Porous α-Fe2O3 Research Articles

Highly sensitive ethylene sensors using Pd nanoparticles and rGO modified flower-like hierarchical porous α-Fe2O3

To develop a feasible approach to detect ethylene in low concentration is of great significance to reduce losses of farm products during storage and logistics. However, it is really difficult to detect it due to the lack of polar chemical functionality of ethylene and its small size. While appropriate Pd nanoparticles (NPs) and reduced graphene oxide (rGO) modified flower-like hierarchical porous α-Fe2O3 was designed and successfully synthesized in this article, which can detect ethylene with high sensitivity and low temperature. Experiment results reveal that Pd/rGO/α-Fe2O3 can detect ehylene in the concentration as low as 10 ppb, which is the best one among all the ethylene gas sensors and has made a major breakthrough in the detection limit of ethylene. Besides, other sensing performance, including operation temperature (250 °C), the response-recovery time (18 s and 50 s), and examination range (from 10 ppb to 1000 ppm) all have been significantly improved. The high specific surface area of flower-like hierarchical porous structure, the catalysis of Pd nanoparticles, and chemically active defect sites of rGO all contribute to the high sensing performances of Pd/rGO/α-Fe2O3 in detecting ethylene. These do provide a practical method for detecting low concentrations of ethylene and make it more competitive to detect ethylene with low cost and convenient gas sensors.

3D α-Fe2O3 nanorods arrays@graphene oxide nanosheets as sensing materials for improved gas sensitivity

Hybridizing nanostructured metal oxides with grapheme oxide (GO) is highly desirable for the improvement of gas sensing performance of gas sensors. Herein, we develop an in situ fluorine directed solution process combined with heat treatment to grow highly ordered, porous α-Fe2O3 nanorods arrays (NRAs) onto graphene oxide (GO) sheets, resulting in flexible three-dimensional nanostructures. The α-Fe2O3 NRAs have heights of ∼50 nm and widths of 10–20 nm, which are densely and vertically attached to both sides of GO sheets, thereby generating an interesting “blanket-like” geometry. When tested as sensing materials for gas sensors, the nanocomposite displays a high sensitivity of 19.14 toward 50 ppm acetone at a work temperature of 220 °C, which was 5.4 times of that of α-Fe2O3. Even after 50 days, a stable sensitivity as high as 18.9 toward 50 ppm acetone could be maintained. The improved high sensitivity, fast response and recovery, and extraordinary stability of GO/α-Fe2O3 can be attributed to the highly ordered, porous structure and the synergistic effect between α-Fe2O3 and GO.

Hierarchical porous nanorod@core-shell α-Fe2O3/TiO2 microspheres: Synthesis, characterization, and gas-sensing applications

Hierarchical porous α-Fe2O3/TiO2 nanorod@core-shell microspheres were synthesized by a facile one-step hydrothermal approach without templates or surfactants. The as-obtained α-Fe2O3/TiO2 nanorod@core-shell microspheres had an average diameter of 3.5 μm. Porous nanorods, with an average length of 1.5 μm, were randomly grown on the core-shell microsphere surfaces. The morphology, microstructure, and composition of the α-Fe2O3/TiO2 heterostructures were characterized by various analytical techniques. Changes in the morphology and composition of the microspheres had an effect on the final gas sensing performance. Gas sensors based on the porous nanorod@core-shell α-Fe2O3/TiO2 microspheres exhibited an excellent gas-sensing performance, with markedly enhanced responses in comparison with the pristine α-Fe2O3 sensor. The response of the porous nanorod@core-shell α-Fe2O3/TiO2 microspheres to 20 ppm acetone was approximately 34, which was 2.7 times higher than that of pure α-Fe2O3 at 220 °C. Furthermore, the sensor could be easily recovered to its initial state following a short exposure to fresh air. The remarkably enhanced acetone-sensing performance was attributed to the unique porous nanorod@core-shell microsphere morphology, the strong interfacial interaction between TiO2 and α-Fe2O3, and the presence of α-Fe2O3/TiO2 heterojunctions. Thus, the prepared porous nanorod@core-shell α-Fe2O3/TiO2 microspheres sensors showed an outstanding performance in acetone detection.

Controlled Synthesis of Hollow α-Fe2O3 Microspheres Assembled With Ionic Liquid for Enhanced Visible-Light Photocatalytic Activity.

