Cobalt Ferrite Nanocrystals Research Articles

Caracterização de nanopartículas de ferrita de cobalto e avaliação de seu efeito tóxico em camundongos experimentais

This study investigated the characterization of cobalt ferrite nanoparticles (CoFe2O4) prepared by the pulsed laser deposition (PLD) method, using various techniques such as energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and in vitro drug release test (IVRT). It also evaluated the toxicity of these nanoparticles on liver, spleen, heart, and kidney tissues using a mouse model. CoFe2O4 nanoparticles were synthesized from an aqueous solution containing 1mg of CoFe2O4 powder dissolved in DMSO and RPMI serum-free media. XRD analysis revealed the characteristic peaks of the spinel lattice of cubic-shaped cobalt ferrite nanocrystals, with an average crystallite size of 12 nm calculated using Scherrer’s formula. SEM and EDX were used to study the surface morphology and chemical compositions, respectively. The in vivo experiments determined the LD50 of CoFe2O4 to be 3000 mg/kg body weight. Administration of CoFe2O4 nanoparticles at a dosage of 75 mg/kg body weight for 14 days did not cause any changes to the histological structure of the tissues in the mouse model, indicating their potential biocompatibility.

Cobalt Ferrite Nanorods Synthesized with a Facile "Green" Method in a Magnetic Field.

We report a new facile method for the synthesis of prolate cobalt ferrite nanoparticles without additional stabilizers, which involves a co-precipitation reaction of Fe3+ and Co2+ ions in a static magnetic field. The magnetic field is demonstrated to be a key factor for the 1D growth of cobalt ferrite nanocrystals in the synthesis. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy are applied to characterize the morphology and structure of the obtained nanoparticles. According to TEM, they represent nanorods with a mean length of 25 nm and a diameter of 3.4 nm that have a monocrystalline structure with characteristic plane spacing of 2.9 Å. XRD and Raman spectroscopy confirm the spinel CoFe2O4 structure of the nanorods. After aging, the synthesized nanorods exhibit maximum saturation magnetization and coercivity equal to 30 emu/g and 0.3 kOe, respectively. Thus, the suggested method is a simple and "green" way to prepare CoFe2O4 nanorods with high aspect ratios and pronounced magnetic properties, which are important for various practical applications, including biomedicine, energy storage, and the preparation of anisotropic magnetic nanocomposites.

Corrigendum: Size‐controlled Cobalt Ferrite Nanocrystals: Magnetically separable Reusable Nanocatalysts for Selective Oxidation of Styrene

Corrigendum: Size‐controlled Cobalt Ferrite Nanocrystals: Magnetically separable Reusable Nanocatalysts for Selective Oxidation of Styrene

Yttrium vanadate coupled with cobalt ferrite nanocrystals for enhanced photocatalytic H2 production under visible light irradiation

Yttrium vanadate (YVO4) nanocrystals are synthesized by a modified sol-gel route followed by coupling with 4.0–16.0 wt% of cobalt ferrite (CoFe2O4) nanoparticles. The synthesized heterostructures were laboured for photocatalytic H2 generation in a water/glycerol system below visible light in the presence of platinum cocatalyst traces. The addition of CoFe2O4 nanoparticles has improved the physicochemical characteristics of YVO4 in terms of light harvesting and photoinduced charge separation. The 12.0 wt% CoFe2O4/YVO4 indicates the narrowest bandgap of 2.5 eV and the highest visible-light activity with a slight reduction of its surface area from 185 to 168 m2 g−1. Moreover, the H2 evolution rate has augmented utilizing this photocatalyst at 2.557 mmol g−1h−1 compared to 0.044 mmol g−1h−1 over the pure YVO4. Furthermore, the dose optimization of 12% CoFe2O4/YVO4 at 2.0 gL−1 has endorsed the photocatalytic generation of H2 to 3.389 mmol g−1h−1 with recyclability of 97% after the fifth cycle.

