Monodisperse CoFe2O4 Nanoparticles Research Articles

Degradation of bisphenol S by peroxymonosulfate activation through monodispersed CoFe2O4 nanoparticles anchored on natural palygorskite

• Monodispersed CoFe 2 O 4 nanoparticles anchored on palygorskite to activate PMS. • 16%-CFO@PAL/PMS oxidation system can effectively degrade BPS in water. • 16%-CFO@PAL composite exhibits high activity and low metal leaching property. • SO 4 · - and 1 O 2 mainly contributed degradation of BPS in 16%-CFO@PAL/PMS system. • Fe-O-Al bond between CoFe 2 O 4 and PAL improved the stability of 16%-CFO@PAL. Bisphenol S (BPS) has been detected frequently in water bodies, which poses a serious threat to human health and the environment. The sulfate radical-based advanced oxidation process is considered as a promising water purification technology by activating peroxymonosulfate (PMS). However, a catalyst with low metal leaching rate and high effective catalytic ability is needed to activate PMS. In this study, natural clay of palygorskite (PAL) was used to mediate monodispersed CoFe 2 O 4 nanoparticles to degrade BPS by PMS activation. The monodispersed CoFe 2 O 4 nanoparticles were distributed and anchored on the surface of PAL, which caused the 16%-CoFe 2 O 4 @PAL (16%-CFO@PAL) composite expose more reaction sites, thus exhibiting excellent catalytic performance. A satisfactory BPS removal rate (> 99%) was obtained by introducing 50 mg L -1 16%-CFO@PAL and 0.16 mM PMS. The interaction mechanism between CoFe 2 O 4 nanoparticles and PAL was discussed. The Al-O-Fe bond between CoFe 2 O 4 nanoparticles and PAL endowed the 16%-CFO@PAL composite with low metal leaching property, high stability and reusability. SO 4 ·- and 1 O 2 played a dominant role in the degradation of BPS. The generation mechanism of reactive species was proposed. The influences of various degradation parameters (e.g., catalyst dosage, PMS concentration, initial solution pH, and BPS concentration) and water constituents (e.g., inorganic anions and NOM) on the degradation of BPS were investigated. Based on the identified intermediates and density functional theory (DFT) calculations, the possible degradation pathways of BPS were discussed. This study provides a new idea for the preparation of high-efficiency natural clay-based PMS catalysts for water purification.

Effects of Process Variables on Properties of CoFe2O4 Nanoparticles Prepared by Solvothermal Process

Controlling the morphology and magnetic properties of CoFe2O4 nanoparticles is crucial for the synthesis of compatible materials for different applications. CoFe2O4 nanoparticles were synthesized by a solvothermal method using cobalt nitrate, iron nitrate as precursors, and oleic acid as a surfactant. The formation of CoFe2O4 nanoparticles was systematically observed by adjusting synthesis process conditions including reaction temperature, reaction time, and oleic acid concentration. Nearly spherical, monodispersed CoFe2O4 nanoparticles were formed by changing the reaction time and reaction temperature. The oleic acid-coated CoFe2O4 nanoparticles inhibited the growth of particle size after 1 h and, therefore, the particle size of CoFe2O4 nanoparticles did not change significantly as the reaction time increased. Both without and with low oleic acid concentration, the large-sized cubic CoFe2O4 nanoparticles showing ferromagnetic behavior were synthesized, while the small-sized CoFe2O4 nanoparticles with superparamagnetic properties were obtained for the oleic acid concentration higher than 0.1 M. This study will become a basis for further research in the future to prepare the high-functional CoFe2O4 magnetic nanoparticles by a solvothermal process, which can be applied to bio-separation, biosensors, drug delivery, magnetic hyperthermia, etc.

