α-Fe2O3 Composites Research Articles

Fabrication and enhancement in photoconductive response of $$\alpha$$ α -Fe2O3/graphene nanocomposites as anode material

We report a facile fabrication for the synthesis of graphene based α-Fe2O3 nanocomposites as anode material for photoelectrochemical water splitting. The effect of introduction of graphene as a solid-state electron material has been investigated in detail by controlling the synthesis parameters. The XRD pattern of hematite α-Fe2O3 nanoparticles were indexed to rhombohedral structure of α-Fe2O3, while the TEM images illustrate the flaky structure of graphene supported by hematite nanoparticles. The rGO/ $$\alpha$$ -Fe2O3 nanocomposites showed enhanced photocurrent of ~ 4 mA cm−2 at (1.23 V vs. RHE) under standard illumination conditions (AM 1.5 G 100 mW cm−2). The enhanced photoelectrochemical performance may be attributed to synergistic effect of graphene and $$\alpha$$ -Fe2O3 by improving the charge transport properties. The optical properties were also observed to be influenced by the coupling of rGO and α-Fe2O3 composites as witnessed in the DRS spectra.

Fabricating of Fe2O3/BiVO4 heterojunction based photoanode modified with NiFe-LDH nanosheets for efficient solar water splitting

It is essential to develop a high activity and stability photoanode for enhancing PEC water splitting performance. According to energy band matching principle the Fe2O3/BiVO4 heterojunction based photoanode is constructed by electrodeposition and metal organic decomposition, following by electrodeposited NiFe-LDH on heterojunction to structure a trinary integrating photoanode. The structure of material and PEC properties of the photoanode are systemically studied, the results show that the photoanode achieves the highest photocurrent density that is about 4.25 times and 2 times higher than that of pristine α-Fe2O3 and BiVO4 photoanodes. The IPCE value is 3.7 times higher than α-Fe2O3 and the onset potential has a significant cathodic shift of 400 mV compared to the pristine α-Fe2O3 for the ternary integrating photoanode. These results are higher than or are comparable to other α-Fe2O3 composites reported in literatures, which is attributed to the efficient separation of the photoexcited electron-hole pairs and alleviates holes accumulation at the surface of electrode due to the double action of semiconductor junction and co-catalyst of NiFe-LDH.

Facile synthesis of Au@α-Fe2O3@RGO ternary nanocomposites for enhanced electrochemical sensing of caffeic acid toward biomedical applications

Demonstrated herewith is a novel eco-friendly Au@α-Fe2O3@RGO ternary nanocomposites using chlorophyll as reductants and stabilizers. Systematic characterizations studies confirm Au and α-Fe2O3 nanoparticles are uniformly decorated on the surfaces of reduced graphene oxide (RGO) nanosheets. As a proof-of-concept, the developed Au@α-Fe2O3@RGO ternary nanocomposites were coated on a glass carbon electrode (GCE) and evaluated for electrochemical detection of caffeic acid. The electrochemical mechanism involves the synergistic electrocatalytic activity of Au and α-Fe2O3 towards caffeic acid oxidation, with the RGO serving as an efficient electron shuttling mediator–enhancing the sensor performance. The Au@α-Fe2O3@RGO modified GCE caffeic acid sensor exhibited a wide linear response range of 19–1869 μM, sensitivity of 315 μA μM−1 cm-2, and a detection limit of 0.098 μM at very low potential of 0.21 V. This ternary nanocomposite provides high catalytic performance as well as excellent selectivity toward caffeic acid. To demonstrate real life application of the Fe2O3@RGO modified GCE caffeic acid sensor, caffeic acid in a coffee sample was measured. The α-Fe2O3, Au-NPs, and conductive graphene sheets composites, result in a highly catalytic and stable electrode system, with no pulverization problems. As such, it is demonstrated herewith that the Fe2O3@RGO ternary nanocomposite electrode is rapid, highly stable, and sensitive, with promised for utilization in fabrication of other multifarious biosensors.

Novel α-Fe2O3/BiVO4 heterojunctions for enhancing NO2 sensing properties

We report a novel composite of α-Fe2O3/BiVO4 with n-n heterojunctions for the first time and application in detecting low concentration NO2 gas. The flower-like α-Fe2O3 hierarchical nanostructures were prepared by the solvothermal method followed by BiVO4 nanoparticles decorated on α-Fe2O3 surface by metal-organic decomposition to structure the heterojunctions of α-Fe2O3/BiVO4. The structure and morphology of material were characterized and the sensing properties to NO2 were examined. The results show that the α-Fe2O3/BiVO4 composite (atomic ratio of 8:1:1 for Fe: Bi: V) to 2 ppm NO2 exhibits a four times higher response than pristine α-Fe2O3 at 110 °C, excellent selectivity, and long-term stability. The enhanced sensing properties can be attributed to the porous hierarchical structure of composite and the formation of inner electronic field (IEF) caused by n-n heterojunction at interface between α-Fe2O3 and BiVO4.