Interfaceless Exchange Bias in CoFe2O4 Nanocrystals.

Oxidized cobalt ferrite nanocrystals with a modified distribution of the magnetic cations in their spinel structure give place to an unusual exchange-coupled system with a double reversal of the magnetization, exchange bias, and increased coercivity, but without the presence of a clear physical interface that delimits two well-differentiated magnetic phases. More specifically, the partial oxidation of cobalt cations and the formation of Fe vacancies at the surface region entail the formation of a cobalt-rich mixed ferrite spinel, which is strongly pinned by the ferrimagnetic background from the cobalt ferrite lattice. This particular configuration of exchange-biased magnetic behavior, involving two different magnetic phases but without the occurrence of a crystallographically coherent interface, revolutionizes the established concept of exchange bias phenomenology.

Chiral, Magnetic, and Photosensitive Liquid Crystalline Nanocomposites Based on Multifunctional Nanoparticles and Achiral Liquid Crystals.

Nanoparticles serving as a multifunctional and multiaddressable dopant to modify the properties of liquid crystalline matrices are developed by combining cobalt ferrite nanocrystals with organic ligands featuring a robust photosensitive unit and a source of chirality from the natural pool. These nanoparticles provide a stable nanocomposite when dispersed in achiral liquid crystals, giving rise to chiral supramolecular structures that can respond to UV-light illumination, and, at the same time, the formed nanocomposite possesses strong magnetic response. We report on a nanocomposite that shows three additional functionalities (chirality and responsiveness to UV light and magnetic field) upon the introduction of a single dopant into achiral liquid crystals.

Enhanced Fenton-like catalysis for pollutants removal via MOF-derived CoxFe3−xO4 membrane: Oxygen vacancy-mediated mechanism

Traditional batch configuration is not sustainable due to catalyst leaching and ineffective recovery. Herein, a novel membrane-based catalyst with oxygen vacancies is developed, which assembled metal-organic-framework cobalt ferrite nanocrystals (MOF-d CoxFe3−xO4) on polyvinylidene fluoride membrane to activate peroxymonosulfate (PMS) for catalytic degradation of emerging pollutants. MOF-d CoxFe3−xO4 are synthesized by one-step pyrolysis using Co/Fe bimetallic organic frameworks (CoxFe3−x bi-MOF) with tunable cobalt content as a template (x/3−x represented the molar ratio of Co and Fe in MOF). Intriguingly, MOF-d Co1.75Fe1.25O4 membrane exhibits excellent PMS activation efficiency as indicated by 95.12% removal of the probe chemical (bisphenol A) at 0.5 mM PMS (∼100 L m−2 h−1 at the loading of 10 mg), which is significantly higher than the traditional Co1.75Fe1.25O4 suspension system (34.16%). Experimental results show that the membrane has excellent anti-interference ability to anions and dissolved organic matter, and can effectively degrade a variety of emerging pollutants, and its performance is not inhibited by the change of solution pH (3–9) or the long-term (20 h) continuous flow operation. EPR and quenching experiments show that catalytic degradation is the result of the synergistic effect of radicals and non-radicals. The oxygen vacancy-mediated mechanism can explain the formation of active substances, and the formation of 1O2 plays an important role in the degradation of bisphenol A. This study provides a membrane-based strategy for effective and sustainable removal of emerging pollutants.

Eco-friendly green synthesis and characterizations of CoFe2-x AlxO4 nanocrystals: analysis of structural, magnetic, electrical, and dielectric properties

