Ultrafine Fe3O4 Nanoparticles Research Articles

Hollow carbon nanosphere embedded with ultrafine Fe3O4 nanoparticles as high performance Li-ion battery anode

Hollow carbon nanospheres embedded with ultrafine Fe3O4 nanoparticles (Fe3O4@HCNS) were synthesized by using carboxyl functionalized polystyrene latexes as template and poly dopamine as carbon precursor. The ultrafine Fe3O4 nanoparticles (NPs) had a small size of 3∼5nm and the HCNS had a thin shell thickness of 15nm in the Fe3O4@HCNS. As a promising anode material for lithium-ion batteries, the Fe3O4@HCNS exhibited high reversible capacity, excellent cycling stability (1380mAhg−1 after 200 cycles at 1Ag−1) and high-rate capability (475mAhg−1 at 5Ag−1, 290mAhg−1 at 10Ag−1). The outstanding performance was attributed to the unique structure of the Fe3O4@HCNS, which greatly shorten the path of Li ions intercalation during charging and discharging.

Grape-Like Fe3O4 Agglomerates Grown on Graphene Nanosheets for Ultrafast and Stable Lithium Storage.

An in situ simple and effective synthesis method is effectively exploited to construct MOF-derived grape-like architecture anchoring on nitrogen-doped graphene, in which ultrafine Fe3O4 nanoparticles are uniformly dispersed (Fe3O4@C/NG). In this hybrid hierarchical structure, new synergistic features are accessed. The graphene oxide plane with functional groups is expected to alleviate the aggregation problem in the MOFs' growth. Moreover, the morphology and size of iron-based MOFs and carbon content are conveniently controlled by controlling the solution concentration of precursor. Through making use of in situ carbonization of the organic ligands in MOFs, Fe3O4 subunits are effectively protected by 3D interconnected conductive carbon at microscale. Consequently, when applied as anode materials, even as high as 10 A g(-1) after 1000 cycles, Fe3O4@C/NG still maintains as high as 458 mA h g(-1).

In-situ TEM examination and exceptional long-term cyclic stability of ultrafine Fe3O4 nanocrystal/carbon nanofiber composite electrodes

Scalable synthesis of electrode materials with long cyclic life, high energy and power densities is a prerequisite for next-generation Li ion batteries. Freestanding composite films are prepared by one-pot electrospinning, in which ultrafine Fe3O4 nanoparticles are uniformly dispersed in a continuous carbon nanofiber (CNF) matrix. The Fe3O4/CNF electrodes deliver remarkable electrochemical performance, e.g. a reversible capacity of 881mAhg−1 at 0.2Ag−1, excellent cyclic stability of 687mAhg−1 after 350 cycles at 0.5Ag−1 and a high-rate capability of 422mAhg−1 after 1000 cycles at 5.0Ag−1 with 84% capacity retention. These values are among the highest ever reported for various nanostructured iron oxide-based electrodes. Even after prolonged cycles, the CNF matrix containing ultrafine nanocrystals remains structurally sound without damage. In contrast, the Fe3O4/CNF-750 electrode containing larger Fe3O4 particles obtained at a higher carbonization temperature of 750°C presents faster capacity decay and cracking of CNF matrix due to larger volume expansion. The in-situ TEM analysis is used to provide an insight into real-time structural evolution and conversion reactions. It is revealed that (i) upon initial lithiation, the Fe3O4 nanoparticles embedded in the CNF are gradually reduced to Fe nanograins along the Li ion diffusion direction; and (ii) after delithiation, a new oxidation product, FeO, emerges, instead of Fe3O4. The irreversible phase conversion from Fe3O4 to Fe is the first of its kind reported for Fe3O4 electrodes although a similar phenomenon has been proposed for other electrode materials, like Fe2O3 and Co3O4.

Synthesis of three-dimensional rare-earth ions doped CNTs-GO-Fe3O4 hybrid structures using one-pot hydrothermal method

Rechargeable lithium ion batteries (LIBs) are currently the dominant power source for all sorts of electronic devices due to their low cost and high energy density. The cycling stability of LIBs is significantly compromised due to the broad satellite peak for many anode materials. Herein, we develop a facile hydrothermal process for preparing rare-earth (Er, Tm) ions doped three-dimensional (3D) transition metal oxides/carbon hybrid nanocomposites, namely CNTs-GO-Fe3O4, CNTs-GO-Fe3O4-Er and CNTs-GO-Fe3O4-Tm. The GO sheets and CNTs are interlinked by ultrafine Fe3O4 nanoparticles forming three-dimensional (3D) architectures. When evaluated as anode materials for LIBs, the CNTs-GO-Fe3O4 hybrid composites have a bigger broad satellite peak. As for the CNTs-GO-Fe3O4-Er and CNTs-GO-Fe3O4-Tm hybrid composites, the broad satellite peak can be completely eliminated. When the current density changes from 5 C back to 0.1 C, the capacity of CNTs-GO-Fe3O4-Tm hybrid composites can recover to 1023.9 mAhg−1, indicating an acceptable rate capability. EIS tests show that the charge transfer resistance does not change significantly after 500 cycles, demonstrating that the cycling stability of CNTs-GO-Fe3O4-Tm hybrid composites are superior to CNTs-GO-Fe3O4 and CNTs-GO-Fe3O4-Er hybrid structures.

Rationally Separating the Corona and Membrane Functions of Polymer Vesicles for Enhanced T₂ MRI and Drug Delivery.

