemite (γ-Fe2O3), xwater = 0.67 produces hematite, and xwater = 1 produces a mixture of goethite (α-FeOOH) and hematite. The dependence of the nanocrystal size on ligand chain length is attributed to decreasing solubility of partially hydrolyzed iron(III) carboxylate precursors in the reaction solvent mixture with increasing chain length. The dependence of nanocrystal phase on solvent composition is attributed to the different reactivities of water and ethanol toward hydrolysis of the iron(III) carboxylate precursors.

A low cost synthesis method for functionalised iron oxide nanoparticles for magnetic hyperthermia from readily available materials.

The synthesis of iron oxide nanocrystals from reagents taken from high street sources using thermal decomposition of an iron-fatty acid precursor in a high boiling point solvent in the presence of surfactants is presented. The nanocrystals were characterised using a variety of techniques including: electron microscopy, X-ray dispersive spectroscopy, infrared spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and magnetometry. Thermogravimetric analysis (TGA) is also used to compare the decomposition behaviour of iron oleate and iron palmitate, our nanoparticle precursors. The nanoparticles also exhibit shape anisotropy when prepared under optimum conditions. We show that these nanoparticles have potential in magnetic hyperthermia after transfer to aqueous media via an amphiphilic polymer.

Gas-Bubble Effects on the Formation of Colloidal Iron Oxide Nanocrystals

This paper reports that gas bubbles can be used to tailor the kinetics of the nucleation and growth of inorganic-nanocrystals in a colloidal synthesis. We conducted a mechanistic study of the synthesis of colloidal iron oxide nanocrystals using gas bubbles generated by boiling solvents or artificial Ar bubbling. We identified that bubbling effects take place through absorbing local latent heat released from the exothermic reactions involved in the nucleation and growth of iron oxide nanocrystals. Our results show that gas bubbles display a stronger effect on the nucleation of iron oxide nanocrystals than on their growth. These results indicate that the nucleation and growth of iron oxide nanocrystals may rely on different types of chemical reactions between the iron-oleate decomposition products: the nucleation relies on the strongly exothermic, multiple-bond formation reactions, whereas the growth of iron oxide nanocrystals may primarily depend upon single-bond formation reactions. The identification of exothermic reactions is further consistent with our results in the synthesis of iron oxide nanocrystals with boiling solvents at reaction temperatures ranging from 290 to 365 °C, by which we determined the reaction enthalpy in the nucleation of iron oxide nanocrystals to be -142 ± 12 kJ/mol. Moreover, our results suggest that a prerequisite for effectively suppressing secondary nucleation in a colloidal synthesis is that the primary nucleation must produce a critical amount of nuclei, and this finding is important for a priori design of colloidal synthesis of monodispersed nanocrystals in general.

Shape- and Size-Controlled Synthesis of Iron Oxide Nanocrystals

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