CoFe2O4 Nanotubes Research Articles

Cobalt-iron oxide nanotubes decorated with polyaniline as advanced cathode hosts for Li-S batteries

Lithium-sulfur (Li-S) batteries are generally considered as potential candidates for sustainable energy storage systems owing to low cost and high theoretical energy storage capability. However, the actual implementation of sulfur cathode in Li-S batteries is seriously hampered by the undesirable shuttle effect of lithium polysulfides (LiPS), inferior electroconductibility of S/Li2S and huge volume change during lithiation/delithiation process. Herein, the CoFe2O4 nanotubes decorated with polyaniline (PANI) are rationally designed and fabricated as efficient sulfur hosts to handle these challenges. Specifically, both CoFe2O4 and PANI components possess strong chemical affinity to the soluble intermediate LiPS. Meanwhile, from the perspective of structural superiority, the internal void space of nanotubes can effectively accommodate active sulfur particles and tolerate the large volume change upon cycling. Besides, the conductive polymer of PANI can greatly improve the cathode conductivity and facilitate the electron transfer for active materials. More importantly, the S/CoFe2O4@PANI electrode achieves excellent cycling performance with superior initial capacity of 864.1 mAh g−1 and good reversible capacity retention with 582.6 mAh g−1 even after 500 cycles at 2 C rate.

Magnetic properties of cobalt ferrite octahedrons obtained from calcination of granular nanotubes growing on bacterial nanocellulose

We present an in-depth magnetic study of polycrystalline, microstain-free, magnetic, and thermally stable cobalt ferrite (CoFe2O4) octahedrons with an edge dimension of 214 nm. Nanoparticles were synthesized from granular CoFe2O4 nanotubes growing on bacterial nanocellulose and annealed at T = 1273 K. SEM, XRD, and VSM were used to investigate the morphology, structure and magnetic properties of the octahedral particles. The results indicate that heat treatment increases the sizes of the crystallites (2 times) and of the particles (4 times), compared with the starting material. The particles show a change of the magnetization saturation and magnetic anisotropy around 150 K compared with canonical ferrimagnetic materials, associated with a First Order Magnetization Process. The magnetization process as a function of temperature, cooling without (ZFC) and with (FC) different applied magnetic fields are explained by multi-domain theory. ZFC-FC curves show an irreversible branching temperature, which is highly sensitive to the applied magnetic field. In contrast, the temperature for the maximal magnetization value in the ZFC curves, change slightly with the external applied magnetic field, H.

Fabrication of cobalt ferrite/cobalt sulfide hybrid nanotubes with enhanced peroxidase-like activity for colorimetric detection of dopamine

The development of highly sensitive and low-cost biosensors for the detection of dopamine is of paramount importance for medical diagnostics. Herein, we report the preparation of a new peroxidase-like catalyst with a uniform heterostructure by using a technique involving electrospinning, annealing and solvothermal reaction. In this catalyst system, cobalt sulfide (CoS) nanoparticles were homogenously distributed and supported on the surface of cobalt ferrite (CoFe2O4) nanotubes. The as-prepared CoFe2O4/CoS hybrid nanotubes showed remarkably high catalytic efficiency as peroxidase mimics toward the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2. Owing to the synergistic effect between the CoFe2O4 and CoS component, the prepared CoFe2O4/CoS hybrid nanotubes exhibited enhanced peroxidase-like activity, exceeding that of either the CoS nanoparticles or CoFe2O4 nanotubes alone. Dopamine has been widely investigated due to its unique function in the nervous system. Consequently, various approaches have been developed for the sensitive determination of dopamine. In this work, a simple and sensitive colorimetric route for the detection of dopamine was established based on the ability of dopamine to induce the reduction of oxidized TMB to TMB with consequent fading of the blue color. This method shows a wide linear range (0–50μM) and a low detection limit of 0.58μM. The unique heterostructure with spinel/sulfide interfaces represents a new concept for the construction of highly efficient and multifunctional biocatalysts.

