Porous α-Fe2O3 Research Articles

Investigation on transformation of spindle-like Fe3O4 nanoparticles from self-assembling α-Fe2O3

Porous monodisperse spindle-like α-Fe2O3 nanomaterials are first synthesized successfully by a hydrothermal method, and then the as-prepared nanoparticles are annealed at different temperatures under various atmospheres to achieve the spindle-like Fe3O4 nanoparticles. The evolution of the features of nanoparticles, including the changes of the structures and microstructures as well as the magnetic properties, during the reduction process has been investigated by using the Raman spectrum and Mössbauer spectrum. Our research reveals that the α-Fe2O3 nanoparticles annealed by covering of the C powder become a mixture of α-Fe2O3 and Fe3O4 in the range of annealing temperature from 300 °C to 800 °C. With reduced atmospheric H2, spindle-like α-Fe2O3 nanoparticles are transferred to mixture of α-Fe2O3, Fe3O4 and Fe as temperature increases. They are also converted from a typical rhombohedral structure to a cubic α-Fe phase at 500 °C. Finally, with the atmosphere of H2/Ar (5%/95%), a pure Fe3O4 phase, and its excellent magnetic properties are achieved at 450 °C.

Facial synthesis of porous hematite supported Pt catalyst and its photo enhanced electrocatalytic ethanol oxidation performance

The porous α-Fe2O3 supported Pt catalyst is synthesized by a facial thermal treatment assisted precipitation method. The particle size of Pt is less than 3nm. The pore diameters of α-Fe2O3 particles are concentrated to 2.46nm in a mesooporous scale. Its electrochemical performance is tested. The ethanol oxidation current of the Pt/Fe2O3 catalsyt obviously improves under illumination, compared with that in the dark, during the optical switching operation. Moreover, with the addition of α-Fe2O3, the ethanol oxidation current of Pt/C grows about 51% under illumination and 32% in the dark; the onset potential shifts negtively for about 20mV. This work demostrates an optical strategy which can be a potential alternative to accelerate electrode reactions towards ethanol oxidation reaction.

Ultralong Durability of Porous α-Fe2O3 Nanofibers in Practical Li-Ion Configuration with LiMn2O4 Cathode.

Prelithiated, electrospun α-Fe2O3 nanofibers display an exceptional cycleability when it is paired with commercial LiMn2O4 cathode in full-cell assembly. The performance of such α-Fe2O3 nanofibers is mainly due to the presence of unique morphology with porous structure, appropriate mass balance, and working potential. Also, synthesis technique cannot be ruled out for the performance.

Porous Flower-like α-Fe2O3 Nanostructure: A High Performance Anode Material for Lithium-ion Batteries

Porous flower-like α-Fe2O3 nanostructures have been synthesized by ethylene glycol mediated iron alkoxide as an intermediate and studied as an anode material of Li-ion battery. The iron alkoxide precursor is heated at different temperatures from 300 to 700°C. The α-Fe2O3 samples possess porosity and high surface area. There is a decrease in pore volume as well as surface area by increasing the preparation temperature. The reversible cycling properties of the α-Fe2O3 nanostructures have been evaluated by cyclic voltammetry, galvanostatic charge discharge cycling, and galvanostatic intermittent titration measurements at ambient temperature. The initial discharge capacity values of 1063, 1168, 1183, 1152 and 968mAhg−1 at a specific current of 50mAg−1 are obtained for the samples prepared at 300, 400, 500, 600 and 700°C, respectively. The samples prepared at 500 and 600°C exhibit good cycling performance with high rate capability. The high rate capacity is attributed to porous nature of the materials. As the iron oxides are inexpensive and environmental friendly, the α-Fe2O3 has potential application as anode material for rechargeable Li batteries.

