Ferrite Nanocrystals Research Articles

Correction: Truncated hexagonal bi-pyramidal gallium ferrite nanocrystals: integration of structural details with visible-light photo-activity and self-cleaning properties

Correction for ‘Truncated hexagonal bi-pyramidal gallium ferrite nanocrystals: integration of structural details with visible-light photo-activity and self-cleaning properties’ by Monali Mishra et al., J. Mater. Chem. A, 2018, DOI: 10.1039/c8ta02749h.

Effect of Nd Substitution on Properties of Multiferroic Bismuth Ferrite Synthesized by Sol-Gel Auto-combustion Method

In this work, pure and Nd-doped bismuth ferrite nanocrystals with the general formula of Bi1−x Nd x FeO3 (x = 0, 0.05, 0.1, 0.15, 0.2) were synthesized via the sol-gel auto-combustion method at two different calcination temperatures (550 and 650∘C). Phase analysis and investigating structural, thermal, and magnetic properties and measuring the size of nanoparticles have been done by using X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric and differential thermal analysis (TG/DTA), and vibrating sample magnetometry (VSM). For undoped BiFeO3 (BFO), increasing calcination temperature will increase the average size of nanocrystals. On the other hand, the average size of nanoparticles is decreased by increasing the concentration of neodymium in the structure of BFO. By entering neodymium to the structure of bismuth ferrite at the calcination temperature of 550∘C, the ferromagnetic properties decline. However, at 650∘C, ferromagnetic properties are improved which is due to a fall in the number of Fe2+ ions. In this case, by decreasing the Fe2+ ions, remanent and saturation magnetization increase.

The effect of calcination conditions on structural and magnetic behavior of bismuth ferrite synthesized by co-precipitation method

In this paper the effect of calcination conditions on structural properties, particle size, as well as the presence of secondary phases and magnetic characteristics of BiFeO3 nanocrystals have been investigated. Bismuth ferrite nanocrystals were synthesized at room temperature by chemical co-precipitation method. Phase analysis, structural and magnetic features and size of the produced nanopowders were studied via X-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer. The formation of the single phase compounds were confirmed by XRD. By analyzing the results from different measurements it was shown that products have the perovskite phase with space group R3C and the average nanocrystal size around 50 nm. The structural studies showed that calcination temperature and duration has crucial roles in disappearing impurities and secondary phases. Magnetic results in an applied field at room temperature indicated that the nanoparticles of bismuth ferrite have weak ferromagnetic order.

Construction of molybdenum dioxide nanosheets coated on the surface of nickel ferrite nanocrystals with ultrahigh specific capacity for hybrid supercapacitor

Recently, nickel ferrite with high theoretical capacity over the other metal oxide has been applied as electrode material for batteries and supercapacitors. However, owing to the serious aggregation and low specific surface area, the electrochemical performance of nickel ferrite (NiFe2O4) should be in urgent need of improvement. Here, we report the synthesis of unique molybdenum dioxide (MoO2) and nickel ferrite composite (MoO2/NiFe2O4) material via a facile strategy for the first time. The composite material presents a nanosheets-nanocrystals heterostructure. When evaluated as an electrode for hybrid supercapacitor in an alkaline solution, the MoO2/NiFe2O4 composite material presents a greatly enhanced specific capacity (2105 mA h/g at 4 A/g), which is better than those of individual component and exceeds some of the reported MoO2 and NiFe2O4 based electrodes. The capacity retention of MoO2/NiFe2O4 composite is about 81.1% after 1900 cycles. Such composite material also has great potential in other energy storage and conversion system.

Study of structural, dielectric and magnetic properties of Li0.5+0.5xFe2.5–1.5xPbxO4 ferrite nano-crystals synthesized by citrate gel method

