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# Ferromagnetic FeCo nanoparticles for biotechnology

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## Abstract

Calculated magnetophoretic mobility of a variety of magnetic compounds has identified FeCo to be an alternative for magnetite in in vitro biological cell separations. The synthesis of FeCo nanoparticles and the resulting microstructure is discussed as a function of the particle size. Their synthesis kinetics is modeled using a consecutive decomposition and growth model and is compared to experimental data. (c) 2005 Published by Elsevier B.V.

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... This Iron group magnetic nanoparticles of Fe [1], Co [2], Ni [3] and CoNi [4], FeNi [5] and FeCo [6][7][8] binary alloys have been the subject of extensive research due to their usage in developing advanced micro electronic devices [9], microwave absorbing materials [6], as catalyst [7], in medicinal biology and biomedical [8] for past two decades. Among this class of magnetic materials, the ferromagnetic FeCo nanoparticles have gained special attention due to their unique magnetic properties including high Curie temperatures, saturation magnetization, and permeability, which are desired for many applications [9]. ...
... This Iron group magnetic nanoparticles of Fe [1], Co [2], Ni [3] and CoNi [4], FeNi [5] and FeCo [6][7][8] binary alloys have been the subject of extensive research due to their usage in developing advanced micro electronic devices [9], microwave absorbing materials [6], as catalyst [7], in medicinal biology and biomedical [8] for past two decades. Among this class of magnetic materials, the ferromagnetic FeCo nanoparticles have gained special attention due to their unique magnetic properties including high Curie temperatures, saturation magnetization, and permeability, which are desired for many applications [9]. ...
... The formation of toxic oxide layer over the FeCo nanoparticles weakens its magnetic properties and limits their usage in biomedical applications. In this context, several research efforts have been directed towards the development of inert layer such as silica [12], carbon [7], gold [13], silver [14], copper [8] and polymer [15] to coat FeCo nanoparticles to enhance their chemical stability leading to the formation of multifunctional material. Various coating techniques such as micro-emulsion, displacement reaction and high-temperature trans-metallation reaction were recommended for coating material surfaces. ...
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FeCo/Cu core shell structure with FeCo as a core and copper as the shell has been successfully synthesized by displacement reaction. The morphology, grain size, lattice strain, and magnetic properties of all the samples were examined by using transmission electron microscopy (TEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Annealing temperatures and its effect on magnetic properties of the FeCo/Cu core shell particles was investigated. A maximum coercivity (Hc) of 398.84 Oe was recorded for the sample heat treated in magnetic field. The blocking temperatures (TB) and squareness (Mr/Ms) of the sample gradually increased due to the influence of temperature and magnetic field.
... Examples include capture of heavy metal pollutants in water, capture of microalgae in biofuels, microfluidics, and controlled protein assays. [1][2][3] The aggregation of magnetic colloids is a highly complex process, involving fundamental aspects of self-organization in magnetism and hydrodynamics. On the theoretical side, magnetic suspensions present a challenge in equilibrium thermodynamics, out-of-equilibrium physics (selforganization under equilibrium and non-equilibrium conditions), and fluid mechanics (lubrication, contact mechanics, convection induced by magnetism, and turbulence). ...
... These equations have a maximum of 20 complex and pure real solutions from which 4 real (green/gray points) and complex (black points) solutions are selected (see Fig. 11). The solutions ofn are plotted for values of B in the range [1,26] G at ϕ 0 = 0.003 and C 1 = 0.25 × 10 −2 [G −2 ] (points) in good agreement with experimental measurements (circles). Numerical results can be easily modified by tuning ϕ 0 and C 1 . ...
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The self-assembly of monomers, chains, and bundles is often observed in magnetic mixtures. The most probable interaction between the aggregates in a superparamagnetic colloidal suspension is associated with the minimum of the effective magnetic potential in the two and three dimensional relative shift space, which yields a concrete criterion to be employed for prediction of the cohesive energy and the mean length of the aggregates in the fluid bulk.
... Positive effect of Fe 3 O 4 NPs in destroying the oncological tumors by MHT is caused by their ability to heat up effectively under the action of AMF [7]. Moreover, Fe 3 O 4 particles with sizes less than 30 nm possess superparamagnetic properties [17], which is one of the important requirements of MHT to magnetic nanomaterials, since such particles do not interact with each other in the absence of AMF. However, it should be mentioned that Fe 3 O 4 NPs have high value of the phase transition temperature (Curie point) from ferromagnetic into paramagnetic state (approx. ...
... Taking into account this fact, it is necessary to choose the optimal method of synthesis of NPs with the spinel structure suitable for MHT. In the other words, method of synthesis has to provide (i) obtaining NPs with small sizes and narrow size distribution, (ii) NPs should possess superparamagnetic properties (for ferrites with the spinel structure, superparamagnetism appears in NPs, which sizes are less than 30 nm [17,22]), (iii) ability to heat up effectively and self-controlled in AMF. In this context, it should be mentioned that Ni 1−x Zn x Fe 2 O 4 NPs investigated in [25] were synthesized by the precipitation in an aqueous solution using sodium hydroxide as a precipitator and treated at 800 °C. ...
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Ni0.5Zn0.5Fe2O4 nanoparticles (NPs) with the spinel structure were synthesized by the cryo-chemical method with further heat treatment in the temperature range of 200–800 °C. Crystalline NPs began to form in one-stage and the degree of crystallinity grew with the increase of the heating temperature. Particles sizes, their size distributions and magnetization also tended to growth directly with the increasing the heating temperature of NPs. Magnetic fluids based on the obtained Ni0.5Zn0.5Fe2O4 NPs demonstrated effective and self-controlled heating up to the certain temperatures under the effect of an alternating magnetic field in contrast to known in literature Fe3O4 NPs with the spinel structure, which heated up uncontrolled to the extremely high phase transition temperature. Graphic abstract
... This would cause the loss of attraction to external magnetic elds and, more signicantly, further contaminate the water by releasing metal ions. 26,35 To circumvent these limitations, zero-valent metals such as Fe, Co, and FeCo with strongest magnetic properties (M s of a bulk FeCo ¼ 235 emu g À1 ) 36 were applied as magnetic materials in adsorbents, mainly with some form of carbon-containing material. An Fe nanoparticle-graphene composite prepared via reduction of graphene oxide and iron chloride showed great potential as an efficient adsorbent of lead. ...