This work reports, thermal, structural, magnetic, electric, and dielectric investigations of the CoFe2-xAlxO4 nanocrystals synthesized through eco-friendly green sol–gel auto-ignition route. X-ray diffractograms exposed the uni-phasic geometry with Fd3m_ $${\text{O}}_{{\text{h}}}^{7}$$ space group. The standard crystallite sizes were found in between 24 and 44 nm, confirming the nano-crystalline dimension. FTIR analysis confirmed the two specific vibrational stretching bands corresponding to the spinel ferrite geometry. The surface topology of ferrite nanocrystals with size distribution was effectively observed from TEM micrographs. The magnetic study at room temperature showed lessening in saturation magnetization with rise in Al3+ concentrations, ascribed to the replacement of Fe3+ ions by paramagnetic Al3+ ions. The M–H loops showed the perfect loop of typical soft ferromagnetic behavior of the produced nano-ferrites. The saturation magnetization, coercivity, and magneto-crystalline anisotropy declines with the upsurge in Al3+ ions which is owing to the non-magnetic contamination in the magnetic matrix. The DC-electrical resistivity was enhanced with growing temperature along with Al3+ content x. The dielectric parameters boosted pointedly with Al3+ substitution and decline exponentially with a rise in frequency in compliance with ‘Koops’ phenomenological theory. All the outcomes show that Al3+ substitution influences the physical characteristics of cobalt ferrite nanocrystals which shows its suitability in various technological applications. The graphical abstract presenting the synthesis reaction, TEM micrograph (along with crystallite size distribution) and M–H plots for CoFe2-xAlxO4 nanocrystals.

Band-gap engineering of tungsten oxide nanoplates by cobalt ferrite co-catalyst for solar water oxidation

Abstract Tungsten oxide exhibits a favourable band gap for photo-electrochemical applications like water splitting and photo oxidation of water pollutants but suffers from its fast recombination of photo generated electrons and holes due to poor electrical conductivity and its hydrogen evolution level being below the conduction band minimum. In this work, we have incorporated cobalt ferrite nanocrystals as co-catalyst in a hydrothermally synthesized tungsten oxide (WO3) photoanode with an aim to arrest the fast recombination process. Characterization of the nanocomposite containing 5 mol% cobalt ferrite by multiple te chniques confirmed formation of monoclinic WO3nanoplate like structures containing stoichiometric CoFe2O4phase whereas optical absorption spectroscopy gave its optical band gap as 2.1 eV. Electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis and linear sweep voltammetry (LSV) were conducted under illuminated (1.5AM G solar simulated light) and dark conditions that revealed a reduction in the onset potential of pristine tungsten oxide photoanode by ~0.25 V as a result of incorporation of 5 mol% cobalt ferrite nanocrystals owing to an efficient electron transfer before recombination. The photocurrent obtained from the composite photoanode was also found to be 10 times higher than that from bare tungsten oxide photoanode suggesting its potential use as anode material for photoelectrochemical water splitting.

Impact of nickel substitution on structure, magneto-optical, electrical and acoustical properties of cobalt ferrite nanoparticles

In this study, we have investigated the impact of nickel substituted cobalt ferrite nanocrystals, which were synthesized by a facile co-precipitation technique. The various physical properties such as structural, electrical, magneto-optical and thermal were studied. These properties were characterized using XRD (X-ray diffraction), FT-IR (Fourier-transform infrared spectroscopy), VSM (vibrating sample magnetometer), UV-visible (Ultraviolet–visible) spectra, LCR (Inductance capacitance resistance) meter and photoacoustic spectrophotometer, respectively. From XRD analysis, single face cubic structure (Fd3m) was determined. It was found that as the nickel substitution increased, the crystallite size (D) was decreased from 17.4 ± 1.7 nm to 6.7 ± 1.2 nm. Various structural parameters such as oxygen positional parameters, bond length and cation distribution were determined. Using FT-IR technique, various types of interionic bonds and the elastic properties with their distribution of ions in the formation of spinel phase was found between 400 and 600 cm−1 for the as-synthesized nanocrystals. The aspect of morphology was determined using TEM (transmission electron microscopy). Surface analysis for the as-synthesized products was found to increase from about 41.8 ± 0.6 m2/g to around 92.7 ± 2.1 m2/g with the increase in concentration of Ni ions. From UV-visible spectrum, empirical relation was calculated which indicates the nature of nano crystallinity of the as-synthesized sample. The electrical properties of the as-synthesized samples were premeditated by utilizing LCR meter; at a function of frequencies (10 Hz −10 MHz) at room temperature (RT) impedance was analyzed. Impedance study confirmed that the as-synthesized sample with major grain boundary contributes to conduction. The product with x = 0.9 shows a low dielectric loss and high dielectric constant and henceforth it can used in electromagnetic devices with high frequency. The hysteresis loop elucidates a steadily decrease in Bohr magneton and saturation magnetization, which indeed exhibited a non-linear conduct, where else we could observe a significant increase of anisotropy constant. The thermal properties such as diffusivity, conductivity and effusivity were determined using photoacoustic spectrophotometer and it was found that highly substituted nano-sample has high thermal stability when compared to the other concentrations.

