Magnetic and magneto-optical properties of Fe3O4 nanoparticles modified with Ag
TL;DR: In this paper, the effect of Ag inclusions on magnetic properties and magnetic circular dichroism (MCD) of Fe3O4 nanoparticles (NPs) in the mixed system of Fe 3O4 and Ag NPs in dependence on the relative concentration of the components is presented.
About: This article is published in Journal of Magnetism and Magnetic Materials.The article was published on 2020-01-01. It has received 19 citations till now. The article focuses on the topics: Superparamagnetism & Magnetic circular dichroism.
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TL;DR: In this paper, the authors applied magnetic nanoparticles (MNPs) and silver-loaded magnet nanoparticles(Ag-MNPs), respectively, in the advanced treatment and disinfection of the secondary effluent from a municipal WWTP.
38 citations
TL;DR: A review of magnetically recoverable nanocatalysts and their applications in carbon-carbon and carbon-heteroatom bond formation can be found in this paper, where the authors give an insight into the important work done in the field of magnetic recoverable nano-catalysts.
Abstract: Nanocatalysis is an emerging area of research that has attracted much attention over the past few years. It provides the advantages of both homogeneous as well as heterogeneous catalysis in terms of activity, selectivity, efficiency and reusability. Magnetically recoverable nanocatalysts provide a larger surface area for the chemical transformations where the organic groups can be anchored and lead to decrease in the reaction time, increase in the reaction output and improve the atom economy of the chemical reactions. Moreover, magnetic nanocatalysts provide a greener approach towards the chemical transformations and are easily recoverable by the aid of an external magnet for their reusability. This review aims to give an insight into the important work done in the field of magnetically recoverable nanocatalysts and their applications in carbon–carbon and carbon–heteroatom bond formation.
21 citations
TL;DR: In this article, the effect of modified nanomagnetite, Fe3O4 (nM), for biocatalytic support on properties associated with catalytic behavior and potential use in MSFBR is investigated.
Abstract: Magnetically stabilized fluidized bed reactor (MSFBR) is a sustainable and cost-effective biotechnological process, which justifies the increasing search for biocatalytic superparamagnetic supports to enzyme immobilization. This work, investigates the effect of modified nanomagnetite, Fe3O4 (nM), for biocatalytic support on properties associated with catalytic behavior and potential use in MSFBR. The nM was either synthesized and then modified with 3-aminopropyltriethoxysilano (nM-APTES) or stabilized with oleic acid (nM-OA) and later modified with chitosan (nM-OA-Cs). A novel correlation study was carried out about the support dimension effect, enzymatic surface loading and retained activity. Both nM-based supports were morphologically, structurally and magnetically characterized by X-ray diffraction, thermogravimetry, Mossbauer and Fourier-transform Infrared spectroscopies, as well as vibration sample magnetometry, scanning (SEM) and transmission (TEM) electron microscopies. The nM-APTES and nM-OA samples disclosed crystal sizes of 8.07 and 8.69 nm, respectively. From TEM imagens, the average particles sizes were 10.9 nm for nM-APTES and 12.6 nm for nM-OA. The nM-OA-Cs displayed an average particles size of 918.6 μm. These magnetic supports displayed high saturated magnetization, 79.6 emu/g for nM-APTES and 72.7 emu/g for nM-OA. The amano lipase AK enzyme was immobilized on supports activated with glutaraldehyde. The enzyme loading density of nM-APTES-GA-Lip (122 mg/g) with 61% immobilization yield was higher than that of nM-OA-Cs-GA-Lip (46 mg/g) with 23% immobilization yield. The catalytic activity of nM-APTES-GA-Lip (85%) was higher than that of nM-OA-Cs-GA-Lip (46%), which reflected the correlation between enzyme loading efficiency on the magnetic nanosupports and their relative activity, essential to potential use in MSFBR.
7 citations
TL;DR: Core-shell FexOy@C nanoparticles modified with Ag were studied with X-ray diffraction, transmission electron microscopy, energy dispersive elemental mapping, Mössbauer spectroscopy, static magnetic measurements, and optical magnetic circular dichroism (MCD).
Abstract: Core-shell FexOy@C nanoparticles (NPs) modified with Ag were studied with x-ray diffraction, transmission electron microscopy, energy dispersive elemental mapping, Mossbauer spectroscopy, static magnetic measurements, and optical magnetic circular dichroism (MCD). FexOy@C NPs synthesized by the pyrolysis process of the mixture of Fe(NO3)3 · 9H2O with oleylamine and oleic acid were added to a heated mixture of oleylamine and AgNO3 in different concentrations. The final product was a mixture of iron oxide crystalline NPs in an amorphous carbon shell and Ag crystalline NPs. The iron oxide NPs were presented by two magnetic phases with extremely close crystal structures: Fe3O4 and γ-Fe2O3. Ag is shown to form crystalline NPs located very close to the iron oxide NPs. An assumption is made about the formation of hybrid FexOy@C-Ag NPs. Correlations were obtained between the Ag concentration in the fabricated samples, their magnetic properties and the MCD spectrum shape. Introducing Ag led to a approximately linear decrease of the NPs saturation magnetization depending upon the Ag concentration, it also resulted into the MCD spectrum shift to the lower light wave energies. MCD was also studied for the Fe3O4@C NPs synthesized earlier with the same one-step process using different heat treatment temperatures, and MCD spectra were compared for two series of NPs. A possible contribution of the surface plasmon excitation in Ag NPs to the MCD spectrum of the FexOy@C-Ag NPs is discussed.
7 citations
References
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TL;DR: This work is able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size-sorting process, and the particle size could be controlled simply by varying the experimental conditions.