Porous self-assembled α-Fe2O3 hollow microspheres were fabricated via an ionic liquid-assisted solvothermal reaction and sequential calcinations. The concentration of the ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate [C4Mim]BF4) was found to play a crucial role in the control of these α-Fe2O3 hollow structures. Trace amounts ionic liquid was used as the soft template to synthesize α-Fe2O3 hollow spheres with a large specific surface (up to 220 m2/g). Based on time-dependent experiments, the proposed formation mechanisms were presented. Under UV light irradiation, the as-synthesized α-Fe2O3 hollow spheres exhibited excellent photocatalysis in Rhodamine B (RhB) photodegradation and the rate constant was 2–3 times higher than α-Fe2O3 particles. The magnetic properties of α-Fe2O3 hollow structures were found to be closely associated with the shape anisotropy.

Purification of starch and phosphorus wastewater using core-shell magnetic seeds prepared by sulfated roasting

Core-shell magnetic seeds with certain adsorption capacity that were prepared by sulfated roasting, served as the core of a magnetic separation technology for purification of starch wastewater. XRD and SEM results indicate that magnetite's surface transformed to be porous α-Fe2O3 structure. Compared with magnetite particles, the specific surface area was significantly improved to be 8.361 from 2.591 m2/g, with little decrease in specific susceptibility. Zeta potential, FT-IR and XPS experiments indicate that both phosphate and starch adsorbed on the surface of the core-shell magnetic seeds by chemical adsorption, which fits well with the Langmuir adsorption model. The porous surface structure of magnetic seeds significantly contributes to the adsorption of phosphate and starch species, which can be efficiently removed to be 1.51 mg/L (phosphate) and 9.51 mg/L (starch) using magnetic separation.

Porous Fe2O3 nanotubes with α-γ phase junction for enhanced charge separation and photocatalytic property produced by molecular layer deposition

Constructing nanotubular morphologies and heterojunctions are two effective strategies to enhance the charge separation and transport of α-Fe2O3 for improved photocatalytic performance, while the fabrication of porous α-Fe2O3 nanotubes with precisely tailored wall thickness, pore structure, crystallinity, and junctions still remains a big challenge. Herein, two novel molecular layer deposition (MLD) procedures are designed to prepare porous Fe2O3 nanotubes with tunable pore structure and phase junction. The organic fractions of the obtained Fe-hybrid MLD films not only act as soft templates to generate nanopores in nanotube walls but also play a key role in the formation of phase-junction. The porous structure and phase-junction significantly improve the mass diffusion and charge separation efficiency of Fe2O3 nanotubes, leading to a drastically increased photocatalytic activity for photo-Fenton reaction. Especially, the porous α-γ Fe2O3 nanotubes produced by two-step AB MLD from iron tert-butoxide and ethylene glycol exhibit the highest photocatalytic activity, which is more than a 6.5-fold and 20-fold improvement compared with the nonporous pure α-Fe2O3 nanotubes and commercial α-Fe2O3 nanoparticles, respectively. The MLD method provides a new bottom-up approach to develop efficient Fe2O3 based heterostructure porous photocatalysts for waste-water cleaning and water splitting.

Porous α-Fe2O3 nanorods@graphite nanocomposites with improved high temperature gas sensitive properties

In order to improve the high temperature sensitivity of α-Fe2O3 based gas sensor, the porous α-Fe2O3 nanorods@graphite nanocomposites were synthesized using a simple low temperature hydrolysis method. A series of analyses were performed to characterize the morphology, structure and composition. As a result, uniform porous α-Fe2O3 nanorods with a length of about 200–300 nm directly grown on the surface of graphite nanoplatelets. When tested as sensing materials for gas sensors, the nanocomposites display a high sensitivity of 16.9 toward 50 ppm acetone at a work temperature of 260 °C, which was 2.2 times of that of pure α-Fe2O3. Even at a work temperature of 320 °C, a stable sensitivity as high as 10.4 toward 50 ppm acetone could be maintained. The improved high temperature sensitivity of porous α-Fe2O3 nanorods@graphite nanocomposites can be attributed to p-n heterojunction, the porous structure of α-Fe2O3 nanorods, the high temperature stability of graphite and large specific surface areas.

