Amorphous Fe2O3 Nanoparticles Research Articles

Uniform, Scalable, High-Temperature Microwave Shock for Nanoparticle Synthesis through Defect Engineering

Summary Here we demonstrate a thermal shock synthesis method triggered by microwave irradiation for the rapid synthesis of nanoparticles on reduced graphene oxide (RGO) substrate. With properly controlled reduction, RGO has high electrical conductivity while maintaining functional groups, leading to an extremely efficient microwave absorption of ∼70%. The high utilization of microwaves results in the ability to raise the temperature to 1,600 K in just 100 ms, which is followed by rapid quenching to room temperature. The defects on the RGO are crucial for achieving this record-high microwave-induced temperature as these defects play a fundamental role in absorbing the radiation as well as the self-quenching mechanism. By loading precursors onto RGO, we can utilize rapid temperature change to synthesize nanoparticles. The nanoparticles are ∼10 nm with uniform distribution. This facile, rapid, and universal synthesis technique has the potential to be employed in large-scale production of nanomaterials and suggests a new direction for nanosynthesis.

Graphene oxide-induced synthesis of button-shaped amorphous Fe2O3/rGO/CNFs films as flexible anode for high-performance lithium-ion batteries

Constructing high-performance flexible lithium-ion batteries (LIBs) is imperative to satisfy the rapid demand of flexible and wearable electronics. Herein, we demonstrate a novel strategy to fabricate button-shaped amorphous Fe2O3/rGO/carbon nanofibers (am-Fe2O3/rGO/CNFs) films as freestanding flexible anodes for LIBs through in-situ electrospinning and subsequent one-step carbonization. Intercalating highly oxidized GO into the electrospun precursor not only induces tight growth of button-shaped amorphous Fe2O3 nanoparticles onto rimous CNFs matrix, but also substantially enhances the mechanical flexibility of the resulting films. Owing to the distinctive hierarchical structure, especially amorphous nature of Fe2O3 and intimate connection between am-Fe2O3 and the conductive substrate, the am-Fe2O3/rGO/CNFs-20 film delivers an excellent reversible capacity of 811 mA h g−1 at 0.1 A g−1, as well as remarkable rate performance and cycling stability (584 mA h g−1 over 400 cycles at a high current density of 2 A g−1). The electrode also exhibits impressive flexibility, which can power an array of light-emitting diodes, even bended and folded, demonstrating great potential for flexible LIBs. The facile synthesis strategy and excellent electrochemical performance endow it with great potential for application in flexible energy storage.

Amorphous Fe2O3 nanoparticles embedded into hypercrosslinked porous polymeric matrix for designing an easily separable and recyclable photocatalytic system

The use of polymer sorbents in wastewater treatment can generate large-scale secondary waste due to the oxidation of the polymer matrix, stemming from the ionogenic functional groups or impurities. In this work, amorphous Fe2O3 nanoparticles were embedded into a porous non-ionogenic polymer matrix (Porolas) using two different Fe(III) salts (iron nitrate and iron oxalate) for designing an easily separable and recyclable photocatalytic system. The Fe2O3-Porolas composites were prepared by a simple method: an impregnation of the Porolas by Fe(III) salts and calcination at 250 °C for 1 h. The sorption capacity and photocatalytic activity of the Fe2O3-Porolas composites were evaluated by the removal of methylene blue (MB) from model-contaminated water under UV light irradiation in the presence of oxalic acid. The characterization results, particularly from X-ray photoelectron spectroscopy and Mössbauer spectroscopy, confirmed the formation of highly dispersed amorphous Fe2O3 nanoparticles that are embedded in the Porolas matrix. An increase in the content of the embedded Fe2O3 nanoparticles decreased specific surface area (SBET), MB sorption capacity, and apparent photodegradation rate constant (kapp) but increased the photodegradation efficiency of MB. The enhancement in MB removal can be attributed to the photocatalytic activities of the Porolas and Fe2O3 nanoparticles (heterogeneous photocatalysis), sorption effect, and leaching of Fe ions in aqueous solution (homogeneous photocatalysis). The scaffold network of the Porolas and highly dispersed Fe2O3 nanoparticles additionally contributed to the enhancement of photocatalytic activity of the Fe2O3-Porolas composite. Almost complete decolorization of MB (96–98%) and more than 97% TOC were achieved in this study, confirming simultaneous mineralization of both MB and OA in aqueous solution. The Fe2O3-Porolas composite can be easily prepared and inexpensive to design an easily separable and recyclable photocatalytic system for wastewater treatment.