... Note that FeCo/GC NCs not only have $3 times higher saturation magnetization values than those of iron oxide NCs, but also exhibit superior chemical stability against acid etching in contrast to magnetic metals without graphitic carbon shells, or metal oxides such as iron oxides and ferrites. 36 In fact, the 130 nm FeCo/GC NCs@MSNs were very stable in a 35% HCl solution over a one-week monitoring period and was very quickly attracted when the sample was placed next to a cubic magnet. In contrast, 130 nm FeCo NCs@MSNs, in which the FeCo NCs were not encapsulated with carbon shells, turned the solution green right aer addition of the HCl solution owing to the etching of Fe and Co ( Fig. S5a and b, ESI †). ... Article Full-text available Highly stable and magnetically separable mesoporous silica nanospheres (MSNs) embedded with 4.6 ± 0.8 nm FeCo/graphitic carbon shell nanocrystals (FeCo/GC NCs@MSNs) were synthesized by thermal decomposition of metal precursors in MSNs and subsequent methane CVD. The FeCo/GC NCs@MSNs had a high specific surface area (442 m² g⁻¹), large pore volume (0.65 cm³ g⁻¹), and tunable size (65 nm, 130 nm, and 270 nm). Despite the low magnetic metal content (8.35 wt%), the FeCo/GC NCs@MSNs had a sufficiently high saturation magnetization (17.1 emu g⁻¹). This is due to the superior magnetic properties of the FeCo/GC NCs, which also enable fast magnetic separation of the nanospheres. The graphitic carbon shell on the FeCo NCs not only protects the alloy core against oxidation and acid etching in 35% HCl(aq), but also facilitates non-covalent, hydrophobic interactions with the hydrocarbon chains of organic dyes such as methyl orange and methylene blue. Surface functionalization of the FeCo/GC NCs@MSNs with thiol groups provides efficient capacity for binding with Hg²⁺ ions. We have shown that the thiol-functionalized FeCo/GC NCs@MSNs (FeCo/GC NCs@MSNs-SH) work as multifunctional adsorbents for organic dyes (target organic pollutants) and Hg²⁺ ions (target inorganic pollutant). We also demonstrated that the FeCo/GC NCs@MSNs-SH are excellent recyclable adsorbents for methyl orange. ... Magnetic nanoparticles (MNPs) are of high interest because of their multidisciplinary applications, including biomedicine [1][2][3][4][5][6][7][8], magnetic fluids [9,10], catalysis [11,12], magnetic resonance imaging [13][14][15][16], data storage [17,18], thermal management [9,10,[19][20][21][22][23], magneto-resistance sensors [24], spintronics [25], environmental remediation and water treatment [26][27][28]. Magnetic nanoparticles can be found almost everywhere, even inside us. ... ... There are a number of methods for synthesizing the MNPs, including high-energy ball milling, microemulsion, co-precipitation, micelles, polyols, mechanochemical, etc. [2,9,15,19,21,22,. All these methods have their own advantages and limitations (Table 1). ... ... On account of their high saturation magnetization and associated high magnetophoretic mobility, in the form of nanoparticles Fe-Co alloys are considered as promising candidates for the realization of advanced biological and biomedical functions such as highly specified biological in vitro cell separations [11], therapeutic (hyperthermia treatment [12] and drug delivery [13]) and diagnostic (magnetic contrast agents in magnetic resonance imaging [14]) applications. Their use is also considered as advantageous in industrial magnetic heating applications, for example in the form of solder-nanoparticle composites that enable localized reflow soldering by the use of AC magnetic fields [15]. ... ... In particular, Fe-Co alloys have the highest saturation magnetization among the binary transition metal alloys. Therefore, Fe-Co alloys have potential applications in ultrahigh-density recording memories, magnetic resonance imaging, biomedicines, and building blocks for high-performance permanent magnets [1][2][3][4]. So various chemical and physical methods have been utilized in the preparation of Fe-Co alloys, such as solution reductive method, hydrothermal reduction method, polyol process, and ball milling method [5][6][7][8]. ... Article Full-text available Fe1−x Cox alloys were synthesized by sol–gel autocombustion method. The atomic ratios of Fe:Co were easily controlled by adjusting the relative concentration of Fe3+ and Co2+ in the preparation of the precursor gels. Their phases and compositions were confirmed by X-ray diffraction and energy-dispersive X-ray spectroscopy analysis. Morphology characterization revealed the porous structure with micron-size pores. Synthetic mechanism was studied by thermogravimetry and differential scanning calorimetry. Magnetic properties of the alloys were investigated at room temperature. The highest saturation magnetization was found to be about 231 emu/g, which is much larger than that of the corresponding alloys synthesized through other chemical methods. Graphical Abstract SEM images and magnetic hysteresis loop of Fe0.7Co0.3 alloy synthesized by sol–gel autocombustion method. ... The obvious choice of metal precursors for the synthesis of FeCo NPs is Fe-and Co-carbonyls. This has been demonstrated in the synthesis of monodisperse FeCo NPs via the simultaneous thermal decomposition of Fe(CO) 5 and Co 2 (CO) 8 in 1,2-dichlorobenzene. 139 However, the slower decomposition rate of Fe(CO) 5 made it difficult to control the composition in the final FeCo NPs. To overcome this problem, a new Co-precursor Co(η 3 -C 8 H 13 )(η 4 -C 8 H 12 ) or Co(N-(SiMe 3 ) 2 ) 2 was developed to react with Fe(CO) 5 under H 2 in the presence of HDA and oleic acid to form FeCo NPs. ... Article Full-text available In the past two decades, the synthetic development of magnetic nanoparticles (NPs) has been intensively explored for both fundamental scientific research and technological applications. Different from the bulk magnet, magnetic NPs exhibit unique magnetism, which enables the tuning of their magnetism by systematic nanoscale engineering. In this review, we first briefly discuss the fundamental features of magnetic NPs. We then summarize the synthesis of various magnetic NPs, including magnetic metal, metallic alloy, metal oxide, and multifunctional NPs. We focus on the organic phase syntheses of magnetic NPs with precise control over their sizes, shapes, compositions, and structures. Finally we discuss the applications of various magnetic NPs in sensitive diagnostics and therapeutics, high-density magnetic data recording and energy storage, as well as in highly efficient catalysis. ... 4 The functional properties are derived from the synthesis and processing parameters; such as: controlled nucleation, growth of nanoparticles within the silica matrix, heat treatment using different inert atmosphere etc. These materials have potential applications in various fields; such as: catalysis, 5 biomedical, 6 magnetic recording media, 7 microwave absorption materials 8 etc. Alloy nps embedded in silica matrix show altered magnetic properties (M S , H C , K eff etc.). The values of the saturation magnetizations (M S ) can be different from that of the bulk materials. ... Article Magnetic characteristics of nanocrystalline CoNi alloy materials embedded in silica matrix (KIT-6) have been investigated. CoNi alloys with different loading (4–12 wt%) were synthesized via a novel chemical reduction route. The materials are characterized by UV–VIS, IR, powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and studied for their adsorption–desorption and magnetic properties. CoNi alloys crystallize in pure fcc phase with lattice parameters (a) and crystallite sizes in the range of 3.53(±2)–3.54(±2) Å and 13.6(±1)–16.3(±1) nm, respectively. TEM microscopy studies reveal nanocrystalline nature of the materials. Enhancement of magnetic moment with the increase in loading wt% for CoNi alloys embedded in silica matrix is observed. The values of coercivity tend to decrease after dispersion in silica matrix and thereafter increase with increasing loading wt% of various CoNi loaded samples. The observed magnetic properties have been explained on the basis of size, surface effects, and dipolar interactions. ... The bottom-up