β-FeOOH Nanorods Research Articles

Elaboration and characterization of nanoplate structured α-Fe2O3 films by Ag3PO4

A new strategy for surface treatment of hematite nanoplates for efficient photoelectrochemical (PEC) performances is proposed. Silver orthophosphate (Ag3PO4) has been adopted to mediate the formation of α-Fe2O3 films. Phosphate ions in Ag3PO4 is found to cause a significant morphology change during annealing process, from β-FeOOH nanorod arrays to hematite nanoplates. Meanwhile, Ag ions is doped into α-Fe2O3 film. The obtained nanoplate structured Fe2O3–Ag–P films demonstrate much higher photoelectrochemical performance as photoanodes than the bare Fe2O3 nanorod thin films. The effects of phosphate and silver ions on the morphology, surface characteristics and the PEC properties of the photoanodes are investigated.

Glucose assisted synthesis of the BiOCl/β-FeOOH composite with enhanced photocatalytic performance

The BiOCl/β-FeOOH composite was prepared using one-step glucose assisted hydrothermal method at 100°C. The as-synthesized sample was characterized by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope and UV–vis spectrophotometer. The photocatalytic performance of the composite was evaluated through photo-degradation of Rhodamine B (RhB) under visible light irradiation. It was found that the used glucose played a significant role in the combination of the BiOCl with β-FeOOH. The obtained composite exhibited much better photocatalytic activity in degradation of RhB than the pure BiOCl and β-FeOOH, which would be of great promise for the industrial application of this catalyst to oxidize organic pollutants for wastewater treatment. The enhanced photocatalytic performance can be attributed to the introduction of β-FeOOH nanorods which leads to the relative reduction of the band gap (Eg) of the composite, because of which electrons and holes are easily generated.

Fabrication of rod-shaped β-FeOOH: the roles of polyethylene glycol and chlorine anion

β-FeOOH nanorods of 40 nm wide and 450 nm long were fabricated through precisely regulating the hydrolysis kinetics of Fe3+ in polyethylene glycol and the concentration of Cl- as the structure-directing agent. Detailed structural and chemical analyses of the intermediates during the synthesis identified that the strong interaction between PEG and Fe3+ modulated the hydrolysis kinetics of Fe3+ and prevented the aggregation of β-FeOOH nanorods; while Cl- provided sufficient nucleation sites, stabilized the hollow channel of β-FeOOH, and more importantly induced the growth of the nanorods along [001] direction.

Construction of layer-by-layer coating based on graphene oxide/β-FeOOH nanorods and its synergistic effect on improving flame retardancy of flexible polyurethane foam

The binary hybrid-filled layer by layer coating, composed of graphene oxide and β-FeOOH nanorods, was fabricated onto flexible polyurethane (FPU) foams by layer by layer assembly technique to reduce its flammability. Scanning electron microscopy images showed that the coexistence phenomenon between GO nanosheets with β-FeOOH nanorods can be found to cover on the FPU foam surface. The analysis by thermogravimetric analysis/infrared spectrometry (TGA-IR) indicated that the binary-hybrid filled coating has greater advantages in suppression of gaseous product generation, meaning that less “fuel” was fed back to the flame. Compared with the single component (graphene oxide or β-FeOOH nanorods)-filled coatings, the binary hybrid-filled coating has greater reduction (49.5%) in peak heat release rate (PHRR) and could almost eliminate the second PHRR for FPU foams in the cone test, which indicates its superiority. As a result, the complementary effect between graphene oxide nanosheets with β-FeOOH nanorods enhanced the flame retardant effect for FPU foams.

