Electrospun nanocomposite polyacrylonitrile fibers containing carbon nanotubes and cobalt ferrite

Nanocomposite fibers made from polyacrylonitrile (PAN) containing carbon nanotubes (CNTs) and cobalt ferrite (CoFe₂O₄) nanoparticles were fabricated by electrospinning. The 10–25 nm CoFe₂O₄ nanoparticles were made by a simple hydrothermal process. Characterization by X‐ray diffraction confirmed that the CNTs and the CoFe₂O₄ nanoparticles were successfully incorporated into the PAN matrix. Scanning electron microscopy showed nanocomposite fibers with regular morphologies. Transmission electron microscopy revealed the internal distribution of the CNTs and CoFe₂O₄ nanoparticles. The nanocomposite fibers exhibited effective electromagnetic interference shielding attenuation of about 3.9 dB. Magnetic measurement using a vibrating sample magnetometer showed saturation magnetization of 4.7 emu g⁻¹, thus this property can be accurately tailored by adjusting the loading of CoFe₂O₄ nanoparticles. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Tailoring of complex permittivity,permeability, and microwave-absorbing properties of CoFe2O4/NG/PMMA nanocomposites through swift heavy ions irradiation

In this study, the influence of swift heavy ions (SHI) [C⁶⁺ (80 MeV) and O⁷⁺ (100 MeV)] irradiation on microwave (MW) absorbing properties of cobalt ferrite nanoparticles/exfoliated nanographites/poly(methylmethacrylate) (CoFe₂O₄/NG/PMMA) nanocomposites was investigated in the frequency range of 2–18 GHz. This work is the first attempt to study the comprehensive effects of SHI irradiation on MW absorbing properties of polymer nanocomposites. The scanning electron micrographs of the nanocomposites reveal monotonic improvement in the dispersion of nanofillers (CoFe₂O₄ and NG) with an increase of irradiation dose. With an increase in the fluence of ions, the room temperature saturation magnetization was observed to decrease monotonically, whereas a reverse trend was detected for the coercivity. The SHI irradiated nanocomposites exhibited a relatively stronger MW absorption as well as a higher effective bandwidth of absorption. A minimum reflection loss (R_Lmin) of −36.7 dB (99.98% MW absorption) and a broad bandwidth (for R_L ≤ −10 dB) of ~7.1 GHz were detected in O⁷⁺ (100 MeV) SHI irradiated nanocomposite at the fluence of 1 × 10¹² ions/cm². The results demonstrate that SHI irradiation can used as an effective tool to tailor and enhance the MW absorption in light-weight CoFe₂O₄/NG/PMMA nanocomposites.     

Electrical transport and magnetic properties of PEDOT‐ferrite nanocomposites

We have studied the temperature‐dependent transport and magnetic properties of the nanocomposites, containing varied amounts of CoFe₂O₄, NiFe₂O₄, and Fe₃O₄ nanoparticles embedded in the conducting poly(3,4‐ethylenedioxythiophene) or PEDOT matrix, in the temperature range 77–300 K. Resistivities of all the composites, including pure PEDOT follows the Mott VRH relation ρ = ρ₀ T^−1/4 over the studied temperature range. This suggests that hopping is the mechanism of transport in these systems. Plots of (lnρ − lnρ₀)/A as a function of temperature for all the studied samples are found to collapse on a single curve. Although, the conduction mechanism does not change with nanoparticle inclusions in the polymer matrix, the hopping parameters change in the nanocomposites. Magnetic studies of ferrite nanoparticles and nanocomposites show signature of superparamagnetic blocking, with a distribution of particle size. The spin structure on the surface of any particle is different from that of the core. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Kinetics of Estrone Ozone/Hydrogen Peroxide Advanced Oxidation Treatment

