α-Fe2O3 Nanofibers Research Articles

The Design of Hetero-nanojunction of RGO/\(\alpha\)-Fe\(_2\)O\(_3\) Nanofibers for Ethanol Gas Sensor

Enhanced gas sensing properties of hematite \(\alpha\)-Fe2O3 by loaded reduced graphene oxides (RGO) have attracted considerable attention. In this study, RGO-loaded \(\alpha\)-Fe2O3 nanofibers were fabricated via the facile electrospinning method and subsequent calcination process. The scanning electron microscopy (SEM) images showed that RGO-loaded \(\alpha\)-Fe2O3 nanofibers with diameters of 50-100 nm have typical morphologies of spider nets. The X-ray diffraction (XRD) patterns revealed the rhombohedral structure of the RGO-loaded α-Fe2O3 nanofibers. The energy dispersive X-ray spectroscopy (EDS) results exhibited the presence of Fe, O, and C elements in the synthesized nanofibers. The gas sensing results also confirmed that the sensors based on RGO-loaded \(\alpha\)-Fe2O3 nanofibers could be applied for detecting ethanol gas.

In Situ Electrochemical Impedance Measurements of α-Fe2O3 Nanofibers: Unravelling the Li-Ion Conduction Mechanism in Li-Ion Batteries

Unravelling the lithium-ion transport mechanism in α-Fe2O3 nanofibers through in situ electrochemical impedance studies is crucial for realizing their application in high-performance anodes in lithium-ion batteries. Herein, we report the effect of heat treatment conditions on the structure, composition, morphology, and electrochemical properties of α-Fe2O3 nanofibers as an anode for lithium-ion batteries. The α-Fe2O3 nanofibers were synthesized via electrospinning and post-annealing with differences in their annealing temperature of 300, 500, and 700 °C to produce FO300, FO500, and FO700 nanofibers, respectively. Improved electrochemical performance with a high reversible specific capacity of 599.6 mAh g−1 at a current density of 1 A g−1 was achieved after 50 cycles for FO700. The in situ electrochemical impedance spectroscopy studies conducted during the charge/discharge process revealed that the charge transfer and Li-ion diffusion behaviors were related to the crystallinity and structure of the as-synthesized α-Fe2O3 nanofibers. The surfaces of the α-Fe2O3 nanofibers were converted into Fe metal during the charging/discharging process, which resulted in improved electrical conductivity. The electron lifetime, as determined by the time constant of charge transfer, revealed that, when a conversion reaction occurred, the electrons tended to travel through the iron metal in the α-Fe2O3 nanofibers. The role of iron as a pseudo-resistor with negligible capacitance was revealed by charge transfer resistance analysis.

Novel hollow α-Fe2O3 nanofibers with robust performance enabled multi-functional applications

The synthetic strategies of achieving low-cost and high-performance nanofibers are of great significance in the field of catalysis and detection. In this work, a series of electrospun α-Fe2O3 nanofibers with hollow structure were prepared via combination technology of electrospinning, hydrothermal synthesis, and controlled calcination process. Especially, the influences of the crystal structure and morphology on the comprehensive properties of nanofibers have been explored in detail. The results indicated that α-Fe2O3 nanofibers could be obtained via the calcination at 600–800 °C. Rice-like α-Fe2O3 particles were observed to assemble a stable exoskeleton, supporting a robust tubular cavity. And this tubular structure turned gradually into groove-like structure as the calcination temperature increased, accompanied by tunable crystallization, specific surface area and magnetic property. Finally, combined with series of validation tests, including dye decolorization, electrochemical detection of trace cadmium ions and Fenton degradation of polyvinyl alcohol, the resultant α-Fe2O3 nanofibers have been demonstrated to show the potential application prospects.

Porous α-Fe2O3 nanofiber combined with carbon nanotube as anode to enhance the bioelectricity generation for microbial fuel cell

Microbial fuel cell (MFC) is a potential technology for bioelectricity generation from waste. Unfortunately, it is still a challenge for practical application due to the low power density. Immense efforts have been extended to boost the design of bioanode, mainly including the improvement on bacterial adhesion and extracellular electron transfer (EET) between bacteria and anode. Herein, electrospun porous α-Fe2O3 nanofibers integrated with carbon nanotubes (CNTs) are developed for MFC. Benefiting from the good electricity, ultrahigh porosity and three-dimensional interpenetrated network of fabricated CNTs/α-Fe2O3, the decorated anode is capable of enriching active bacteria and promoting effective EET rate. Consequently, the MFC based on CNTs/α-Fe2O3 nanofibers as anode achieves the eminent power density of 1959 mW/m2 and high COD removal efficiency of 85.04%, superior to that of α-Fe2O3 anode (940 mW/m2; 81.66%) and bulk carbon cloth anode (432 mW/m2; 65.83%). More importantly, the CNTs/α-Fe2O3 modified anode is favorable for electrogenic active bacteria attachment, thus improving the bioelectricity performance. The consequence suggests that this strategy can offer a potential application in power production and pollutant removal.