Phase-controlled synthesis of iron phosphates via phosphation of β-FeOOH nanorods

Iron phosphates comprise an important class of materials with a wide range of applications. We have designed novel routes for the controlled synthesis of iron phosphate dihydrates of varying crystallographic phases (monoclinic and orthorhombic) and morphologies. Our approach comprises the phosphation of β-FeOOH nanorods with aqueous phosphoric acid solutions. Through a systematic parametric study coupled to an array of characterisation techniques, including XRD, TEM, HAADF-STEM, AAS, N2 sorption, TGA-MS, FTIR, UV-Vis, XPS, EXAFS, EPR, and 57Fe Mossbauer spectroscopy, we unravel the complex synthesis chemistry on both the macroscopic and microscopic levels. It is found that the formation of iron phosphates occurs exclusively under acidic conditions and in general involves the dissolution of β-FeOOH which, upon reaction with H3PO4, precipitates as FePO4·2H2O. The pH of the treatment solution determines the crystallographic phase of the resulting product by regulating the rate of β-FeOOH dissolution and of the precipitation of the iron phosphates, while the treatment time is decisive for the preservation of the morphology. The formation of the monoclinic phase entails a fast iron dissolution and subsequent precipitation in the solution. The generation of the orthorhombic analogue involves an interfacial reaction between H3PO4 and β-FeOOH, forming an amorphous layer of iron phosphate, which crystallises into a pure phase with increasing treatment time. The thermal transformation of hydrated to anhydrous iron phosphates is dependent on the phase and morphology of the precursors. The rod shape of iron-rich orthorhombic FePO4·2H2O can be preserved even after annealing at 923 K, with the formation of mesopores. These novel nanostructures may widen the applications of iron phosphates and the routes developed herein can be anticipated to guide the fabrication of other metal phosphates.

Gelatin assisted wet chemistry synthesis of high quality β-FeOOH nanorods anchored on graphene nanosheets with superior lithium-ion battery application

High quality β-FeOOH nanorods anchored on graphene nanosheets to form β-FeOOH/rGO hybrid nanostructures were synthesized by using a gelatin assisted wet chemistry strategy.

Sandwichlike Coating Consisting of Alternating Montmorillonite and β-FeOOH for Reducing the Fire Hazard of Flexible Polyurethane Foam

A novel nanocoating, composed of montmorillonite (MMT) nanosheets and β-FeOOH nanorods, was deposited on the surface of flexible polyurethane (FPU) foams through a layer-by-layer assembly technique to reduce its flamability. The coating growth was performed by alternately immersing FPU foams into polyethylenimine (PEI) solution, MMT-alginate suspension, and β-FeOOH dispersion. Structural and morphological characterization indicated that MMT nanosheets and β-FeOOH nanorods were distributed homogeneously on the surface of the matrix and formed a sandwichlike topology. The coated FPU foams showed the lower peak heat release rate (PHRR), compared to the counterparts fabricated by introduction of MMT nanosheets or β-FeOOH nanorods alone. Furthermore, the concentration of volatile products released from the coated FPU foams was reduced remarkably, indicating that the binary components had tremendous advantages in reducing the flamability of the material. These significant improvements in flame retardancy and to...

Bunched akaganeite nanorod arrays: Preparation and high-performance for flexible lithium-ion batteries

Significant effort has been made to explore high-performance anode materials for flexible lithium-ion batteries. We report a facile hydrothermal route to synthesis self-organized bunched akaganeite (β-FeOOH) nanorod arrays directly grown on carbon cloth (CC/β-FeOOH NRAs). Interestingly, the single nanorod is assembled by numerous small nanowires. A possible growth mechanism for this unique structure is proposed. Owning to the essential crystal structure of β-FeOOH (body-centered cubic), porous morphology, high surface area and direct growth on current collector, the prepared CC/β-FeOOH NRAs manifest a very high reversible capacity of ≈2840 mAh g−1 (2.21 mAh cm−2), remarkable rate capability 568 mAh g−1 (0.43 mAh cm−2) at 10C, stable cycling performance and greater mechanical strength.