method is of greater interest for producing magnetic nanostructures. Many methods have been used to synthesize MNPs, including high-energy ball milling; microemulsion; coprecipitation; thermal decomposition; hydrothermal synthesis; mechanochemical, solvothermal, sonochemical, and microwave-assisted methods: chemical vapor deposition; combustion; carbon arc; and laser pyrolysis [20,21,[34][35][36][37][38][39][40]. Fig. 21.2 shows a schematic diagram of different synthetic method for magnetic particles. ... Chapter Magnetic nanoparticles (MNPs) are suitable candidates for wastewater treatment processes, including flocculation, demulsification, adsorption, filtration, and photocatalytic activities, because their magnetic properties make treatment easy and unique. The use of an external magnetic field makes possible the removal of contaminants from the solution in an efficient and facile manner. This chapter covers water treatment processes based on MNPs, and studies different types of MNPs, their synthesis routes, pollutants they can remove, and their particular uses in separation, filtration, and membrane-based processes. The future ahead of MNPs usage in wastewater treatment and challenges in the field are discussed. ... Incorporated in cancer tissue and exposed to high-frequency magnetic field, nanoparticles warm up locally and destroy the cancer cells [7,10]. The outstanding magnetization value of cobalt ferrite is useful for hyperthermia because more energy is needed to magnetize it; thus more energy is spent on heating [11]. Along with biocompatibility, this makes cobalt ferrite nanoparticles a good prospect fornanotechnology [12]. ... Article The hollow microcapsules made of silica-coated CoFe2O4 nanoparticles were synthesized using chemical co-precipitation, followed by the sol-gel method. Poly(MMA-co-MAA) microspheres were used as a core template which can be completely removed after annealing at 450 degrees C. The microcapsules are monodisperse with the outer diameter of about 450 nm and the thickness of the shell is about 50 nm. The nanoparticles of Co-ferrite are single crystalline. The size of the nanoparticles and magnetic properties of CoFe2O4/SiO2 hollow spheres can be tuned with high accuracy at the annealing stage. The Mossbauer data indicate that CoFe2O4 ferrite is an inverse spinel, in which Fe3+ and Co2+ ions are distributed in both octahedral and tetrahedral sites with the inversion degree close to the bulk ferrite value. At low temperature the CoFe2O4/SiO2 nanoparticles are in antiferromagnetic (AFM) state due to the canted or triangular magnetic structure. Under heating in the applied field, AFM structure transforms to the ferrimagnetic. (FM) structure, that increases the magnetization. The Mossbauer data revealed that the small size CoFe2O4/SiO2 particles do not show superparamagnetic behavior, but they transit to the paramagnetic state by the jump-like first order magnetic transition (JMT). This effect is a specific property of the magnetic nanoparticles isolated by inert material. The suggested method of synthesis can be modified with various bio-ligands on the silane surface, and such materials can find many applications in diagnostics and bio-separation. ... Magnetic beads and nanoparticles are promising candidates for various lab-on-a-chip applications [1][2][3]. Their magnetic moments allow for the manipulation by external magnetic gradient fields [4,5]. Detection of magnetic beads or nanoparticles may be achieved by the use of magnetoresistive sensors due to their magnetic stray field [6]. ... Article Full-text available The authors present a method for the formation of highly ordered two-dimensional arrays of magnetic beads based on dipolar particle interactions in rotating magnetic fields. Growth mechanisms of the arrays inside the carrier liquid are presented. After evaporation of the carrier liquid, the resulting bead monolayers on silicon substrates are analyzed with respect to size and defect structure. ... The NPs tested were capped by oleic acid, their size was in the range 1-11 nm and the stoichiometric (Fe 50 Co 50 ) alloy was the best one from the magnetophoretic mobility point of view. 346 Bharti et al. published a report on the magnetophoretic assembly of flexible NPs/lipid microfilaments. In the presence of a uniform magnetic field, the magnetophoretic attraction of the particles combined with interparticle dipole-dipole attraction drives the microfilament assembly. ... Article Full-text available Nanostructures have attracted a huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one techniques. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of the nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this Review is to summarize the present knowledge on the use, the advances, the advantages and the weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques, their operation principles and we give various examples on their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case. ... According to table 1 the diameter of the catalyst particles are below the single domain limit, 12 nm for Fe [102] and 41 nm for bcc FeCo [103]. ... Article This work presents Hall magnetometry studies on individual Fe-filled carbon nanotubes (CNT). For this approach high sensitivity micro Hall sensors based on a GaAs/AlGaAs heterostructure with two dimensional electron gas (2DEG) were developed. Electron beam lithography and wet chemical etching were utilized for patterning Hall sensors onto the heterostructure surface. The devices were characterized by means of scanning electron microscopy, atomic force microscopy and transport measurements. Individual Fe-filled CNTs were placed on active part of devices (800 × 800 nm2) with aid of micromanipulator system. Measurements on an individual iron nanowires confirmed devices applicability for measurements of nanoscale magnets. High nucleation fields were found of about 900 mT for a Fe nanowire with diameter of d = 26 nm. The magnetization reversal mechanism was found to be a localized process whereas the angular dependence of nucleation fields is in a good agreement with a curling mode. Through magnetization studies performed on differently functionalized ensembles of CNT by means of Alternating Gradient – and Superconducting Quantum Interference Device (SQUID) magnetometry a strong influence of a remaining ferromagnetic catalyst material on the magnetic properties of CNT was observed. Magnetization studies proved that a post annealing method removes catalyst material completely. ... Fabrication of multifunctional composite metallic nanoparticles (NPs), particularly with «core-shell» structure is an important and actual problem of modern nanochemistry [1]. High saturation magnetization at room temperature and biocompatibility of such NPs offers important prospective for their application as magnetic carriers for drug delivery and in vitro and in vivo cell separation as well as contrast agents for magnetic resonance imaging or surface enhanced Raman spectroscopy [2][3][4]. Besides, considered NPs could be effectively used in cancer therapy based on local microwave hyperthermia applying target heating by free-electron maser [5]. The heating of such NPs might be initialized simultaneously by magnetic resonance absorption of magnetic cores and localized surface plasmon resonance absorption of shells [6]. ... Article Composite nanoparticles (NPs) of FeCo-Ag and FeCo-Au fabricated by the redox-transmetalation technique are characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD), Mössbauer spectroscopy and magnetometry. TEM images prove the formation of agglomerated quasi-spherical NPs with mean value of diameter about 28 nm. As indicated by XRD and Mössbauer spectroscopy composite NPs constitute cores containing Fe³⁺Co-based oxides with smaller contribution of bcc α-FeCo alloy and shells representing well crystallized Ag and Au. Mean value of diameters of magnetic cores (≈10 nm) and non-magnetic shells (≈18 nm) in composite NPs are estimated by complementary analysis of TEM images, broadening of XRD reflections and approximation of hysteresis curves M(H) with Langevin function. ... The