Effects of amount of benzyl ether and reaction time on the shape and magnetic properties of Fe3O4 nanocrystals

A guide to the design of magnetic particle imaging tracers for biomedical applications

Magnetic Particle Imaging (MPI) is a novel and emerging non-invasive technique that promises to deliver high quality images, no radiation, high depth penetration and nearly no background from tissues. Signal intensity and spatial resolution in MPI are heavily dependent on the properties of tracers. Hence the selection of these nanoparticles for various applications in MPI must be carefully considered to achieve optimum results. In this review, we will provide an overview of the principle of MPI and the key criteria that are required for tracers in order to generate the best signals. Nanoparticle materials such as magnetite, metal ferrites, maghemite, zero valent iron@iron oxide core@shell, iron carbide and iron-cobalt alloy nanoparticles will be discussed as well as their synthetic pathways. Since surface modifications play an important role in enabling the use of these tracers for biomedical applications, coating options including the transfer from organic to inorganic media will also be discussed. Finally, we will discuss different biomedical applications and provide our insights into the most suitable tracer for each of these applications.

Magnetorheological Fluids with Surface-Modified Iron Oxide Magnetic Particles with Controlled Size and Shape

This study is focused on surface-modified Fe₃O₄@SiO₂ particles with precisely controlled sizes and shapes applied in magnetorheological (MR) fluids. After the preparation of the monodisperse spindle-shaped and cubic Fe₃O₄@SiO₂ particles, surface modification with dodecyltrimethoxysilane (DTM) was carried out via a silane coupling reaction to increase the dispersion stability of the particles. Afterward, MR fluids were prepared by mixing the DTM-modified Fe₃O₄@SiO₂ particles with silicon oil. Transmission electron microscopy observations demonstrated that spindle-shaped Fe₃O₄@SiO₂ particles could form a more stable chain-like structure than cubic Fe₃O₄@SiO₂ particles upon application of an external magnetic field. The rheological measurements of MR fluids also indicated that the surface modification with DTM, the introduction of anisotropic shapes, and the increase in the particle size all played positive roles in the improvement in MR properties.

Bayesian Particle Instance Segmentation for Electron Microscopy Image Quantification

Automating the analysis portion of materials characterization by electron microscopy (EM) has the potential to accelerate the process of scientific discovery. To this end, we present a Bayesian deep-learning model for semantic segmentation and localization of particle instances in EM images. These segmentations can subsequently be used to compute quantitative measures such as particle-size distributions, radial- distribution functions, average sizes, and aspect ratios of the particles in an image. Moreover, by making use of the epistemic uncertainty of our model, we obtain uncertainty estimates of its outputs and use these to filter out false-positive predictions and hence produce more accurate quantitative measures. We incorporate our method into the ImageDataExtractor package, as ImageDataExtractor 2.0, which affords a full pipeline to automatically extract particle information for large-scale data-driven materials discovery. Finally, we present and make publicly available the Electron Microscopy Particle Segmentation (EMPS) data set. This is the first human-labeled particle instance segmentation data set, consisting of 465 EM images and their corresponding semantic instance segmentation maps.

Selective Control over the Morphology and the Oxidation State of Iron Oxide Nanoparticles

Iron oxide nanoparticles (NPs) have been extensively used for both health and technological applications. The control over their morphology, crystal microstructure, and oxidation state is of great importance to optimize their final use. However, while mature in understanding, it is still far from complete. Here we report on the effect of the amount of 1,2-hexadecanediol and/or 1-octadecene in the reaction mixture on the thermal decomposition of iron(III) acetylacetonate in oleic acid for two series of iron oxide NPs with sizes ranging from 6 to 48 nm. We show that a low amount of either compound leads to both large, mixed-phase NPs composed of magnetite (Fe₃O₄) and wüstite (FeO) and high reaction yields. In contrast, a higher amount of either 1,2-hexadecanediol or 1-octadecene gives rise to smaller, single-phase NPs with moderate reaction yields. By infrared spectroscopy, we have elucidated the role of 1,2-hexadecanediol, which mediates the particle nucleation and growth. Finally, we have correlated the magnetic response and the structural features of the NPs for the two series of samples.

Recyclable Magnetic Cu/CuFe2O4 Nanocomposites for the Rapid Degradation of 4-NP

Magnetic Cu/CuFe2O4 nanocomposites were prepared by the one-pot thermal decomposition of acetylacetone compounds. Adjusting the molar ratios of Fe to Cu was used to control the content of Cu in the synthetic process. XRD, TEM, XPS and UV-Vis were employed to reveal detailed structural and catalytic activities of Cu/CuFe2O4 nanocomposites. Magnetic measurements demonstrated that Cu/CuFe2O4 nanocomposites possessed a considerable magnetic saturation. Cu/CuFe2O4 nanocomposites showed superb efficiency in the degradation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). 4-NP could be reduced by Cu/CuFe2O4 nanocomposites within 40 s in the attendance of NaBH4. Cu nanocrystals played an indispensable rose in the enhancement of catalytic performance. The synergistic effect of Cu and CuFe2O4 nanocrystals achieved the high-efficiency catalytic reduction for 4-NP. After six recycling experiments, the efficiency of Cu/CuFe2O4 nanocomposites was almost stable. Our work advances a straightforward strategy to synthesize efficient and recoverable Cu/CuFe2O4 nanocomposites, which has promising utilizations in the purifying of nitrophenolic contamination.