Facile synthesis of α-Fe2O3@SnO2 core–shell heterostructure nanotubes for high performance gas sensors

A facile hydrothermal method was employed to synthesize porous α-Fe2O3@SnO2 heterostructure nanotubes. The morphologies and structures of the as-prepared samples were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and N2 adsorption–desorption techniques. The hollow α-Fe2O3 nanotubes with outer diameters of about 90nm were uniformly coated by a 10nm thick layer of SnO2 nanoparticles, demonstrating apparent heterostructures. The α-Fe2O3@SnO2 heterostructure nanotubes were applied to construct gas-sensor devices which exhibited high sensitivity, fast response–recovery, good selectivity and excellent repeatability to acetone. Because of the porous structure and large specific surface area, the heterogeneous core–shell nanocomposites show a markedly enhanced gas sensing performance in comparison with the initial α-Fe2O3 nanotubes and the pure SnO2 nanoparticles. For example, the sensitivity of the α-Fe2O3@SnO2 composites to 100ppm acetone can reach as high as 33.4 at the optimum operating temperature of 300°C, which was about twice of the value for pure α-Fe2O3 nanotubes and even up to 5-fold higher than that of pure SnO2 nanoparticles.

Ultrahigh sensitivity of Nd-doped porous α-Fe2O3 nanotubes to acetone

Abstract Pure and Nd-doped porous α-Fe2O3 nanotubes were successfully synthesized via a facile single-capillary electrospinning method, followed by calcination treatment. The morphologies of the as-prepared samples were characterized by scanning electron microscopy. The crystal structures and components were determined by X-ray diffraction and energy-dispersive X-ray spectroscopy, respectively. The gas-sensing properties of the as-prepared samples were studied, and the results indicate the ultrahigh sensitivity of Nd-doped porous α-Fe2O3 nanotubes to acetone. The response of Nd-doped porous α-Fe2O3 nanotubes to 50 ppm of acetone is about 44 at an operating temperature of 240 °C, which is 17 times larger than that of pure porous α-Fe2O3 nanotubes. Furthermore, the lowest detection limit of acetone is 500 ppb, with a response of 2.4. The response and recovery times to 50 ppm of acetone are about 19 and 50 s, respectively. In addition, the Nd-doped porous α-Fe2O3 nanotubes possess good selectivity and long-term stability.

Flexible superior electrode architectures based on three-dimensional porous spinous α-Fe2O3 with a high performance as a supercapacitor.

Flexible supercapacitors have recently attracted increasing attention as they show unique promising advantages, such as flexibility and shape diversity, and they are light-weight and so on. Herein, we designed a series of 3D porous spinous iron oxide materials synthesized on a thin iron plate through a facile method under mild conditions. The unique nanostructural features endow them with excellent electrochemical performance. The electrochemical properties of the integrated electrodes as active electrode materials for supercapacitors have been investigated using different electrochemical techniques including cyclic voltammetry, and galvanostatic charge-discharge in Na2SO4 and LiPF6/EC : DEC electrolyte solutions. These integrated electrodes showed high specific capacitance (as high as 524.6 F g(-1) at the current density of 1 A g(-1)) in 1.0 M Na2SO4 (see Table S1). Moreover, the integrated electrodes also show high power densities and high energy densities in a LiPF6/EC : DEC electrolyte solution; for example, the energy densities were 319.3, 252.5, 152.1, 74.13 and 38.6 W h kg(-1) at different power densities of 8.81, 21.59, 56.65, 92.09 and 152.64 kW kg(-1), respectively. Additionally, the flexible superior electrode exhibited excellent stability with capacitance retention of 92.9% after 5000 cycles. Therefore, such flexible integrated devices might be used in smart and portable electronics.

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres for superior lithium/sodium storage capability

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres with hollow inner cavity and porous outer shell exhibit outstanding electrochemical properties for LIBs/SIBs.

High-quality elliptical iron glycolate nanosheets: selective synthesis and chemical conversion into FexOynanorings, porous nanosheets, and nanochains with enhanced visible-light photocatalytic activity

