Characterisation of Co@Fe3O4 core@shell nanoparticles using advanced electron microscopy

Abstract

Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.

A magnetically-separable H 3 PW 12 O 40 @Fe 3 O 4 /EN-MIL-101 catalyst for the one-pot solventless synthesis of 2H-indazolo[2,1- b ] phthalazine-triones

“…Bright and dark-field TEM of the iron oxide functionalized EN-MIL-101 sample revealed the presence of high contrast nanoparticles with a relatively broad size distribution between 5-50 nm, and lattice fringes of 0.25 nm consistent with Fe3O4 (Fig. S2) [51]. Subsequent heteropolyacid addition resulted in a uniform distribution of high contrast features throughout the Fe3O4/EN-MIL-101 sample.…”

Interplay between microstructure and magnetism in NiO nanoparticles: breakdown of the antiferromagnetic order

“…[1][2][3][4][5][6][7] The growing research activity in this field has been propelled by the development of new chemical routes that allowed the synthesis of NPs with tuneable size distributions and being embedded in different insulating matrices. [8][9][10][11][12][13][14][15][16] It is worth noting that NPs of the same material and similar size but synthetized using different fabrication routes show a strong dependence of the magnetic properties on the morphology, microstructure or the nature of the matrix. 1,8,10,13 Moreover, 3d metal oxide NPs with different core-shell morphologies are also good candidates for a number of applications due to the possibility of tuning the magnetic response and/or the coating with a functional layer.…”

“…1,8,10,13 Moreover, 3d metal oxide NPs with different core-shell morphologies are also good candidates for a number of applications due to the possibility of tuning the magnetic response and/or the coating with a functional layer. 2,4,[13][14][15] Therefore, a comprehensive study combining advanced structural characterization techniques and meticulous magnetic measurements is needed to elucidate the microstructure-magnetism interplay at the nanoscale.Nickel oxide (NiO) has been under extensive research for decades due to its importance in numerous technological applications (i.e., catalysis, batteries, ceramics, etc.). Nowadays, nanosized NiO particles have generated a renewed interest because the combination of their unique properties (i.e., high surface area, short diffusional paths, exceptional magnetic properties, etc.)…”

Chemical synthesis, structure and magnetic properties of Co nanorods decorated with Fe3O4 nanoparticles

“…. . observed in the inside nanorod and outer nanoparticle, corresponding to the lattice spacing of the Co (002) facet [27] and the Fe 3 O 4 (311) facet [40], separately. Besides, it is worth noting that there is a transition layer between the nanorod and the nanoparticle structure, and the fringe of the layer is 0.245 nm, which is in accordance with the lattice spacing of (111) facet for CoO [41,42], suggesting that the fresh surface of the Co NRs is prone to be oxidized during the reaction firstly and then the Fe 3 O 4 NPs will grow on the Co NRs.…”

“…The Co-Fe 3 O 4 heterostructures were synthesized by adding iron precursor (Fe(CO) 5 ) to the solution of the preprepared Co NRs [40]. In a typical process, 1.0 mmol of Co NRs in ODE (20 mL), OAm (2.0 mL), OA (0.5 mL) and 3.5 mg of NH 4 Br were mixed in a four-neck flask and degassed under forming gas (Ar 95%+H 2 5%) at 120°C for at least 30 min.…”