Efficient in situ growth of platinum nanoclusters on the surface of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> for the detection of latent fingermarks

Hydrophobic Fe₃O₄ nanoparticles were modified with polyethyleneimine (PEI) to obtain hydrophilic Fe₃O₄ nanoparticles. By reducing the content of H₂PtCl₆ solution by using l-ascorbic acid (AA) as a reductive agent, fluorescent platinum nanoclusters (Pt NCs) were incubated into the PEI-modified Fe₃O₄ nanoparticles. The prepared Fe₃O₄@Pt NCs microspheres possessed a uniform size, improved monodispersity, high magnetization (40.8 emu/g) and high fluorescence quantum yield (9.0%). Moreover, compared to the reported methods, this method demonstrated that the incubation of Pt NCs on the surface of PEI-Fe₃O₄ was more convenient and needed less reaction time (about 10 min). The experimental results showed that latent fingermarks developing with Fe₃O₄@Pt NCs powder exhibit excellent ridge details. The Fe₃O₄@Pt NCs with superparamagnetism and excellent fluorescence showed great potential in forensic science.     

Fabrication and characterization of uniform Fe3O4 octahedral micro-crystals

Uniform Fe₃O₄ octahedral microcrystals with perfect appearance have been successfully synthesized by a Triton X100-assisted polyol process. During the polyols process for the preparation of Fe₃O₄ octahedra, the introduction of Triton X100 decreases significantly the needed concentration of NaOH. The results show that Fe₃O₄ octahedra are composed of eight triangular sheets, which are equilateral triangles. The edge size of Fe₃O₄ octahedron is about 4 μm. The magnetic properties of Fe₃O₄ octahedral particles were evaluated on a SQUID magnetometer at room temperature. The value of saturation magnetization for Fe₃O₄ octahedra is 90 emu/g, which is close to the value of bulk magnetite. The remnant magnetization and coercive force of Fe₃O₄ octahedra are considerably low, which are rare for the Fe₃O₄ particles with the size scale of micrometers. The Fe₃O₄ octahedral microcrystals show high saturation magnetizations and very low coercivities.     

Synthesis and properties of Fe/Fe3O4 nanocomposites coated with ZnS

Multifunctional Fe/Fe₃O₄@ZnS nanocomposites were synthesized by hydrothermal method, with Fe/Fe₃O₄ doped Co ion as the magnetic core and ZnS as the luminescent shell. The morphology, structure, luminescent and magnetic properties of the nanocomposites were investigated by XRD, FESEM, photoluminescence PL and VSM. The maximum emission peak and special saturation magnetization Ms of the nanocomposites are at 467 nm and 78.6 emu/g, respectively. For the nanocomposites, it is shown that there are both better magnetic behavior and fluorescence properties.     

Synthesis and characterization of Fe- and Co-based ferrite nanoparticles and study of the T 1 and T 2 relaxivity of chitosan-coated particles

In pursuit of newer and more effective contrast agents for magnetic resonance imaging, we report in this article the use of biocompatible chitosan-coated ferrite nanoparticles of different kinds with a view to determine their potential applications as the contrast agents in the field of nuclear magnetic resonance. The single-phase ferrite particles were synthesized by chemical co-precipitation (CoFe₂O₄ and Fe₃O₄) and by applying ultrasonic vibration (CoFe₂O₄ and Co_0.8Zn_0.2Fe₂O₄). Although magnetic anisotropy of CoFe₂O₄ nanoparticle leads to finite coercivity even for nanoensembles, it has been reduced significantly to a minimum level by applying ultrasonic vibration. Fe₃O₄ synthesized by chemical co-precipitation yielded particles which already possess negligible coercivity and remanence. Substitution of Co by Zn in CoFe₂O₄ increases the magnetization significantly with a small increase in coercivity and remanence. Particles synthesized by the application of ultrasonic vibration leads to the higher values of T ₂ relaxivities than by chemical coprecipitation. We report that the T ₂ relaxivities of these particles are of two orders of magnitude higher than corresponding T ₁ relaxivities. Thus, these particles are evidently suitable as contrast agent for T ₂ weighted MR images.     