This paper describes an original and facile polyol-mediated solvothermal synthesis of elliptical iron glycolate nanosheets (IGNSs) combined with precursor thermal conversion into γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 porous nanosheets (PNSs), α-Fe2O3 nanochains (NCs), and elliptical Fe3O4 nanorings (NRs). The IGNSs were produced via the oxidation-reduction and co-precipitation reactions in the presence of iron(III) salts, ethylene glycol, polyethylene glycol, and ethylenediamine. Control over Fe(3+) concentration, temperature, and time can considerably modulate the size and phase of the products. The IGNSs can be transformed to γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 PNSs, α-Fe2O3 NCs, and elliptical Fe3O4 NRs by heat treatment under various annealing temperatures and ambiences. The PNSs and NCs exhibited high soft magnetic properties and coercivity, respectively. Visible-light photocatalytic activity toward RhB in the presence of H2O2 by PNSs and NCs was phase-, SBET, size-, porosity-, and local structure-dependent, following the order: α-Fe2O3 NCs > α-Fe2O3/γ-Fe2O3 PNSs > γ-Fe2O3 PNSs > IGNSs. In particular, α-Fe2O3/γ-Fe2O3 PNSs possessed significantly enhanced photocatalytic activity with good recyclability and could be conveniently separated by an applied magnetic field because of high magnetization. We believe that the as-prepared α-Fe2O3/γ-Fe2O3 PNSs have potential practical use in waste water treatment and microwave absorption.

Fabrication and structural optimization of porous single-crystal α-Fe2O3 microrices for high-performance lithium-ion battery anodes

Porous α-Fe2O3 microrices have been prepared as a model system to study the effect of structural optimization of porous microstructures on LIB performance.

Heating-rate-induced porous α-Fe2O3 with controllable pore size and crystallinity grown on graphene for supercapacitors.

Porous α-Fe2O3/graphene composites (S-PIGCs) have been synthesized by a simple hydrothermal method combined with a slow annealing route. The S-PIGCs as a supercapacitors electrode material exhibit an ultrahigh specific capacitance of 343.7 F g(-1) at a current density of 3 A g(-1), good rate capability, and excellent cycling stability. The enhanced electrochemical performances are attributed to the combined contribution from the optimally architecture of the porous α-Fe2O3, as a result of a slow annealing, and the extraordinary electrical conductivity of the graphene sheets.

Facile synthesis of single crystalline mesoporous hematite nanorods with enhanced supercapacitive performance

α-Fe2O3 nanorods with a length of 400–700nm and a diameter of 20–80nm, which have single-crystalline and mesoporous structure, could be obtained from these α-FeOOH precursors after calcining at 300°C in air. The as-prepared single-crystalline mesoporous α-Fe2O3 nanorodes exhibited a large specific surface area and porosity, effectively increasing the contact area between the electrode materials and electrolyte, minimizing both the ionic and electronic transportation in the Fe2O3 during the charge-discharge process. The porous nanostructure facilitates the faster faradic reaction toward electrolytes and delivers highest specific capacitance (534Fg−1) and an excellent long cycle life (upto 1500 cycles) in 1M KOH electrolyte at current density of 4Ag−1, demonstrating that the porous α-Fe2O3 nanorods can serve as an excellent electrode material for supercapacitors. It is believed that the single-crystalline mesoporous α-Fe2O3 nanorods are beneficial to the charge transfer in the electrode and to the ion transport in the solution during redox reaction.

Electrochemical performance of hematite nanoparticles derived from spherical maghemite and elongated goethite particles

We report here an interesting observation on the electrochemical performance of hematite nanoparticles derived from cubic maghemite nanoparticles and hexagonal goethite rods prepared by a sonochemical process. We prepared hematite (α-Fe2O3) particles by annealing the as-prepared spherical cubic maghemite (γ-Fe2O3) nanoparticles and rod shaped hexagonal goethite (α-FeOOH) particles at 600 °C in air and investigated their performance as a Li-ion battery anode. Interestingly, annealing of spherical maghemite particles resulted in the formation of plate like interconnected hematite particles exhibiting unimodal pore distribution whereas rod shaped goethite has resulted in the formation of irregularly shaped porous hematite particles having a wide and multimodal pore distribution. The plate like α-Fe2O3 cells delivered a reversible capacity of ∼1160 and the porous α-Fe2O3 nanoparticles exhibited a slightly lower capacity of ∼1100 mAh g–1. The test cells rendered a reversible capacity of ∼926 and ∼841 mAh g–1 for nanoparticles derived from maghemite and goethite, respectively, after 40 galvanostatic cycles and a capacity of 611 and 522 mAh g−1 at 0.1C rate after 100 cycles. In other words, the investigated α-Fe2O3 nanomaterials retained a reversible capacity of ∼80 and 75%, respectively after 40 galvanostatic cycles. The basic difference in the electrochemical performance of the studied hematite particles have been attributed to the difference in the porosity of the samples. Moreover, the adopted synthesis technique is very simple and easily up scalable compared to most of the methods available in the literature for the synthesis of hematite nanoparticles.