Catalytic activities of ultra-small β-FeOOH nanorods in ozonation of 4-chlorophenol

We report the catalytic properties of ultra-small β-FeOOH nanorods in ozonation of 4-chlorophenol (4-CP). XRD, TEM, EDS, SAED, FTIR and BET were used to characterize the prepared material. Interaction between O3 and β-FeOOH was evident from the FTIR spectra. The removal efficiency of 4-CP was significantly enhanced in the presence of β-FeOOH compared to ozone alone. Removal efficiency of 99% and 67% was achieved after 40min in the presence of combined ozone and catalyst and ozone only, respectively. Increasing catalyst load increased COD removal efficiency. Maximum COD removal of 97% was achieved using a catalyst load of 0.1g/100mL of 4-CP solution. Initial 4-CP concentration was not found to be rate limiting below 2×10−3mol/L. The catalytic properties of the material during ozonation process were found to be pronounced at lower initial pH of 3.5. Two stage first order kinetics was applied to describe the kinetic behavior of the nanorods at low pH. The first stage of catalytic ozonation was attributed to the heterogeneous surface breakdown of O3 by β-FeOOH, while the second stage was attributed to homogeneous catalysis initiated by reductive dissolution of β-FeOOH at low pH.

Silica-Coated and Bare Akaganeite Nanorods: Structural and Magnetic Properties

We report on structural and magnetic properties of uniform silica-coated akaganeite nanorods with length of L ∼ 80 ± 15 nm and diameter D ∼ 15 ± 5 nm as well as silica shell thickness of about 5 nm. Unexpected negative difference between field-cooled (FC) and zero-field-cooled (ZFC) magnetization ΔM = MFC – MZFC < 0, room temperature ferromagnetism, and exchange bias effect have been found. The nanorods are investigated by X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) measurements. The magnetic measurements were also performed on bare akaganeite nanorods in order to discriminate the effects of silica coating on the magnetic properties. The measured coercivity and exchange bias effect of bare β-FeOOH nanorods are much lower compared with same properties of SiO2@β-FeOOH nanorods, emphasizing the effect of silica coating on the magnetic properties. These results are discussed considering the core–shell structure of akaganeite nanorods; i.e., ...

Polydopamine-Coated Porous Substrates as a Platform for Mineralized β-FeOOH Nanorods with Photocatalysis under Sunlight.

Immobilization of photo-Fenton catalysts on porous materials is crucial to the efficiency and stability for water purification. Here we report polydopamine (PDA)-coated porous substrates as a platform for in situ mineralizing β-FeOOH nanorods with enhanced photocatalytic performance under sunlight. The PDA coating plays multiple roles as an adhesive interface, a medium inducing mineral generation, and an electron transfer layer. The mineralized β-FeOOH nanorods perfectly wrap various porous substrates and are stable on the substrates that have a PDA coating. The immobilized β-FeOOH nanorods have been shown to be efficient for degrading dyes in water via a photo-Fenton reaction. The degradation efficiency reaches approximately 100% in 60 min when the reaction was carried out with H2O2 under visible light, and it remains higher than 90% after five cycles. We demonstrate that the PDA coating promotes electron transfer to reduce the electron-hole recombination rate. As a result, the β-FeOOH nanorods wrapped on the PDA-coated substrates show enhanced photocatalytic performance under direct sunlight in the presence of H2O2. Moreover, this versatile platform using porous materials as the substrate is useful in fabricating β-FeOOH nanorods-based membrane reactor for wastewater treatment.

Ferromagnetic behavior and exchange bias effect in akaganeite nanorods

We report ferromagnetic-like properties and exchange bias effect in akaganeite (β-FeOOH) nanorods. They exhibit a Néel temperature TN = 259 K and ferromagnetic-like hysteresis behavior both below and above TN. An exchange bias effect is observed below TN and represents an interesting behavior for akaganeite nanorods. These results are explained on the basis of a core-shell structure in which the core has bulk akaganeite magnetic properties (i.e., antiferromagnetic ordering) while the shell exhibits a disordered spin state. Thus, the nanorods show ferromagnetic properties and an exchange bias effect at the same time, increasing their potential for use in practical applications.

