Fe3O4 Nanocrystals Research Articles

Magnetite Nanocrystals as Anode Electrode Materials for Rechargeable Li-Ion Batteries.

Monodispersed magnetite (Fe3O4) nanocrystals were synthesized and their electrochemical properties as anode electrode materials for rechargeable lithium ion batteries were measured. The magnetite anodes, in the form of monodispersed nanospheres with average diameters (< 10 nm), show particle size effects. Specifically, the first discharge curves show that the nanocrystals can hold much more Li+ per formula unit than their counterparts in bulk before the reduction begins. The electrolyte decomposition takes place before the reduction reaction is completed. The cycling performance of the Fe3O4 nanocrystals after being heated at 300 degrees C for different lengths of time show that heating can improve the integration of the nanocrystals and increase their capacity retention in consequence.

Multiscale Assembly of Grape-Like Ferroferric Oxide and Carbon Nanotubes: A Smart Absorber Prototype Varying Temperature to Tune Intensities.

Ideal electromagnetic attenuation material should not only shield the electromagnetic interference but also need strong absorption. Lightweight microwave absorber with thermal stability and high efficiency is a highly sought-after goal of researchers. Tuning microwave absorption to meet the harsh requirements of thermal environments has been a great challenge. Here, grape-like Fe3O4-multiwalled carbon nanotubes (MWCNTs) are synthesized, which have unique multiscale-assembled morphology, relatively uniform size, good crystallinity, high magnetization, and favorable superparamagnetism. The Fe3O4-MWCNTs is proven to be a smart microwave-absorber prototype with tunable high intensities in double belts in the temperature range of 323-473 K and X band. Maximum absorption in two absorbing belts can be simultaneously tuned from ∼-10 to ∼-15 dB and from ∼-16 to ∼-25 dB by varying temperature, respectively. The belt for reflection loss ≤-20 dB can almost cover the X band at 323 K. The tunable microwave absorption is attributed to effective impedance matching, benefiting from abundant interfacial polarizations and increased magnetic loss resulting from the grape-like Fe3O4 nanocrystals. Temperature adjusts the impedance matching by changing both the dielectric and magnetic loss. The special assembly of MWCNTs and magnetic loss nanocrystals provides an effective pathway to realize excellent absorbers at elevated temperature.

A novel Trojan-horse targeting strategy to reduce the non-specific uptake of nanocarriers by non-cancerous cells

One big challenge with active targeting of nanocarriers is non-specific binding between targeting molecules and non-target moieties expressed on non-cancerous cells, which leads to non-specific uptake of nanocarriers by non-cancerous cells. Here, we propose a novel Trojan-horse targeting strategy to hide or expose the targeting molecules of nanocarriers on-demand. The non-specific uptake by non-cancerous cells can be reduced because the targeting molecules are hidden in hydrophilic polymers. The nanocarriers are still actively targetable to cancer cells because the targeting molecules can be exposed on-demand at tumor regions. Typically, Fe3O4 nanocrystals (FN) as magnetic resonance imaging (MRI) contrast agents were encapsulated into albumin nanoparticles (AN), and then folic acid (FA) and pH-sensitive polymers (PP) were grafted onto the surface of AN-FN to construct PP-FA-AN-FN nanoparticles. Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), transmission electron microscope (TEM) and gel permeation chromatography (GPC) results confirm successful construction of PP-FA-AN-FN. According to difference of nanoparticle-cellular uptake between pH 7.4 and 5.5, the weight ratio of conjugated PP to nanoparticle FA-AN-FN (i.e. graft density) and the molecular weight of PP (i.e. graft length) are optimized to be 1.32 and 5.7 kDa, respectively. In vitro studies confirm that the PP can hide ligand FA to prevent it from binding to cells with FRα at pH 7.4 and shrink to expose FA at pH 5.5. In vivo studies demonstrate that our Trojan-horse targeting strategy can reduce the non-specific uptake of the PP-FA-AN-FN by non-cancerous cells. Therefore, our PP-FA-AN-FN might be used as an accurately targeted MRI contrast agent.