It is an important challenge to in situ grow ultrafine super-paramagnetic iron oxide nanoparticles (SPIONs) in drug carriers such as polymer vesicles (also called polymersomes) while keeping their biodegradability for enhanced T2-weighted magnetic resonance imaging (MRI) and drug delivery. Herein, we present a new strategy by rationally separating the corona and membrane functions of polymer vesicles to solve the above problem. We designed a poly(ethylene oxide)-block-poly(ε-caprolactone)-block-poly(acrylic acid) (PEO43-b-PCL98-b-PAA25) triblock copolymer and self-assembled it into polymer vesicle. The PAA chains in the vesicle coronas are responsible for the in situ nanoprecipitation of ultrafine SPIONs, while the vesicle membrane composed of PCL is biodegradable. The SPIONs-decorated vesicle is water-dispersible, biocompatible, and slightly cytotoxic to normal human cells. Dynamic light scattering, transmission electron microscopy, energy disperse spectroscopy, and vibrating sample magnetometer revealed the formation of ultrafine super-paramagnetic Fe3O4 nanoparticles (1.9 ± 0.3 nm) in the coronas of polymer vesicles. Furthermore, the CCK-8 assay revealed low cytotoxicity of vesicles against normal L02 liver cells without and with Fe3O4 nanoparticles. The in vitro and in vivo MRI experiments confirmed the enhanced T2-weighted MRI sensitivity and excellent metastasis in mice. The loading and release experiments of an anticancer drug, doxorubicin hydrochloride (DOX·HCl), indicated that the Fe3O4-decorated magnetic vesicles have potential applications as a nanocarrier for anticancer drug delivery. Moreover, the polymer vesicle is degradable in the presence of enzyme such as Pseudomonas lipases, and the ultrafine Fe3O4 nanoparticles in the vesicle coronas are confirmed to be degradable under weakly acidic conditions. Overall, this decoration-in-vesicle-coronas strategy provides us with a new insight for preparing water-dispersible ultrafine super-paramagnetic Fe3O4 nanoparticles with promising theranostic applications in biomedicine.

Removal of As(III) from Aqueous Solution Using Functionalized Ultrafine Iron Oxide Nanoparticles

Arsenic toxicity has become a major concern worldwide. Remediation of this problem needs the development of technology with improved materials and systems with high efficiency. We have demonstrated a simple and efficient method for the absolute removal of As(III) from high concentration As(III) treated water with a low contact time period. The process of As(III) adsorption follows pseudo-second-order kinetic model. The mechanism for high-adsorption efficiency is attributed to fatty acid binding domain-mediated surface conjugation of ultrafine Fe2O3 nanoparticles with As(III). We have also ensured the simultaneous separation of arsenic sorbed nanoparticles by entrapping them in hydrophilic calcium alginate beads and thereby a pure arsenic free solution has been obtained.

Curie temperature reduction in SiO2-coated ultrafine Fe3O4 nanoparticles: Quantitative agreement with a finite-size scaling law

We report high-temperature magnetic measurements for SiO2-coated ultrafine Fe3O4 nanoparticles. The Curie temperatures of the ultrafine Fe3O4 nanoparticles are significantly reduced and follow a finite-size scaling law predicted from Monte Carlo simulations. Our current result provides the first quantitative confirmation of the finite-size scaling law for quasi-zero-dimensional magnetic systems.

Protein assisted hydrothermal synthesis of ultrafine magnetite nanoparticle built-porous oriented fibers and their structurally enhanced adsorption to toxic chemicals in solution

A facile and green route is presented for mass production of oriented magnetite porous fibers (with >96% in yield), based on the protein assisted hydrothermal method in citric aqueous solution. The magnetite fibers are nearly cylindrical in shape, several ten micrometres in length and 120 nm in mean diameter. The whole single fibers are packed by the ultrafine Fe3O4 nanoparticles with similar crystal orientation (along [111] direction), and show porous structure with pore size below 5nm and high specific surface area (123 m2 g−1), exhibiting good magnetic property at room temperature. Further experiments have revealed that the formation of such porous submicro-fibers is mainly attributed to the protein directed/magnetic dipole-induced orientation assembling of Fe3O4 nanoparticles. The proper conditions, including the moderate protein and citric acid concentrations, pH value in the precursor solution and suitable reaction temperature, are crucial to formation of the magnetite porous fibers. More importantly, such magnetite porous fibers can be used as an effective adsorbent for removal of some toxic chemicals, not only heavy metal anions and cations with good recycling performance, but also some non-polar contaminant molecules in solution, and have exhibited significantly structurally enhanced adsorption performance and very high removal performance for Cr(VI) (anions), Hg(II) (cations) and the polychlorinated biphenyl (non-polar molecules). This material makes it possible to develop lower magnetic separation process to highly efficiently enrich and remove the toxic chemicals, which are usually difficult to remove, in one step. This is particularly important in environmental remediation.

Synthesis of Ultra-Fine Iron-Oxide Nano-Particles in a Diffusion Flame with Electro-Spraying Assistance

Ultra-fine Fe2O3 nano-particles are synthesized using H2/O2 co-axial diffusion flame with the state-of-the-art electro-spraying (e-spray) technique at atmospheric condition. Fe(CO)5 is used as a precursor and the liquid phase Fe(CO)5 is injected directly into the center of the flame using the electro-spraying method. The synthesized particle morphology sampled from the inside of flame is analyzed by TEM. The synthesized particles showed different crystal structures for different particle collection method and the collection positions.