Abstract: The development of nanocrystals has been intensively pursued, not only for their fundamental scientific interest, but also for many technological applications. The synthesis of monodisperse nanocrystals (size variation <5%) is of key importance, because the properties of these nanocrystals depend strongly on their dimensions. For example, the colour sharpness of semiconductor nanocrystal-based optical devices is strongly dependent on the uniformity of the nanocrystals, and monodisperse magnetic nanocrystals are critical for the next-generation multi-terabit magnetic storage media. For these monodisperse nanocrystals to be used, an economical mass-production method needs to be developed. Unfortunately, however, in most syntheses reported so far, only sub-gram quantities of monodisperse nanocrystals were produced. Uniform-sized nanocrystals of CdSe (refs 10,11) and Au (refs 12,13) have been produced using colloidal chemical synthetic procedures. In addition, monodisperse magnetic nanocrystals such as Fe (refs 14,15), Co (refs 16-18), gamma-Fe(2)O(3) (refs 19,20), and Fe(3)O(4) (refs 21,22) have been synthesized by using various synthetic methods. Here, we report on the ultra-large-scale synthesis of monodisperse nanocrystals using inexpensive and non-toxic metal salts as reactants. We were able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size-sorting process. Moreover, the particle size could be controlled simply by varying the experimental conditions. The current synthetic procedure is very general and nanocrystals of many transition metal oxides were successfully synthesized using a very similar procedure.
3,704 citations
TL;DR: In this article, a review of the most relevant finite-size and surface effects in the magnetic and transport properties of magnetic fine particles and granular solids is presented, where the stability of the particle magnetization, superparamagnetic regime and the magnetic relaxation are discussed.
Abstract: Some of the most relevant finite-size and surface effects in the magnetic and transport properties of magnetic fine particles and granular solids are reviewed. The stability of the particle magnetization, superparamagnetic regime and the magnetic relaxation are discussed. New phenomena appearing due to interparticle interactions, such as the collective state and non-equilibrium dynamics, are presented. Surface anisotropy and disorder, spin-wave excitations, as well as the enhancements of the coercive field and particle magnetization are also reviewed. The competition of surface and finite-size effects to settle the magnetic behaviour is addressed. Finally, two of the most relevant phenomena in the transport properties of granular solids are summarized namely, giant magnetoresistance in granular heterogeneous alloys and Coulomb gap in insulating granular solids.
1,083 citations
TL;DR: In this article, a reproducible and simple strategy using generic chemicals is introduced for controlling the size, shape, and size distribution of oxide nanocrystals, which is based on pyrolysis of metal fatty acid salts, the most common metal compounds compatible with nonaqueous solutions.
Abstract: A general, reproducible, and simple strategy using generic chemicals is introduced for controlling the size, shape, and size distribution of oxide nanocrystals. The reaction system was generally composed of the metal fatty acid salts, the corresponding fatty acids, and a hydrocarbon solvent. The method is based on the pyrolysis of metal fatty acid salts, the most common metal compounds compatible with nonaqueous solutions. Synthesis of nearly monodisperse Fe3O4 nanocrystals in a large size range (3−50 nm) was developed as the model system. The method was further applied for the growth of oxide nanocrystals of the other magnetic metals in the fourth rowCr2O3, MnO, Co3O4, and NiO nanocrystals. The size and shape control of the nanocrystals were achieved by varying the reactivity and concentration of the precursors. The reactivity was tuned by changing the chain length and concentration of the ligands, the fatty acids. Alcohols or primary amines could be used as the activation reagents when a given metal fat...
818 citations
TL;DR: In this paper, a detailed x-ray study of a large number of oxides having a spinel structure was carried out, and it was established whether they crystallize in the ''normal'' spinel-type structure, XY2O4, or in the ``inversed'' type of structure, Y(XY)O4.
Abstract: By means of a detailed x‐ray study of a large number of oxides having a spinel structure, it has been established whether they crystallize in the ``normal'' spinel‐type structure, XY2O4, or in the ``inversed'' type of structure, Y(XY)O4, discovered by Barth and Posnjak. Certain rules can be derived which are also applicable to more complicated spinels or to solid solutions of different spinel oxides. Madelung constants have been calculated for different spinel types in order to investigate their stability on the basis of an ionic concept of the chemical bond (Born's lattice theory). The experimental results are only partially explainable on this basis. All exceptions to the electrostatic principles can be understood by assuming that Fe3+, Ga3+, In3+, Zn2+, and Cd2+ favor a configuration having the coordination number 4, because of a considerable covalent contribution to the chemical bond for that configuration.
732 citations
TL;DR: In this paper, the relationship between the electronic conductivity of certain spinels and the arrangement of the cations in the crystal structure was studied, and it was shown that the activation energy of the spinels is lowest for those cases in which the electrons can travel along the Fe of the 16-fold position.
Abstract: The relations between the electronic conductivity of certain spinels and the arrangement of the cations in the crystal structure (see preceding paper) are studied. Several arguments favor the assumption that Fe3O4 contains both divalent and trivalent iron in the 16‐fold position. The transition point in the neighborhood of liquid‐air temperature is probably associated with an increased degree of order at low temperature in the distribution of the 8 electrons between the 16 Fe‐lattice points per unit cell. The considerably increased conductivity below the transition points shows tetragonal anisotropy when the crystal is cooled in a magnetic field. The possible distributions of the electrons in the crystal at low temperature are discussed. In more complicated spinels, containing other metal atoms as well as iron in both the divalent and the trivalent state, the electronic interchange is more or less inhibited by the foreign metal atoms. The higher values of their resistance in comparison to that of Fe3O4 can be roughly described by an increased activation energy. The investigation of a number of substances with different arrangements of the cations shows that the activation energy (and therefore the electrical resistance) is lowest for those cases in which the electrons can travel, as in Fe3O4, along the Fe of the 16‐fold position.
569 citations