Facile synthesis of magnetically separable reduced graphene oxide/magnetite/silver nanocomposites with enhanced catalytic activity

In this study, the combination of magnetite (Fe3O4) with reduced graphene oxide (RGO) generates a new hybrid substrate for the dispersion of noble metal nanoparticles. Well-dispersed silver (Ag) nanoparticles loaded on the surface of Fe3O4 modified RGO are achieved by an efficient two-step approach. Through reducing Ag+ ions, highly dispersed Ag nanoparticles are in-situ formed on the RGO/Fe3O4 substrate. It is found that the existence of Fe3O4 nanocrystals can significantly improve the dispersity and decrease the particle size of the in-situ formed Ag nanoparticles. Magnetic study reveals that the as-prepared RGO/Fe3O4/Ag ternary nanocomposites display room-temperature superparamagnetic behavior. The catalytic properties of the RGO/Fe3O4/Ag ternary nanocomposites were evaluated with the reduction of 4-nitrophenol into 4-aminophenol as a model reaction. The as-synthesized RGO/Fe3O4/Ag ternary catalysts exhibit excellent catalytic stability and much higher catalytic activity than the corresponding RGO/Ag catalyst. Moreover, the RGO/Fe3O4/Ag catalysts can be easily magnetically separated for reuse. This study further demonstrates that nanoparticles modified graphene can act as an effective hybrid substrate for the synthesis of multi-component and multifunctional graphene-based composites.

Fabrication of Supported AuPt Alloy Nanocrystals with Enhanced Electrocatalytic Activity for Formic Acid Oxidation through Conversion Chemistry of Layer-Deposited Pt(2+) on Au Nanocrystals.

The exploitation of nanoconfined conversion of Au- and Pt-containing binary nanocrystals for developing a controllable synthesis of surfactant-free AuPt nanocrystals with enhanced formic acid oxidation (FAO) activity is reported, which can be stably and evenly immobilized on various support materials to diversify and optimize their electrocatalytic performance. In this study, an atomic layer of Pt(2+) species is discovered to be spontaneously deposited in situ on the Au nanocrystal generated from a reverse-microemulsion solution. The resulting Au/Pt(2+) nanocrystal thermally transforms into a reduced AuPt alloy nanocrystal during the subsequent solid-state conversion process within the SiO2 nanosphere. The alloy nanocrystals can be isolated from SiO2 in a surfactant-free form and then dispersedly loaded on the carbon sphere surface, allowing for the production of a supported electrocatalyst that exhibits much higher FAO activity than commercial Pt/C catalysts. Furthermore, by involving Fe3O4 nanocrystals in the conversion process, the AuPt alloy nanocrystals can be grown on the oxide surface, improving the durability of supported metal catalysts, and then uniformly loaded on a reduced graphene oxide (RGO) layer with high electroconductivity. This produces electrocatalytic AuPt/Fe3O4/RGO nanocomposites whose catalyst-oxide-graphene triple-junction structure provides improved electrocatalytic properties in terms of both activity and durability in catalyzing FAO.

Size Dependence of Metal-Insulator Transition in Stoichiometric Fe₃O4₄Nanocrystals.

Magnetite (Fe3O4) is one of the most actively studied materials with a famous metal-insulator transition (MIT), so-called the Verwey transition at around 123 K. Despite the recent progress in synthesis and characterization of Fe3O4 nanocrystals (NCs), it is still an open question how the Verwey transition changes on a nanometer scale. We herein report the systematic studies on size dependence of the Verwey transition of stoichiometric Fe3O4 NCs. We have successfully synthesized stoichiometric and uniform-sized Fe3O4 NCs with sizes ranging from 5 to 100 nm. These stoichiometric Fe3O4 NCs show the Verwey transition when they are characterized by conductance, magnetization, cryo-XRD, and heat capacity measurements. The Verwey transition is weakly size-dependent and becomes suppressed in NCs smaller than 20 nm before disappearing completely for less than 6 nm, which is a clear, yet highly interesting indication of a size effect of this well-known phenomena. Our current work will shed new light on this ages-old problem of Verwey transition.

A General Method to Fabricate Free-Standing Electrodes: Sulfonate Directed Synthesis and their Li+ Storage Properties

For materials based on a spatially varied conversion reaction, Li+ storage properties largely hinge on the rational design of the concurrent electronic and ionic pathways in the electrode. We herein present a scalable approach for integrating size-tunable Fe3O4 nanocrystals with hierarchical porous carbon foam by employing sulfonated high internal phase emulsion polymers (polyHIPE) as the carbon source and substrate. To verify the feasibility of our configuration design, the electrodes of such a type were directly evaluated in pouch cells without using an auxiliary binder or a metallic current collector: The best performing composite electrode, with optimized oxide size range, exhibits a good capacity retention of 89.7% of the first charge capacity after 100 cycles and high rate durability up to 4 A g–1. Furthermore, this synthetic approach was also applied to develop carbon/FeS free-standing anodes using the sulfonate groups as the sulfur source, demonstrating its generic applicability to the fabrication...