Highly efficient and recyclable catalyst: porous Fe3O4-Au magnetic nanocomposites with tailored synthesis

In this work, we reported the tailored design of highly efficient Fe₃O₄-Au magnetic nanocomposite (MNP) catalysts. Fe₃O₄ nanocrystals with three different morphologies have been developed with engineered amounts of urea, and the plausible mechanism has been proposed. Then by controlling the amount of Au seeds, Fe₃O₄-Au MNPs with different morphologies and tunable Au deposition have been realized. Characterizations including x-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectra, and elemental mapping are implemented to unveil the structural and physical characteristics of the successfully developed Fe₃O₄-Au MNPs with different morphologies. The catalytic ability of Fe₃O₄-Au MNPs with different morphologies have been compared by applying them to degrading RhB and 4-NP, meanwhile the correlation between the amount of Au seeds and the turnover frequency as well as the catalytic ability of Fe₃O₄-Au MNPs is investigated systematically. We found that the flower-like Fe₃O₄-Au MNPs with 20 ml Au seeds added achieved the best degradation efficiency of 96.7%, and their catalytic ability were almost unchanged after recycling. Out study sheds the light into the tailored design of highly efficient and recyclable catalysts for RhB and 4-NP.

Facile synthesis of Fe3O4@Au core-shell nanocomposite as a recyclable magnetic surface enhanced Raman scattering substrate for thiram detection

The Fe₃O₄@Au core-shell nanocomposites, as the multifunctional magnetic surface enhanced Raman scattering (SERS) substrates, were fabricated successfully by the seeds growth method based on the Fe₃O₄-Au core-satellite nanocomposites. The SERS properties of the Fe₃O₄-Au core-satellite nanocomposites and the Fe₃O₄@Au core-shell nanocomposites were compared using 4-aminothiophenol (4-ATP) as the probe molecule. It was found that Fe₃O₄@Au core-shell nanocomposites showed better SERS performance than Fe₃O₄-Au core-satellite nanocomposites. The Au shell provided an effectively large surface area for forming sufficient plasmonic hot spots and capturing target molecules. The integration of magnetic core and plasmonic Au nanocrystals endowed the Fe₃O₄@Au core-shell nanocomposites with highly efficient magnetic separation and enrichment ability and abundant interparticle hot spots. The Fe₃O₄@Au core-shell nanocomposites could be easily recycled because of the intrinsic magnetism of the Fe₃O₄ cores and had good reproducibility of the SERS signals. For practical application, the Fe₃O₄@Au core-shell nanocomposites were also used to detect thiram. There was a good linear relationship between the SERS signal intensity and the concentration of thiram from 1 × 10^-3 to 1 × 10^-8 M and the limit of detection was 7.69 × 10^-9 M. Moreover, residual thiram on apple peel was extracted and detected with a recovery rate range of 99.3%. The resulting substrate with high SERS activity, stability and strong magnetic responsivity makes the Fe₃O₄@Au core-shell nanocomposites a perfect choice for practical SERS detection applications.

Enhanced Catalytic Reduction of 4-Nitrophenol Driven by Fe₃O₄-Au Magnetic Nanocomposite Interface Engineering: From Facile Preparation to Recyclable Application

In this work, we report the enhanced catalytic reduction of 4-nitrophenol driven by Fe₃O₄-Au magnetic nanocomposite interface engineering. A facile solvothermal method is employed for Fe₃O₄ hollow microspheres and Fe₃O₄-Au magnetic nanocomposite synthesis via a seed deposition process. Complementary structural, chemical composition and valence state studies validate that the as-obtained samples are formed in a pure magnetite phase. A series of characterizations including conventional scanning/transmission electron microscopy (SEM/TEM), Mössbauer spectroscopy, magnetic testing and elemental mapping is conducted to unveil the structural and physical characteristics of the developed Fe₃O₄-Au magnetic nanocomposites. By adjusting the quantity of Au seeds coating on the polyethyleneimine-dithiocarbamates (PEI-DTC)-modified surfaces of Fe₃O₄ hollow microspheres, the correlation between the amount of Au seeds and the catalytic ability of Fe₃O₄-Au magnetic nanocomposites for 4-nitrophenol (4-NP) is investigated systematically. Importantly, bearing remarkable recyclable features, our developed Fe₃O₄-Au magnetic nanocomposites can be readily separated with a magnet. Such Fe₃O₄-Au magnetic nanocomposites shine the light on highly efficient catalysts for 4-NP reduction at the mass production level.

Eco-friendly seeded Fe3O4-Ag nanocrystals: a new type of highly efficient and low cost catalyst for methylene blue reduction

Hybrid Fe₃O₄-Ag nanocrystals, a new type of highly efficient and reusable catalyst for methylene blue (MB) reduction, are fabricated by a novel seed deposition process. X-ray diffraction and Mössbauer spectroscopy results show that the developed iron oxides are in a pure magnetite Fe₃O₄ phase. Upon manipulating the amount of Ag seeds capsuled on the modified surfaces of Fe₃O₄ nanocrystals, the catalytic capacities on the reduction of MB can be precisely adjusted with a tunable fabrication cost control. The linear correlation of the reduced MB concentration versus reaction time catalyzed by our developed hybrid Fe₃O₄-Ag nanocrystals is coherent with pseudo first order kinetics. Importantly, with remarkable recyclability features, the hybrid Fe₃O₄-Ag nanocrystals can be easily separated by applying an external magnetic field. The tailored catalytic performances of the hybrid Fe₃O₄-Ag nanocrystals during MB reduction are attributed to the optimized dynamic electron transfer process, which dominates the electrochemical mechanism wherein the nucleophilic BH₄⁻ ions donate electrons to electrophilic organic MB through Ag seeds in a regulated amount. Such developed hybrid Fe₃O₄-Ag nanocrystals pave the way towards the mass production of highly efficient and low cost catalysts for methylene blue reduction.

Hybrid Fe₃O₄-Ag nanocrystals, a new type of highly efficient and reusable catalyst for methylene blue (MB) reduction, are fabricated by a novel seed deposition process.