C@CoFe2O4 fiber-in-tube mesoporous nanostructure: Formation mechanism and high electrochemical performance as an anode for lithium-ion batteries

In this paper, C@CoFe2O4 with a fiber-in-tube mesoporous nanostructure has been fabricated via a one-step single-spinneret electrospinning technique. This unique nanostructure is made of an outer spinel CoFe2O4 tube and a loose inner fiber composed of the residual carbonaceous materials and metal precursors. The nanostructure's properties, such as morphology, components, structures and thermal stability, are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD), thermogravimetric analysis (TGA), Brunauer, Emmett and Teller type specific area (SBET) determination, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). As an anode material for lithium-ion batteries, the C@CoFe2O4 composite (6.25 wt% carbon content) exhibits a high reversible capacity of 740 mA h g−1 after over 200 cycles at the current density of 200 mA g−1 with excellent cycling stability, which is attributed to its one dimensional continuous fiber-in-tube mesoporous morphology, as well as its stable structure benefiting from the existence of carbonaceous yolk. In addition, pure CoFe2O4 nanotubes can also be obtained by sequentially agitating this product in water, which provides more potential applications of CoFe2O4.

Single-spinneret electrospinning fabrication of CoFe2O4 nanotubes as high-performance anode materials for lithium-ion batteries

Novel CoFe2O4 nanotubes (CFNs) are successfully prepared by the electrospinning technique and subsequent annealing process. When evaluated as anode materials for lithium-ion batteries (LIBs), the CFNs exhibited good electrochemical performance with high specific capacity of 1228mAhg−1, long cycling stability over 160 cycles, and good rate capability (214.7mAhg−1 at 2Ag−1). The improved electrochemical performance can be attributed to the hollow and continuous one dimensional (1D) nanostructure.

Palladium nanoparticles modified electrospun CoFe2O4 nanotubes with enhanced peroxidase-like activity for colorimetric detection of hydrogen peroxide

Herein, we report a simple procedure to decorate small palladium nanoparticles (Pd NPs) on the surface of CoFe2O4 nanotubes; the decorated nanotubes possess intrinsic peroxidase-like activity for the sensitive detection of H2O2.

Fabrication of Au nanoparticles supported on CoFe2O4 nanotubes by polyaniline assisted self-assembly strategy and their magnetically recoverable catalytic properties

This article reports the fabrication of magnetically responsive Au nanoparticles supported on CoFe2O4 nanotubes through polyaniline (PANI) assisted self-assembly strategy which can be used as an efficient magnetically recoverable nanocatalyst. The central magnetic CoFe2O4 nanotubes possess a strong magnetic response under an externally magnetic field, enabling an easy and efficient separation from the reaction system for reuse. The thorn-like PANI layer on the surface of CoFe2O4 nanotubes provides large surface area for supporting Au nanocatalysts due to the electrostatic interactions. The as-prepared CoFe2O4/PANI/Au nanotube assemblies exhibit a high catalytic activity for the hydrogenation of 4-nitrophenol by sodium borohydride (NaBH4) at room temperature, with an apparent kinetic rate constant (Kapp) of about 7.8×10−3s−1. Furthermore, the composite nanocatalyst shows a good recoverable property during the catalytic process. This work affords a reliable way in developing multifunctional nanocomposite for catalysis and other potential applications in many fields.

Synthesis and characterization of CoFe2O4 magnetic nanotubes, nanorods and nanowires. Formation of magnetic structured elastomers by magnetic field-induced alignment of CoFe2O4 nanorods

Magnetic CoFe2O4 nanotubes, nanorods and nanowires were synthesized by the template method. The materials are highly crystalline and formed by compactly packed ceramic particles whose equivalent size diameter depends on the nanostructure type. Nanotubes and nanorods present the remarkable characteristic of having very large coercive fields (1000–1100 Oe) in comparison with nanoparticles of the same crystallite size (400 Oe) while keeping similar saturation magnetization (53–55 emu/g). Nanorods were used as filler material in polydimethylsiloxane elastomer composites, which were structured by curing in the presence of uniform magnetic field, H curing. In that way the nanorods agglomerate in the cured elastomer, forming needles-like structures (pseudo-chains) oriented in the direction of H curing. SEM analysis show that pseudo-chains are formed by bunches of nanorods oriented in that direction. At the considered filler concentration (1 % w/w), the structured elastomers conserve the magnetic properties of the fillers, that is, high coercive fields without observing magnetic anisotropy. The elastomer composites present strong elastic anisotropy, with compression constants about ten times larger in the direction parallel to the pseudo-chains than in the perpendicular direction, as determined by compression stress–strain curves. That anisotropic factor is about three-four times higher than that observed when using spherical CoFe2O4 nanoparticles or elongated Ni nanochains. Hence, the use of morphological anisotropic structures (nanorods) results in composites with enhanced elastic anisotropy. It is also remarkable that the large elastic anisotropy was obtained at lower filler concentration compared with the above-mentioned systems (1 % w/w vs. 5–10 % w/w).