Carbon-coated Fe2O3 nanocrystals with enhanced lithium storage capability

Homogeneous and highly crystalline Fe2O3 nanocrystals (∼8nm) embedded in interconnected carbon nanospheres (∼50nm) (Fe2O3@C) have been fabricated by one-step hydrothermal reaction followed by annealing with Ar. When used as the anode materials for lithium-ion batteries, the Fe2O3@C nanospheres with 55.24wt% Fe2O3 deliver high reversible lithium storage capacity (826mAh/g at 0.1A/g after 20 cycles), high Coulombic efficiency (∼99%) and good cycling stability, which are much better than that of commercial Fe2O3 nanoparticles. These excellent electrochemical performances could be attributed to the robust and high-conducting interconnected carbon nanospheres embedded with a mass of small Fe2O3 nanocrystals, which not only can offer large quantity of accessible active sites for lithium-ion reaction as well as good conductivity and short diffusion length for electron and ion transport, but also can effectively suppress the aggregation and buffer the volume expansion of Fe2O3 nanocrystals during the repeated lithiation and delithiation processes.

Graphene nanosheets decorated with tunable magnetic nanoparticles and their efficiency of wastewater treatment

Magnetic graphene–Fe3O4 nanocomposites (G/Fe3O4) were fabricated by a facile and fast one-pot method and used as adsorbent to remove dye for wastewater using Rhodamine B as the adsorbate. Samples with different weight ratios of graphene oxide (GO) to Fe3O4 were prepared. The transmission electron microscopy results exhibit that the sizes of Fe3O4 nanocrystals decrease with the increasing of weight ratio of GO to Fe3O4. The magnetic characterization demonstrates that the saturation magnetization of nanocomposites decreases with the decreasing sizes of Fe3O4 nanocrystals. The investigation of adsorption kinetics and isotherm indicates the adsorption process can be described by Langmuir model and nanocomposites with the smaller sizes of Fe3O4 nanoparticles show better adsorption ability. Furthermore, the adsorbents could be recovered conveniently by magnetic separation and recyclable used after desorption process, and the decline in efficiencies of all samples is not more than 1.5% after five cycling runs.

ChemInform Abstract: A Sustainable Iron‐Based Sodium Ion Battery of Porous Carbon—Fe3O4/Na2FeP2 O7 with High Performance.

AbstractA porous C—Fe3O4 composite anode material consisting of highly dispersed Fe3O4 nanocrystals within the porous carbon is fabricated from an EtOH solution of Pluronic F127, Fe(NO3)3, and resol‐EtOH by stirring for 1 h followed by careful drying at 100 °C and calcination under Ar (500 °C, 2 h).

Highly ordered mesoporous few-layer graphene frameworks enabled by fe3 o4 nanocrystal superlattices.

While great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self-assembled superlattices of Fe3 O4 nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face-centered-cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium-ion batteries, thus retaining a specific capacity of 520 mAh g(-1) at a current density of 300 mA g(-1) after 400 cycles.

Highly Ordered Mesoporous Few‐Layer Graphene Frameworks Enabled by Fe3O4 Nanocrystal Superlattices

AbstractWhile great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self‐assembled superlattices of Fe3O4 nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face‐centered‐cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium‐ion batteries, thus retaining a specific capacity of 520 mAh g−1 at a current density of 300 mA g−1 after 400 cycles.

P‐Si/SnO2/Fe2O3 Core/Shell/Shell Nanowire Photocathodes for Neutral pH Water Splitting

Silicon is one of the promising materials for solar water splitting and hydrogen production; however, it suffers from two key factors, including the large external potential required to drive water splitting reactions at its surface and its instability in the electrolyte. In this study, a successful fabrication of novel p‐Si/n‐SnO2/n‐Fe2O3 core/shell/shell nanowire (css‐NW) arrays, consisting of vertical Si NW cores coated with a thin SnO2 layer and a dense Fe2O3 nanocrystals (NCs) shell, and their application for significantly enhanced solar water reduction in a neutral medium is reported. The p‐Si/n‐SnO2/n‐Fe2O3 css‐NW structure is characterized in detail using scanning, transmission, and scanning transmission electron microscopes. The p‐Si/n‐SnO2/n‐Fe2O3 css‐NWs show considerably improved photocathodic performances, including higher photocurrent and lower photocathodic turn‐on potential, compared to the bare p‐Si NWs or p‐Si/n‐SnO2 core/shell NWs (cs‐NWs), due to increased optical absorption, enhanced charge separation, and improved gas evolution. As a result, photoactivity at 0 V versus reversible hydrogen electrode and a low onset potential in the neutral solution are achieved. Moreover, p‐Si/n‐SnO2/n‐Fe2O3 css‐NWs exhibit long‐term photoelectrochemical stability due to the Fe2O3 NCs shell well protection. These results reveal promising css‐NW photoelectrodes from cost‐effective materials by facile fabrication with simultaneously improved photocathodic performance and stability.

