As-made Nanoparticles Research Articles

Structural and magnetic properties of iodide-mediated chemically synthesized L12 FePt3 nanoparticles

In this work, we study the effect of elemental iodine as a halide intermediary in the synthesis of FePt3 nanoparticles using a co-reduction of Fe(acac)3 and (NH4)2PtCl2 with 1,2-hexadecanediol. Our study shows that elemental iodine facilitates the formation of FePt3 nanoparticles with the L12 structure. When iodine is not used, the as-made nanoparticles have mostly the disordered fcc FePt3 structure. The as-made nanoparticles are ferromagnetic and have a Curie temperature close to 380 K. Annealing of the as-made nanoparticles leads to an increased particle size and a transformation to the ordered L12 FePt3 phase. Nanoparticles annealed at 700°C for 30 minutes show a mixture of two magnetic phases, a ferromagnetic phase with a lower ordering temperature of ∼300 K and an antiferromagnetic phase with a Néel temperature around 135 K.

The influence of oxidation process on exchange bias in egg-shaped FeO/Fe3O4 core/shell nanoparticles

Egg-shaped nanoparticles with a core–shell morphology were synthesized by thermal decomposition of an iron oleate complex. XRD and M(T) magnetic measurements confirmed the presence of FeO (wustite) and Fe3O4 (magnetite) phases in the nanoparticles. Oxidation of FeO to Fe3O4 was found to be the mechanism for the shell formation. As-made nanoparticles exhibited high values of exchange bias at 2K. Oxidation led to decrease of exchange field from 2880Oe (in as-made sample) to 330Oe (in oxidized sample). At temperatures higher than the Néel temperature of FeO (200K) there was no exchange bias. An interesting observation was made showing the exchange field to be higher than the coercive field at temperatures close to magnetite's Verwey transition.

In vivo magnetic resonance and fluorescence dual imaging of tumor sites by using dye-doped silica-coated iron oxide nanoparticles

The difficulty in delineating tumor is a major obstacle for better outcomes in cancer treatment of patients. The use of single-imaging modality is often limited by inadequate sensitivity and resolution. Here, we present the synthesis and the use of monodisperse iron oxide nanoparticles coated with fluorescent silica nano-shells for fluorescence and magnetic resonance dual imaging of tumor. The as-synthesized core–shell nanoparticles were designed to improve the accuracy of diagnosis via simultaneous tumor imaging with dual imaging modalities by a single injection of contrast agent. The iron oxide nanocrystals (~11 nm) were coated with Rhodamine B isothiocyanate-doped silica shells via reverse microemulsion method. Then, the core–shell nanoparticles (~54 nm) were analyzed to confirm their size distribution by transmission electron microscopy and dynamic laser scattering. Photoluminescence spectroscopy was used to characterize the fluorescent property of the dye-doped silica shell-coated nanoparticles. The cellular compatibility of the as-prepared nanoparticles was confirmed by a trypan blue dye exclusion assay and the potential as a dual-imaging contrast agent was verified by in vivo fluorescence and magnetic resonance imaging. The experimental results show that the uniform-sized core–shell nanoparticles are highly water dispersible and the cellular toxicity of the nanoparticles is negligible. In vivo fluorescence imaging demonstrates the capability of the developed nanoparticles to selectively target tumors by the enhanced permeability and retention effects and ex vivo tissue analysis was corroborated this. Through in vitro phantom test, the core/shell nanoparticles showed a T2 relaxation time comparable to Feridex® with smaller size, indicating that the as-made nanoparticles are suitable for imaging tumor. This new dual-modality-nanoparticle approach has promised for enabling more accurate tumor imaging.

Enhancing photocatalytic oxygen evolution activity of cobalt-based spinel nanoparticles

Photocatalytic water oxidation is one of the critical reactions for solar fuel production from abundant sources. Among all the metal oxides, Co3O4 spinel exhibits a high activity as an oxygen evolution catalyst. In this paper, we demonstrate that the photocatalytic oxygen evolution activity of Co3O4 spinel can be further enhanced by substituting cobalt with manganese in the spinel structure. Using a facile hydrothermal approach, we have successfully synthesized pure, Mn-substituted, and Ni-substituted Co3O4 nanoparticles with a typical particle size of 5–7nm. The morphologies and crystal structures of the as-synthesized nanoparticle catalysts have been carefully examined using various structural characterization techniques, including PXRD, TEM, gas adsorption, and XAS. The photocatalytic activities of as-made nanoparticles have been investigated using a well-studied visible light driven [Ru(bpy)3]2+-persulfate system. In both Clark electrode and reactor/GC systems, Mn-substituted Co3O4 nanoparticles exhibited the highest TOF among all the three catalysts. The data presented in this paper suggest that the photocatalytic water oxidation activity of Co3O4 spinel catalyst could be further enhanced by Mn3.1+ substitution at the octahedral sites.

The IP6 micelle-stabilized small Ag cluster for synthesizing Ag–Au alloy nanoparticles and the tunable surface plasmon resonance effect

The stable small Ag seeds (size in diameter < 10 nm) were obtained in the presence of inositol hexakisphosphoric (IP6) micelles. Then Ag–Au bimetallic nanoparticles were synthesized through a replacement reaction with the rapid interdiffusion process between such small Ag seeds in nanoclusters and HAuCl4. Adjusting the dosage of HAuCl4 resulted in different products, which possessed unique surface plasmon resonances (SPR). The morphologies of the as-made nanoparticles were observed using transmission electron microscopy and field emission scanning electron microscopy and their compositions were determined by energy-dispersive x-ray spectroscopy. Among them, the Ag–Au alloy nanoparticles with the cauliflower-like structure had a suitable SPR for highly sensitive Raman detection application as a surface-enhanced Raman scattering (SERS) substrate with a long-term stability of six months.