Photocatalytic activities of ultra-small β-FeOOH and TiO2 heterojunction structure under simulated solar irradiation

Photocatalytic performance of β-FeOOH/TiO2 heterojunction structure, created from ultra-small β-FeOOH nanorods (2–6nm diameter) and spherical anatase phase of TiO2 nanoparticles (∼100nm), is reported in this study. Three different β-FeOOH mol% of (2, 5 and 10%) β-FeOOH/TiO2 composite was prepared. 5% β-FeOOH/TiO2 composite material showed the highest photocatalytic activity. XRD, high temperature XRD, FTIR, TEM, UV–vis diffuse reflectance spectra (DRS) were used to characterise the prepared catalyst. The developed catalyst showed excellent photocatalytic activity in photodegradation of methyl orange (MO) than β-FeOOH and TiO2 under simulated solar irradiation. Two commercial metal complex dyes and real textile effluent were efficiently photodegraded under identical conditions. The developed catalyst exhibited good recyclability without the need of sintering. No significant loss in efficiency was observed during the recycling cycle. These characteristics highlight the potential application of the developed photocatalyst in textile effluent treatment via photocatalysis. The enhanced photocatalytic activity was attributed to the relative energy band positions and very good electron, e− and hole, h+ conduction ability of TiO2 and β-FeOOH particles respectively.

Controlled synthesis of high-performance β-FeOOH anodes for lithium-ion batteries and their size effects

β-FeOOH has recently been reported to have a very high lithium storage capacity of ~1400mAhg−1, 20–40% higher than those widely reported for iron-based anodes, such as Fe2O3 and Fe3O4. However, many properties of this material that are important for their use in lithium-ion batteries remain unknown. Here, we present a study on the effects of particle size on their lithium storage performance and the kinetics associated with the redox reactions. The study is based on β-FeOOH nanorods prepared by a simple hydrolysis method which is able to control the size of the rods in a wide range, diameter from tens of nanometers down to ~5nm. Three materials with different sizes, mean diameter 5, 13 and 53nm, are investigated for lithium storage. They show a very high and comparative capacity at a low current density, but different initial Coulombic efficiencies and rate capabilities. The kinetic study reveals the initial size of the material influences the formation of the SEI layers on the material and has significant effects on the kinetics of the redox reactions that lead to different rate behaviors. This study provides fundamental information and understanding of β-FeOOH anodes for their further development.

Metal-like fluorine-doped β-FeOOH nanorods grown on carbon cloth for scalable high-performance supercapacitors

At present, supercapacitors employed in the market have been growing rapidly, including portable electronics, hybrid electric vehicles, and industrial electric systems. Nevertheless, there are some limitations in supercapacitor devices, such as low energy density and high production cost, which are recognized as the major challenges for their developments. The performance of these devices depends intimately on the properties of electrode materials, therefore one of the most intensive approaches is to design novel electrode materials. Herein, a new scalable electrode material, metal-like fluorine-doped β-FeOOH nanorods grown on carbon cloth has been engineered for enhancing the energy density meanwhile retaining the high power density of the supercapacitor via an easy, low-cost, and large-scale fabrication approach. The optimal supercapacitor device exhibits a high-class supercapacitor performance with a good rate capability, high energy density (1.85mWhcm−3), large power density (11.11Wcm−3), and long cycle span (no decrease of capacitance after 5000 cycles). Moreover, this kind of material represents an alternative promising candidate for large-scale and high-performance energy storage devices.

Surface engineered doping of hematite nanorod arrays for improved photoelectrochemical water splitting.

Given the narrow band gap enabling excellent optical absorption, increased charge carrier density and accelerated surface oxidation reaction kinetics become the key points for improved photoelectrochemical performances for water splitting over hematite (α-Fe2O3) photoanodes. In this study, a facile and inexpensive method was demonstrated to develop core/shell structured α-Fe2O3 nanorod arrays. A thin, Ag-doped overlayer of ~2–3 nm thickness was formed along α-Fe2O3 nanorods via ultrasonication treatment of solution-based β-FeOOH nanorods in Ag precursor solution followed by high temperature annealing. The obtained α-Fe2O3/AgxFe2−xO3 core/shell nanorod films demonstrated much higher photoelectrochemical performances as photoanodes than the pristine α-Fe2O3 nanorod film, especially in the visible light region; the incident photon-to-current efficiency (IPCE) at 400 nm was increased from 2.2% to 8.4% at 1.23 V vs. RHE (Reversible hydrogen electrode). Mott-Schottky analysis and X-ray absorption spectra revealed that the Ag-doped overlayer not only increased the carrier density in the near-surface region but also accelerated the surface oxidation reaction kinetics, synergistically contributing to the improved photoelectrochemical performances. These findings provide guidance for the design and optimization of nanostructured photoelectrodes for efficient solar water splitting.

