Influence of Capping Groups on the Synthesis of γ-Fe₂O₃ Nanocrystals

Abstract

Monodisperse and uniform ␥-Fe 2 O 3 (maghemite) nanocrystals of variable size were prepared by thermal decomposition of iron pentacarbonyl [Fe(CO) 5 ] in the presence of surfactants, following controlled oxidation with trimethylamine N-oxide as a mild oxidant. The influence of carboxylic acids with variable alkyl carbon chain lengths on the synthesis of ␥-Fe 2 O 3 nanocrystals was investigated. The effect of the molar ratios of surfactant to iron precursor was also studied. The nanocrystals were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD showed the particles were highly crystalline at the nanometer scale. The results showed that the size and shape of the nanocrystal is strongly influenced by the decomposition temperature of iron pentacarbonyl and closely related to the length of carbon chain of the capping groups and the molar ratio of surfactant to iron precursor. Following controlled evaporation from nonpolar solvents, self-assembly into two-dimensional arrays could be observed by TEM. It was also found that the distance between the nanocrystals in self-assembled structures matched the length of the capping molecules very well.

Effect of precursor concentration on size evolution of iron oxide nanoparticles

“…As a result, less monomer is available for the growth and hence smaller nanoparticles are formed. 30,31,48 To substantiate the role of the surfactant to precursor ratio, we systematically varied the amount of surfactant in the next step.…”

“…As the amount of surfactant increases, more oleate molecules react with the precursor and more stable monomers with reduced reactivity are formed. 28,30,31,48,49,53 According to LaMer's model 33 for nucleation and growth, a reduced active monomer concentration reduces the nucleation rate and hinders the formation of a large number of nuclei and hence favors the growth of larger nanoparticles. We have also plotted the size evolution for both series B and C as a function of precursor/surfactant ratio in Fig.…”

“…3g. It has also been shown that an excess of surfactants prevents nanoparticle growth by blocking the growth sites and stabilizing the growth species, 28,48 and manifests a dramatic drop in the mass reaction yield of the nanoparticles. The magnetic properties of particles depend on their size.…”

Toward the Syntheses of Universal Ligands for Metal Oxide Surfaces: Controlling Surface Functionality through Click Chemistry

“…13 XRD and TEM images show that the nanoparticles are crystalline and well dispersed. Within one reaction vessel the nanoparticles vary in size only slightly (<5% rms).…”

Nanofluids for Heat Transfer

“…By binding to the surface of the NPs, these surfactants give rise to a steric barrier against aggregation, limiting the growing phase of the nanoparticles. Basing on the choice of the ligand properties (molecular length, decomposition temperature) and on the ligand/precursor ratio, it is possible to control the size and size distribution of the synthesized NPs (Yin et al, 2004). Using the thermal decomposition of the acetylacetonate copper precursor dissolved in oleylamine in the presence of oleic acid, we have synthesized copper oxide nanoparticles of mean diameter 7 nm with a quasi-spherical shape and low size dispersion ( Fig.…”