Synthesis of air stable FeCo nanoparticles

Nanoparticulate FeCo alloys have been synthesized by Fe(CO)5 and Co2(CO)8 thermal decomposition in paraffin oil in the presence of oleic acid and oleyl amine. The crystal structure and morphology of the nanoparticles were confirmed by powder x-ray diffraction and transmission electron microscopy. The size and crystallinity of the particles was found to depend on the reaction conditions such as the precursors concentration, reaction time, and carbonyls injection temperature. Also the Fe/Co ratio can be easily controlled by controlling the Fe and Co carbonyls ratio. The as-made nanoparticles were annealed at 500 °C under CH4 stream in order to be protected from future oxidation. This treatment leads to the formation of a graphitic shell around the particles which also protects them from sintering. Additionally, these particles can be functionalized with 1-pyrenebutiric acid in order to be soluble in various solvents.

Evolution of texture and atomic order in annealed sinter-free FePt nanoparticles

Monodisperse FePt nanoparticles have been synthesized chemically. Thespherically shaped as-made nanoparticles were 6.0 nm in size and they weresingle crystals. The average composition of these particles is determined asFe50Pt50. The nanoparticles did not show any sign of sintering after annealing at800 °C for up to 120 min. The texture and order parameters of as-made and annealed FePtnanoparticles were determined from azimuthally integrated selected area electrondiffraction patterns. The close to perfect axial texture in as-made particles degraded with increasing annealing time, in contrast tothe order parameter, which showed a monotonic dependence on annealing time. With60 min annealing, a 0.8 degree of chemical ordering has been achieved and the particles weresinter-free as observed from bright field images.

Order–disorder transformation in FePt nanoparticles studied by ferromagnetic resonance

We have investigated the ferromagnetic resonance (FMR) response of as-made and temperature annealed FePt magnetic nanoparticles. The as-made nanoparticles, which have been fabricated by a chemical route, crystallize in the low magnetic anisotropy fcc phase and have a diameter in the range of 2–4 nm. The annealing of the particles at high temperatures ( T A = 550 , 650 and 750 ° C) in an inert Ar atmosphere produces a partial transformation to the high magnetocrystalline anisotropy L1 0 phase, with a significant increase in particle size and size distribution. FMR measurements at X-band (9.5 GHz) and Q-band (34 GHz) show a single relatively narrow line for the as-synthesized particles and a structure of two superimposed lines for the three annealed samples. The origin of this line shape has been attributed to the presence of the disordered fcc phase. Assuming that the system consists of a collection of identical particles with a random distribution of easy axes, we have been able to estimate a mean value for the magnetic anisotropy constant of the particles in the fcc phase, K ∼ 2 × 1 0 6 erg/cm 3. The measured line shape in the annealed samples can be explained if we consider that the magnetic anisotropy of the particles has a gaussian distribution with a relatively broad width.

The effect of Mn doping in FePt nanoparticles on the magnetic properties of theL10 phase

FePtMn nanoparticles with a narrow size distribution and an averagediameter of 3 nm were synthesized by the chemical reduction ofFe(acac)3 andPt(acac)2 byNaBH4 and the thermaldecomposition of Mn2(CO)10 in phenyl ether. The as-made nanoparticles have a disordered face-centredcubic (fcc) structure, which transformed after thermal treatment at650 °C to an ordered face-centred tetragonal (fct) structure, possessing coercivity values up to13.7 kOe at room temperature. The coercivity of the annealed samples depends on theamount of Mn added to the reaction mixture, with the coercive field increasing significantlywith the partial substitution of Pt by Mn, while the partial substitution of Fe by Mn doesnot affect the magnetic properties strongly.

Investigations on magnetic properties and structure for carbon encapsulated nanoparticles of Fe, Co, Ni

In the present work, experiments aim at the encapsulation of foreign materials within hollow graphitic cage have been carried out for iron group metals (Fe, Co, Ni) using a modified arc-discharge (carbon arc) reactor. HRTEM (high resolution transmission electron miscroscope), and XRD (X-ray diffractometer) studies, for three carbon encapsulated materials, showing nanoparticles of both a metallic phase (α-Fe, γ-Fe; hcp-Co, fcc-Co; fcc-Ni) and also a carbide phase (M 3C, M=Fe, Co, Ni) are encapsulated in graphitic carbon. The magnetic measurement for the three as-made nanoparticles, indicating that the values of saturation magnetic moment of three nanoparticle are 37.6, 55.5 and 15.7% of the bulk ferromagnetic elements counterparts, respectively. The different comparison values ( M r/ M s) of remanent magnetization ( M r) and saturation magnetization ( M s) suggest, the encapsulated Fe and Co nanoparticles are shown to be ferromagnetic with a ratio of remnant to saturation magnetization M r/ M s∼0.3; whereas, the encapsulated Ni nanoparticles exhibits superparamagnetic behavior at room temperature.