Ozone/hydrogen peroxide batch treatment was utilized to study the degradation of the steroidal hormone estrone (E1). The competition kinetics method was used to determine the rate constants of reaction for direct ozone and E1, and for hydroxyl radicals and E1 at three pH levels (4, 7, and 8.5), three different molar O₃/H₂O₂ ratios (1:2, 2:1, and 4:1) and a temperature about 20°C. The average second-order rate constants for direct ozone-E1 reaction were determined as 6.2?×?10³?±?3.2?×?10³ M^?1s^?1, 9.4?×?10⁵?±?2.7?×?10⁵ M^?1s^?1, and 2.1?×?10⁷?±?3.1?×?10⁶ M^?1s^?1 at pH 4, 7, and 8.5, respectively. It was found that pH had the greatest influence on the reaction rate, whereas O₃/H₂O₂ ratio was found to be slightly statistically significant. For the hydroxyl radical-E1 reaction, apparent rate constants ranged from 1.1?×?10¹⁰ M^?1s^?1 to 7.0?×?10¹⁰ M^?1s^?1 with an average value of 2.6?×?10¹⁰ M^?1s^?1. Overall, O₃/H₂O₂ is shown to be an effective treatment for E1.     

Electrochemical synthesis of ammonia from water and nitrogen catalyzed by nano-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> suspended in a molten LiCl-KCl-CsCl electrolyte

Nano-Fe₂O₃ and CoFe₂O₄ were suspended in molten salt of alkali-metal chloride (LiCl-KCl-CsCl) and their catalytic activity in electrochemical ammonia synthesis was evaluated from potentiostatic electrolysis at 600 K. The presence of nanoparticle suspension in the molten chloride resulted in improved production of NH₃, recording NH₃ synthesis rate of 1.78×10^?10 mol s^?1 cm^?2 and 3.00×10^?10 mol s^?1 cm^?2 with CoFe₂O₄ and Fe₂O₃, which are 102% and 240% higher than that without the use of a nanocatalyst, respectively. We speculated that the nanoparticles triggered both the electrochemical reduction of nitrogen and also chemical reaction between nitrogen and hydrogen that was produced from water electro-reduction on cathode. The use of nanocatalysts in the form of suspension offers an effective way to overcome the sluggish nature of nitrogen reduction in the molten chloride electrolyte.     

Effect of the rare-earth substitution on the structural,magnetic and adsorption properties in cobalt ferrite nanoparticles

Rare-earth (RE) substituted cobalt ferrite CoFe_1.9RE_0.1O₄ (RE=Pr³⁺, Sm³⁺, Tb³⁺, Ho³⁺) nanoparticles are synthesized by a facile hydrothermal method without any template and surfactant. The effects of RE³⁺ substitution on structural, magnetic and adsorption properties of cobalt ferrite nanoparticles are investigated. Structure, morphology, particle size, chemical composition and magnetic properties of the ferrite nanoparticles are studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), high solution transmission electron microscopy (HRTEM), energy-dispersive spectrometer (EDS), Fourier transform spectroscopy (FTIR), Raman spectra and vibrating sample magnetometry (VSM). The results indicate that the as-synthesized samples have the pure spinel phase, uniform crystallite size and narrow particle size distribution. Meanwhile, the RE³⁺ substitution leads to the decrease in the particle size, magnetization and coercivity of the CoFe₂O₄ ferrite. Notably, it demonstrates that the RE³⁺ doping can apparently enhance the adsorption capacity for Congo red (CR) onto ferrite nanoparticles. Adsorption equilibrium studies show that adsorption of CR follows the Langmuir model. The monolayer adsorption capacities of CoFe_1.9Sm_0.1O₄ and CoFe_1.9Ho_0.1O₄ are 178.6 and 158.0 mg/g, respectively. The adsorption kinetics can be described by the pseudo-second-order model.     