Visible-Light-Responsive Nanofibrous α-Fe2O3 Integrated FeOx Cluster-Templated Siliceous Microsheets for Rapid Catalytic Phenol Removal and Enhanced Antibacterial Activity.

Visible-light-driven environmental contaminants control using 2D photocatalytic nanomaterials with an unconfined reaction-diffusion path is advantageous for public health. Here, cost-effective siliceous composite microsheets (FeSiO-MS) combined with two distinct refined α-Fe2O3 nanospecies as photofunctional catalysts were constructed via a one-pot synthesis approach. Through precise control of Fe2+ precursor addition, specially configured α-Fe2O3 nanofibers combined with FeOx cluster-functionalized siliceous microsheets of ∼15 nm gradually evolved from the iron oxide-bearing molecular sieve, endowing a superior light-response characteristic of the formed nanocomposite. The catalytic experiment along with the ESR study demonstrated that the produced FeSiO-MS showed reinforced photo-Fenton reactivity, which was effective for rapid phenol degradation under visible light radiation. Moreover, the phenol removal process was found to be regulated by the specially configured types and concentrations of iron oxides. Notably, the obtained composites exhibited a considerable visible-light-induced bactericidal effect against E. coli. The constructed FeSiO-MS nanocomposites as integrated and eco-friendly photocatalysts exhibit enormous potentials for environmental and hygienic application.

Enhanced H2S gas-sensing performance of α-Fe2O3 nanofibers by optimizing process conditions and loading with reduced graphene oxide

We systematically investigated the effects of process conditions and reduced graphene oxide (RGO) loading on the H2S gas-sensing performance of the α-Fe2O3 nanofibers (NFs) fabricated via on-chip electrospinning. The annealing temperature and precursor solution contents strongly influenced on the morphology and structure of the α-Fe2O3 NFs that accordingly affected on the gas-sensing performance. The optimum process conditions with the annealing temperature of 600 °C and the precursor solution contents of 11 wt% PVA and 4.0 wt% Fe(NO3)3.9H2O led to the α-Fe2O3 NF sensors having a high response of ∼6.1 at 1 ppm H2S gas. The RGO loading further improved the gas response, increasing the response to 1 ppm H2S gas up to ∼9.2. Also, the RGO-loaded α-Fe2O3 NF sensors enhanced their selectivity and detection limit as compared with pure α-Fe2O3 NF sensors. The enhanced gas-sensing performance was attributed to the presence of nanograins, the increase of surface-to-volume ratio and the formation of potential barriers at nanograin homojunctions and RGO/α-Fe2O3 heterojunctions.

Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition.

In the last years, hematite has been utilized in a plethora of applications. High aspect-ratio nanohematite and hematite/silica core-shell nanostructures are arousing growing interest for applications exploiting their magnetic properties. Atomic layer deposition (ALD) is utilized here to produce SiO2-coated α-Fe2O3 nanofibers (NFs) through two synthetic routes, viz. electrospinning/calcination/ALD or electrospinning/ALD/calcination. The number of ALD cycles (10-100) modulates the coating thickness, while the chosen route controls the final nanostructure. Porous and partially hollow NFs are produced. Their hierarchical structure and the nature and density of the lattice defects and strain are characterized by combining electron microscopy, diffraction, and spectroscopy techniques. The uncoated hematite NFs mostly have surface-related strain, which is attributed to oxygen vacancies/Fe2+ sites. ALD coating causes microstrain release and decrease of surface states. NFs calcined after ALD have extensive bulk strain, which is ascribed to the presence of dislocations throughout the volume of the NF grains. Bulk strain determines the remanent magnetization, whereas both surface and bulk strain influence the coercive field and the thermal behavior across the Morin temperature, including the magnetic memory effect. To the best of the authors' knowledge, the correlation between lattice defects/strain and magnetic properties of SiO2-coated α-Fe2O3 NFs has never been reported before.