Preparation and characterization of magnetic polyimide composite films copolymerized with aminophthalocyanine-coated Fe3O4 nanocrystals

Iron-aminophthalocyanine-coated Fe3O4 hybrid nanospheres were synthesized by a one-step solvent-thermal method and followed by a catalytic hydrogenation route. To effectively utilize the excellent magnetic sensitivity of the functional aminophthalocyanine/Fe3O4 hybrid nanospheres, we have developed a novel series of flexible Fe3O4@polyimide (PI) composite films, which was prepared with various Fe3O4/FePc–NH2 nanoparticle loadings (7, 15, 27 and 40 wt%). All of the flexible thin films have uniform morphology without any agglomeration, which had been confirmed by the analysis of scanning electron microscope images. The above composite films, which have the higher saturation magnetization compared with that of the corresponding pure Fe3O4/PI films, illustrate that the excellent compatibility and homogeneous dispersion of the amine-coated Fe3O4 particles in the PI matrix based on the strong chemisorptions of PI onto the Fe3O4 surfaces and polymerization reactions between the amine groups and anhydride groups could significantly affect the magnetic properties of nanocomposite materials. The observed enhanced thermal stabilities, dramatic increased storage modulus and increased glass transfer temperatures (Tgs) of the magnetic films with increasing the particle loadings indicate that the composites could be a candidate to be used as high-performance absorbing materials.

Controlled synthesis of Fe3O4/ZIF-8 nanoparticles for magnetically separable nanocatalysts.

Fe3O4/ZIF-8 nanoparticles were synthesized through a room-temperature reaction between 2-methylimidazolate and zinc nitrate in the presence of Fe3O4 nanocrystals. The particle size, surface charge, and magnetic loading can be conveniently controlled by the dosage of Zn(NO3)2 and Fe3O4 nanocrystals. The as-prepared particles show both good thermal stability (stable to 550 °C) and large surface area (1174 m(2) g(-1)). The nanoparticles also have a superparamagnetic response, so that they can strongly respond to an external field during magnetic separation and disperse back into the solution after withdrawal of the magnetic field. For the Knoevenagel reaction, which is catalyzed by alkaline active sites on external surface of catalyst, small Fe3O4/ZIF-8 nanoparticles show a higher catalytic activity. At the same time, the nanocatalysts can be continuously used in multiple catalytic reactions through magnetic separation, activation, and redispersion with little loss of activity.

One-pot hydrothermal synthesis of Pd/Fe3O4 nanocomposite in HEPES buffer solution and catalytic activity for Suzuki reaction

The Pd/Fe3O4 nanocomposite integrates versatile Pd nanocatalysts with magnetic separation, and has great potential in fine chemical and pharmaceutical synthesis. Its preparation usually involves multi-steps. Herein it was prepared via a facile one-pot hydrothermal synthesis in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer solution with the assistant of polyvinylpyrrolidone (PVP). HEPES plays multi-functions, particularly as a ligand to enhance the oxidation of Fe2+ to Fe3+ and as a buffer to control the pH value at slightly basic conditions (ca. 7.4) for the formation of crystalline Fe3O4 phase via Fe2+/Fe3+ co-precipitation. PVP works as a dispersant to prevent the particle from aggregation. The obtained Pd/Fe3O4 nanocomposite comprised uniform Pd nanoparticles (ca. 5nm) deposited on Fe3O4 nanocrystals (ca. 15nm). It exhibited excellent catalytic activity and stability for various Suzuki coupling reactions, and could be efficiently recovered with a magnet and recycled for at least 10 cycles without losing catalytic activity.

Protease-activated ratiometric fluorescent probe for pH mapping of malignant tumors.