Synthesis and humidity sensing property of α-Fe2O3 and polyaniline composite

The present paper reports the synthesis of α-Fe2O3 by nitrate eutectic melt method and PANI/α-Fe2O3 composite by in-situ polymerization and composite formation (I.P.C.F.) technique at ambient condition. The prepared samples were characterized using infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and UV–VIS spectroscopy (UV–VIS). The result reveals that prepared composite is crystalline in nature along with improved stability. Further, electrical properties reveals the formation of PANI/α-Fe2O3 composite with improved electrical conductivity than α-Fe2O3 and polyaniline. The electrical resistance of a PANI/α-Fe2O3 film casted on a glass substrate was measured as function of relative humidity in the range of 10–95% maintained by salt solution method to explore its use for humidity monitoring purposes. Finally, PANI/α-Fe2O3 promises a perspective materials for humidity sensing applications.

Photocatalytic activity of SnO2–α-Fe2O3 composite mixtures: exploration of number of active sites, turnover number and turnover frequency

Schematic diagram showing energy band edge positions, vectorial charge transfer process and electron hole separation process in the SnO2–α-Fe2O3 composite under UV/visible light irradiation.

Achieving the broader frequency electromagnetic absorber by development of magnetic core-shell composite with tunable shell/core sizes

Magnetic absorber has been regarded as the advanced electromagnetic energy transfer material to solve the increasingly high frequency electromagnetic interference issue. Even so, the pure magnetic material, in particular magnetic metal nanoparticle, suffering from the poor chemical stability and strong eddy current effect, thus limits it further application. To overcome this shortage, surrounded the magnetic metal nanoparticle (MPs) with insulated oxide shell has been considered to be an efficient route to suppress such an eddy current effect. Meanwhile, the combined insulated shell with good impedance matching feature, shows a positive role on the electromagnetic energy transfer intensity. In this regard, the binary Fe@α-Fe2O3 composite with the average size of∼20nm was prepared by a facile self-oxidation reaction. Interestingly, both the core diameter and shell thickness is controllable by controlling the oxide degree. The electromagnetic energy transfer performance revealed the maximum absorption frequency bandwidth of the optimal Fe@α-Fe2O3 composite is up to 5.3 G(8.2-13.5 GHz)under a small coating thickness of 1.5mm.

The efficacy of the ZnO:α-Fe2O3 composites modified carbon paste electrode for the sensitive electrochemical detection of loperamide: A detailed investigation

The efficacy of the ZnO-α-Fe2O3 composites as carbon paste electrode (CPE) modifier for sensitive electrochemical detection of loperamide was explored. The composites were synthesized in 1:1, 2:1, and 3:1 (ZnO:α-Fe2O3) ratios by the gradual amalgamation of pre-synthesized α-Fe2O3 and hydrated gel of Zn2+ that later transformed to the ZnO by thermal treatment. The lattice parameters of the composite ZnO and the probable variations in the oxidation states of the components during the adopted coating procedure were assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The field-emission scanning electron microscopy (FESEM) imaging of the as-synthesized and carbon paste (CP) dispersed composite powders at various resolutions exposed the increased surface coverage of the α-Fe2O3 by the ZnO particles with the increasing loading and the uniform distribution of the composite materials in the matrix of carbon paste. Compared to bare CPE, the composites modified CPEs exhibited significantly decreased charge transfer impedance at the electrode/electrolyte interface evaluated by electrochemical impedance spectroscopy (EIS). The sensing ability of the composites modified electrodes for the detection of loperamide in the aqueous medium was investigated. A higher and affectedly improved cyclic voltammetric (CV) oxidation signal of loperamide was noticed at the prepared ZnO:α-Fe2O3/CPEs compared to pure components modified CPEs i.e. ZnO/CPE and α-Fe2O3/CPE. Based on the EIS and CV investigations, a superior electrochemical performance of (2:1) ZnO:α-Fe2O3/CPE was established. Additionally, under optimized experimental conditions of pH, deposition potential, and accumulation time, loperamide was quantified by square wave stripping voltammetry (SWSV) that resulted in the linear calibration ranges from 0.08–1 and 2–10μmolL−1 with detection limits (S/N=3) of 7.9 and 3.6nmolL−1. The findings of various electrochemical investigations were correlated to establish the mechanism of charge transport and oxidation of loperamide.