FeCo-based soft magnetic alloys belong to a class of nanomaterials which has some unique features, such as large permeability, high saturation magnetization, and high Curie temperature [2][3][4]. The FeCo alloys are being widely studied due to the great technological importance and their multiple applications, such as the medicine related to cancer treatments [5], the biomedicine to the controlled release of drugs in the body [6], in the catalytic process [7][8][9], in magnetic bearings [10], and thin films [11]. ... ... Magnetic properties of nanoparticles can be tuned by varying chemical composition and thickness of the coating materials, as it was reported for the composite FePt-MFe 2 O 4 (M = Fe, Co) core-shell nanoparticles [48]. While iron oxide-based magnetic nanoparticles are the most frequently used, some alternative magnetized materials have been suggested for various biomedical and bioanalytical applications [49]. For example, ferromagnetic FeCo nanoparticles demonstrated superior properties that make them promising candidates for magnetically assisted bioseparation methods and analysis, as well as for various electrochemical and bioelectrochemical applications. ... Article Full-text available Magnetic nanoparticles and magnetic nano-species of complex topology (e.g., nanorods, nanowires, nanotubes, etc.) are overviewed briefly in the paper, mostly giving attention to the synthetic details and particle composition (e.g., core-shell structures made of different materials). Some aspects related to applications of magnetic nano-species are briefly discussed. While not being a comprehensive review, the paper offers a large collection of references, particularly useful for newcomers in the research area. ... Researchers have tried to minimise the size of the implanted magnetic material and have used some magnetite and maghemite nanoparticles. For example, MnFe 2 O 4 (Kim et al. 2009), CoFe 2 O 4 (Fischer et al. 2005), (Co)Fe 3-δ O 4 (Kita et al. 2008), NiFe 2 O 4 (Bae et al. 2006), Fe 2 Co (Goya et al. 2008), FeCo (Hutten et al. 2005), and γ-Fe 3 O 4 (Hergt et al. 2004) are found to be good in this regard, because of their good biocompatible properties and nontoxic nature in the human body. Ferromagnetic nanoparticles are suspended in a polysaccharide aqueous solution and this ferrofluid is injected through a needle into the cavity of the tumour. ... Chapter Full-text available Induction heating is now used for hyperthermia on deep-seated tumors or hepatic cellular carcinoma. Ferromagnetic particles in nano-micron size are mixed with polysaccharide solution and injected into the cavity of tumor or cancer cell. Heat is then generated locally with the application of an external magnetic field. The generated heat within the tissue happens due to three kind of losses: hysteresis, relaxation and resonance. Frequency and magnetic field intensity plays an important role in this process. Moreover, at high frequency the amplitude of magnetic field intensity can produce unnecessary heating which can lead to lesion of surrounding healthy tissue via eddy current. So, the parameters of alternating magnetic field must be chosen accurately. ... For various applications of magnetorheological fluids, certain requirements are imposed on their properties. The properties of magnetically controlled liquids strongly depend on the composition of the colloidal system [4][5][6][7][8][9]. ... Article Full-text available The article describes an installation for producing nanopowders by the method of electrical explosion of a wire. The powders are supposed to be used as a basis for magnetorheological fluids. The article describes the functional installation and the model of the power converter. The electric explosion of the wire was carried out at a voltage of 500 V and 1000 V. The experimental data coincide with the results of the study on the model. The pulse duration is ∼ 10 ⁻⁴ s, and the power is in the range from 1.5 MW to 4 MW. Spherical particles are obtained in the size of 500-5000 n with such parameters of an electric explosion. The surface of the particles was examined on a Tescan VEGA II electron microscope. ... The method based on thermal decomposition of Fe(CO) 5 is not limited to the fabrication of monometallic Fe nanoparticles but it has been extended to the preparation of a variety of bimetallic and trimetallic Fe-based nanoparticles of specific shapes and sizes. An excellent study discussing the advantages and disadvantages of the thermal procedure, a comparative analysis of numerous precursors, intermediates involved in the thermolysis reaction and the kinetic studies of the reaction is presented by Hutten et al [69] for the preparation of FeCo nanoparticles. ... Article Full-text available The usage of zero valent iron (Fe) nanoparticles for various organic transformations has been extensively reported in the last decade because of high natural abundance, low toxicity and low cost of Fe metal. The development of synthetic strategies used for fabrication of iron nanoparticles and their stabilization using various supporting materials has made a significant contribution to their use in catalysis. This critical review gives research progress of synthesis, stabilization and characterization of zero valent Fe nanoparticles. It specially emphasizes on their use as reducing agent and as catalyst in various reduction reactions in the last ten years. Catalytic reductions of different organic substrates in the presence of Fe nanoparticles using different hydrogen sources have been mainly described critically in this review. Challenges and future perspectives for further development in the field of Iron nanoparticles catalyzed reduction reactions have been described. Chapter Magnetic particles of nano- and micro-size functionalized with various biomolecules were synthesized and extensively used for many bioanalytical and biomedical applications. Different biosensors, including immunosensors and DNA sensors, were developed using functionalized magnetic particles for their operation in vitro and in vivo. Their use for magnetic targeting (drugs, genes, radiopharmaceuticals), magnetic resonance imaging, diagnostics, immunoassays, RNA and DNA purification, gene cloning, cell separation and purification has been developed. The present chapter summarizes the recent advances in the bioanalytical and biomedical applications of functional magnetic particles. Article We succeeded in the efficient preparation of well-dispersed Fe–Co nanoalloys (NAs) using the arc plasma deposition method. Synchronous shots of dual arc plasma guns were applied to a carbon support to prepare the solid-solution type Fe–Co NAs having an approximately 1:1 atomic ratio. The alloy structures with and without a reductive thermal treatment under hydrogen atmosphere were examined using X-ray powder diffraction, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray analysis, high resolution STEM, and magnetic measurements, suggesting that highly crystalline spherical particles of ordered B2-type Fe–Co NAs form by the thermal treatment of the deposited grains. Article Full-text available Abstract. We report the results of calculations which were performed to investigate the magnetic properties and energetic properties of equilibrium structures of small FeSnx (x = 1–8) clusters, within the framework of the density functional theory by using the SIESTA code. The presence of the Fe impurity modifies the equilibrium geometries and the spin state of the free Sn clusters. All the FeSn clusters present magnetic order and show a dependence with the concentration x; in some cases the magnetic order into the cluster is ferromagnetic-like, generally the magnetic coupling in Sn atoms is ferromagnetic-like but our results show than in some clusters coexist the antiferromagnetic-like order with the ferromagnetic-like order in the Sn atoms. We have studied the fragmentation of the clusters and our results show the absence of a predominant fragmentation channel. The presence of the impurity induces a low value of HOMO-LUMO gap with respect to free Sn clusters. Article We have developed a highly stable and magnetically recyclable