Simulating magnetic nanotubes using a chain of ellipsoid-rings model with a magnetization reversal process by fanning rotation.

Recently, magnetic nanotubes have attracted great attention owing to the advantages of tubular geometry. Of all the physical properties of magnetic nanotubes, the magnetic behavior plays a pivotal role in potential applications, particularly in biotechnology. Modeling magnetic nanotubes provides an effective way to determine the geometry dependent magnetic properties. In the present article, we model the nanotube as a chain of ellipsoid-rings; thus the magnetic behavior of nanotubes is simulated by the fanning rotation of magnetic moments. Based on this model, we further discuss the influence of tubular geometric parameters on the magnetic properties. The calculated magnetic properties of Fe, Co, Ni, Fe3O4 and CoFe2O4 nanotubes are all consistent with their experimental data. Consequently, our model provides an easy and general approach to magnetic nanotubes.

Preparation and characterization of multiferroic CoFe2O4/Bi0.97Ce0.03FeO3 coaxial nanotubes

Multiferroic CoFe2O4 (CFO)/Bi0.97Ce0.03FeO3 (BCFO) coaxial nanotubes were prepared by a sol-gel template method. Transmission electron microscopy revealed that the coaxial nanotubes featured with inner CFO and outer BCFO nanotubes. Selected area electron diffraction confirmed the coexistence of spinel CFO and perovskite BCFO phases in the coaxial nanotubes. Vibrating sample magnetometer measurements showed that the saturated magnetization of the coaxial nanotubes was 3.3 emu/g, smaller than that of CFO nanotubes. The P–E hysteresis loop of the coaxial nanotubes was of poor shape due to possible high conductivity in the inner CFO nanotubes. Dielectric measurements exhibited that the dielectric constant of the coaxial nanotubes decreased while the dielectric loss increased due probably to the small dielectric constant and high conductivity in the inner CFO nanotube. Ferroelectric and magnetic properties were simultaneously demonstrated in the CFO/BCFO coaxial nanotubes.

Preparation and properties of the CoFe2O4/Bi3.15Nd0.85Ti3O12 multiferroic composite coaxial nanotubes

The CoFe2O4 (CFO)/Bi3.15Nd0.85Ti3O12 (BNT) multiferroic composite coaxial nanotubes were prepared by a sol–gel template method. The morphologies of the coaxial nanotubes were characterized and the selected area electron diffraction patterns confirmed the coexistence of spinel CFO and perovskite BNT phase. The vibrating sample magnetometer measurements showed that the saturation magnetization and coercive field of the coaxial nanotubes were 1emu/g and 0.7kOe, respectively, which was contributed totally from the inner CFO nanotubes. The CFO/BNT coaxial nanotubes showed typical ferroelectric hysteresis loop, while the increased leakage current density is likely due to the high conductivity in the inner CFO nanotubes. Our study demonstrated that the CFO/BNT coaxial nanotubes were of both ferroelectric and magnetic features in nanoscale.

Unique magnetic properties and magnetization reversal process of CoFe2O4 nanotubes fabricated by electrospinning

CoFe(2)O(4) nanotubes have been directly fabricated by single-capillary spinneret electrospinning. The external diameter of the CoFe(2)O(4) nanotubes ranges from 60 nm to 160 nm. The morphology and structure characterizations show that individual CoFe(2)O(4) nanotubes are made of CoFe(2)O(4) nanocrystals stacking along the nanotubes with no preferred growth directions and these individual nanocrystals are single crystal with a cubic spinel structure. Each nanocrystal was shown to be a single magnetic domain. The magnetic measurements show that the coercivity (H(c)) of the CoFe(2)O(4) nanotubes decreases from 10 400 Oe at 5 K to 300 Oe at 360 K. The CoFe(2)O(4) nanotubes have a spin reorientation (SR) at 5 K, which is different from CoFe(2)O(4) nanorods and nanoparticles. Based on the observed morphology and crystal structure, a micromagnetic model, "chain-of-rings", is developed to interpret the magnetic behavior of the CoFe(2)O(4) nanotubes. The theoretical coercivity (534 Oe) is in good agreement with the experimental results (509 Oe). It is believed that our work should open a new route to prepare various magnetic ferrite nanotubes and is significant for expanding the application of CoFe(2)O(4) into the new fields.