Structural and magnetic properties of porous FexOy nanosheets and nanotubes fabricated by electrospinning

2D porous α-Fe2O3 nanosheets and 1D porous FexOy nanotubes were synthesized using electrospinning technique under different conditions. XRD results show that the α-Fe2O3 nanosheets are pure α-Fe2O3 phase, and the FexOy nanotubes are mainly composed of α-Fe2O3 phase accompanied by weak Fe3O4 phase. The EDX mappings demonstrate that the elements of O and Fe were uniformly distributed in nanosheets and nanotubes. The valence of iron ion is pure 3 + in the α-Fe2O3 nanosheets, and it shows 3 + with a small amount of 2 + in the FexOy nanotubes. Magnetic properties of the synthesized samples were studied by vibrating sample magnetometer and Mössbauer spectrometer, the results show that the α-Fe2O3 nanosheets have the room temperature ferromagnetism and the FexOy nanotubes have a higher saturation magnetization of 18.91 emu/g. Mössbauer spectrometer proved further the microstructure of nanosheets and nanotubes, which are consistent with the results of XPS. Our results will be helpful for the application of nanoporous materials.

MOF-derived porous hollow α-Fe2O3 microboxes modified by silver nanoclusters for enhanced pseudocapacitive storage

Porous hollow α-Fe2O3 microboxes with high surface area are prepared by using metal-organic framework as precursor and self-template. To improve the conductivity of the derived α-Fe2O3 microboxes and thus enhance their capacitive storage and rate capability as effective electrode material, especially as anode material for supercapacitors, Ag nanoclusters are uniformly deposited on the surface of the α-Fe2O3 microboxes (α-Fe2O3@Ag microboxes) through a facile solution method. As pseudocapacitive material, the α-Fe2O3@Ag microbox electrode displays a high specific capacitance of 701 F g−1 at a current density of 0.1 A g−1, and remains 191 F g−1 at a high current density of 10 A g−1. Furthermore, the material shows 80% specific capacitance retention after 2000 charge-discharge cycles, and 72% retention after 10,000 cycles at a current density of 10 A g−1. In addition, asymmetric supercapacitors are assembled with the α-Fe2O3@Ag as negative electrodes and commercial activated carbon as positive electrodes. A maximum specific capacitance of 123 F g−1 and an energy density of 41.8 W h kg−1 are demonstrated within a cell voltage of 1.6 V for the device.

Magnetic/catalytic properties and strain induced structural phase transformation from β-FeOOH to porous α-Fe2O3 nanorods

Revealing detailed catalytic and magnetic properties and the corresponding structural changes of Fe oxide materials are extremely important for their diverse applications. For this, magnetic properties of thermally phase transformed β-FeOOH nanorods (NRs) (to porous α-Fe2O3) were examined in the temperature up to 550 °C. The thermal treatment enhances the lattice strain (ε) that facilitates in creating pore structures. Fundamental physicochemical properties were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), diffuse reflectance UV–visible absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS). An average size of pores and pore-size distribution were characterized by Brunauer-Emmett-Teller (BET) surface area analysis. Temperature and field dependent magnetic properties of calcination samples were investigated by vibrating sample magnetometer (VSM) for understanding the morphology-dependent magnetic behavior of NRs. The phase transformation behavior of these thermally treated magnetic NRs was analyzed through magnetic property characterization by considering all possible relationships with lattice strain effects, oxygen vacancies, magnetic, and morphology anisotropy.

Hierarchical Porous α-Fe2O3 Formation by Thermal Oxidation of Iron as Catalyst for Cr(Vi) Reduction

α-Fe2O3 is a semiconductor photocatalyst that can adsorb and reduce heavy metal ions from contaminated water. Here, hierarchical porous structured α-Fe2O3 was synthesised by thermal oxidation of iron wire at 400 °C – 700 °C in the presence of water vapour for 1 hour. The mechanism of formation of the iron oxide nanowires is proposed to follow stress-driven mechanism and when the nanowires merged, nanoblades resulted hierarchical porous structure. Field emission electron microscope (FESEM) images of the oxidized iron had shown the formation of surface oxide comprising of a hierarchical porous structures. High resolution transmission electron microscope (HRTEM) and Raman spectroscopy results confirmed that the iron oxide is consisted of α-Fe2O3 in the surface whereas Fe3O4 and FeO are in the inner layer. The oxides were immersed in Cr(VI) solution and illuminated under sunlight to produce reducing electrons. The highest reduction precentage of Cr(VI) at pH 2 on the hierarchical porous structure is 80.78% for synthesized sample at 500 °C. It may be due to the higher surface area of the porous hierarchical structure which provide more catalytic reaction sites hence improving the photocatalytic activity.