Synthesis of intracellular cobalt ferrite nanocrystals by extreme acidophilic archaea Ferroplasma thermophilum

Ferroplasma thermophilum, a sort of extreme acidophilic archaea, which can synthesize intracellular cobalt ferrite nanocrystals, is investigated in this study. The nanocrystals were analyzed with ultrathin sections and transmission electron microscope, with the size of 20–60 nm, the number of more than 30 in each cell at average, which indicated that F. thermophilum can synthesize intracellular nanocrystals and also belongs to high-yield nanocrystals-producing strain. Intriguingly, the nanocrystals contain ferrite and cobalt characterized by EDS X-ray analysis, suggesting that both cobalt and ferrite are potentially contributed to the formation of nanocrystals. Moreover, under the different energy source culture conditions of FeSO4 and CuFeS2, the size and the morphology of the nanocrystals are different. It was also found that the higher initial Fe availability leads to an induced synthesis of larger nanocrystals and the lower oxidation-reduction potential (ORP) leads to an induced effect on the synthesis of nanocrystals with abnormal unhomogeneous size, which suggested that the higher initial Fe availability and the lower oxidation-reduction potential lead to a higher uptake efficiency of iron ions of F. thermophilum by iron and ORP gradient culture.

Size‐controlled Cobalt Ferrite Nanocrystals: Magnetically separable Reusable Nanocatalysts for Selective Oxidation of Styrene

AbstractSuperparamagnetic cobalt ferrite (CFO) nanocrystals (NCs) with sizes ∼6 nm and ∼4 nm were synthesized using a facile solvothermal method using fatty acids, lauric acid and stearic acid, as the capping agents. The synthesized nanocrystals were well characterized by XRD, FT‐IR, XPS, SEM and TEM. The formation mechanism was explored and it was shown that the fatty acid was actually chemisorbed as a carboxylate onto the surface of CFO NCs. The experimental results specify that the size and size distribution of the CFO NCs were highly dependent on the length of fatty acid hydrophobic chain. Corresponding changes of the magnetic properties were investigated by measuring magnetization as a function of field and temperature, which suggest that the CFO NCs were superparamagnetic in nature. The catalytic properties for the oxidation of styrene in organic medium were examined by using the synthesized CFO NCs with sizes ∼6 nm and ∼4 nm. The synthesized CFO NCs, well dispersible in organic media, were demonstrated to be highly catalytically active, reached 100% conversion of styrene in 12 h with ∼77% and ∼82% selectivity for styrene oxide respectively. The magnetic CFO nanocatalysts were easily separated and recovered from the reaction medium by an external magnet, and reused for several cycles without losing catalytic selectivity for styrene oxide.

Synthesis, structure and magnetic properties of multipod-shaped cobalt ferrite nanocrystals

A non-aqueous sol–gel route followed by oriented attachment to make multi-pod CoFe2O4 nanocrystals showing large room temperature saturation magnetization.

