Shape control of new Fe_xO–Fe₃O₄and Fe_1–yMn_yO–Fe_3–zMn_zO₄ nanostructures

Abstract

New nanoparticle shapes of iron oxide (FexOFe3O4, where 0.8 < x < 1) and iron‐manganese oxide (Fe1–yMnyOFe3–zMnzO4, where 0 < y < 1, and 0 < z < 3) were synthesized by decomposition of the corresponding metal formates in tri‐n‐octylamine/oleic acid mixtures at elevated temperatures (ca. 370 °C), under an inert atmosphere. Details of the syntheses leading to the various shapes of nanoparticles are provided as a function of the reactions parameters, that is, precursor type and concentration, surfactant concentration, water concentration, reaction time, and temperature. Different electron microscopy techniques were used to characterize the crystal phases and the novel shapes of these nanostructures. Nanoparticles of FexOFe3O4 were produced with different shapes, that is spheres, hexagons, and cubes, depending on the reaction conditions. By tuning the conditions, iron oxide nanocubes with concave faces were produced exclusively. Electron and X‐ray diffraction data reveal these nanocubes to be single‐crystal FexO (wüstite) with small amounts of Fe3O4 (magnetite). For the mixed metal system, solid solutions of Fe1–yMnyO with very small amounts of Fe3–zMnzO4 were observed, in which the produced oxide had a larger Fe:Mn ratio than present in the starting reagents. Adjusting the iron to manganese ratio in the mixed‐metal nanoparticles resulted in different shapes. Nanoparticles with ca. 1:1 (Fe:Mn) ratios displayed a ‘dog‐bone‐like’ morphology, which can be considered a shape in between a pure FexOFe3O4 nanocube and the rod‐like nanostructures previously reported for the manganese oxide system. In general, higher Fe:Mn ratios (e.g., 9:1) in the product resulted in nanostructures with cubic shapes, while lower Fe:Mn values (e.g., 2:8) resulted in long (ca. 200 nm) rod‐like nanostructures with flared ends. All of the nanostructures reported here exhibit internal structures that suggest a growth mechanism with etching on negatively curved rough crystal faces. Oxidation of the nanoparticles occurred with retention of their original shape.

Synthesis of CuO@NiO core-shell nanoparticles by homogeneous precipitation method

“…The diffraction pattern of CuO precursor ( Fig. 1(b)) matches with that of copper hydroxy nitrate Cu 2 (OH) 3 Thus these peaks in the mixed metal oxide precursor also look broader compared to those peaks due to the pure CuO precursor. Fig.…”

“…Sometimes, the combination of two metals in a common oxide matrix can result in materials with novel structures such as hollow spheres, nanorods decorated with nanoparticles, etc. [3,4]. Homogeneity of the synthesized mixed metal oxide nanoparticles affects the physicochemical properties of the nanoparticles.…”

Shape Evolution and Tunable Properties of Monodisperse Magnetite Crystals Synthesized by a Facile Surfactant‐Free Hydrothermal Method

“…[7] While shape-controlled studies have been actively pursued on metal and semiconductor nanocrystals, [8][9][10] only a few studies focus on magnetic iron oxide systems -α-Fe 2 O 3 , [11] γ-Fe 2 O 3 , [12] β-FeOOH [13] and Fe x O-Fe 3 O 4 . [14] Systematic shape-controlled studies related to magnetite (Fe 3 O 4 ) are rare despite its distinguished role in basic magnetism and technological applications, which include magnetic resonance imaging (MRI), [15] magnetic storage media, [16] ferrofluids, [17] catalysis, [18] and clinical diagnosis and that all of the spherical structures are formed by the highly oriented assembly of Fe 3 O 4 nanoparticles. The evolution of the morphology from spheres to octahedrons can be attributed to the competition effect between ethylene glycol and NaOH under the reaction conditions.…”

Damascene Process for Controlled Positioning of Magnetic Colloidal Nanocrystals

“…Towards these aims, significant progress has been made in the synthesis of magnetic NCs with well-defined compositions, shapes, structures, and sizes. [14,15] Nevertheless, one major challenge remains, namely, to produce assemblies of colloidal magnetic NCs on well-controlled sites, which is essential to enable separate identification and addressability for single-magnetic nanoparticle units.…”