nanocatalyst system for alkene hydrogenation. The materials are composed of mesoporous silica spheres (MSS) embedded with FeCo/graphitic shell (FeCo/GC) magnetic nanoparticles and Pt nanocatalysts (Pt-FeCo/GC@MSS). The Pt-FeCo/GC@MSS exhibit superparamagnetism at room temperature and show type IV isotherm typical for mesoporous silica, ensuring a large enough inner space (surface area of 235.3 m2 g-1, pore volume of 0.165 cm3 g-1, and pore diameter of 2.8 nm) to undergo catalytic reactions. We have shown that Pt-FeCo/GC@MSS readily convert cyclohexene to cyclohexane as a only product and can be seperated very quickly by an external magnetic field after the catalytic reaction. We have demonstrated that the recycled Pt-FeCo/GC@MSS can be reused further for the same hydrogenation reaction at least four times without loss of the initial catalytic activity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Article We report the results of DFT calculations wich were performed to investigate equilibrium structures, electronic properties and stability of small free Fex Sny clusters with x + y ≤ 5 within the framework of density functional theory as implemented in SIESTA code. We find that optimized structures of these binary clusters prefer geometries with high coordinations and show significant variations as compared to that of the pure clusters; all the clusters show magnetic behavior independently of the Fe concentration, the antiferromagnetic-like coupling betwen Fe-Sn is present generally. Also the electronic behavior is analized through the ionization potential, the electron affinity, the hardness and the HOMO-LUMO gap. Graphical abstract Article Nanostructured (Fe xCo 1-x) 75C 25 alloys were prepared by mechanical alloying. Local ordering around the central atom was examined for various Fe contents by using extended X-ray absorption fine structure. X-ray diffraction patterns indicate a cohenite-like phase for composition of x = 0.2, 0.5, and 0.8. The first shell of the Fourier transformed spectra changed with Fe content, indicating a change in the local ordering around the central Fe or Co atom. The x = 0.5 composition was well fitted to a (FeCo) 3C phase, and the interatomic distance between the central atom and neighboring atoms was determined. The temperature dependence of magnetization was also studied for various Fe contents. Article As an emerging new class of materials comprising two different metals, bimetallic nanoparticles (NPs) exhibit new functions because of the synergistic rather than merely additive effects of the metals. Compared with monometallic Fe NPs, bimetallic Fe NPs have markedly enhanced physical and chemical properties, including magnetism and reducing ability. However, bimetallic Fe NPs with controlled morphology, size, composition, and structure are often difficult to synthesize. This review summarizes recent advances in the synthesis and environmental application of bimetallic Fe NPs. Different methods of synthesizing bimetallic NPs with different structures, sizes, compositions, and surface properties are summarized. Focus is also given to the catalytic elimination of various environmental pollutants using bimetallic Fe NPs because they have emerged as a promising catalyst for environmental remediation. Their strong reducing ability can be used to remove numerous environmental pollutants (e.g., heavy metals, halogenated organic compounds, nitro and azo compounds, and oxyanions). Reactions between the bimetallic NPs and these pollutants mainly fall into four categories: (1) catalytic replacement reaction for heavy-metal removal, (2) hydrodehalogenation for halogenated hydrocarbons, (3) nitro and azo hydrogenation for nitro and azo compounds, and (4) hydrodeoxygenation for oxyanions. Compared with monometallic Fe NPs, bimetallic Fe NPs have considerable separability and catalytic ability to degrade nonbiodegradable pollutants. Article Full-text available Magnetic nanoparticles, because of their unique properties, are expected to find many prospective applications including data storage, ferrofluids, catalysis, and biomedicine. In this critical review, synthesis methods as well as the characteristics of magnetic nanoparticles are presented. In addition, the benefits and drawbacks of using nano-particles in biomedical applications are clearly presented. Article Due to their unique characteristics including superparamagnetic or fluorescent properties and small size comparable to biomolecules, multifunctional magnetic nanoparticles (MFMNPs) have emerged as novel bioimaging, diagnostic and therapeutic agents in biomedical field. The combinations of various nanostructured materials with different propeties and magnetic nanoparticles ( MNPs) can offer synergetic multifunctional nanomedical platforms, which make it possible to accomplish multimodal imaging and simultaneous diagnosis and therapy. This review summarizes the synthesis of MNPs and fabrication of MFMNPs, especially focuses on the three types of MFMNPs core/shell MFMNPs, dumbbell MFMNPs and multicomponent hybrid nanoparticles. Furthermore, to perform real-time monitoring and drug treatment with high accuracy in vivo, stabilizing modification and target modification of MFMNPs are needed to enhance the stability of MFMNPs in physiological environment and localize MFMNPs in the special area in vivo. This paper reviews the general strategies for surface modification of MFMNPs and biomedical applications of these MFMNPs for multimodal imaging, target-specific drug delivery, gene transfection and so on. The development of MFMNPs fusing multiple fluorescent dyes, drugs, and MNPs into a single nanoprobe should provide superior fluorescent, enhanced magnetic resonance imaging (MRI) contrast, and targeted delivery capabilities. Finally, problems to be solved in the current research are also pointed out. Article We have synthesized highly uniform and single bcc-phased FeCo/graphitic carbon shell (FeCo/GC) nanocrystals with an average diameter of 5.7 +/- 0.3 nm by thermal decomposition of metal precursors in SBA-15 and subsequent methane CVD. Small-angle XRD data and N-2 adsorption-desorption isotherms of the SBA-15 before and after loading with FeCo/GC nanocrystals clearly demonstrate that the structure of SBA-15 was retained during the nanocrystal growth and most of the channels of the mesoporous silica were stucked by the FeCo/GC nanocrystals. The nanocrystal sizes of 5-6 nm are consistent with the pore diameters of the SBA-15. The yield of nanocrystals in silica has been increased 6-fold and the Fe/Co ratio of the FeCo/GC nanocrystals has been improved from 34:66 to 46:54 by using SBA-15 instead of fumed silica. The FeCo/GC nanocrystals exhibit superparamagnetism with high saturation magnetization of 209 emu/g metal at room temperature. Chapter One of the most important issues in the alternative tumors therapy using magnetic nanoparticles is the biocompatibility, toxicity, and safety of the use of nanoparticles in this therapy, as an alternative to the classic methods of chemotherapy and radiotherapy currently used in cancer treatment. In addition to nanoparticles, the techniques itself must be applied safely and without toxicity so that healthy tissues are not affected. The classic techniques of chemo- and radiotherapy even if they are quite advanced today, still have a high toxicity on the human body, and in many more advanced cases of tumors, they are even ineffective. Therefore, finding an alternative method to these classic techniques for the effective therapy of cancer with as little toxicity as possible or even without toxicity is a major problem today in research in this field. Thus, targeted drug delivery, magnetic hyperthermia, and recently superparamagnetic hyperthermia with magnetic nanoparticles are very promising new alternative techniques in cancer therapy. However, this new technique and the magnetic nanoparticles used in order to be safely applied in cancer therapy must be effective in destroying tumors and have less or no toxicity compared to classical techniques. This chapter focuses on the toxicity and safety of magnetic nanoparticles in order to use in noninvasive