Synthesis, characterization and magnetic hyperthermia properties of nearly monodisperse CoFe2O4 nanoparticles

In this study, the hyperthermia efficiency of CoFe2O4 nanoparticles (CFNPs) was enhanced by narrowing their size distribution and increasing their magnetic moment. The CFNPs were synthesized using the solvothermal reflux method. The NPs were crystallized in the face-centered cubic spinel structure (lattice parameter of 8.373 Å) and had a particle size of ~10 nm, as revealed by the X-ray diffraction and transmission electron microscopy (TEM) results, respectively. The high-resolution TEM images of the NPs revealed their single crystal nature. The infrared absorption bands above 700 cm−1 confirmed the formation of octahedral and tetrahedral ligands on the surface of the NPs. The thermal analysis profiles of the synthesized NPs showed that the surface ligands decomposed at approximately 360 °C. The nanocolloids prepared using the NPs showed stable dispersion with a zeta potential of −17.7 mV. The X-ray photoelectron spectroscopy results revealed the presence of Co2+, Fe3+, and O2− in the NPs. The NPs existed in the superparamagnetic state with a maximum mass magnetization of 71 emu g−1, which is close to the theoretical value. The magnetic hyperthermia property of the NPs was investigated by determining their specific heat generation rate (SHGR) under biocompatible alternate magnetic field parameters. The NPs were capable of heating 185.32 W g−1. This value is greater than the SHGR reported previously for CFNPs synthesized by other methods.

Natural diatomite mediated spherically monodispersed CoFe2O4 nanoparticles for efficient catalytic oxidation of bisphenol A through activating peroxymonosulfate

Porous magnetic CoFe2O4/diatomite catalyst (CFD) was rationally synthesized via a facile citrate combustion process. The relationship between catalytic performance and material properties of the prepared catalysts was comprehensively investigated by various characterizations, especially for the interface interaction between CoFe2O4 and diatomite as well as crystallization regulation of CoFe2O4. Overall, higher specific surface area, overspreading surface hydroxyl groups, better crystal dispersion and abundant surface-active sites make CFD have better degradation performance of bisphenol A (BPA) than pure CoFe2O4 in the presence of peroxymonosulfate (PMS), and the pseudo-first-order reaction rate constant of 40-CFD (40% CoFe2O4/diatomite) is almost 5.32 times higher than that of pure CoFe2O4. Besides, CFD has excellent magnetic properties, lower metal dissolution rate and good reusability. In addition, electron paramagnetic resonance (EPR) and radical quenching experiments show that sulfate radicals (SO4−) and singlet oxygen radicals (1O2) generated from the electron transfer of BPA molecule and valence state change of transition metals should be the predominant oxidation species. Moreover, possible degradation pathways of BPA are determined by the detection of intermediates derived from the results of liquid chromatograph–mass spectrometer (LC–MS). In brief, it is indicated that the CoFe2O4/diatomite composite material is an efficient and environmentally friendly catalyst, which has a great potential application in wastewater treatment by activating PMS.

Dynamic magnetic properties of monodisperse CoFe2O4 nanoparticles synthesized by a facile solvothermal technique

Monodisperse, unagglomerated nanoparticles of CoFe2O4 were synthesized by a solvothermal technique using various capping agents. Three sets of particles were synthesized having size ∼7 nm, ∼14 nm and ∼23 nm. Detailed morphology study was done by X ray diffraction and High resolution Transmission Electron Microscope. Ac hysteresis loops of these samples were measured at room temperature within a frequency range of 50 Hz–600 Hz. We have reported the frequency dependence of coercivity and Specific absorption rate (SAR) and have found a very interesting result that the coercivity varies with different power of frequency for the particles of different size. Particles of sample A followed the Néel type of relaxation. The relaxation measurements were also done on all the samples to vindicate the occurrence of Néel type of relaxation. The SAR values and the fast relaxation proves that these particles can be utilized for hyperthermia treatment.

Expanding the Horizon of Multicomponent Oxidative Coupling Reaction via the Design of a Unique, 3D Copper Isophthalate MOF-Based Catalyst Decorated with Mixed Spinel CoFe2O4 Nanoparticles.