The effect of Pb substitution on the structure, dielectric, impedance and magnetic properties of Li0.5+0.5xFe2.5–1.5xPbxO4 ferrite nano-crystals prepared by citrate gel method has been investigated. X-ray diffraction analysis confirmed the formation of cubic spinel phase and broadness of reflection peaks indicates the formation of smaller sized crystallites. The average crystallite size was observed to increase from 21.3 to 26.1 nm on increasing Pb substitution in Li0.5+0.5xFe2.5–1.5xPbxO4 ferrite. The surface analysis of the samples was performed using scanning electron microscopy. An improvement in the microstructure has been obtained on Pb doping. Dielectric and impedance measurements were carried out in the frequency range of 100 Hz–10 MHz. The dielectric properties of Li0.5+0.5xFe2.5–1.5xPbxO4 ferrite samples were improved much by the substitution of Pb ions. The low dielectric loss at higher frequencies identifies the potential of these ferrites for high frequency applications. Interestingly, a very large value for dielectric constant of the order of 107 has been obtained on Pb doping. The impedance spectroscopy technique was used to study the effect of grain and grain boundary on the electrical properties of the material. From the present investigation on Li0.5+0.5xFe2.5–1.5xPbxO4 ferrite, one can conclude that the substitution of Pb4+ ions play an important role to modify the magnetic and electrical properties of lithium ferrite desired for microwave devices and power applications.

High-index faceted nickel ferrite nanocrystals encapsulated by graphene with high performance for lithium-ion batteries

Uniform octahedral nickel ferrite nanocrystals wrapped by graphene (GNFO) have been synthesized and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analysis techniques, which reveal that the NiFe2O4 nanocrystals are enclosed by high index (111) facets and encapsulated by reduced graphene oxide sheets. When applied as anode electrodes for lithium ion batteries, GNFO nanocomposites present excellent electrochemical performances. The electrode maintains 1275mAhg−1 after 30 cycles at 0.1Ag−1 and a reversible capacity up to 937mAhg−1 after 250 cycles at 1Ag−1. A prominent rate capability is also obtained and the specific capacity remains 312mAhg−1 at 10.0Ag−1. The superior electrochemical properties could benefit from open surface structure of octahedral NiFe2O4 and synergistic effect between graphene and NiFe2O4, which shows promising applications in lithium-ion storage devices.

Activity Tuning of Cobalt Ferrite Nanoparticles Anchored on N‐Doped Reduced Graphene Oxide as a Potential Oxygen Reduction Electrocatalyst by Zn Substitution in the Spinel Matrix

AbstractDevelopment of highly efficient and durable ORR catalysts by using non‐platinum group metals (such as Co, Fe, Mn, and Zn) is a challenging task in the forward path towards the realization of low‐cost energy devices in the commercial stream. The present work deals with an effective strategy wherein an efficient Pt‐free electrocatalyst for oxygen reduction reaction (ORR) is prepared by stoichiometrically substituting some fraction of Fe with Zn in cobalt ferrite and anchoring these spinel nanoparticles on nitrogen doped reduced graphene oxide (N‐rGO). Zn substitution is found to be significantly altering the ratio of Fe2+/Fe3+ in the cobalt ferrite nanocrystal system with a concomitant promotional influence on its electrocatalytic activity towards ORR. The nanoparticle composition with a Co, Fe and Zn molar ratio of 1.0:1.7:0.3, represented by the formula CoFe1.7Zn0.3O4(CFZn(0.3)), supported over N‐rGO has shown 10 mV and 20 mV positive shift in the onset and half‐wave potentials, respectively, for ORR in 0.1 M KOH in comparison to the nanoparticles of CoFe2O4 supported over N‐rGO (CF/N‐rGO). The optimum Zn substitution is found to be narrowing down the difference with the state‐of‐the‐art Pt/C for ORR by 100 and 110 mV in terms of the onset and half‐wave potentials, respectively. Most significantly, the homemade catalyst is found to be clearly outperforming the Pt catalyst in terms of the limiting current density and electrochemical durability.

Synthesis of calcium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

In this study, we prepared calcium ferrite (CaFe2O4) nanocrystal clusters by a solvothermal method and evaluated their application potential in magnetorheological (MR) fluid. The morphology, composition, microstructure and magnetic properties of the CaFe2O4 nanocrystal clusters were investigated in detail. The as-prepared CaFe2O4-based MR fluid showed typical Bingham fluid behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with carbonyl iron (CI) particles, the MR fluid based on CaFe2O4 nanocrystal clusters showed enhanced sedimentation stability, which can be mainly due to the reduced density mismatch between dispersed phase and carrier fluid. In conclusion, the as-prepared CaFe2O4 nanocrystal clusters are considered as a promising candidate for high-performance MR fluid.