Synthesis,characterization, and magneto‐electric properties of (1−x)BCZT‐xCFO ceramic particulate composites

Synthesis of a new magnetoelectric [(1?x)(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃‐xCoFe₂O₄] (weight fraction x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1) ceramic particulate composites with its structural characterization and magneto‐electric properties have been reported here in this study. Lead free piezoelectric (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) and ferrimagnetic CoFe₂O₄ (CFO) were synthesized using sol‐gel and combustion methods respectively. (1?x)BCZT‐xCFO magnetoelectric composites were then synthesized by mixing of the calcined individual ferroic phases with required weight fractions. Powder X‐ray diffraction studies indicate the coexistence of BCZT and CFO phases in the composites sintered at 1300°C. 0.5BCZT‐0.5CFO composite showed high strain sensitivity (dλ/dH) of 52×10^?9 Oe^?1, which is comparable to that of pure CFO (50×10^?9 Oe^?1). A high piezoelectric voltage constant (g₃₃) of 8×10^?3 V m/N was measured for 0.8BCZT‐0.2CFO sample. All the composites showed magnetoelectric effect and a high magnetoelectric coupling coefficient (α_ME) of 6.85 mV/cm Oe was measured for 0.5BCZT‐0.5CFO composite at 1 kHz and a large ME coefficient of 115 mV/cm Oe at its resonance frequency. The effect of microstructure on the magnetoelectric properties of [(1?x)BCZT‐(x)CFO] composites has been studied and reported here as a function of its piezoelectric (BCZT)/ferrite (CoFe₂O₄) content.     

Augmenting the photocatalytic performance of cobalt ferrite via change in structural and optical properties with the introduction of different rare earth metal ions

In the present study, synthesis of different rare earth (RE) doped cobalt ferrite nanoparticles was done via facile sol-gel auto-combustion method using four different RE metal ions: Eu, Gd, Dy and Nd. The RE substituted cobalt ferrite nanoparticles were then characterized using FT-IR, powder XRD, HR-TEM, SAED, EDX, VSM and DRS techniques. From the characterization results, a significant variation in the structural, magnetic and optical properties of pure cobalt ferrite was observed with the introduction of different RE metal ions. This change in the properties was emerged due to the distortion of the ferrite crystal lattice due to replacement of smaller ionic radii Fe³⁺ ions with the comparatively larger ionic radii RE³⁺ metal ions. The catalytic activity of the fabricated RE doped cobalt ferrite nanoparticles was studied for the photo-Fenton degradation of cationic and anionic dyes. Under visible light irradiation, the as prepared RE doped nanoparticles exhibited great enhancement in the photo-Fenton degradation of dye molecules as compared to pure cobalt ferrite nanoparticles. The enhancement in the degradation rate was ascribed to the generation of defects in the crystal lattice, lower crystallite size and reduced band gap energy values which facilitated the facile transfer of photo-generated holes and electrons. Best catalytic results were obtained for CoNd_0.08Fe_1.92O₄ for SO dye (k?=?2.23?×?10^?1 min^?1) which were found to be around 9 times higher than the pure cobalt ferrite nanoparticles (k?=?0.23?×?10^?1 min^?1).     

Cobalt ferrite thin films as anode material for lithium ion batteries

Spinel cobalt ferrite (CoFe₂O₄) thin films have been fabricated by 355 nm reactive pulsed laser deposition on stainless steel substrates. XRD and SEM analyses showed that the CoFe₂O₄ films exhibited a polycrystalline structure and were composed of nanoparticles with an average size of 80 nm. At 1C rate, the initial irreversible capacity of polycrystalline CoFe₂O₄ film electrode cycled between 0.01 and 3.0 V reached 1280 mAh/g. After 20 cycles, the reversible discharge capacities decreased and sustained about 610 mAh/g. The diffusion coefficient of Li ion for CoFe₂O₄ films was determined by ac impedance method, and the average value was estimated to be 1.1 × 10⁻¹³ cm²/S. Based on ex situ XRD, SEM and XPS data, the electrochemical mechanism of CoFe₂O₄ film with lithium upon cycling was proposed. During the first discharge, the amorphization process of CoFe₂O₄ film electrode is accompanied with the reduction of Co²⁺ and Fe³⁺ into metal Co and Fe, respectively, and then the reversible oxidation/reduction processes of Co, Fe and Li₂O take place in the subsequent charge/discharge cycles.     