This work discloses the first ever magnetically retrievable copper isophthalate-based metal-organic framework (MOF) decorated with surface-modified cobalt ferrite (CoFe2O4) nanoparticles that have been utilized as catalytic reactors for obtaining a relatively large number of biologically active benzimidazole scaffolds. A facile one-pot solvothermal approach was employed for obtaining spherical and monodisperse CoFe2O4 nanoparticles, which were subsequently modified using suitable protecting and functionalizing agents. Finally, these functionalized magnetic nanoparticles were anchored onto the three-dimensional copper isophthalate MOF via a covalent immobilization methodology. The exploitation of advanced microscopic tools such as transmission electron microscopy and scanning electron microscopy provided valuable insights into the morphology of the immobilized MOF. These results indicated that the surface-modified magnetic nanoparticles had grown onto the surface of copper-5-nitroisophthalic acid MOF. A greener C–H functionalization strategy that involves the multicomponent oxidative cross-coupling between two different set of amines (sp2-hybridized nitrogen-containing anilines and sp3-hybridized nitrogen-containing alkyl/aryl amine derivatives) and sodium azide has been incorporated to provide access to a broad spectrum of the value-added target benzimidazole moieties. It is interesting to note that this magnetic MOF-catalyzed protocol not only replaces toxic solvents with water, which is a green solvent, but also enhances the economic competitiveness since the magnetic catalyst can be readily recovered and recycled for eight consecutive runs.

Synthesis and magnetic properties of monodisperse CoFe2O4 nanoparticles coated by SiO2

The monodisperse CoFe2O4 nanoparticles were synthesized by a modified chemical coprecipitation method. Coating SiO2 on the surface of the CoFe2O4 nanoparticles was carried out to keep single domain particles non-interacting with cubic magnetocrystalline anisotropy. The Curie temperatures (Tc) of the monodisperse CoFe2O4 nanoparticles can be accurately measured because the SiO2 shells prevented the aggregation and growth of nanoparticles at high temperature. The magnetic properties of the CoFe2O4@SiO2 nanoparticles with core-shell structure in a wide temperature range (300～950 K) were investigated. It is remarkable that the coercive field (Hc) of CoFe2O4 nanoparticles increased from about 760 Oe to 1806 Oe after being coated with SiO2, which increased by 137.6% compared to the uncoated samples at 300 K. The saturation magnetization (Ms) of the CoFe2O4@SiO2 nanoparticles is 34.59 emu/g, which is about 52% of the naked CoFe2O4 nanoparticles value (66.51 emu/g) at 300 K. The hysteresis loops of the CoFe2O4@SiO2 nanoparticles showed an orderly magnetic behavior at high temperature, such as the Ms, remanence magnetization (Mr) and Hc decreased as temperature increasing, being equal to zero near Tc. This is a good indication that the CoFe2O4@SiO2 nanoparticles are suitable for a wide variety of technological applications at high temperature.

Defect locating: One-step to monodispersed CoFe2O4/rGO nanoparticles for oxygen reduction and oxygen evolution

In this work, monodispersed CoFe2O4/reduced graphene oxide (rGO) nanoparticles have been successfully synthetized in one step from Co(Ⅱ) acetylacetonate, Fe(Ⅲ) acetylacetonate, benzylamine and graphene oxide (GO). A facile solvent method was designed to skillfully integrate the crystal growth process of CoFe2O4, the reduction process of GO and their compound process. In synthesis process, large numbers of defects on GO thin layers were smartly used to disperse CoFe2O4 nanoparticles. The micromorphology and the distribution of as-prepared samples were identified via X-ray diffraction (XRD), transmission electron microscope (TEM) and element mapping spectra. Results showed that the monodispersed CoFe2O4 nanoparticles were uniformly coupled with rGO thin layers. Good performance for both oxygen reduction and oxygen evolution of as-prepared CoFe2O4/rGO (0.92 V onset potential for oxygen reduction and 1.59 V overpotential at 10 mA cm−2 for oxygen evolution, vs. RHE) were found during a series of electrochemical tests, which make it a promising bi-functional catalyst in the field of fuel cells and metal-air batteries.