Synthesis and characterisation of doxorubicin-loaded functionalised cobalt ferrite nanoparticles and their <i>in vitro</i> anti-tumour activity under an AC-magnetic field

Purpose: To synthesise and evaluate the anti-tumour properties of doxorubicin-loaded xanthan gumfunctionalised cobalt ferrite nanoparticles (CoFe 2 O 4 .NPs@XG-Doxo) under an AC-magnetic field. Methods: Multidimensional magnetic cobalt ferrite (CoFe 2 O 4 ) nanoparticles (NPs) were synthesised by a co-precipitation method. The synthesised cobalt ferrite nanoparticles (CFNPs) were functionalised with xanthine gum (XG) and subsequently characterised by Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and contact angle studies. Vibrating sample magnetometry (VSM) was used for magnetic measurements of the native and XG-coated CFNPs. The microstructural morphology of the uncoated and XG-coated CFNPs was established using scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic light scattering (DLS) studies. Finally, the doxorubicin release profile of the drug-loaded functionalised CFNPs was evaluated using an oscillating magnetic field (OMF) apparatus in the presence of an externally applied magnetic field. Results: XG coating decreased the contact angle of the native CFNPs from 92° to 40°, which indicates that it modified the CFNP surface from hydrophobic to hydrophilic. VSM analysis demonstrated that CoFe 2 O 4 .NPs@XG also retained the magnetic characteristics of the bare cobalt ferrite nanocrystals, endorsing its application as a promising magnetic nanovector (MNV). The synthesised CoFe 2 O 4 .NPs@XG-Doxo exhibited significantly higher controlled discharge of doxorubicin at acidic pH (5.0) than at neutral pH (7.4). In vitro analysis revealed the remarkable lower systematic toxicity of XGcoated CoFe 2 O 4 .NPs compared with uncoated CFNPs against Chinese hamster ovary (CHO) and Huh7 cell lines. Conclusion: These results indicate that XG-coated CFNPs are a biocompatible MNV for doxorubicin. Keywords: Cobalt ferrite, Cytotoxicity, Drug delivery, Nanoparticles, Xanthan gum

Effect of ferrite nanocrystals on raman spectra of potassium-aluminaborate glass

Effect of ferrite nanocrystals on raman spectra of potassium-aluminaborate glass

Role of Composition and Size of Cobalt Ferrite Nanocrystals in the Oxygen Evolution Reaction

AbstractSub‐10 nm CoFe2O4 nanoparticles with different sizes and various compositions obtained by (partial) substitution of Co with Ni cations have been synthesized by using a one‐pot method from organic solutions by the decomposition of metal acetylacetonates in the presence of oleylamine. The electrocatalytic activity of CoFe2O4 towards the oxygen evolution reaction (OER) is clearly enhanced with a smaller size (3.1 nm) of the CoFe2O4 nanoparticles (compared with 4.5 and 5.9 nm). In addition, the catalytic activity is improved by partial substitution of Co with Ni, which also leads to a higher degree of inversion of the spinel structure. Theoretical calculations attribute the positive catalytic effect of Ni owing to the lower binding energy differences between adsorbed O and OH compared with pure cobalt or nickel ferrites, resulting in higher OER activity. Co0.5Ni0.5Fe2O4 exhibited a low overpotential of approximately 340 mV at 10 mA cm−2, a smaller Tafel slope of 51 mV dec−1, and stability over 30 h. The unique tunability of these CoFe2O4 nanocrystals provides great potential for their application as an efficient and competitive anode material in the field of electrochemical water splitting as well as for systematic fundamental studies aiming at understanding the correlation of composition and structure with performance in electrocatalysis.

Deformation of a bismuth ferrite nanocrystal imaged by coherent X-ray diffraction

Perovskite materials that contain transition metal-oxides often exhibit multifunctional properties with considerable utility in a device setting. BiFeO3 is a multiferroic perovskite material that exhibits room temperature anti-ferromagnetic and ferroelectric ordering. Optical excitation of BiFeO3 crystals results in an elastic structural deformation of the lattice with a fast response on the pico-second time scale. Here we report on dynamic optical excitation coupled with Bragg coherent X-ray diffraction measurements to investigate the structural properties of BiFeO3 nanoscale crystals. A continuous distortion of the diffraction speckle pattern was observed with increasing illumination. This was attributed to strain resulting from photo-induced lattice deformation.