Phase transition behavior in Fe2O3 nanofibers

Hematite (α-Fe2O3) nanofibers were fabricated using the electro-spinning technique and followed by an annealing process in air. The crystalline structure and morphology of the nano-fibers were studied using XRD, SEM, Raman spectra and high-resolution TEM. Zero-field-cooled (ZFC), field-cooling (FC) and field heated (FH) type temperature dependence of magnetization curves of α-Fe2O3 nanofibers are measured in the temperature range 15–390 K. Two kinds of magnetization steps were observed in the temperature dependence of magnetization curves, one is at 300 k which is very weak and the other is in the temperature range of 245–257 K with large thermal hysteresis (12 K). The tiny step at 300 K can be attributed to normal Morin transition in α-Fe2O3 and this was suppressed by the consequent α- to β- phase transition, which caused the pronounced step in the temperature dependence of magnetization curves. This α- to β- phase transition in Fe2O3 nanofibers was further confirmed by in situ TEM observations. This is the first study to describe novel α- to β-phase transition upon cooling.

Effect of CuFe2O4 ferrite on photocatalysis and carrier dynamics of electrospun α-Fe2O3 nanofibers by time-resolved transient absorption spectroscopy

Abstract Pristine and Cu-doped α-Fe2O3 nanofibrous photocatalysts were prepared facilely by electrospinning followed by thermal calcination for removal of the polymeric template. The addition of Cu resulted in formation of copper ferrite (CuFe2O4) in the α-Fe2O3 matrix. Photogenerated electrons and holes in the photocatalysts were found trapped in semiconducting midgaps by the time-resolved transient absorption spectroscopy under pulsed light irradiations (355 nm wavelength). The Cu-doped α-Fe2O3 showed an increased carriers population when compared to the pristine counterpart. The finding was in good agreement with the methylene-blue (MB) dye degradation under ultraviolet-light irradiations, in which an enhanced MB removal was found for the Cu-doped α-Fe2O3 photocatalyst. The MB dye removal was directly correlated with the presence of CuFe2O4 ferrite in the α-Fe2O3 matrix; from which, the semiconducting heterojunction at the interface led to a prolonged lifetime of the carriers and a resultant increase on the carriers population and MB photodegradation.

Synchronous synthesis and sensing performance of α-Fe2O3/SnO2 nanofiber heterostructures for conductometric C2H5OH detection

A synthesis procedure based on single-capillary electrospinning and hard-template method was provided to synthesize hierarchical α-Fe2O3/SnO2 nanofibers. The samples exhibit unique microstructure where α-Fe2O3 nanoparticles were evenly decorated on three-dimensional SnO2 fibrous scaffold. During preparation, the α-Fe2O3 nanoparticles and SnO2 nanofibers were formed synchronously. Within the composite nanomaterials, the Fe/Sn content ratio can be adjusted by changing the diameter of SnO2 nanofibers backbone. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and nitrogen adsorption-desorption analysis were used to characterize the structure of the synthesized products. By loading α-Fe2O3 nanoparticles, the grain growth of SnO2 was effectively restrained during heat treatment in air. The optimum Fe/Sn content ratio of α-Fe2O3/SnO2 heterostructures with the highest sensitivity was obtained through ethanol sensing measurements. Compared to pure α-Fe2O3 and SnO2 nanofibers, the binary composite nanofibers exhibits not only enhanced ethanol sensing response, but also higher dependence of response to the change of ethanol concentration. The remarkable improvement of sensing performance can be attributed to the synergetic effect of the component phases. The influences of heterojunctions on the gas sensing properties of α-Fe2O3/SnO2 nanofibers were discussed.

Fabrication and characterization of the magnetic ferrite nanofibers by electrospinning process

Since the magnetic properties of materials are greatly affected by their microstructure, nanostructuring of magnetic materials is attempted in various directions. Various processes have been used to synthesis one dimensional nanomaterials: template, hydrothermal, anodizing, and electrospinning. Among these processes, nanofibers fabricated by the electrospinning method are excellent for reproducibility and have a large aspect ratio. In addition, there have been many attempts to fabricate ceramic nanofibers with a more intricate shape using a sol-gel reaction. In this study, the electrospinning conditions for synthesizing ferrite (α-Fe2O3) nanofiber were optimized by the preliminary results of polyvinyl alcohol (PVA) nanofiber. As-spun composite nanofibers of PVA/Fe(NO3)3·9H2O were transformed to an α-Fe2O3 phase by heat treatment at 550 °C. After heat treatment, the diameters ranged from 105 nm to 124 nm in as-spun composite nanofibers, and with a decrease in PVA content after heat treatment, the diameters ranged from 59 nm to 96 nm. We investigated the magnetization properties with the microstructure of α-Fe2O3 nanofiber by a vibrating sample magnetometer. The saturation magnetization increased with an increasing diameter of the α-Fe2O3 nanofiber, and highest value of 26.2 A·m2/kg was measured in the α-Fe2O3 nanofibers with the largest diameter with a PVA content of 0.12 g/ml. The microstructure and magnetic properties of the α-Fe2O3 nanofibers were controlled by an electrospinning process, and we were able to optimize the α-Fe2O3 nanofibers for various application fields, such as electromagnetic interference and electromagnetic pulse absorbers.