Effect of Mg Substitution on Room Temperature Dielectric and Magnetic Properties of Sr-Doped Bismuth Ferrite

Mg-co-substituted BiFeO₃ was synthesized. We investigated the structure and multiferroic properties of Sr- and Mg-co-substituted bismuth ferrite. The purity and structural changes induced by Mg doping are confirmed by X-ray powder diffraction and Raman spectra. It was found that a small amount of Mg doping leads to dramatic enhancement in dielectric permittivity, along with an apparent improvement in ferromagnetism .Meanwhile, the co-substitution can effectively reduce the leakage current and increase the dielectric constant. The release of latent magnetization after Sr and Mg co-doping is stronger than the sum of two single dopings, indicating a nonlinear enhancement in Sr and Mg codoping. The ferromagnetism can be ascribed to the creation of unbalanced Fe³⁺ spins and relative long-range coupling mediated by the oxygen vacancies trapped localized electrons. Compared to the pristine bismuth ferrite, Bi_0.95Sr_0.05Fe_0.9Mg_0.1O₃ exhibits more than fivefold improved magnetization with simultaneously improved electrical properties demonstrating the possibility of co-doped BiFeO₃ for practical applications.     

Synthesis, Structural and Magnetic Properties of Polypyrrole Coated Ni0.2Ca0.8Fe2O4 Nanocomposite

The nanoparticles of spinel ferrites having composition Ni_0.2Ca_0.8Fe₂O₄ were synthesized by an advanced sol-gel method and subsequently coated with intrinsically conducting polypyrrole (PPy) by chemical oxidative polymerization of the corresponding monomer (pyrrole) using ammonium peroxodisulphate as oxidant. The X-ray diffraction and TEM measurements were obtained to understand the crystalline structure, size and morphology of evolution of the samples. The dc electrical investigation revealed that at room temperature the surface conductivity increased from 2.8×10^?5 S?cm^?1 to 1.5×10^?3 S?cm^?1 on polymerization. M?ssbauer investigations revealed that the polymerization causes migration of Fe³⁺ ions from A to B site, resulting to the enhancement of the observed hyperfine field. In agreement with this, the dc magnetization measurements performed on VSM revealed an enhancement in saturation magnetization in the M?CH curves on polymerization. The value of blocking temperature (T _B) is found to have credibly increased from 110 K to 130 K, which confirms the increase in crystallite size after polymerization.     

Hydrothermal synthesis and characterization of single-crystalline Fe3O4 nanowires with high aspect ratio and uniformity

Uniform, ultra-thin, single-crystalline Fe₃O₄ nanowires with narrow diameter distribution centered at 15 nm and length up to several microns, were synthesized by a simple hydrothermal route with the assistance of polyethylene glycol (PEG) 400. The morphologies and structure of the obtained nanowires were examined by means of X-ray diffraction (XRD), Mössbauer spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The effect of PEG content and molecular weight on the yield and morphology of Fe₃O₄ nanowires was investigated. Saturation magnetization of Fe₃O₄ nanowires was determined to be 23.0 emu/g, which is distinctly lower than that of Fe₃O₄ nanoparticles.     

Ferroelectric and magnetic studies on unpoled Poly (vinylidine Fluoride)/Fe3O4 magnetoelectric nanocomposite structures

The fabrication of flexible Poly (vinylidine Fluoride)/Fe₃O₄ magnetoelectric nanocomposite films with different weight fractions of Fe₃O₄ nanoparticles is explained in this paper. The effects of nano Fe₃O₄ content on the structural, chemical, thermal, and magnetoelectric properties of PVDF matrix are discussed. XRD and FTIR results reveal the interaction between the filler and the matrix and also they suggest that the β phase contribution can be significantly controlled by the inclusion of nano Fe₃O₄. Thermal stability and melting point behavior of the composite films are investigated through TG/DTA. The existence of ferrimagnetism and ferroelectric properties in the films are proved through the magnetization and polarization studies. The hysteresis loops show the largest polarization and magnetization values at 0.14 wt% of Fe₃O₄. Also, the dependence of ferroelectric polarization on temperature is investigated and reported.     