Controlled Growth of Monodisperse Ferrite Octahedral Nanocrystals for Biomass-Derived Catalytic Applications

Metal/metal oxide nanoparticles with controllable size and shape are of importance to tailor the catalytic performances of metal nanoparticles. However, a facile synthesis of supported monodisperse metal/oxide polyhedra in the absence of capping agents remains a significant challenge, especially at high metal loadings. In this work, a surfactant-free MOF (metal–organic framework) thermolysis strategy is developed for the synthesis of monodisperse ferrite octahedral nanocrystals with uniform composition for the first time. The achievement of our synthesis relies on the use of CO as directing agent that may control the growth rate of specific facets at the solid/gas interface and, subsequently, the shape of the resultant metal oxide nanostructures. As-prepared octahedral ferrite materials exhibited an interesting shape-dependent catalytic performance in 5-hydroxymethylfurfural (HMF) oxidation, achieving significantly improved activity and selectivity, compared to those synthesized under a pure inert atmosph...

In situ synthesis of cobalt ferrites-embedded hollow N-doped carbon as an outstanding catalyst for elimination of organic pollutants

Using polydopamine-metal ions complex as precursor, hollow mesoporous N-doped carbon microspheres encapsulating spinel ferrites nanocrystals (HM-NC/CoFe2O4) were facilely prepared with the aim of creating a novel heterogeneous catalyst for sulfate radical-based oxidation of organic contaminants. The surface morphology, structure and composition of HM-NC/CoFe2O4 catalyst were thoroughly investigated. The applicability of the catalyst was systematically assessed through numerous controlled trials, several operating parameters, as well as different model pollutants by means of peroxymonosulfate (PMS) activation. Outstanding efficiency and excellent reusability were achieved due to the unique structure and composition of HM-NC/CoFe2O4. The HM-NC scaffold with high porosity and surface area not only stabilizes the CoFe2O4 nanoparticles but also greatly facilitates the accessibility and adsorption of substrates to the active sites. In addition, both HM-NC and CoFe2O4 on the material surface can act as active sites. Sulfate radicals and hydroxyl radicals are identified as main active species and a possible enhancement mechanism of catalytic performance is also proposed. Due to the simple synthesis method, low-cost precursors, unique structure and excellent catalytic activity and stability, this novel composite have great potential as new strategic materials for remediation of water pollution.

Hydrothermal synthesis, magnetic properties and characterization of CoFe2O4 nanocrystals

Magnetic cobalt ferrite (CoFe2O4) nanocrystals were synthesized via the hydrothermal method and the crystallite size was measured using Sherrer's equation. Instrumental broadening was a significant parameter for determining crystallite size. The effect of annealing time and calcination on crystallite size and magnetic properties was discussed. It was found that the coercivity was highly dependent on the crystallite size. As the crystallite size increased from 61 to 68.2nm, room temperature coercivity increased from 1488Oe to 1700Oe, while high coercivity (5.2kOe) was achieved at lower temperature (80K). It was found that the presence of hematite could affect the crystallite size after calcination.

Double-layer microwave absorber based on nanocrystalline CoFe2O4and CoFe2O4/PANI multi-core/shell composites

AbstractOrganic-inorganic nano-CoFe2O4/PANI (polyaniline) multi-core/shell composites have been successfully synthesized by chemical oxidative polymerization of aniline. The characterization results showed that the ferrite nanocrystals were efficiently embedded in PANI. The electromagnetic parameters of the composites were measured by a vector network analyser in the frequency range of 2 GHz to 18 GHz. Double-layer absorbers based on the CoFe2O4/PANI composite (matching layer) and calcined CoFe2O4ferrite (absorbing layer) have been designed. The reflection loss of the microwave absorbers of both single layer and double-layer with a total thickness of 2.0 mm and 2.5 mm was calculated according to transmission-line theory. The results indicated that the minimum reflection loss of the CoFe2O4/PANI composite was −19.0 dB at 16.2 GHz at the thickness of 2.0 mm and −23.6 dB at 13.1 GHz at the thickness of 2.5 mm, respectively. The minimum reflection loss for double-layer absorbers reached −28.8 dB at 16.2 GHz at the total thickness of 2.0 mm, and −31.1 dB at 12.8 GHz at the total thickness of 2.5 mm. The absorption bandwidth under −10 dB was 4.2 GHz (13.8 GHz to 18.0 GHz) and 5.5 GHz (10.3 GHz to 15.8 GHz), respectively. The results show that the reflection loss and absorption bandwidth of the double-layer absorbers are obviously enhanced compared to corresponding single layer absorbers.