Selective fabrication of porous iron oxides hollow spheres and nanofibers by electrospinning for photocatalytic water purification

Porous hematite (α-Fe2O3) hollow spheres and nanofibers could be obtained via electrospinning and subsequent thermal decomposition in air. The precursor could be fabricated by electrospinning using Fe(NO3)3 as the iron source and Polyvinylpyrrolidone (PVP) as a complexing reagent. Upon calcination, pure porous α-Fe2O3 hollow spheres and nanofibers could be obtained at 650 °C for 3 h. The novel hollow spheres have an abundantly porous structure as well as large surface areas. Benefitting from the special porous structure, narrow bandgap, and higher surface area, porous α-Fe2O3 hollow materials are used as visible-light-responsive photocatalysts. So we have investigated the visible light photodegradation behavior of porous hematite (α-Fe2O3) hollow spheres and nanofibers towards organic dyes, as Rhodamine B (RhB). The synergetic effects of higher surface area, pore structures promoted the photocatalytic efficiency for RhB degradation under visible light and contributed to achieving the enhanced and stable photocatalytic activity.

Electrospun γ-Fe2O3 nanofibers as bioelectrochemical sensors for simultaneous determination of small biomolecules

Nanofibers of α-Fe2O3 and γ-Fe2O3 have been obtained after the controlled calcination of precursor nanofibers synthesized by electrospinning. α-Fe2O3 nanofibers showed an irregular toruloid structure due to the decomposition of poly (4-vinyl) pyridine in air while γ-Fe2O3 nanoparticles decorated nanofibers were observed after the calcination under N2 atmosphere. Electrochemical measurements showed that different electrochemical behaviors were observed on the glassy carbon electrodes modified by α-Fe2O3 and γ-Fe2O3 nanofibers. The electrode modified by γ-Fe2O3 nanofibers exhibited high electrocatalytic activities toward oxidation of dopamine, uric acid and ascorbic acid while α-Fe2O3 nanofibers cannot. Furthermore, the γ-Fe2O3 modified electrode can realize the selective detection of biomolecules in ternary electrolyte solutions. The synthesis of nanofibers of α-Fe2O3 and γ-Fe2O3 and their electrochemical sensing properties relationship have been discussed and analyzed based on the experimental results.

A Phase Separation Route to Synthesize α-Fe2O3 Porous Nanofibers via Electrospinning for Ultrafast Ethanol Sensing

A facile and economic procedure was provided to synthesize α-Fe2O3 nanofibers. In this procedure, porous α-Fe2O3 nanofibers were obtained by a single-polymer/binary-solvent system, while solid α-Fe2O3 nanofibers were prepared by a single-polymer/single-solvent system. The crystal structure and morphology of both samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption isotherms. The formation mechanism of porous structure was based on solvent evaporation-induced phase separation by the use of mixed solvents with different volatility. Furthermore, ethanol-sensing performance of the porous α-Fe2O3 nanofibers was evaluated and compared with solid α-Fe2O3 nanofibers. Results from gas-sensing measurements reveal that porous α-Fe2O3 nanofibers exhibit higher sensitivity and slightly longer recovery time than solid α-Fe2O3 nanofibers. Over all, the gas sensor based on porous α-Fe2O3 nanofibers shows excellent ethanol-sensing capability with high sensitivity and ultrafast response/recovery behaviors, indicating its potential application as a real-time monitoring gas sensor.

Porous one-dimensional carbon/iron oxide composite for rechargeable lithium-ion batteries with high and stable capacity

Hematite iron oxide (α-Fe2O3) is considered to be a prospective anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity (1007 mAh g−1), nontoxicity, and low cost. However, the low electrical conductivity and large volume change during Li insertion/extraction of α-Fe2O3 hinder its use in practical batteries. In this study, carbon-coated α-Fe2O3 nanofibers, prepared via an electrospinning method followed by a thermal treatment process, are employed as the anode material for LIBs. The as-prepared porous nanofibers with a carbon content of 12.5 wt% show improved cycling performance and rate capability. They can still deliver a high and stable capacity of 715 mAh g−1 even at superior high current density of 1000 mA g−1 after 200 cycles with a large Coulombic efficiency of 99.2%. Such improved electrochemical performance can be assigned to their unique porous fabric structure as well as the conductive carbon coating which shorten the distance for Li ion transport, enhancing Li ion reversibility and kinetic properties. It is, therefore, demonstrated that carbon-coated α-Fe2O3 nanofiber prepared under optimized conditions is a promising anode material candidate for LIBs.