Monodisperse polyvinylpyrrolidone-coated CoFe2O4 nanoparticles: Synthesis, characterization and cytotoxicity study

In this study, monodisperse cobalt ferrite (CoFe2O4) nanoparticles were prepared successfully with various additions of polyvinylpyrrolidone (PVP) by sonochemical method, in which PVP served as a stabilizer and dispersant. The effects and roles of PVP on the morphology, microstructure and magnetic properties of the obtained CoFe2O4 were investigated in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). It was found that PVP-coated CoFe2O4 showed relatively well dispersion with narrow size distribution. The field-dependent magnetization curves indicated superparamagnetic behavior of PVP-coated CoFe2O4 with moderate saturation magnetization and hydrophilic character at room temperature. More importantly, the in vitro cytotoxicity testing exhibited negligible cytotoxicity of as-prepared PVP-CoFe2O4 even at the concentration as high as 150μg/mL after 24h treatment. Considering the superparamagnetic properties, hydrophilic character and negligible cytotoxicity, the monodisperse CoFe2O4 nanoparticles hold great potential in a variety of biomedical applications.

High-Performance Flexible Organic Nano-Floating Gate Memory Devices Functionalized with Cobalt Ferrite Nanoparticles.

Nano-floating gate memory (NFGM) devices are transistor-type memory devices that use nanostructured materials as charge trap sites. They have recently attracted a great deal of attention due to their excellent performance, capability for multilevel programming, and suitability as platforms for integrated circuits. Herein, novel NFGM devices have been fabricated using semiconducting cobalt ferrite (CoFe2O4) nanoparticles (NPs) as charge trap sites and pentacene as a p-type semiconductor. Monodisperse CoFe2O4 NPs with different diameters have been synthesized by thermal decomposition and embedded in NFGM devices. The particle size effects on the memory performance have been investigated in terms of energy levels and particle-particle interactions. CoFe2O4 NP-based memory devices exhibit a large memory window (≈73.84 V), a high read current on/off ratio (read I(on)/I(off)) of ≈2.98 × 10(3), and excellent data retention. Fast switching behaviors are observed due to the exceptional charge trapping/release capability of CoFe2O4 NPs surrounded by the oleate layer, which acts as an alternative tunneling dielectric layer and simplifies the device fabrication process. Furthermore, the NFGM devices show excellent thermal stability, and flexible memory devices fabricated on plastic substrates exhibit remarkable mechanical and electrical stability. This study demonstrates a viable means of fabricating highly flexible, high-performance organic memory devices.

Monodisperse CoFe2O4 nanoparticles supported on Vulcan XC-72: High performance electrode materials for lithium-air and lithium-ion batteries

Addressed herein is the preparation and the electrode performance of monodisperse CoFe2O4 nanoparticles (NPs) supported on Vulcan XC-72 for the Lithium-air battery (LAB) and Lithium-ion battery (LIB). Monodisperse CoFe2O4 NPs were synthesized by the thermal decomposition of cobalt(II) acetylacetonate and iron(III) acetylacetonate in oleylamine and oleic acid in the presence of 1,2-tetradecanediol and benzyl ether. As-prepared CoFe2O4 NPs with a particle size of 11 nm were then supported on Vulcan XC-72 (Vulcan-CoFe2O4) at different theoretical loadings (20, 40 and 60 wt % CoFe2O4 NPs) by using the simple liquid phase self assembly method. CoFe2O4 NPs dispersed on Vulcan-CoFe2O4 composites were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) and atomic absorption spectroscopy (AAS). The AAS analyses indicated that the Vulcan-CoFe2O4 composites with different loadings were included 3.7, 8.1 and 16.4 wt % CoFe2O4 on the metal basis. The electrode performance of Vulcan-CoFe2O4 composites were evaluated as the anode active material for LIB and cathode active material for LABs by performing the galvanostatic charge–discharge tests. The highest discharge capacity for both LAB (7510 mAh g(Vulcan+CoFe2O4)−1; 13380 mAh gCoFe2O4−1 @ 0.1C) and LIB (863 mAh g(Vulcan+CoFe2O4)−1; 9330 mAh gCoFe2O4−1@ 0.1C) was investigated with 16.4 wt % CoFe2O4.