Synthesis and characterization of Piperidine-4-carboxylic acid functionalized Fe3O4 nanoparticles as a magnetic catalyst for Knoevenagel reaction

Piperidine-4-carboxylic acid (PPCA) functionalized Fe₃O₄ nanoparticles as a novel organic–inorganic hybrid heterogeneous catalyst was fabricated and characterized by XRD, FT-IR, TGA, TEM and VSM techniques. Composition was determined as Fe₃O₄, while particles were observed to have spherical morphology. Size estimations using X-ray line profile fitting (10 nm), TEM (11 nm) and magnetization fitting (9 nm) agree well, revealing nearly single crystalline character of Fe₃O₄ nanoparticles. Magnetization measurements reveal that PPCA functionalized Fe₃O₄ NPs have superparamagnetic features, namely immeasurable coercivity and absence of saturation. Small coercivity is established at low temperatures. The catalytic activity of Fe₃O₄–PPCA was probed through one-pot synthesis of nitro alkenes through Knoevenagel reaction in CH₂Cl₂ at room temperature. The heterogeneous catalyst showed very high conversion rates (97%) and could be recovered easily and reused many times without significant loss of its catalytic activity.     

Effect of Carbon Shell on the Structural and Magnetic Properties of Fe3O4 Superparamagnetic Nanoparticles

Carbon-encapsulated iron oxides (Fe₃O₄/C) with a core/shell structure have been successfully synthesized by using a simple two-step hydrothermal method at 180 ^°C. Fe₃O₄ core nanoparticles were prepared by coprecipitation under two conditions. Synthesized nanoparticles were characterized by transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. TEM images and FTIR results prove that carbon coated iron oxide is formed and the estimated size for most of them is below 11 nm, which was consistent with the XRD result. The Williamson–Hall (W–H) method has been used to calculate crystallite sizes and lattice strain based on the peak broadening of the Fe₃O₄ and Fe₃O₄/C nanoparticles. The results of VSM imply that the Fe₃O₄ core and core–shell nanoparticles are superparamagnetic. The saturation magnetization of Fe₃O₄ and Fe₃O₄/C are 49 emu/gr and 40 emu/gr, respectively. The magnetic behaviors reveal that the amorphous carbon shell can decrease the saturation magnetization of Fe₃O₄ nanoparticles due to core–shell interface effects and shielding.     

Facile synthesis of water-soluble and superparamagnetic Fe3O4 dots through a polyol-hydrolysis route

Monodisperse Fe₃O₄ dots with a mean size of about 2.3 nm were successfully synthesized via a polyol-hydrolysis route without adding any dispersant. Inorganic iron nitrate was used as the metal source and triethylene glycol (TEG) was used as the polyol solvent. The Fe₃O₄ dots were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selective area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, N₂ adsorption–desorption, and magnetization measurements. The as-synthesized Fe₃O₄ dots can not only be coagulated from the polyol by ethanol and acetone, but also easily redispersed in water by ultrasonication, resulting in a clear Tyndall effect. The obtained Fe₃O₄ dots exhibited superparamagnetism at room temperature and the saturation magnetization is much lower than those reported in previous works. The formation mechanism of the Fe₃O₄ dots was proposed to be the hydrolysis of iron nitrates and subsequent dehydration and partial reduction of Fe³⁺ to Fe²⁺ at elevated temperatures in TEG.     

Synthesis of phase pure iron oxide polymorphs thin films and their enhanced magnetic properties

The α-Fe₂O₃ thin film was prepared on liquid–vapor interface at room temperature by a facile and cost effective method, which was converted to Fe₃O₄ and γ-Fe₂O₃ films by reduction and oxidation process. The morphological and structural characterizations reveal the average crystallites size in α-Fe₂O₃, Fe₃O₄ and γ-Fe₂O₃ films 12.8, 9.2 and 19 nm with rms roughness 4.35, 4.60 and 8.21 nm, respectively. From magnetic measurements, the α-Fe₂O₃ thin film shows a room temperature super-paramagnetic behavior with saturation magnetization 18 emu/cm³, while Fe₃O₄ and γ-Fe₂O₃ thin films exhibit ferrimagnetic behavior with saturation magnetization values 414.5 and 148 emu/cm³, respectively. A significantly higher value of saturation magnetization is observed in α-Fe₂O₃ film, which is trusted due to the uncompensated surface spins in the film. The converted Fe₃O₄ film also shows enhanced saturation magnetization due to the reduction in antiphase boundaries, whereas the magnetization in γ-Fe₂O₃ film decreases comparatively. The magnetic property of the γ-Fe₂O₃ is explained on the basis of the Fe³⁺ ions vacancy at the octahedral position in its structure.     