Facile synthesis of graphitic carbon nitride/nanostructured α-Fe2O3 composites and their excellent electrochemical performance for supercapacitor and enzyme-free glucose detection applications

The graphitic carbon nitride (g-C3N4)/iron oxide (α-Fe2O3) composites have been prepared by a one-step pyrolysis of Prussian blue (PB) and melamine. The Fe2O3 nanoparticles derived from PB effectively protect the thin layers of g-C3N4 from restacking and expanding. The as-prepared g-C3N4/α-Fe2O3 composites exhibit a large specific surface area, and demonstrate their excellent electrochemical performance in the supercapacitor and non-enzymatic detection of glucose. The g-C3N4/α-Fe2O3 composites facilitate the faster faradic reaction in 1.0M KOH electrolyte, and deliver the highest specific capacitance (580Fg−1) at the current density of 1.0Ag−1. The resultant composites also show an excellent long cycle life (up to 1000 cycles) at the current density of 2Ag−1. In addition, the modified electrode based on the g-C3N4/α-Fe2O3 hybrids are also used for the non-enzymatic detection of glucose. The as-fabricated modified electrode exhibits good electrochemical performance towards the oxidation of glucose with a response time <3s and a linear range of 2.0×10−6−2.4×10−3molL−1. The electrode modified by the g-C3N4/α-Fe2O3 composites exhibits good anti-interference performance and stability. The g-C3N4/α-Fe2O3 hybrids have great potential in the application of electrochemical storage devices and sensors.

A conjugated composite of α-Fe2O3 and BiOBr with enhanced visible-light-induced photocatalytic activity

Owing to its nontoxic property, low cost and narrow band gap, alpha-iron(III) oxide (α-Fe2O3) is a promising material as photocatalyst. However, it has shortcomings such as quick recombination and a short lifetime of the electron-hole pairs, which directly reduce the photocatalytic efficiency of α-Fe2O3 and hinder its wide applications. In this study, a facile hydrothermal method was used to incorporate BiOBr with α-Fe2O3 in an attempt to overcome the previously mentioned limitations of α-Fe2O3, and the synthesized composites were fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–vis diffuse-reflection spectroscopy (DRS). The BiOBr/α-Fe2O3 composite showed much higher visible-light-driven photocatalytic activity than the pure α-Fe2O3 and BiOBr for Rhodamine B (RhB) degradation. Specifically, the composite synthesized at 100°C for 18h with a mass ratio of BiOBr to α-Fe2O3 5:10 performed the best. This work also explored the chemical mechanism and pathway of RhB degradation, and the roles of the oxidative species with the presence of BiOBr/α-Fe2O3 composites in the photocatalytic oxidation process, including holes (h+), hydroxyl radicals (OH), and superoxide radicals (O2−).

Synthesis of cavity-containing iron oxide nanoparticles by hydrothermal treatment of colloidal dispersion

Nanostructured iron oxides have been widely used in catalysis, adsorption, sensor, biomedicine, and so on. In this study, iron oxide nanoparticles containing nanosized cavities were prepared by hydrothermal treatment of a colloidal dispersion of iron hydroxide. The as-prepared sample and the one calcined in air at 450°C were composed of well-dispersed rhombohedral-like α-Fe2O3 nanoparticles; calcining in nitrogen resulted in a composite of α-Fe2O3 and γ-Fe2O3 having superparamagnetic property. Moreover, the iron oxide nanoparticles calcined in air or nitrogen have 7–15nm- and 5–12nm-diameter cavities, respectively. These peculiar structures might be conducive for some applications such as adsorption involving large molecules.

Preparation of iron oxide-loaded bamboo charcoals and their trinitrotoluene red water treatment

Magnetic bamboo charcoals were prepared by loading FeCl3 onto bamboo charcoal and then calcinated at appropriate temperatures. The type of iron oxides on bamboo charcoal and the possible reactions in the process of preparation were analyzed by thermal gravimetric analysis, X-ray fluorescence, and X ray diffraction. The sample obtained by calcination at 400°C was the composite of FeO(OH), α-Fe2O3, and bamboo charcoal, while the product given by calcination at 700°C composed α-Fe2O3, Fe3O4, and SiO2. The magnetic bamboo charcoal calcinated at 400°C had a magnetization of 1.12 emu/g and a slightly higher chemical oxygen demand removal rate to trinitrotoluene red water compared to bamboo charcoal. So, the as-prepared magnetic bamboo charcoals were a kind of useful adsorbents with magnetic separation function.