Preparation and photocatalytic property of porous α-Fe2O3 nanoflowers

Porous α-Fe2O3 nanoflowers were successfully prepared by calcining Fe3S4 precursor. The crystal structures, pore sizes and surface areas of the samples could be tuned through changing heat-treating temperatures. The samples calcined at 600 °C exhibited the highest photocatalytic activity for the degradation of methyl orange (MO) under visible light irradiation, which showed a degradation efficiency of more than 99% within 40 min. The enhanced photocatalytic activity could be attributed to its porous hierarchical structure which could promote light absorption efficiency, largely decrease the distance of charge carriers moving to solution and enlarge its specific surface area. This simple and scalable strategy can also be extended to other porous metal oxide nanostructures for photocatalytic applications.

Porous α-Fe₂O₃@C Nanowire Arrays as Flexible Supercapacitors Electrode Materials with Excellent Electrochemical Performances.

Porous α-Fe2O3 nanowire arrays coated with a layer of carbon shell have been prepared by a simple hydrothermal route. The as-synthesized products show an excellent electrochemical performance with high specific capacitance and good cycling life after 9000 cycles. A solid state asymmetric supercapacitor (ASC) with a 2 V operation voltage window has been assembled by porous α-Fe2O3/C nanowire arrays as the anode materials, and MnO2 nanosheets as the cathode materials, which gives rise to a maximum energy density of 30.625 Wh kg−1and a maximum power density of 5000 W kg−1 with an excellent cycling performance of 82% retention after 10,000 cycles.

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.

Template-engaged synthesis of macroporous tubular hierarchical α-Fe2O3 and its ultrafast transfer performance

The macroporous α-Fe2O3 tubular hierarchical structure has been synthesized by a facile template method. The macroporous α-Fe2O3 has high surface area (120 m2 g−1) and pore volume (0.967 cm3 g−1). To demonstrate its ultrafast mass transfer rate, this porous α-Fe2O3 was employed to remove Congo red from simulated waste-water. The adsorption process of Congo red on macroporous α-Fe2O3 can be finished within only 5 min, which is much faster than those of the other reported similar materials. This macroporous α-Fe2O3 will be very useful for catalysts support, adsorbent, and sensor, wherein accessibility of active sites is an important factor to enhance the performance.

Sandwich-like porous α-Fe2O3 nanorod arrays/hexagonal boron nitride nanocomposites with improved high-temperature gas sensing

Sandwich-like porous α-Fe2O3 nanorod arrays/hexagonal boron nitride (h-BN) nanocomposites were synthesized by low temperature hydrolytic precipitation method. The structure and morphology of nanocomposites were studied by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results show that α-Fe2O3/h-BN nanocomposites are composed of porous α-Fe2O3 nanorod arrays arranged on the h-BN nanosheets in an orderly manner. The gas-sensing properties of α-Fe2O3/h-BN nanocomposites and pure α-Fe2O3 were further investigated. The experimental results show that the response of α-Fe2O3/h-BN-based sensor to 50 ppm acetone at an optimum temperature of 320 °C is 10.2. While the response of the α-Fe2O3-based sensor is 5.6 at same conditions. In addition, the α-Fe2O3/h-BN sensor not only returns to the initial state in a short time after exposure to fresh air, but also has good selectivity. These significantly enhanced acetone sensing properties can be attributed to the fact that the prepared α-Fe2O3/h-BN nanocomposites have a large specific surface area, which are composited of porous α-Fe2O3 nanorods with a pore diameter of about 3.7 nm arranged in sequence on h-BN nanosheets. Secondly, the p–n junction between p-type h-BN and n-type α-Fe2O3 modulates the space charge layer at the interface between h-BN and α-Fe2O3.