Magnetic nanoparticles coated with anacardic acid derived from cashew nut shell liquid

Magnetic nanoparticles functionalized with biomolecules have received special attention due to their various biomedical applications, such as drug delivery and magnetic hyperthermia treatment for cancer. In this study, we present the synthesis and characterization of new nanoparticles coated with anacardic acid derived from cashew nut shell liquid. The results showed that Fe₃O₄ nanoparticles coated with anacardic acid (AA-MAG) have superparamagnetic behavior and the magnetization is almost equal when compared with the pure Fe₃O₄. This coating provides stability by preventing the aggregation nanoparticles without losing its magnetization potential. The AA-MAG demonstrates excellent and fast magneto-temperature response which can be used as high-performance hyperthermia agents.     

Studies of the magnetic field intensity on the synthesis of chitosan-coated magnetite nanocomposites by co-precipitation method

Chitosan-coated magnetite nanocomposites (Fe₃O₄/CS) were prepared under different external magnetic field by co-precipitation method. The effects of the magnetic field intensity on phase composition, morphology and magnetic properties of the Fe₃O₄/CS nanocomposites were investigated by X-ray diffractometer (XRD), Fourier transform infrared analysis (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results showed that the intensity of the magnetic field in the co-precipitation reaction process did not result in the phase composition change of the magnetic chitosan but improved the crystallinity of magnetite. The morphology of Fe₃O₄/CS nanocomposites was greatly changed by the magnetic field. It was varied from random spherical particles to chain-like cluster structure and rod-like cluster structure with the magnetic field intensity increased in the synthetic process. The VSM results indicated that all the products had excellent superparamagnetic properties regardless of the presence or the absence of the magnetic field, and the saturation magnetization values of the Fe₃O₄/CS nanocomposites were significantly improved by the magnetic field.     

Synthesis and microwave absorption properties of sandwich-type CNTs/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/RGO composite with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as a bridge

A novel sandwich-type CNTs/Fe₃O₄/RGO composite with Fe₃O₄ as a bridge was successfully prepared through a simple solvent-thermal and ultrasonic method. The structure and morphology of the composite have been characterized by Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. This new structure can effectively prevent the agglomeration of GO and the combination of CNTs/Fe₃O₄ and RGO shows a strong reflection loss (R_L) (?50 dB) at 8.7 GHz with absorber thickness of 2.5 mm. Moreover, compared with CNTs/Fe₃O₄/GO composite, it is found that the thermal treating process is beneficial to enhance the microwave absorption properties, which may be attributed to high conductivity of RGO. On this basis, the microwave absorbing mechanism is systematically discussed. All the data show that the CNTs/Fe₃O₄/RGO composite exhibits excellent microwave absorption properties with light density and is expected to have potential applications in microwave absorption.     

Rational Design of Multifunctional Fe@γ‐Fe2O3@H‐TiO2 Nanocomposites with Enhanced Magnetic and Photoconversion Effects for Wide Applications: From Photocatalysis to Imaging‐Guided Photothermal Cancer Therapy