Diluted and undiluted monodispersed CoFe2O4 nanoparticles: the effects of post-annealing on magnetic properties

Well-dispersed uniform CoFe2O4 nanoparticles were synthesized by thermal decomposition of Fe(acac)3 and Co(acac)2 in a solution of oleic acid, oleylamine, and benzyl ether. We diluted some of the nanoparticles in a SiO2 matrix, and then annealed undiluted and diluted samples at 300–700 °C. For the undiluted samples, the interparticle dipolar interaction dominated the macroscopic magnetic properties: as the annealing temperature increased, the dipolar interaction strength decreased, increasing the coercivity H c from 1094 to 2297 Oe and the remanence ratio M r/M s from 0.39 to 0.56. Furthermore, as the measurement temperature decreased, both the field cooling and zero-field cooling magnetizations decreased, indicating superspin glass behavior caused by strong interparticle dipolar interaction. For the diluted samples, the strength of their interparticle dipolar interactions was lower than those of the corresponding undiluted samples; additionally, their thermal energy overcame their interparticle dipolar interaction energy, which made the CoFe2O4 nanoparticles tend toward superparamagnetism as well as the decreased H c and M r/M s ratio. Finally, our diluted CoFe2O4 nanoparticles retained higher saturation magnetization M s than those reported before, therefore they may hold promise in biomedical applications.

Tuning of magnetic properties of CoFe2O4 nanoparticles through charge transfer effect

Herein, we report the microscopic origin of surfactant modified magnetic properties of nearly monodispersed CoFe2O4 nanoparticles (NPs). Surface modification is carried out with four surfactants having π-acceptor/π-donor head group along with different chain-length. Upon functionalization, magnetic NPs show a maximum 65.61% increase in coercivity and 78.24% decrease in magnetization as compared to the bare one. Furthermore, π-donor head group surfactant modified CoFe2O4 NPs show higher coercivity and magnetization with respect to π-acceptor head group surfactant modified NPs and with the increase in chain-length of the surfactant, coercivity of NPs enhances slightly. These consequences are explained in context of crystal field splitting energy and steric hindrance offered by the surfactant.

CoFe2O4 nanoparticles as a catalyst: synthesis of a forest of vertically aligned CNTs of uniform diameters by plasma-enhanced CVD

Controlling actively the structures of carbon nanotubes such as the alignment, length, diameter, chirality and the number of walls still remains a crucial challenge. The properties of CNTs are highly structure sensitive and particularly dependent on the diameter and number of walls. In this brief communication, we synthesise monodisperse CoFe2O4 nanoparticles of uniform diameters, i.e. 4.8 and 6.9 nm, which are modified with oleic acid as a catalyst for the growth of CNTs. We show that a forest of vertically aligned CNTs of uniform diameters and lengths can be grown using CoFe2O4 nanoparticles. The internal diameters and lengths of CNTs grown using CoFe2O4 nanoparticles of 4.8 and 6.9 nm diameters are, respectively, 4.4 and 6.2 nm and 10 and 15 μm. It is clearly shown that the number of walls of CNTs can be engineered changing the materials of the catalytic nanoparticles. The present results may well encourage further systematic studies on the growth of CNTs using various combinations of elements for the catalytic nanoparticles under different external conditions, which may provide not only the possibilities of controlling the properties of CNTs but also an insight into the nucleation and growth mechanisms.

Controlled synthesis of monodisperse CoFe2O4 nanoparticles by the phase transfer method and their catalytic activity on methylene blue discoloration with H2O2

Monodisperse spinel CoFe2O4 nanoparticles have been synthesized through the solvothermal-assisted phase transfer method using aqueous soluble metal salts as starting materials and sodium oleate (SO) as the phase-transfer agent. The as-synthesized nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, infrared spectroscopy, vibrating sample magnetometry, ultraviolet and visible spectrophotometry and Mössbauer spectrum. The results revealed that the as-obtained nanoparticles have a cubic spinel structure and an average diameter of 2–6nm. It was found that SO played an important role during the transfer of the hydrophilic inorganic precursor from aqueous phase to the organic phase. On the basis of the experimental results, a possible mechanism for the formation of the nanoparticles was proposed. Surface functionalization of the as-prepared nanoparticles was conducted to render the hydrophobic nanoparticles water-soluble, which makes the nanoparticles suitable for catalytic applications. The nanoparticles showed catalytic activity in the oxidation of methylene blue with H2O2 as an oxidizing agent.