alternative therapy of cancer compared with classical method chemotherapy and radiotherapy. Article Magnetic nanocomposites are multi-component materials, typically containing nanosized magnetic materials to trigger the response to an external stimulus (i.e., an external static or alternating magnetic field). Up to now, the search for novel nanocomposites has lead to the combination of a plethora of different materials (e.g., gels, liquid crystals, renewable polymers, silica, carbon or metal organic frameworks) with various types of magnetic particles, offering exciting perspectives not only for fundamental investigations but also for application in various fields, including medical therapy and diagnosis, separations, actuation, or catalysis. In this review, we have selected a few of the most recent examples to highlight general concepts and advances in the preparation of magnetic nanocomposites and recent advances in the synthesis of magnetic nanoparticles. Article Regulating the structure and ingredients of hollow structures can solve the problems of thickness, heaviness, and narrow broadband faced by metal microwave absorbers. Herein, we have developed for the first time a facile one-pot hydrothermal reduction approach to selectively preparing bimetallic Co1–xCux (x = 0, 0.012, 0.031, 0.062, 0.125, 0.250, 0.498) hollow microspheres (HMs) consisting of urchin-like superstructures. The selective adsorption of surfactants and prenucleated Cu seeds guide the growth of Co into 1D rods, which subsequently assembled into urchin-like Co1−xCux superstructures and further into HMs driven by the minimization of magnetic anisotropic energy or surface free energy. The combination of Co with Cu into Co1–xCux HMs can tune the structure, size, defect, components, conductivity, and magnetic properties. Moreover, urchin-like Co1−xCux HMs consisting of sparse rods with low Cu content (1%) and large diameter (5–10 µm) benefit the excellent absorption capacity by producing good impedance matching, multiple losses, and electrical/magnetic coupling effects. Interestingly, the Co0.990Cu0.010 HMs exhibited a stronger absorption (−37.94 dB), a wider bandwidth (9.68 GHz), a lower loading (30 wt.%), and a smaller matching thickness (1.3 mm) compared with other absorbers. Our findings suggest that the Co1–xCux HMs will perform well as a superior absorber for EM wave absorption and shielding applications due to the adjustable saturation magnetization and outstanding absorption capacity. Article The promise of biocompatible magnetic nanoparticles with high magnetic saturation in the implementation as drug carriers and hyperthermia agents has generated significant interest in functionalised cobalt nanoparticles. Carboxylic acid coatings on metallic nanoparticles have been shown as an attractive option owing to their respectable stability and biocompatibility. However, only limited information is available on the molecular mechanism leading to the formation of such protective coatings. In this study, ab initio molecular dynamics simulations have been used to unravel the functionalisation mechanism starting from a neutral cobalt cluster and valeric acid molecules. Three stages were detected in the coating process: (i) rapid initial adsorption of acid molecules, (ii) simultaneous adsorption of new molecules and dissociation of those already interacting with the cluster, and, finally, (iii) grouping of dissociated hydrogen atoms and subsequent desorption of acid molecules. The fate of the hydrogen atoms was probed through a combination of static and dynamic ab initio modelling approaches, which predicted H2 generation with favourable energetics. A better understanding of the functionalisation and interaction mechanisms will aid the rational design of biocompatible cobalt nanoparticles for various applications. Article Magnetic particle imaging (MPI) has recently emerged as a promising non-invasive imaging technique because of its signal linearly propotional to the tracer mass, ability to generate positive contrast, low tissue background, unlimited tissue penetration depth, and lack of ionizing radiation. The sensitivity and resolution of MPI are highly dependent on the properties of magnetic nanoparticles (MNPs), and extensive research efforts have been focused on the design and synthesis of tracers. This review examines parameters that dictate the performance of MNPs, including size, shape, composition, surface property, crystallinity, the surrounding environment, and aggregation state to provide guidance for engineering MPI tracers with better performance. Finally, we discuss applications of MPI imaging and its challenges and perspectives in clinical translation. Chapter Magnetic nanoparticles (MNPs) have widespread attention because of their unique features. For a few decades, growing development in chemical synthesis of nanomaterials and material surface modification have been seen and performed in numerous applications including biomedicine, biotechnology, catalysis, magnetic chemistry thermoelectric materials, etc. Various methods for fabrication of MNPs which have a controllable size, distribution, and surface modification have been reported. In these methods, several techniques containing irradiation, microwave, ultrasonication, vapor deposition, electrochemical, and microwave are applied to produce MNPs either in bottom-up or top-down processes. Generally, magnetic synthesis of nanoparticles is carried out by using these two processes. Nanomaterials with magnetic properties have wide applications in many fields such as biology, medicine, and engineering. In this section, the recent developments in the structures, occurrences, most commonly used samples, and common areas of use of the MNPs are given. Article We present results of the synthesis and characterization of Fe—Co—V high magnetization ferromagnetic nanoparticles (NPs) fabricated by two physical routes: laser ablation in liquid flow and mechanical ball milling. As characterizing techniques, we used dynamic light scattering, X-ray diffraction, transmission and scanning electron microscopy, and magnetic measurements. The starting material was$\text{Fe}_{49} \text{Co}_{49} \text{V}_2\$ (bulk Vacoflux 50® from Vacuumschmelze), a soft magnetic alloy with a high saturation magnetization of about 2.3 T or 220 emu/g. Using a picosecond pulsed laser at λ = 355 nm and 532 nm with flowing liquid acetone, we obtained NPs about 10-50 nm in size, with saturation magnetization of 3 memu/ml. By employing high energy ball milling (24 h total milling time), we obtained NPs that are about 0.5-1 μm in size, with BCC structure and about 195 emu/g saturation magnetization. All these results indicate that the main differences between the two fabrications methods are the final quantity and morphology of the NPs.
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Nanotechnology is a rapidly evolving field, as evidenced by the large number of publications on the synthesis, characterization, and biological/environmental effects of new nano-sized materials. The unique, size-dependent properties of nanomaterials have been exploited in a diverse range of applications and in many examples of nano-enabled consumer products. In this account we focus on Engineered Nanomaterials (ENM), a class of deliberately designed and constructed nano-sized materials. Due to the large volume of publications, we separated the preparation and characterisation of ENM from applications and toxicity into two interconnected documents. Part 1 summarizes nanomaterial terminology and provides an overview of the best practices for their preparation, surface functionalization, and analytical characterization. Part 2 (this issue, Pure Appl. Chem. 2018; x(x): xxx–xxx) focuses on ENM that are used in products that are expected to come in close contact with consumers. It reviews nanomaterials used in therapeutics, diagnostics, and consumer goods and summarizes current nanotoxicology challenges and the current state of nanomaterial regulation, providing insight on the growing public debate on whether the environmental and social costs of nanotechnology outweigh its potential benefits.