Role of mechanochemical milling in FeVO4 synthesis

Single phase, a FeVO4 triclinic crystalline structure was successfully synthesized by annealing the mechanochemically milled xV2O5·(1−x)α-Fe2O3 composites (x=0.5) at 550°C for 1h. X-ray powder diffraction (XRD), simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC–TGA), Mössbauer spectroscopy, scanning electron microscopy (SEM), and optical diffuse reflectance spectroscopy were combined for a detailed study of the assisting role of the mechanochemical milling process. Mechanochemical milling homogeneously mixed the starting materials of α-Fe2O3 and V2O5 and substantially decreased their average grain sizes. The Mössbauer spectroscopy studies showed that the spectrum of the mechanochemically milled composites consisted of three sextets and one doublet, indicating the occurrence of V5+–Fe3+ ion substitutions in the corresponding α-Fe2O3 and V2O5 lattices, respectively. The partially V5+-substituted α-Fe2O3 phase and Fe3+-substituted V2O5 could be the important intermediate phases in the production of FeVO4 single phase. The synthesized FeVO4 phase had a slightly distorted nature with an unequal ratio in Fe3+ population in three inequivalent sites. Simultaneous DSC–TGA studies indicated that the synthesized FeVO4 is thermally stable up to 600°C. SEM images of the formed FeVO4 confirmed the wide particles size distribution range composed of nano-grains. Optical diffuse reflectance spectroscopy studies showed that the synthesized FeVO4 phase had semiconductor properties, with the band gap energy of ~2.44eV.

Dispersion–precipitation synthesis of nanosized magnetic iron oxide for efficient removal of arsenite in water

Nanosized magnetic iron oxide was facilely synthesized by a dispersion–precipitation method, which involved acetone-promoted precipitation of colloidal hydrous iron oxide nanoparticles and subsequent calcination of the precipitate at 250°C. Characterization by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, nitrogen sorption, and vibrating-sample magnetometry revealed that the material was a composite of α-Fe2O3 and γ-Fe2O3 with primary particle size of 15–25nm and specific surface area of 121m2/g, as well as superparamagnetic property. The material was used as adsorbent for the removal of arsenite in water. Batch experiments showed that the adsorption isotherms at pH 3.0–11.0 fit the Langmuir equation and the adsorption obeys pseudo-second-order kinetics. Its maximum sorption capability for arsenite is 46.5mg/g at pH 7.0. Coexisting nitrate, carbonate, sulfate, chloride, and fluoride have no significant effect on the removal efficiency of arsenite, while phosphate and silicate reduce the removal efficiency to some extent. The As(III) removal mechanism is chemisorption through forming inner-sphere surface complexes. The efficiency of arsenic removal is still maintained after five cycles of regeneration–reuse.

Influence of different materials on the microstructure and optical band gap of α-Fe2O3 nanoparticles

Abstract Composites of hematite (α-Fe2O3) nanoparticles with different materials (NiO, TiO2, MnO2 and Bi2O3) were synthesized. Effects of different materials on the microstructure and optical band gap of α-Fe2O3 nanoparticles were studied. Crystallite size and strain analysis indicated that the pure α-Fe2O3 nanoparticles were influenced by the presence of different materials in the composite sample. Crystallite size and strain estimated for all the samples followed opposite trends. However, the value of direct band gap decreased from ∼2.67 eV for the pure α-Fe2O3 nanoparticles to ∼2.5 eV for α-Fe2O3 composites with different materials. The value of indirect band gap, on the other hand, increased for all composite samples except for α-Fe2O3/Bi2O3.

Effects of vacancy and exchange-coupling between grains on magnetic properties of SrFe12O19 and α-Fe2O3 composites

All samples were synthesized via supercritical (390°C) and low-temperature (190°C) hydrothermal methods followed by annealing at 1000°C, and contained both SrFe12O19 and α-Fe2O3 phases as reported in literature. The magnetic properties sensitively depended on the relative content of each phase, which was generally attributed to phase homogeneity and microstructural characteristics in literature as far as we know. In this paper, we observed a double-peak behavior in the curve of irreversible susceptibilities χirr versus an external magnetic field H, which was assigned to the cation vacancies and their distribution. The coercivity of the sample almost changed linearly with the average value of magnetic fields at which the χirr (H) peak located. Therefore, we conclude that the magnetic parameters, at least the coercivity, are mainly determined by cation vacancies which have usually been neglected before in SrFe12O19.