MOF-templated synthesis of CoFe2O4 nanocrystals and its coupling with peroxymonosulfate for degradation of bisphenol A

Porous magnetic cobalt ferrite nanocrystals (CoFe2O4 NC) are synthesized via a one-step process by using bimetal-organic frameworks (Co/Fe bi-MOFs) as a template for the catalytic degradation of bisphenol A (BPA). The properties of the prepared catalyst are evidenced by a series of characterization techniques. Overall, the unique ferromagnetic nature (34.73 emu/g) make its efficient separation from the liquid phase possible. CoFe2O4 NC activates peroxymonosulfate (PMS) to degrade BPA more efficiently than hydrothermally fabricated CoFe2O4 nanoparticles. The difference in catalytic capacity is attributable to the larger specific surface area (60.4 m2 g−1) and well developed mesoporous structure (0.64 cm3 g−1) of the CoFe2O4 NC. EPR analysis demonstrate the production of HO and SO4− radicals in the CoFe2O4 NC/PMS system. The degradation process positively correlates with the increase of initial solution pH, catalysts dosage, and PMS dosage. The degradation rate of 0.112 min−1 is achieved at [PMS]/[BPA] of 10, catalyst dosage of 0.1 g L−1, temperature of 25 °C, and initial pH of 10.2 in deionized water. The existence of Cl- and HCO3−/CO32− show significant positive synergistic effects on the catalytic process. Moreover, simple thermal treatment at 400 °C for 15 min in open air fully regenerates the catalytic capacity of CoFe2O4 NC for reuse. Findings from this work shed light on the rational design of bimetallic oxide catalysts and provide new insight into the development of high-performance magnetic separable catalysts.

Zirconium-Substituted Cobalt Ferrite Nanoparticle Supported N-doped Reduced Graphene Oxide as an Efficient Bifunctional Electrocatalyst for Rechargeable Zn–Air Battery

Solvothermal synthesis of zirconium-substituted cobalt ferrite nanoparticles was accomplished by the introduction of zirconium (Zr) in the spinel matrix to obtain a cost-effective and robust electrocatalyst that does not use noble metals. A variation in the cobalt ferrite structure CoFe2–xZrxO4 with Zr (0.1–0.4) substitution has significantly altered the overpotential for the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), leading to an optimum composition of CFZr(0.3). The incorporation of the foreign Zr4+ ion in the cobalt ferrite spinel lattices has effectively enhanced the oxygen evolution reaction (OER) activity in comparison to the parent cobalt ferrite (CF) nanocrystals. However, a nominal change in the ORR current density has been observed due to Zr incorporation. For the OER, the Zr-substituted catalyst has shown a 40 mV negative shift in the overpotential in comparison with the CF nanoparticles at 10 mA/cm2 current density. Interestingly, the in situ graftin...

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

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.

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.

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.

Facile Preparation Approaches and Prospective Applications for Nanostructured Ferrites

With the development of synthesis of nanomaterials, magnetic ferrites and the traditional magnetic materials can be prepared by new methods, including top-down and bottom-up approaches. Ferrites are economic magnetic materials and are also being developed for new applications. Recent work on facile preparations and prospective applications for nanostructured ferrites will be discussed. Soft and hard ferrites are generally produced by ceramic routes in industry, but in present work, wet-chemical synthesis routes are utilized. Lithium ferrites were doped with Zn and Mg using co-precipitation method. They have shown promise in absorbers and sensors. Cobalt ferrite nanocrystals were prepared by a simplified sol-gel method namely the WOWS (without water and surfactants) sol-gel method. Cobalt ferrites with adjustable electrical properties have been obtained by doping a small amount of RE elements. Structural analysis of the prepared samples was done by X-ray diffraction (XRD). Lattice parameters and crystallite sizes were determined by using XRD data. Spinel structure was observed for all the prepared samples but with different space groups. DC electrical resistivity was measured as a function of temperature, and activation energies were determined from the Arrhenius plots for all the samples and their comparative study was done. Resistivity of all the samples was decreased with increase in temperature which indicated their semiconductor-like behavior. Polaron hopping was the major conducting mechanism as activation energies for all the samples were above 0.4 eV. The studied materials can be utilized in advanced electronics industries.