Highly oriented Ge-doped hematite nanosheet arrays for photoelectrochemical water oxidation

We report a simultaneous strategy of impurity doping and crystal growth for building highly oriented Ge-doped α-Fe2O3 nanosheet arrays vertically aligned on fluorine-doped tin oxide (FTO) glass substrates in hydrothermal environments, by using β-FeOOH nanorod arrays as sacrificial templates and highly reactive Ge colloidal solutions as dopant source. Microstructure characterization and elemental analysis reveal the preferential growth orientation, distribution of dopants, and doping level of Ge-doped α-Fe2O3 nanosheet arrays. Based on the doping of Ge atoms, proper feature size of nanosheets (with thickness <10nm) and preferential growth orientation within (001) basal plane of perpendicular nanosheet arrays, Ge-doped α-Fe2O3 nanosheet arrays show a photocurrent density of 1.4mAcm−2 at 1.23V vs. RHE, which is more than 50 times of the undoped α-Fe2O3 nanorod arrays. Moreover, we find that the annealing temperature remarkably affects the majority carrier density and optical absorption efficiency, which enabled the determination of photocurrent density of hematite nanostructure arrays.

Doped and Core/Shell Structured Hematite Nanorods for Improved Photoanodic Performance for Solar Water Splitting

In this study, a facile solution-based method was developed to fabricate hematite nanorods coated with ultrathin overlayer of TiO2 or AgxFe2-xO3, as well as doped with Ta5+. The core/shell nanorod structures of α-Fe2O3/TiO2 and α-Fe2O3/AgxFe2-xO3 were obtained by annealing solution-fabricated β-FeOOH nanorod arrays which were first ultrasonicated in TiO2 sol and Ag+ aqueous solution, respectively. In the α-Fe2O3/TiO2 nanorod structure, TiO2 overlayer could extract photogenerated holes from α-Fe2O3 core via the quantum-mechanical tunneling process, resulting in promoted charge carrier separation, and hence greatly improved photoelectrochemical performance for water splitting, with IPCE increased by a factor of 4.5 from ~2.0% to 9.0% at 400 nm. In the α-Fe2O3/AgxFe2-xO3 nanorod structure, the surface doping of Ag+ ions gave rise to increased electron donor density, which also led to the enhancement in photoelectrochemical performance with IPCE at 400 nm increased from ~2.0% to ~7.5%. Ta5+ doping was found to effectively enhance the PEC performace for water splitting, due to the improved conductivity, increased donor density and reduced charge recombination. However, excessive Ta doping will reduce the PEC acitivity, by forming insulating layer of Ta-rich oxide over the hematite surface.

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.

Hydrothermal Synthesis of Octadecahedral Hematite (α-Fe2O3) Nanoparticles: An Epitaxial Growth from Goethite (α-FeOOH)

Driven by the demand for shape-controlled synthesis of α-Fe2O3 nanostructures and the understanding of their growth mechanism and shape-dependent properties, we report the synthesis of octadecahedral α-Fe2O3 nanocrystals with a hexagonal bipyramid shape by introducing F– anions in the solution. The hydrothermal growth process from hydrolysis of Fe3+ precursors involves three steps: the nucleation of akaganeite (β-FeOOH) nanorods, followed by the formation of goethite (α-FeOOH) crystals with acicular and twinned shapes, and a subsequent transformation into hematite (α-Fe2O3) nanoparticles. The phase transformation and growth of α-Fe2O3 particles from α-FeOOH follows dissolution of goethite and reprecipitation as hematite process. The initial nucleation of α-Fe2O3 particles was found to form epitaxially on goethite {001} surfaces due to a perfect lattice match between goethite {001} surface and hematite {001} planes. The structural relationship between goethite and hematite is G(020)//H(030) with G[100]//H[...