Titanium dioxide (TiO₂) has been widely investigated and used in many areas due to its high refractive index and ultraviolet light absorption, but the lack of absorption in the visible–near infrared (Vis–NIR) region limits its application. Herein, multifunctional Fe@γ‐Fe₂O₃@H‐TiO₂ nanocomposites (NCs) with multilayer‐structure are synthesized by one‐step hydrogen reduction, which show remarkably improved magnetic and photoconversion effects as a promising generalists for photocatalysis, bioimaging, and photothermal therapy (PTT). Hydrogenation is used to turn white TiO₂ in to hydrogenated TiO₂ (H‐TiO₂), thus improving the absorption in the Vis–NIR region. Based on the excellent solar‐driven photocatalytic activities of the H‐TiO₂ shell, the Fe@γ‐Fe₂O₃ magnetic core is introduced to make it convenient for separating and recovering the catalytic agents. More importantly, Fe@γ‐Fe₂O₃@H‐TiO₂ NCs show enhanced photothermal conversion efficiency due to more circuit loops for electron transitions between H‐TiO₂ and γ‐Fe₂O₃, and the electronic structures of Fe@γ‐Fe₂O₃@H‐TiO₂ NCs are calculated using the Vienna ab initio simulation package based on the density functional theory to account for the results. The reported core–shell NCs can serve as an NIR‐responsive photothermal agent for magnetic‐targeted photothermal therapy and as a multimodal imaging probe for cancer including infrared photothermal imaging, magnetic resonance imaging, and photoacoustic imaging.     

Controllable synthesis and magnetic property of Fe/Fe3O4 polyhedron synthesized by solvothermal method

Fe/Fe₃O₄ nano-cubes and nano-octahedrons have been successfully synthesized by employing a facile solvothermal method at 180?°C in the presence of ethylene glycol (EG). Well-defined assembly of uniform Fe/Fe₃O₄ with an average size of 400?nm could be obtained without a size-selection process. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy were used to characterize the structure and morphology of the products. The magnetic properties of Fe/Fe₃O₄ nanocomposite were measured by using a vibrating sample magnetometer. The result of magnetic characterization reveals that the magnetic polyhedrons exhibit a ferromagnetic behavior and possess high saturation magnetization. It is expected that these magnetic polyhedron with uniform size would have potential applications in recording media and electrode materials.     

Mechanosynthesis and magnetic characterization of nanocrystalline manganese ferrites

Manganese ferrites, MnFe₂O_4±δ, synthesized via mechanosynthesis from different manganese sources, MnO, Mn₂O₃ and MnO₂, and mixed with Fe₂O₃, were studied. XRD, SEM and magnetometry were used to characterize the synthesized powders. The MnFe₂O₄ spinel phase appeared after 12 h of milling when MnO and MnO₂ mixed with Fe₂O₃ were used as the precursors and showed the maximum saturation magnetization value (49.77 emu/g). Manganese ferrite did not form when MnO₂ was used. Manganese ferrite obtained from Mn₂O₃ showed the lowest saturation magnetization value. An increase in the milling time promoted the increase in the saturation magnetization values.     

Synthesis and magnetic performance of polyaniline/Mn–Zn ferrite nanocomposites with intrinsic conductivity

A reverse microemulsion route was employed to synthesize the electromagnetic functionalized polyaniline/Mn_0.6Zn_0.4Fe₂O₄ nanocomposites (PANI/MZFO NCs) using SDS/water/cyclohexane/n-pentanol microemulsion. The structure and morphology of obtained products were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, and transmission electron microscopy (TEM). The resulting nanocomposites exhibited a superparamagnetic behavior. The conductivity of MZFO nanoparticles was improved after coating with PANI. The probable formation mechanism of PANI/MZFO NCs was proposed. The prepared nanocomposites may have potential applications in magnetoelectric device.     

Synthesis of flexible magnetic nanohybrid based on bacterial cellulose under ultrasonic irradiation

Flexible magnetic membrane based on bacterial cellulose (BC) was successfully prepared by in-situ synthesis of the Fe₃O₄ nanoparticles under different conditions and its properties were characterized. The results demonstrated that the Fe₃O₄ nanoparticles coated with PEG were well homogeneously dispersed in the BC matrix under ultrasonic irradiation with the saturation magnetization of 40.58 emu/g. Besides that, the membranes exhibited the striking flexibility and mechanical properties. This study provided a green and facile method to inhibit magnetic nanoparticle aggregation without compromising the mechanical properties of the nanocomposites. Magnetically responsive BC membrane would have potential applications in electronic actuators, information storage, electromagnetic shielding coating and anti-counterfeit.