Synthesis and Characterization of Superparamagnetic CoFe<SUB>2</SUB>O<SUB>4</SUB>/MWCNT Hybrids for Tumor-Targeted Therapy

Owing to their great potentialities of carbon nanotubes (CNTs)-based magnetic nano-composites, numerous applications of them have been found in nanotechnology, integrated functional system, and in medicine. Herein, nearly monodisperse CoFe2O4 nanoparticles have been deposited on multi-walled carbon nanotubes (MWCNTs) by high-temperature hydrolysis and inorganic polymerization of ionic Co(II) and Fe(III) salts and MWCNTs in a polyol solution. X-ray diffraction, energy-dispersive X-ray spectrometry and transmission electron microscopy were used to characterize the final products. The average size of CoFe2O4 nanoparticles and their coverage density on MWCNTs can be adjusted to some extent by altering the reaction parameters. A proposed formation mechanism of the magnetic hybrids is presented. Magnetic measurements showed that the hybrids were superparamagnetic at room temperature and their saturation magnetization could be fine tuned by changing the loading of CoFe2O4 nanoparticles on the MWCNTs.

Controlled preparation of monodisperse CoFe2O4 nanoparticles by a facile method

CoFe2O4 nanoparticles (NPs) were synthesized by coprecipitation method using FeCl3·6H2O and CoCl2·6H2O as precursors. The synthesized conditions were optimized, such as added means of precipitator, quantity of precipitator, the mol ratio of Fe3+ to Co2+, reaction temperature and pH value. The synthesized material was characterized by XRD, TEM, FTIR, EDS, Raman and its magnetic properties were studied by VSM. The experimental results confirm that the sample is cubic spinel structure CoFe2O4 with a narrow size distribution and a good dispersion feature. CoFe2O4 NPs with well-controlled shape and size was obtained at 70 °C. The magnetic properties indicate superparamagnetic behavior and good saturated magnetization.

Erratum to: Synthesis and Magnetic Properties of Nearly Monodisperse CoFe2O4 Nanoparticles Through a Simple Hydrothermal Condition

Erratum to: Synthesis and Magnetic Properties of Nearly Monodisperse CoFe2O4 Nanoparticles Through a Simple Hydrothermal Condition

Facile and ultra large scale synthesis of nearly monodispersed CoFe2O4 nanoparticles by a low temperature sol–gel route

Nearly monodispersed cobalt ferrite nanoparticles were synthesized by a low temperature sol–gel route using propylene oxide as a gelation agent. The nanoparticles were obtained by the reaction of FeCl2 and CoCl2 in ethanol solution with propylene oxide to form the sol, followed by the boiling of the sol solution. The unique chemistry of this procedure allows the formation of highly homogeneous gel intermediate, resulting in the great reducing of crystallization temperature of ferrites to less than 100 °C without postannealing step. This guarantees the preparation of well defined and non-aggregated ferrite nanoparticles on an ultra-large scale of about 75 g in a single reaction. This large scale synthesis strategy offers important advantages over other conventional routes for the preparation of CoFe2O4 nanoparticles, showing the promising application of this route in the industrial production.

Synthesis of Ordered Layers of Monodisperse CoFe2O4 Nanoparticles for Catalyzed Growth of Carbon Nanotubes on Silicon Substrate

Simple and inexpensive formation of extended and ordered mono- or multilayers of highly monodispersed CoFe2O4 nanoparticles, covered by oleic acid coating, was obtained by the spin-coating method on silicon substrate. Two concentrations of nanoparticles dispersions were employed. The oleic-capped nanoparticles were used as catalysts for the growth of carbon nanotubes by ethylene CCVD. A close correlation of nanotube diameter with nanoparticle size has been verified. Moreover, density and length of nanotubes can be controlled by nanoparticle concentration.