Fabrication and gas sensing properties of hollow core–shell SnO2/α-Fe2O3 heterogeneous structures

Abstract One dimensional hierarchically hollow SnO2/α-Fe2O3 core–shell nanofibers were synthesized by using electrospun SnO2 hollow nanofibers as core followed by the hydrothermal growth and calcination of α-FeOOH nanorods on the outer surface of SnO2 nanofibers. The control experiments indicated that glacial acetic acid introduced in the hydrothermal solution could adjust the nucleation site and density of α-FeOOH nanorods as well as prevent the formation of urchin-like α-FeOOH byproduct. The growth process of α-FeOOH nanorods on SnO2 hollow nanofibers was also investigated. The hierarchical SnO2/α-Fe2O3 hollow nanofibers were then fabricated as gas sensors for the investigation of gas sensing applications. By comparison of sensing properties, the response values of the sensors fabricated with hierarchical SnO2/α-Fe2O3 core–shell nanofibers toward 100 ppm acetone and ethanol could reach to be 30.363 and 20.370, respectively, exhibiting much better performance than those using urchin-like α-Fe2O3 nanostructures and pure SnO2 nanofibers. Meanwhile, the sensors based on hierarchical SnO2/α-Fe2O3 nanofibers also had shorter response and recovery times than those of α-Fe2O3 nanostructures. The synergetic effect of the composite of α-Fe2O3 and SnO2 together with unique hollow core–shell architectures are main contribution for the enhanced gas sensing properties.

Hematite (α-Fe2O3) nanoparticles on vulcan carbon as an ultrahigh capacity anode material in lithium ion battery

We present a first time report on novel and easy low temperature hydrothermal method using glycine to synthesize α-Fe2O3 nanoparticles (NPs) and Vulcan carbon (VC)-supported α-Fe2O3 composite. Formation of complex between glycine and iron metal ions retards iron oxide nucleation process at early stage of reaction, resulting in uniform dispersion of the iron oxide with smaller particle size. The small α-Fe2O3 NPs are highly dispersed on the VC to form an iron oxide-carbon composite, which exhibits a high specific capacity of 1200mAhg−1 as an anode material for lithium battery, significantly improving anode performance. The excellent performance observed with the α-Fe2O3/VC composite is ascribed to well-dispersed small iron oxide particles regulated by the novel glycine-assisted approach and the presence of a carbon support. In particular, remarkably, the activity of the α-Fe2O3/VC composite is much higher than combined sum of respective values of the bare α-Fe2O3 NPs and supporting VC, indicating strong favorable synergistic interaction between α-Fe2O3 and VC in the composite. Our studies demonstrate that the carbon support plays remarkably important roles as a conductive buffer and as active sites for lithium storage in significantly improving Li ion storage capacity, cycle life and rate capability of the anode electrode.

Synthesis and Characterization of g-C&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/α-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Composites with Enhanced Photocatalytic Activity

A novel composite photocatalyst g-C3N4/α-Fe2O3 was prepared through calcination method. The photocatalysts were characterized by thermogravimetric analysis (TG), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The obtained g-C3N4/α-Fe2O3 composites show high efficiency for the degradation of Rhodamine B (RHB). The optimum photocatalytic activity of g-C3N4/Fe2O3 at a g-C3N4 content of 8.6% under visible light irradiation is almost 4.8 times as high as that of pure α-Fe2O3. The enhancement in visible light photoactivity of g-C3N4/α-Fe2O3 composites was attributed to the introduction of g-C3N4 and the interaction between g-C3N4 and α-Fe2O3.

Kinetics and thermodynamic study of phosphate adsorption on the porous biomorph-genetic composite of α-Fe2O3/Fe3O4/C with eucalyptus wood microstructure

A novel porous biomorph-genetic composite of α-Fe2O3/Fe3O4/C (PBGC-Fe/C) was prepared with eucalyptus wood template to removal phosphate from water and wastewater. Adsorption of phosphorus from aqueous solution onto the PBGC-Fe/C adsorbent has been investigated to evaluate the effects of solution pH, adsorbent grain size, contact time, initial P concentration, and temperature on the removal systematically. At the initial P concentrations of 2, 5, and 10mg/L, the adsorption capacities for the unpulverized PBGC-Fe/C (0.841–2mm) were determined to be 0.18, 0.34, and 0.69mg/g, respectively, which exhibited a similar average value to those of fine particles or nanoparticles of iron oxides reported in the literatures. With increasing initial P concentration from 2 to 50mg/L, the amounts of P sorbed on the pulverized PBGC-Fe/C adsorbent (0.074–0.149mm) increased from 0.20 to 1.56mg/g at 25°C, and the corresponding removal efficiencies decreased from 98.0% to 31.3%. The adsorption could well be described by the pseudo-second-order kinetic equation and the Freundlich isotherm equation.