An ultrahigh-sensitivity and selective sensing material for ethanol: α-/γ-Fe2O3 mixed-phase mesoporous nanofibers

A process for synthesizing Fe2O3 based on electrospinning and the hard-template method was proposed such that the crystal phase of Fe2O3 could be tailored with precision. Mesoporous γ-Fe2O3, α-/γ-Fe2O3, and α-Fe2O3 nanofibers could be fabricated successfully by changing the synthesis parameters. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction analyses, Raman spectroscopy, and nitrogen adsorption–desorption analyses were used to characterize the structures of the synthesized products. The optimal calcination conditions for preparing α-/γ-Fe2O3 nanofibers with the highest ethanol response were determined through ethanol-sensing measurements. The mixed-phase material exhibited a significantly higher sensitivity than the corresponding purephase ones. The superior ethanol-sensing performance of the α-/γ-Fe2O3 nanofibers suggested that they may be suitable for use in alcohol sensing. Hence, a novel strategy for improving the sensing performance of metal oxide semiconductors is to assemble the different crystalline forms of the same metal oxide in one structure. Finally, the mechanism responsible for the sensing performance of α-/γ-Fe2O3 being higher than those of γ-Fe2O3 and α-Fe2O3 was elucidated on the basis of data from X-ray photoelectron spectroscopy and resistance measurements.

Synthesis and optimization of Fe2O3 nanofibers for chromate adsorption from contaminated water sources

In this work, α-Fe2O3 nanofibers were synthesized via electrospinning and characterized to observe optimal morphological and dimensional properties towards chromate removal. The Fe2O3 nanofiber samples were tested in aqueous solutions containing chromate (CrO42−) to analyze their adsorption capabilities and compare them with commercially-available Fe2O3 nanoparticles. Synthesized Fe2O3 nanofibers were observed with a variety of different average diameters, ranging from 23 to 63 nm, while having a constant average grain size at 34 nm, point zero charge at pH 7.1, and band gap at 2.2 eV. BET analysis showed an increase in specific surface area with decreasing average diameter, from 7.2 to 59.2 m2/g, due to the increased surface area-to-volume ratio with decreasing nanofiber size. Based on CrO4−2 adsorption isotherms at pH 6, adsorption capacity of the Fe2O3 nanofibers increased with decreasing diameter, with the 23 nm sized nanofibers having an adsorption capacity of 90.9 mg/g, outperforming the commercially-available Fe2O3 nanoparticles by nearly 2-fold. Additionally, adsorption kinetics was also analyzed, increasing with decreasing nanofiber diameter. The enhanced performance of the nanofiber is suggested to be caused solely due to the increased surface area, in part by its size and morphology. Electrospun Fe2O3 nanofibers provide a promising solution for effective heavy metal removal through nanotechnology-integrated treatment systems.

Magnetic α-Fe2O3 Nanofibers: an Efficient and Recyclable Catalyst for Solvent-Free selective Oxidation of Benzylic Alcohols

Magnetically recyclable α-Fe2O3 nanofibers are used as heterogeneous catalysts for the oxidation of benzylic alcohols to the corresponding carbonyl compounds in the presence of hydrogen peroxide as oxidants.

Novel hollow α-Fe2O3 nanofibers via electrospinning for dye adsorption.

Nanomaterials such as iron oxides and ferrites have been intensively investigated for water treatment and environmental remediation applications. In this work, hollow α-Fe2O3 nanofibers made of rice-like nanorods were successfully synthesized via a simple hydrothermal reaction on polyvinyl alcohol (PVA) nanofiber template followed by calcination. The crystallographic structure and the morphology of the as-prepared α-Fe2O3 nanofibers were characterized by X-ray diffraction, energy dispersive X-ray spectrometer, and scanning electron microscope. Batch adsorption experiments were conducted, and ultraviolet-visible spectra were recorded before and after the adsorption to investigate the dye adsorption performance. The results showed that hollow α-Fe2O3 fiber assembles exhibited good magnetic responsive performance, as well as efficient adsorption for methyl orange in water. This work provided a versatile strategy for further design and development of functional nanofiber-nanoparticle composites towards various applications.

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.