Amorphous Fe2O3/Graphene Composite Nanosheets with Enhanced Electrochemical Performance for Sodium-Ion Battery.

With the increasing use of sodium-ion batteries (SIBs), developing cost-effective anode materials, such as metal oxide, for Na-ion storage is one of the most attractive topics. Due to the obviously larger ion radius of Na than that of Li, most metal oxide electrode materials fail to exhibit the same high performance for SIBs like that of Li-ion batteries. Herein, iron oxide was employed to demonstrate a concept that rationally designing an amorphous structure should be useful to enhance Na-ion storage performance of a metal oxide. Amorphous Fe2O3/graphene composite nanosheets (Fe2O3@GNS) were successfully synthesized by a facile approach as anodes for SIBs. It reveals that amorphous Fe2O3 nanoparticles with an average diameter of 5 nm were uniformly anchored on the surface of graphene nanosheets by the strong C-O-Fe oxygen-bridge bond. Compared to well-crystalline Fe2O3, amorphous Fe2O3@GNS exhibited superior sodium storage properties such as high electrochemical activity, high initial Coulombic efficiency of 81.2%, and good rate performance. At a current density of 100 mA/g, amorphous Fe2O3@GNS composites show a specific capacity of 440 mAh/g, which is obviously higher than the specific capacity of 284 mAh/g of crystalline Fe2O3. Even at a high current density of 2 A/g, amorphous Fe2O3@GNS composites still exhibit a specific capacity as high as 219 mAh/g. The excellent electrochemical performance should be attributed to the amorphous structures of Fe2O3 as well as strongly interfacial interaction between Fe2O3 and GNS, which not only accommodate more electrochemical active sites and provide the more transmission channels for sodium ions but also benefit electron transfer as well as effectively buffer the volume change of host materials during sodiation and desodiation. This concept for designing amorphous iron oxide anodes for SIBs is also expected to facilitate preparation of various amorphous nanostructure of other metal oxides and improve their Na-ion storage performance.

Static and thermodynamic properties of liquid and amorphousFe2O3 nanoparticles

Molecular dynamics (MD) simulation of the structure and thermodynamic properties of liquid andamorphous Fe2O3 nanoparticles, with different sizes ranging from 2 to 5 nm, has been carried out based on theBorn–Mayer pair potentials under non-periodic boundary conditions. The partial radialdistribution functions (PRDFs), coordination number distributions, bond-angledistributions and interatomic distances of liquid nanoparticles at 3500 K were calculated indetail. In addition, we show the radial density profile and stoichiometry in nanoparticles.The temperature dependence of the surface structure and surface energy of nanoparticleshas been obtained and presented. Moreover, the size dependence of the glass transitiontemperature has been found and discussed.

Structural properties of amorphous Fe2O3 nanoparticles

We have investigated the microstructure of amorphous Fe2O3 nanoparticles by using molecular dynamics (MD) simulations. Non-periodic boundary conditions with Born-Mayer type pair potentials were used to simulate a spherical model of different diameters of 2, 3, 4 and 5 nm. Structural properties of an amorphous model obtained at 350 K have been analyzed in detail through the partial radial distribution functions (PRPFs), coordination number distributions, bond-angle distributions and interatomic distances. Calculations showed that structural characteristics of the model are in qualitative agreement with the experimental data. The observation of a large amount of structural defects as the particle size is decreased suggested that surface structure strongly depends on the size of nanoparticles. In addition, surface structure of amorphous Fe2O3 nanoparticles have been studied and compared with that observed in the core and in the bulk counterpart. Radial density profiles and stoichiometry in morphous Fe2O3 nanoparticles were also found and discussed.