A protease-activated ratiometric fluorescent probe based on fluorescence resonance energy transfer between a pH-sensitive fluorescent dye and biocompatible Fe3O4 nanocrystals was constructed. A peptide substrate of MMP-9 served as a linker between the particle quencher and the chromophore that was covalently attached to the antitumor antibody. The optical response of the probe to activated MMP-9 and gastric cell line SGC7901 tumor cells was investigated, followed by in vivo tumor imaging. Based on the ratiometric pH response to the tumor microenvironment, the resulting probe was successfully used to image the pH of subcutaneous tumor xenografts.

Renewable chitin from marine sponge as a thermostable biological template for hydrothermal synthesis of hematite nanospheres using principles of extreme biomimetics

AbstractChitin originating from marine sponges possesses a unique nanofibrillar network structure that is the basic element of the microtubular scaffold-like skeleton of these organisms. Sponge chitin represents an intriguing example of thermostability, as it is stable up to 400 °C. It also constitutes a renewable biological source due to the high regeneration ability of Aplysina sponges under marine farming conditions. These properties can be exploited for the facile and environmentally friendly creation of novel, biocompatible organic-inorganic hybrid materials with a range of uses. Here, chitin-based scaffolds isolated from the skeleton of marine demosponge Aplysina aerophoba were used as a template for the in vitro formation of iron oxide from a saturated iron(III) chloride solution, under hydrothermal conditions (pH~1.5, 90 °C). The resultant chitin-Fe2O3 three dimensional composites, prepared for the first time via hydrothermal synthesis route, were thoroughly characterized using light, fluorescence and scanning electron microscopy; as well as with analytical methods like Raman spectroscopy, electron diffraction and HR-TEM. The results show that this versatile method allows for efficient chitin mineralization with respect to hematite. Additionally, we demonstrate that chitin nanofibers template the nucleation of uniform Fe2O3 nanocrystals.

Weaving a two-dimensional fishing net from titanoniobate nanosheets embedded with Fe₃O₄ nanocrystals for highly efficient capture and isotope labeling of phosphopeptides.

Qualitative and quantitative characterization of phosphopeptides by means of mass spectrometry (MS) is the main goal of MS-based phosphoproteomics, but suffers from their low abundance in the large haystack of various biological molecules. Herein, we introduce two-dimensional (2D) metal oxides to tackle this biological separation issue. A nanocomposite composed of titanoniobate nanosheets embedded with Fe₃O₄ nanocrystals (Fe₃O₄-TiNbNS) is constructed via a facile cation-exchange approach, and adopted for the capture and isotope labeling of phosphopeptides. In this nanoarchitecture, the 2D titanoniobate nanosheets offer enlarged surface area and a spacious microenvironment for capturing phosphopeptides, while the Fe₃O₄ nanocrystals not only incorporate a magnetic response into the composite but, more importantly, also disrupt the restacking process between the titanoniobate nanosheets and thus preserve a greater specific surface for binding phosphopeptides. Owing to the extended active surface, abundant Lewis acid sites and excellent magnetic controllability, Fe₃O₄-TiNbNS demonstrates superior sensitivity, selectivity and capacity over homogeneous bulk metal oxides, layered oxides, and even restacked nanosheets in phosphopeptide enrichment, and further allows in situ isotope labeling to quantify aberrantly-regulated phosphopeptides from sera of leukemia patients. This composite nanosheet greatly contributes to the MS analysis of phosphopeptides and gives inspiration in the pursuit of 2D structured materials for separation of other biological molecules of interests.

Au25 cluster functionalized metal-organic nanostructures for magnetically targeted photodynamic/photothermal therapy triggered by single wavelength 808 nm near-infrared light.

Near-infrared (NIR) light-induced cancer therapy has gained considerable interest, but pure inorganic anti-cancer platforms usually suffer from degradation issues. Here, we designed metal-organic frameworks (MOFs) of Fe3O4/ZIF-8-Au25 (IZA) nanospheres through a green and economic procedure. The encapsulated Fe3O4 nanocrystals not only produce hyperthemal effects upon NIR light irradiation to effectively kill tumor cells, but also present targeting and MRI imaging capability. More importantly, the attached ultrasmall Au25(SR)18(-) clusters (about 2.5 nm) produce highly reactive singlet oxygen ((1)O2) to cause photodynamic effects through direct sensitization under NIR light irradiation. Furthermore, the Au25(SR)18(-) clusters also give a hand to the hyperthemal effect as photothermal fortifiers. This nanoplatform exhibits high biocompatibility and an enhanced synergistic therapeutic effect superior to any single therapy, as verified by in vitro and in vivo assay. This image-guided therapy based on a metal-organic framework may stimulate interest in developing other kinds of metal-organic materials with multifunctionality for tumor diagnosis and therapy.