Article
Core-shell few-layer graphene-coated magnetic nanoparticles (GCMNPs) were synthesized by catalytic chemical vapor deposition of methane at atmospheric pressure. The GCMNPs, of cobalt and iron dispersed on an alumina support, catalyze themselves the decomposition of methane, which is the source of carbon. The pretreatment conditions influence the final alumina pore size distribution and GCMNP diameter. The nanoparticles magnetic properties have been found to be strongly dependent on their size. A high-saturation magnetization value of 238 e.m.u./g was found for our monodispersed diameter body-centered-cubic FeCo nanoparticles. The nanoparticles exhibited a significant capacitive performance, including a specific capacitance value of 367.2 F/g, high energy density of 86 Wh/kg, and excellent cyclability in aqueous electrolyte.
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This chapter overviews various electrochemical systems with switchable features that can be controlled by external magnetic fields applied to magnetic micro/nanospecies. The magneto‐switchable single‐microparticle system is particularly important for future miniaturization of the magneto‐controlled electrochemical systems. In all the examples discussed in the chapter, the magnetic species were separated from the electrode surface and were free to move around, either by lateral/vertical translocation of magnetic particles or by reorientation of adaptive nanowires. Extensive work performed in the area of switchable electrode interfaces controlled by external magnetic fields resulted in the design of various systems based on translocation and reorientation of different magnetic micro‐ and nanoparticles, adaptive nanowires, and graphene‐based hybrid materials. The chapter demonstrates a new approach to the reversible magnetic control of redox activity of composite polymeric materials containing magnetic nanoparticles inside.
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We have developed a highly stable and magnetically recyclable yolk-shell nanocatalyst for catalytic reduction of nitroaromatics. This nanocatalyst is composed of a ~13 nm Au nanoparticle encapsulated in a hollow mesoporous carbon (hmC) shell with a diameter of ~120 nm and a thickness of ~15 nm. The hmC shell contains ~6 nm FeCo/graphitic carbon shell (FeCo/GC) nanoparticles. We have synthesized the Au@hmC-FeCo/GC nanocatalyst by thermal decomposition of Fe and Co precursors in silica of a solid core/mesoporous shell structure containing a Au nanoparticle within the core, subsequent ethylene chemical vapor deposition (CVD), and then removal of the silica by treatment with aqueous HF. The Au@hmC-FeCo/GC has superparamagnetism and high saturation magnetization (29.2 emu g-1) at room temperature. It also shows a type IV sorption isotherm, typical for mesoporous carbon (pore diameter = 3.5 nm), thereby ensuring ready accessibility to the Au core by substrates. We have shown that the Au@hmC-FeCo/GC catalyses the reduction of 4-nitrophenol and 4-nitrotoluene more efficiently than Au nanoparticles do, can be separated very quickly from the reaction mixture using an magnet, and can be reused for the same reduction reaction at least five times without loss of the initial level of catalytic activity.
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Magnetic hyperthermia (MHT) is heat dissipation in magnetic nanoparticles (MNPs) in an alternating magnetic field (AMF) of hundreds of kHz. This is an alternative method, non-invasive, and appears to be non-toxic compared to the usual methods – chemotherapy and radiotherapy used today in the therapy of malignant tumours – and with great future potential in cancer therapy. For the MHT to be effective in destroying tumour cells the temperature of biocompatible magnetic nanoparticles (Bio-MNPs) in the tumour must reach 42–43 °C, leading to local necrosis. There are many factors that increase the temperature of MNPs, depending on the nanoparticles’ size (NPs) and type, metals or oxides with metallic ions. In this chapter, I will discuss application of metal/oxide magnetic nanoparticles (Me/O-MNPs) in MHT as possible candidates for increasing the hyperthermic efficiency in cancer therapy. I will present the basic physical aspects of MHT, the magnetic properties of Me/O-MNPs with potential use in MHT, the results obtained in vitro and in vivo and future development trends of the MHT technique, such as superparamagnetic hyperthemia (SPMHT), proposed as alternative, non-invasive and non-toxic cancer therapy.
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The increasing interest in nanoscale materials goes hand in hand with the challenge to reliably characterize the chemical compositions and structural features of nanosized objects in order to relate those to their physical properties. Despite efforts, the analysis of the chemical composition of individual multi-element nanoparticles remains challenging—from the technical point of view as well as from the point of view of measurement statistics. Here, we demonstrate that zero-field solid-state nuclear magnetic resonance (NMR) complements local, single particle transmission electron microscopy (TEM) studies with information on a large assembly of chemically complex nanoparticles. The combination of both experimental techniques gives information on the local composition and structure and provides an excellent measurement statistic through the corresponding NMR ensemble measurement. This analytical approach is applicable to many kinds of magnetic materials and therefore may prove very versatile in the future research of particulate magnetic nanomaterials.
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Nanocrystalline soft magnetic materials come in many forms, including nanoparticles, nanowires, nanorods, nanostructured thin films, nanopatterned films, and nanocrystalline ribbons. This chapter discusses the following nanostructured materials: zero-dimensional nanoparticles, one-dimensional nanorods and nanowires, two-dimensional thin films, and three-dimensional ribbons and bulk materials. In the three-dimensional material, all physical dimensions of the sample are much larger than the grain size. Nonequilibrium processing, including mechanical alloying, rapid solidification, electrochemical synthesis, and quenched chemical synthesis techniques, has been used to make these materials. One-dimensional magnetic nanomaterials have been synthesized in various forms, including nanowires (NW), multilayered nanowires (MNW), nanorods (NR), multilayered nanorods (MNR), nanofibers (NF), nanotubes (NT) and core- shell nanowires (CSNW). Thin film deposition of soft magnetic materials is a well-established field, having significant demonstration of processing by plasma processing, vapor deposition, sputtering, and pulsed laser deposition. Bulk nanocrystalline soft magnets are typically produced by rapid solidification.
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Achieving mastery over the synthesis of metal nanocrystals has emerged as one of the foremost scientific endeavors in recent years. This intense interest stems from the fact that the composition, size, and shape of nanocrystals not only define their overall physicochemical properties but also determine their effectiveness in technologically important applications. Our aim is to present a comprehensive review of recent research activities on bimetallic nanocrystals. We begin with a brief introduction to the architectural diversity of bimetallic nanocrystals, followed by discussion of the various synthetic techniques necessary for controlling the elemental ratio and spatial arrangement. We have selected key examples from the literature that exemplify critical concepts and place a special emphasis on mechanistic understanding. We then discuss the composition-dependent properties of bimetallic nanocrystals in terms of catalysis, optics, and magnetism and conclude the Review by highlighting applications that have been enabled and/or enhanced by precisely controlling the synthesis of bimetallic nanocrystals.