Nanodispersed Fe Oxide Supported Catalysts with Tuned Properties

Catalysts comprising amorphous Fe2O3 nanoparticles dispersed on silica and silica−zirconia are presented. A molecular Fe precursor was grafted on the oxide support surface by an equilibrium−adsorption method. Afterward, calcination of the material produced amorphous Fe2O3 nanoparticles on the oxide support surface. The different nature of the oxide support (SixZr1-xO2, 0.715 < x < 1) imparted tunable electronic (studied by UV−vis diffuse reflectance spectroscopy), dimensional (studied by electron paramagnetic resonance spectroscopy, EPR), and redox (studied by thermal programmed reduction, TPR) properties to the samples, with following down toward their catalytic properties. The different support surfaces were covered by the iron oxide phase (from 5 to 10%), constituted of nanosized particles in a narrow size interval (between 2 and 9 nm, studied by EPR line shape and transmission electron microscopy, TEM, analyses). Homogeneous surface distribution was achieved in any case (studied by scanning electron micrographs coupled with energy dispersive X-ray spectroscopy, SEM-EDS). The precise arrangement and nuclearity of the iron oxide nanoparticles on the surface depended on the support nature. Besides, from Fe2O3 nanoaggregates (3d and 2d nanoparticles), the presence of isolated Fe3+ ions in strong interaction with the oxide support was revealed, the amount increasing with the zirconia content in the support.

Magnetism of amorphous Fe 2 O 3 nanopowders synthesized by solid‐state reactions

Monodispersed amorphous Fe2O3 nanoparticles with the size ranging from 1 to 4 nm have been prepared by thermally induced oxidative decomposition of Prussian Blue, Fe4[Fe(CN)6]3, in air. Amorphous nanopowders exhibit specific magnetic behaviour strongly affected by interparticle interactions and extremely low particle size with a high contribution of the surface anisotropy as illustrated by temperature dependent and external field Mossbauer spectroscopy and magnetization measurements (4–300 K). Some of the properties are in close similarity to those of spin glasses including the fast thermal variation of superparamagnetic fraction in the Mossbauer spectra, or the particle size independence of the blocking temperature, and non-saturation of magnetization even at 5 K and magnetic field of 10 T. The reduced value of internal magnetic hyperfine field (∼49 T at 5 K) and no indications of the tetrahedral Fe3+ sites in the 5T/5K external field Mossbauer spectra are the principal found differences in comparison with the magnetic behaviour of nanocrystalline γ-Fe2O3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Iron(III) Oxide Nanoparticles in the Thermally Induced Oxidative Decomposition of Prussian Blue, Fe4[Fe(CN)6]3

The thermally induced decomposition of Prussian Blue, Fe4[Fe(CN)6]3 (PB), was studied in air at 250 and 350 °C. Amorphous Fe2O3 nanoparticles, cubic bixbyite β- and cubic spinel γ-Fe2O3 (maghemite) polymorphs, have been identified as the products of the decomposition under different reaction conditions. 57Fe Mossbauer spectroscopy, XRD, AFM, TEM, quasielastic light scattering method (QELS) of particle size analysis, BET surface area, and magnetization measurements were used to understand the influence of the PB particle size and oxidation conditions on the decomposition mechanism at 250 and 350 °C. At a minimum decomposition temperature of 250 °C, amorphous Fe2O3 nanoparticles were formed with the size ranging from 1 to 4 nm and large surface area of 400−200 m2/g in dependence on the PB particle size. Such small amorphous Fe2O3 nanoparticles were obtained by the solid-state route for the first time. At 350 °C, cubic β-Fe2O3 and γ-Fe2O3 polymorphs were identified and their contents were found to be strongl...

Self-Assembled Monolayers of Alkanesulfonic and -phosphonic Acids on Amorphous Iron Oxide Nanoparticles

We have functionalized amorphous Fe2O3 nanoparticles with alkanesulfonic and octadecanephosphonic acids. TEM reveals nanoparticles 5−10 nm in diameter. FTIR spectra suggest that while in all cases the alkyl chains are packed in a solid-like arrangement, packing disorder increased with decreasing chain length. TGA of the sulfonic acid-functionalized Fe2O3 nanoparticles shows that moieties started to decompose and desorb from the iron oxide surface at about 260 °C. In the case of the octadecanephosphonic acid (OPA)-functionalized Fe2O3, moieties started to decompose and desorb at 340 °C. It is suggested that free Fe−OH groups can serve as proton donors to assist in the sulfonic acid desorption process and that because of the diprotic nature of the phosphonic acid these free surface Fe−OH groups may no longer be available. Among all, the octadecanesulfonic acid coating displays the lowest magnetization, which may be explained by the high packing and ordering of the alkyl chains on the particle surface. The s...

The “Melting Point” of Alkanethiol-Coated Amorphous Fe2O3 Nanoparticles

The “Melting Point” of Alkanethiol-Coated Amorphous Fe2O3 Nanoparticles