Synthesis of cobalt ferrite in organic solvents

The possibility of synthesizing the nanosized CoFe₂O₄ particles in organic solvents, such as glycerol and diphenyl oxide, at 250°C and atmospheric pressure under conditions of distillation of the formed water was studied. In the case of glycerol, we obtained the adduct of the latter with cobalt ferrite. The reaction in diphenyl oxide resulted in the formation of ferrite particles sized 8–10 nm.     

Structure and magnetic properties of CoFe2O4/SiO2 nanocomposites obtained by sol-gel and post annealing pathways

The influence of the CoFe₂O₄ nanoparticles concentration in silica matrix on the structural and magnetic properties of xCoFe₂O₄/(100−x)SiO₂ nanocomposites with x=10, 30, 50, 70 and 90 was studied. Magnetic CoFe₂O₄ nanoparticles dispersed in silica matrix was obtained by sol-gel method, followed by annealing at 1100 °C. The X-ray diffraction pattern and FT-IR spectra revealed the single spinel ferrite structure for all samples. The FT-IR spectra also suggested the formation of the amorphous silica matrix. The results showed that the increase of cobalt ferrite concentration (x) in the silica matrix leads to high crystallinity, specific surface area and particle size. The magnetic CoFe₂O₄ nanoparticles have spherical shapes and size in the 6–35 nm range. The Mössbauer measurements were fitted with two Zeeman sextets, indicating that all the samples were completely magnetically ordered. The vibrating sample magnetometer studies showed that the saturation magnetization (Ms) and coercivity (Hc) of the CoFe₂O₄ nanocrystals embedded in silica matrix possessed a linear relationship with the mean crystallite size. Also, the saturation magnetization of the studied nanocomposites increases with the increase of cobalt ferrite concentration (x) in the silica matrix.     

Formation of CoFe2O4/PVA-SiO2 nanocomposites: Effect of diol chain length on the structure and magnetic properties

The paper presents the influence of diol (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol) on the formation of magnetic crystalline cobalt ferrite embedded in polyvinyl alcohol-silica hybrid matrix at 200?°C. Formation of crystalline oxides (CoFe₂O₄, Co₃O₄ and Co₂SiO₄) was studied by X-ray diffraction and Fourier transformed infrared spectroscopy. The effect of annealing temperature and diol chain length on the cobalt ferrite nanocrystallites size was investigated. Using transmission electron microscopy, the size and shape of particles obtained at 200?°C were recorded and compared to those obtained by annealing at 500, 800 and 1100?°C. The saturation magnetization (M_s) and coercive field were calculated from the magnetic hysteresis loops of nanocomposites. The M_s was influenced by the particle size and crystallinity only for nanocomposites annealed at 800 and 1100?°C, when the magnetic domains started to form and to be larger than the critical particle size. The diols used in the synthesis influence both the oxidic phase formation and its properties.     

Fabrication and characterization of magnetic cobalt ferrite/polyacrylonitrile and cobalt ferrite/carbon nanofibers by electrospinning

An electrospinning process was used to fabricate cobalt ferrite (CoFe₂O₄)-embedded polyacrylonitrile (PAN) nanofibers. Oleic acid-modified CoFe₂O₄ nanoparticles were dispersed in the PAN before spinning. The surface morphologies and structures of the nanofibers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observation showed that the average diameter of the CoFe₂O₄/PAN nanofibers was 110 nm, and the magnetic CoFe₂O₄ nanoparticles were embedded in the PAN nanofibers. X-ray photoelectron spectroscopy was used to characterize the CoFe₂O₄/PAN and CoFe₂O₄/carbon nanofibers. Fiber magnetic properties were measured by vibrating sample magnetometry, showing that the saturation magnetization of the CoFe₂O₄/PAN nanofibers was 45 emu/g and that the fibers demonstrated superparamagnetic behavior.     