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We have prepared magnetite nanoparticles (Fe3O4_NPs) almost spherical in shape with average particle size of 10 nm and successfully encapsulated them in an envelope of polypyrrole (PPY) chains via an emulsion polymerization route using sodium dodecyl sulfate as surfactant. The resulting PPY-coated Fe3O4_NPs (Fe3O4_NPs/PPY) suspensions were stable with particles exhibiting a triangular prismatic morphology and an average diameter below 100 nm. In fact, all colloidal solutions were stable in aqueous media with typical ζ-surface potential values of −33.9 mV (Fe3O4_NPs) and −20.0 mV (Fe3O4_NPs/PPY). Although X-ray diffraction studies revealed the presence of a magnetic phase Fe3O4, the identified diffraction peaks are consistent with the presence of a spinel structure of magnetite. A ferromagnetic behavior, such as lower coercive force (Hc = 0.065 T), was observed for all magnetic nanoparticles examined. The 1H NMR relaxation times T1 and T2 of selected Fe3O4_NPs/PPY samples were also measured and their relaxivities r1 (1.1 s−1 mM−1) and r2 (61.9 s−1 mM−1) compare favorably to those of contrast agents commercially used in human examinations. We suggest that the present results indicate that these hybrid nanocomposites are promising materials for the development of a platform of specialized contrast agents for 1H Magnetic Resonance Imaging. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
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This paper provides an overview of the synthetic techniques used to prepare colloidal nanocrystals (NCs) of controlled composition, size, shape, and internal structure and the methods for manipulation of these materials into ordered NC assemblies (superlattices). High-temperature solution-phase synthesis (100–300°C) is followed by size-selective separation techniques in the preparation of monodisperse NC samples tunable in size from ∼1 to 15 nm in diameter with <5% standard deviation. Each NC consists of a crystalline inorganic core coordinated by an organic monolayer. These monodisperse NC samples enable systematic studies of structural, electronic, magnetic, and optical properties of materials as a function of size evolution from molecular species (<100 atoms) to bulk solids (>100 000 atoms). We illustrate size-dependent properties for magnetic materials using Co and for semiconducting materials using PbSe. These NC samples are sufficiently uniform in size to self-assemble into close-packed, ordered NC superlattices, also known as colloidal crystals.
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Synthesis of monodisperse iron-platinum (FePt) nanoparticles by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers is reported. The FePt particle composition is readily controlled, and the size is tunable from 3- to 10-nanometer diameter with a standard deviation of less than 5%. These nanoparticles self-assemble into three-dimensional superlattices. Thermal annealing converts the internal particle structure from a chemically disordered face-centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies. These assemblies are chemically and mechanically robust and can support high-density magnetization reversal transitions.
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A method of constructing <30-nanometer structures in close proximity with precise spacings is presented that uses the step-by-step application of organic molecules and metal ions as size-controlled resists on predetermined patterns, such as those formed by electron-beam lithography. The organic molecules serve as a ruler for scaling down a larger “parent” structure. After metal deposition and lift-off of the organic multilayer resist, an isolated smaller structure remains on the surface. This approach is used to form thin parallel wires (15 to 70 nanometers in width and 1 micrometer long) of controlled thickness and spacing. The structures obtained were imaged with field emission scanning electron microscopy. A variety of nanostructures could be scaled down, including structures with hollow patterns.
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Die kinetische Kontrolle des Kristallwachstums in Gegenwart eines koordinierenden Liganden spielt eine entscheidende Rolle bei der Bildung einer neuen Struktur elementaren Cobalts (ε-Cobalt, die Elementarzelle mit den zwei Arten von Cobaltatomen ist gezeigt). Diese wurde bei der Analyse des metallischen Pulvers entdeckt, das bei der thermischen Zersetzung von Octacarbonyldicobalt in Lösung in Gegenwart von Trioctylphosphanoxid (TOPO) entsteht [Gl. (1)].
General synthetic routes to monodisperse e-cobalt (β-Mn type phase) nanocrystals (e-Co) and controlled assembly of these nanocrystals are presented in this paper. The e-Co particles are obtained by superhydride reduction of cobalt chloride (anhydrous or hexahydrate) in a high temperature solution phase (200°C) in the presence of a combination of long chain diol, oleic acid and trialkylphosphine. Monodisperse nanocrystals are isolated by size selective precipitation. As synthesized cobalt particles are each a single crystal with a complex cubic structure related to the beta phase of elemental manganese (β-Mn). Self-assembly of these uniform cobalt particles on solid substrates is induced by evaporation of the carrier solvent producing 2-D and 3-D magnetic superlattices. Annealing of assembled e-Co nanocrystal arrays converts them to the hep cobalt crystal arrays. The inter-particle distance can be adjusted by selected thermal treatments or by chemical ligand exchange. This control over particle dimensions, crystallinity and assembly offers a model system for the study of ultra-high density recording media. re 1999 Materials Research Society.
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1. Monodispersed colloids exhibiting higher order Tyndall spectra have been prepared by precipitation of sulfur from ethanol and acetone solutions by the careful addition of water. 2. The relationship between the concentration of sulfur and the volume fraction of water at the critical point of sulfur-ethanol-water solutions has been investigated. 3. Sols prepared by this dilution method have been investigated as to dispersion of wave length in their angular scattering of visible light and their transmission as a function of wave length. 4. The size, number and charge of the particles of such sols are in the same range as those prepared by the acid decomposition of sodium thiosulfate. 5. The rates of growth of sols prepared by such a dilution method have been investigated. The growth rates obtained have been reproduced from previous theoretical considerations which allow the estimation of the value of the diffusion coefficient of S 8 in alcohol-water and acetone-water mixtures. The value of this diffusion coefficient lies in the range 7-8 × 10 -6 cm. 2/sec. for both media. The application of this method for estimating diffusion coefficients is valid for any colloidal system that is characterized by a small particle size distribution at all stages of its growth. 6. A qualitative explanation is offered for the necessary conditions under which monodispersed colloids may be prepared for both the dilution and acid decomposition of sodium thiosulfate methods.
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An instrument is described and discussed which can determine the magnetophoretic mobility of immunomagnetically labeled cells and paramagnetic particles. Through the use of a well-characterized magnetic energy gradient and a computer algorithm, cell tracking velocimetry, it is possible to obtain the mean and distribution of the magnetophoretic mobility for samples with greater than 10 individuals. 1999 Published by Elsevier Science B.V. All rights reserved.
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The anisotropy and magnetostriction of single crystals of several ferromagnetic materials have been determined experimentally. The materials include the metals iron and nickel, binary alloys of nickel iron, silicon iron, aluminum iron, cobalt nickel, and cobalt iron, ternary alloys of molybdenum nickel iron, nickel cobalt iron, and molybdenum aluminum iron, and magnetite. The effect of the order‐disorder reaction on these properties was measured for several of the alloys. The present data for the nickel iron and silicon iron systems agree well with recently published values. Ordering generally raises the magnetostriction and lowers the anisotropy of the aluminum iron alloys near the Fe 3 Al composition. The first anisotropy constant, K 1 , for the cobalt nickel system as derived from torque curves is similar to old data derived from magnetization curves. However, K 1 for cobalt iron (30, 35, and 45% cobalt) appears to be considerably larger than previously reported. In general, the addition of cobalt to nickel and to iron changes the magnetostriction constants (λ 100 and λ 111 ) toward large positive values. Thus, λ 100 increases to 100×10<sup>-6</sup> for 50% cobalt nickel and to 130×10<sup>-6</sup> for 45% cobalt iron; λ 111 increases to 30×10<sup>-6</sup> for 45% cobalt iron but remains approximately constant for the cobalt nickel alloys.
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