Room-temperature, high selectivity and low-ppm-level triethylamine sensor assembled with Au decahedrons-decorated porous α-Fe2O3 nanorods directly grown on flat substrate

Chemiresistive based gas sensors with low operating temperature (e.g. room-temperature), high selectivity, and fast response for specific target gas are highly desired. Herein, we successfully construct triethylamine (TEA) gas sensors with gold (Au) decahedrons (DHs)-decorated porous α-Fe2O3 nanorods, which can work at 40 °C and exhibit high selectivity and low-ppm-level response. Porous α-Fe2O3 nanorods with high specific surface area are directly grown on seeded flat substrate with electrodes by a cost-effective hydrothermal method. Au DHs synthesized by one-pot polyol reaction method are deposited onto such α-Fe2O3 nanorods by spin-coating. Such Au DHs/α-Fe2O3 nanorods sensor working at temperature as low as 40 °C and relative humidity (RH) of 30% exhibits high response (17–50 ppm TEA), low detection concentration (∼1 ppm), and short response/recovery time (12/8 s), which are all much better than the control α-Fe2O3 nanorods sensor. When the RH increases, the sensor response decreases due to the water molecules adsorption. Furthermore, the enhanced sensing properties toward TEA are discussed in terms of the formation of Au/Fe2O3 metal/semiconductor Schottky contact and the catalytic activity of Au DHs.

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.

Tetsubo-like α-Fe2O3/C nanoarrays on carbon cloth as negative electrode for high-performance asymmetric supercapacitors

To explore novel negative electrode materials with high special capacitance for high-performance asymmetric supercapacitors, in this article, α-Fe2O3/C nanoarrays on carbon cloth with tetsubo-like structure was synthesized as a free-standing negative electrode for supercapacitor. The characterizations indicated that these α-Fe2O3/C nanoarrays are hollow structure and composed of α-Fe2O3 nanocrystals and carbon nanoparticles. In addition, there are plenty of mesopores existed between these α-Fe2O3 nanocrystals and carbon nanoparticles. Due to the hollow porous structure of α-Fe2O3/C nanoarrays and the presence of carbon nanoparticles not only in favor of accelerating the transport of electron and ion in α-Fe2O3/C electrode, but also increasing the active sites for energy storage, the as-synthesized α-Fe2O3/C electrode delivered much enhanced electrochemical performance including a high specific capacitance up to 430.8 mF cm−2 and 391.8 F g−1 at a current density of 1 mA cm−2, good rate capability with a capacitance retention of 73.2% of capacitance retention at 10 mA cm−2 and great cycling stability with only 8.2% capacitance loss after 4000 cycles at a scan rate of 200 mV s−1. By using α-Fe2O3/C as negative electrode and MnO2 as positive electrode, an asymmetric supercapacitor was assembled to examine the electrochemical performance of α-Fe2O3/C in-depth. Benefit from the unique design of the α-Fe2O3/C electrode, the asymmetric supercapacitor exhibited a high energy density of 0.64 mWh cm−3 at the power density of 14.8 mW cm−3 in 1 M Na2SO4 electrolyte and 0.56 mWh cm−3 at the power density of 16.8 mW cm−3 in Na2SO4/CMC gel electrolyte. These satisfactory results prompt the as-fabricated hollow porous α-Fe2O3/C to use as a promising negative electrode material for high-performance supercapacitors.

A facile coating method to construct uniform porous α-Fe2O3@TiO2 core-shell nanostructures with enhanced solar light photocatalytic activity

A new synthetic approach has been developed to prepareα-Fe2O3@TiO2 core-shell nanostructures at ambient conditions (e.g., in water, ≤100 °C). This approach shows a few unique features, including: short reaction time (a few minutes) for forming core-shell nanostructures, no requirement of high temperature calcinations for generating TiO2 (e.g., at 80–100 °C), tunable TiO2 shell thickness, high yield and good reproducibility. The experimental results show that the α-Fe2O3@TiO2 core-shell nanostructures exhibit enhanced photocatalytic activity compared to the pure TiO2 and pure Fe2O3 in degradation of organic dye molecules with solar light irradiation. This could be attributed to the large surface area of TiO2 nanoparticles for maximum harvesting light adsorption, enhanced visible light absorption, and the effective charge separation at the heterojunction of α-Fe2O3 and TiO2. The findings may open a new strategy to synthesize TiO2-based photocatalysts with enhanced efficiency for environmental remediation applications.