Microwave-assisted solution synthesis,microwave sintering and magnetic properties of cobalt ferrite

A simple, soft, and fast microwave-assisted hydrothermal method was used for the preparation of nanocrystalline cobalt ferrite powders from commercially-available Fe(NO₃)₃?9H₂O, Co(NO₃)₂?6H₂O, ammonium hydroxide, and tetrapropylammonium hydroxide (TPAH). The synthesis was conducted in a sealed-vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized by XRD, FE-SEM, TEM, and HR-TEM. After a systematic study of the influence of the microwave variables (temperature, reaction time and nature of the bases), highly crystalline CoFe₂O₄ nanoparticles with a high uniformity in morphology and size, were directly obtained by heating at 130?°C for 20?min using the base TPAH. Dense ceramics of cobalt ferrite were prepared by non-conventional, microwave sintering of synthesized nanopowders at temperatures of 850–900?°C. The magnetic properties of both the nanopowders and the sintered specimens were determined in order to establish their feasibility as a permanent magnet.     

Controlled synthesis of L-cysteine coated cobalt ferrite nanoparticles for drug delivery

In the present work, we reported a facile synthesis of cobalt ferrite (CoFe₂O₄) nanoparticles in the presence of L-cysteine (Lys). The morphology and size of samples were characterized by SEM and TEM. The successful coating of Lys on the surface of CoFe₂O₄ was confirmed by XRD, XPS and TGA. The investigation of magnetic properties showed that both bare CoFe₂O₄ and Lys-coated CoFe₂O₄ nanoparticles exhibited room-temperature superparamagnetic behavior. The results of MTT experiments revealed insignificant cytotoxicity of Lys-coated CoFe₂O₄ nanoparticles even after 24?h incubation. More importantly, Lys-coated CoFe₂O₄ nanoparticles displayed an excellent drug loading capacity and a pH-sensitive drug release behavior. In summary, the prepared Lys-coated CoFe₂O₄ nanoparticles demonstrated a promising application potential in controlled drug delivery.     

Influence of cobalt ferrite content on the structure and magnetic properties of (CoFe2O4)X (SiO2-PVA)100-X nanocomposites

(CoFe₂O₄)_X(SiO₂-PVA)_100-X (X = 5, 25, 50, 75 and 95%) nanocomposites were prepared via sol-gel route and annealed at 700 and 1100 °C. The influence of CoFe₂O₄ content on the structure, morphology and magnetic properties of nanocomposites was studied. X-ray diffraction patterns, Mössbauer and Fourier transform infrared spectra revealed the formation of CoFe₂O₄ as unique magnetic phase. The crystallinity degree increases with the CoFe₂O₄ content and the annealing temperature. Transmission electron microscopy images revealed the spherical shape of the obtained nanocomposites. Mössbauer spectra exhibit typical magnetic sextets, allowing the calculation of the cations distribution among tetrahedral and octahedral sites and the stoichiometry of CoFe₂O₄. A strong correlation between the particle morphology and the magnetic properties of nanocomposites was found. The highest saturation magnetization was identified for (CoFe₂O₄)₉₅(SiO₂-PVA)₅ nanocomposite.     

A Resumable Fluorescent Probe BHN-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> Hybrid Nanostructure for Fe<Superscript>3+</Superscript> and its Application in Bioimaging

A multifunctional fluorescent probe BHN-Fe₃O₄@SiO₂ nanostructure for Fe³⁺ was designed and developed. It has a good selective response to Fe³⁺ with fluorescence quenching and can be recycled using an external magnetic field. With adding EDTA (2.5?×?10^?5 M) to the consequent product Fe³⁺-BHN-Fe₃O₄@SiO₂, Fe³⁺ can be removed from the complex, and its fluorescence probing ability recovers, which means that this constituted on-off type fluorescence probe could be reversed and reused. At the same time, the probe has been successfully applied for quantitatively detecting Fe³⁺ in a linear mode with a low limit of detection 1.25?×?10^?8 M. Furthermore, the BHN-Fe₃O₄@SiO₂ nanostructure probe is successfully used to detect Fe³⁺ in living HeLa cells, which shows its great potential in bioimaging detection.     