Peculiar porous α-Fe2O3, γ-Fe2O3 and Fe3O4 nanospheres: Facile synthesis and electromagnetic properties

We reported a facile approach to prepare peculiar porous α-Fe2O3, γ-Fe2O3 and Fe3O4 nanospheres by combining a facile hydrothermal route with a calcination process in Ar or H2 atmosphere. The synthesized monodisperse porous α-Fe2O3 nanospheres with uniform average diameters of ~60nm in fact contained randomly distributed pores. A close view further revealed that there are two types of pores, one is large mesopores (ca. 15–20nm) in the center, and the other is small mesopores (ca. <10nm) in the outside. After calcining in Ar or H2, the obtained α-Fe2O3, γ-Fe2O3 and Fe3O4 nanospheres preserved the similar morphology and particle size as the uncalcined α-Fe2O3 nanospheres, indicating the as-prepared α-Fe2O3 nanospheres are stable under Ar and H2-annealing heat treatment. Comparing with all the paraffin composites, it was found that the porous α-Fe2O3 nanosphere/paraffin composites exhibit a higher permittivity level. A minimum reflection loss (RL) of −25dB was observed at ~13GHz for the porous α-Fe2O3 nanosphere/paraffin composites with a thickness of 3.5mm, and the effective absorption frequency (RL<−10dB) ranged from 9.9 to 15.1GHz. The composites exhibited better absorption properties than the magnetic porous γ-Fe2O3 and Fe3O4 nanosphere/paraffin composites.

Facile fabrication of porous flower-like α-Fe2O3 microspheres and their applications for water treatment

Flower-like α-Fe2O3 microspheres with an average diameter of about 1.5 μm were successfully synthesised with the assistance of ethylenediamine (EDA) through a facile high temperature solution method in ethylene glycol (EG) solvent. The morphologies and microstructure of the samples were characterised by scanning electron microscopy (SEM) and X-ray diffraction techniques. It was found that the size and morphology of the products were greatly influenced by the amount of EDA, EG and refluxing time, and a possible growth mechanism of such flower-like shape was proposed based on the controlled experiments. Because of the high specific surface area and porous structure, the α-Fe2O3 microflowers showed excellent adsorption performances with maximum removal capacities of 212 mg g−1 for Congo red in waste water treatment. The samples obtained from controlled experiments were also tested for the adsorption capacities, and the comparative dates were displayed distinctly. The prepared porous α-Fe2O3 spheres might have promising application in water treatment including the adsorption for toxic metal ions and the photocatalytic degradation.

Porous α-Fe2O3 nanorods supported on carbon nanotubes-graphene foam as superior anode for lithium ion batteries

A novel flexible and lightweight Fe2O3-based lithium-ion battery anode has been developed by growing porous α-Fe2O3 nanorods onto carbon nanotubes–graphene foam (CNT–GF). The CNT–GF 3D network provides a highly conductive, high surface areas and lightweight scaffold for the active Fe2O3 nanorods. Such unique electrodes for lithium-ion battery exhibit an 80% initial columbic efficiency, high-rate capabilities, and >1000mAh/g capacities at 200mA/g up to 300 cycles without obvious fading. These properties can be attributed to the fast electrochemical reaction kinetics and electron transport rendered by the conductive 3D network. Our structural design protocol can be extended to many other nanostructured metal oxides or sulfides, and thus provides a new strategy for construction of high-performance electrodes for energy storage.

One-pot synthesis of bundle-like β-FeOOH nanorods and their transformation to porous α-Fe2O3 microspheres

Bundle-like β-FeOOH nanostructures were successfully synthesized by a simple hydrolysis process in the presence of urea. The as-prepared products were characterized by X-ray power diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results indicated that bundle-like nanostructures were composed of well-aligned single crystalline nanorods with the diameters of 20–25nm and the lengths of 100–150nm. The corresponding porous α-Fe2O3 microspheres can be easily obtained by calcining the bundle-like β-FeOOH precursor. The achieved porous hematite microspheres, which are several hundreds of nanometers in diameter, exhibited high response for detecting ethanol, because the unique porous architecture effectively shortened the gas diffusion distance and provided highly accessible open channels and active surfaces for the target gas.

