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.…”

Nanoparticles by Decomposition of Long Chain Iron Carboxylates: From Spheres to Stars and Cubes

“…We also report on the influence of volatile impurities including water on NP formation, a parameter which is rather overlooked in the majority of studies. To the best of our knowledge, only a few papers reported the influence of added water on the NP size in decomposition of (i) Fe(CO) 5 in the presence of oleic acid and (ii) iron formates in TOA/oleic acid mixtures . Comparison of our data on the influence of this and other parameters with the published work allows us to conclude that the structure−condition relationships for NPs prepared by thermal decomposition of long-chain carboxylates are different from those observed for other precursors.…”

“…To the best of our knowledge, only a few papers reported the influence of added water on the NP size in decomposition of (i) Fe(CO) 5 in the presence of oleic acid 36 and (ii) iron formates in TOA/oleic acid mixtures. 32 Comparison of our data on the influence of this and other parameters with the published work allows us to conclude that the structure-condition relationships for NPs prepared by thermal decomposition of long-chain carboxylates are different from those observed for other precursors. Considering the importance of iron oxide NPs in biomedical research and the handful of available methods to make large iron oxide NPs, we believe the findings presented in this paper are of paramount significance.…”

Molecular Precursors for CdS Nanoparticles: Synthesis and Characterization of Carboxylate−Thiourea or −Thiosemicarbazide Cadmium Complexes and Their Decomposition

“…In our TEM studies of CdS as well as many other materials [e.g., Bi 2 S 3 , PbS, MnO x , Fe x O, Fe 1− y Mn y O, In 2 O 3 , Fe 2 P] we have never observed NPs totally free of defects (point, linear, planar) even when their size is as small as 2−4 nm. Also, we have never observed NP growth via oriented attachment in these materials. ,− …”