Solvothermal synthesis, characterization, and magnetorheological study of zinc ferrite nanocrystal clusters

In this study, zinc ferrite (ZnFe2O4) nanocrystal clusters were synthesized successfully with a surfactant-assistant solvothermal method and investigated as a potential magnetorheological material. The morphology, structure, and magnetic properties of the obtained ZnFe2O4 nanocrystal clusters were investigated in detail using a scanning electron microscope, transmission electron microscope, X-ray diffraction, and superconducting quantum interference device. It was found that the ZnFe2O4 nanocrystal clusters showed well-defined shape and homogeneous dispersion with narrow size distribution of 276 nm in diameter. The field-dependent magnetization curve indicated superparamagnetic properties of as-prepared ZnFe2O4 nanocrystal clusters with saturation magnetization ( Ms) of 86.6 emu/g at room temperature. The magnetorheological fluid with 25% particle mass fraction was prepared by ZnFe2O4 nanocrystal clusters, and the corresponding magnetorheological properties were also tested using a Physica MCR301 rheometer fitted with a magnetorheological module. The prepared magnetorheological fluid changed from a liquid-like to a solid-like state under an external magnetic field, suggesting typical Bingham plastic behavior. Compared with conventional carbonyl iron particles, ZnFe2O4 nanocrystal clusters–based magnetorheological fluid showed enhanced sedimentation stability. The obtained ZnFe2O4 nanocrystal clusters are considered as an ideal candidate for magnetorheological fluid with typical magnetorheological effect as well as improved sedimentation stability.

Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

In this study, magnesium ferrite (MgFe2O4) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe2O4 nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe2O4 nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe2O4 nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe2O4 nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.

Selective oxidation of styrene catalyzed by cerium-doped cobalt ferrite nanocrystals with greatly enhanced catalytic performance

The rare earth metal Ce-doped cobalt ferrite samples CexCo1−xFe2O4 (x=0.1, 0.3, 0.5) were prepared by the sol–gel autocombustion route. The as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, ICP–atomic emission spectroscopy, and N2 physisorption. Their catalytic performance was evaluated in oxidation of styrene using hydrogen peroxide (30%) as oxidant. Compared with pristine CoFe2O4, the Ce-doped samples were found to be more efficient catalysts for the oxidation of styrene to benzaldehyde, with greatly enhanced catalytic performance. Especially, when Ce0.3Co0.7Fe2O4 was used as catalyst, 90.3% styrene conversion and 91.5% selectivity for benzaldehyde were obtained at 90°C for 9h reaction. The catalyst can be magnetically separated easily for reuse, and no obvious loss of activity was observed when it was reused in five consecutive runs.

The effects of synthesis conditions on the magnetic properties of zinc ferrite spinel nanoparticles

Zinc ferrite nanocrystals were synthesized from metal chloride precursors via chemical co-precipitation method, using different synthesis conditions. Characterization measurements including X-ray diffraction (XRD), transmission electron microscopy (TEM) and super conductiong quantum device (SQUID) were used to study the influence of precursor's concentration and reaction time on the crystalline structure, average sizes and magnetic properties of zinc ferrite nanoparticles. The transmission images show spherical, homogenous shape and particle size ranging from 16 to 22 nm. DC magnetization (2-300 K) measurements reveal a superparamagnetic behavior for the ZnFe2O4 samples with a blocking temperature in the range of 18-24 K. Our results demonstrate that magnetic properties of magnetic particles can be largely modified by just changing the reaction condition such as concentration and reaction time, which might be a useful way to design novel magnetic materials.