Synthesis of one-dimensional nanostructured anode materials with high-yield, low-cost and their application in lithium ion batteries

The electrochemical performances of lithium-ion batteries are highly dependent on their electrode materials. The currently used graphite anode is limited by the low theoretical capacity and cant meet the demand of the next generation lithium-ion batteries with higher energy and power density. Although great progress has been achieved with the development of new anode materials instead of graphite, it is still far from realizing commerce success. One of the most important points is the large-scale production of the new anode materials with high-yield and low-cost. This short article reviews the recent progress in large scale synthesis of one dimensional nanostructured anode materials in our research group, including one dimensional porous α-Fe2O3, Co3O4, anhydrous oxalates and zinc ferrite.

Fabrication of porous α-Fe2O3nanoshuttles and their application for toluene sensors

1D unique porous α-Fe2O3 nanoshuttles (NSs) were synthesized by a template-/surfactant-free low temperature hydrothermal approach (60 °C, 48 h), followed by a simple annealing process (300 °C, 1 h). The prepared α-Fe2O3 NSs (ca. 40 nm in diameter and 250 nm in length) have a rugged surface and a porous structure with numerous nanopore inlets (about 1–10 nm in diameter). The hydrothermal time dependent experiment demonstrated that the formation of the NSs is a gradual process, which underwent growth, strong, spilt, and re-spilt processes as reaction times were prolonged from 6 to 48 h. The reaction temperature also has a significant influence on the morphology of the α-Fe2O3 products. Increasing reaction temperature to 100 and 120 °C led to the formation of rod-like nanostructures instead of NSs, and a higher reaction temperature of 140 °C produced a large solid sphere-like morphology (700 nm–1 μm in diameter). Gas sensing properties of the porous α-Fe2O3 NSs were investigated for toluene detection. The sensor showed excellent gas sensing performance for toluene with good reproducibility, short response and recovery time (3–8 and 2–4 s, respectively), and high response. Notably, the α-Fe2O3 NS sensor showed a nearly linear response in the range of 10–100 ppm of toluene, indicating the potential for application in ppm-level toluene gas sensors. The present work is expected to provide new insights into the easy and effective development of 1D porous α-Fe2O3 nanostructures.

Hematite nanorods with tunable porous structure: Facile hydrothermal-calcination route synthesis, optical and photocatalytic properties

One-dimensional hematite (α-Fe2O3) nanostructures have attracted much concern due to their distinguished utilizations in nanomagnetism, photoanodes, and gas sensors. In order to extend the applications of hematite, a facile fast nontoxic method to synthesize 1D hematite nanostructures is highly required. In this contribution, α-Fe2O3 nanorods with tunable porous structure and optical absorbance properties were successfully synthesized via a facile hydrothermal-calcination route. Uniform high aspect ratio α-FeOOH nanorods with a length of ca. 600nm, diameter of ca. 30nm, and aspect ratio of ca. 20 were synthesized via a mild hydrothermal treatment (150°C, 6.0h) of the co-precipitation of FeCl3 and NaOH solutions followed by a subsequent calcination (400 or 700°C in the presence of NaCl). The presence of the CTAB with a mass ratio of 5.0% favored the preferential growth of the α-FeOOH nanorods with larger aspect ratio, while the thermal decomposition of α-FeOOH at 400 or 700°C in the presence of NaCl led to the high aspect ratio (ca. 15) porous or low aspect ratio (ca. 5) nonporous α-Fe2O3 nanorods, respectively. The UV–vis spectra showed that the optical absorbance properties of the calcined porous/nonporous α-Fe2O3 nanorods were well tuned, and the photocatalytic evaluation revealed that the nonporous α-Fe2O3 nanorods exhibited higher degradation efficiency for RhB than porous α-Fe2O3 nanorods. The as-obtained α-Fe2O3 nanorods with tunable porous structure as well as the tunable optical and photocatalytic properties suggested their great potential applications in the near future.