Magnetic and dielectric properties of natural rubber and polyurethane composites filled with cobalt ferrite

Abstract

Cobalt ferrite (CoFe₂O₄) powders synthesised by sol–gel techniques were incorporated into natural rubber (NR) and polyurethane (PU) by two-roll milling at different loadings from 0 to 45 phr. In either NR or PU composites, the magnetisations were proportional to the CoFe₂O₄ loading, but the coercive field remained rather insensitive to the loading. The frequency response from 1 MHz to 1 GHz revealed that the real part of the magnetic permeability increased significantly only in the case of 45 phr CoFe₂O₄, while the imaginary part was modest in both NR and PU composites. In contrast, the electrical permittivity of CoFe₂O₄–PU was larger than that of CoFe₂O₄–NR composites, and both parts at 100 MHz had linear variations with the loading, in agreement with Wagner’s equation.     

Simple fabrication of strongly coupled cobalt ferrite/carbon nanotube composite based on deoxygenation for improving lithium storage

An easy method to synthesize a strongly coupled cobalt ferrite/carbon nanotube (CoFe₂O₄/CNT) composite with oxygen bridges between CoFe₂O₄ and reduced carbon nanotubes (CNTs) by calcining the precursor material was reported. The precursor was prepared by an electrostatic self-assembly of the exfoliated Co(II)Fe(II)Fe(III)-layered double hydroxide (CoFeFe-LDH) nanosheets and acid treated CNTs. The deoxygenation effect of ferrous ion (Fe²⁺) in CoFeFe-LDH nanosheets on the oxygen-containing groups of acid treated CNTs was investigated by X-ray photoelectron spectroscopy (XPS) measurement. After thermal conversion, the obtained CoFe₂O₄ was bonded to the reduced CNTs through Metal–O–C (oxygen bridge), which was characterized by XPS, Fourier transform infrared spectroscopy, and Raman spectroscopy. When applied as an anode for lithium-ion battery, the CoFe₂O₄/CNT composite exhibited a low resistance of charge transfer and Li-ion diffusion, good cycle performance, and high rate capability. At a lower current density of 0.15 A·g⁻¹, a specific discharge capacity of 910 mA·h·g⁻¹ was achieved up to 50 cycles. When current density was increased to 8.8 A·g⁻¹, the CoFe₂O₄/CNT composite still delivered 500 mA·h·g⁻¹.     

Mg and Cu incorporated CoFe2O4 catalyst: characterization and methane cracking performance for hydrogen and nano-carbon production

The Cobalt ferrite (CoFe₂O₄) and cobalt ferrite incorporated with Cu (Cu–CoFe₂O₄) and Mg (Mg–CoFe₂O₄) have been synthesized by wet chemical route. In fixed-bed reactor, the CoFe₂O₄, Cu–CoFe₂O₄ and Mg–CoFe₂O₄ were used as catalysts for direct cracking of methane at temperature of 800 °C and 20 mL/min of feed gas flow rate for hydrogen and nano-carbon production. Different characterizations techniques namely XRD, FESEM, XPS, Raman spectroscopy, TGA, BET for fresh and spent catalysts have been executed. The X-ray powder diffraction and Raman spectra confirmed that the fresh catalysts possess a cubic spinel crystal structure. The FESEM images for spent catalysts displayed that filamentous carbons were not formed over catalysts surfaces except a few amount was observed over the spent CoFe₂O₄ catalyst. XPS results confirmed the purity of the synthesized catalysts and qualitatively evaluate the cation distribution between the tetrahedral and octahedral sites from Co 2p_3/2 and Fe 2p_3/2 spectra. BET surface area revealed no significant effects in surface area and pore size of CoFe₂O₄ catalyst by incorporation of Mg and Cu metals. Activity studies showed that incorporation Mg metal on CoFe₂O₄ improved methane conversion up to 40.03% and hydrogen formation rate of 79.90 mol H₂ g⁻¹ min⁻¹ as compared to 31.61% and 66 mol H₂ g⁻¹ min⁻¹ for CoFe₂O₄ catalyst. Whilst, Cu metal incorporation in CoFe₂O₄ catalyst led to decline the catalyst performance. Structure activity relationship was described in details.