α-FeOOH Nanorods Research Articles

Synthesis and influence of alkaline concentration on α-FeOOH nanorods shapes

α-FeOOH nanorods having uniform morphology were synthesized by water bath process. X-ray diffraction and transmission electron microscopy revealed that the single-crystalline orthorhombic α-FeOOH nanorods are about 10 nm in diameter and hundreds of nanometer in length. The effect of concentration of KOH on morphology of α-FeOOH nanorods was investigated. pH values of solution play an important role in the process of transformation of ferrihydrite into goethite. The inconsistent growth rate along different facets can be effected by pH values of the solution. The influence and growth mechanism of α-FeOOH nanorods were discussed in detail. This method may be widely used as reference to fabricate other inorganic one-dimensional nanostructured materials and easily realized in industrial-scale synthesis.

Hydrothermal synthesis of goethite (α-FeOOH) nanorods in the presence of ethylenediamine:thiourea

Goethite (α-FeOOH) nanorods were synthesized via the hydrothermal method with the assistance of coordinating ligands, i.e. ethylenediamine and thiourea. The homogeneity of the nanorod size distribution increased and the propensity to agglomerate decreased when ethylenediamine and thiourea were used in conjunction; contrary to goethite synthesis in the presence of a single ligand. The type and mode of structure-directing plays a critical role in the morphology of the final products. When using thiourea only or in combination with ethylenediamine, nanorods and nanoparticles of various morphologies were formed. Conversely, when exclusively using ethylenediamine, in addition to the nanorods, fine needles with a significantly smaller diameter were discernible. With all combinations, structurally uniform α-FeOOH nanorods were formed. This improved nanorod formation in the presence of both ligands might be attributed to a more ordered alignment and regular conformation of ethylenediamine molecules in the presence of thiourea and thus less susceptibility to thermal perturbations. Finally, higher concentrations of ligand influence the final product and increases particle aggregation.

Hybrid Nanocomposites with Tunable Alignment of the Magnetic Nanorod Filler

For many important applications, the performance of polymer–anisotropic particle nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite (α-FeOOH) nanorods, we produced goethite–poly(hydroxyethyl methacrylate) nanocomposites in which the alignment direction and the level of orientation of the nanorods could easily be tuned by simply adjusting the intensity of a magnetic field applied during polymerization. Because the particle volume fraction was kept low (1–5.5 vol %), we used the orientational order induced by the field in the isotropic phase rather than the spontaneous orientational order of the nematic phase. At the strongest field values (up to 1.5 T), the particles exhibit almost perfect antinematic alignment, as measured by optical birefringence and small-angle X-ray scattering. The results of these two techniques are in remarkably good agreement, validating the use of birefringence measurements for quantifying the degree of orientational order. We also demonstrate that the ordering induced by the field in the isotropic suspension is preserved in the final material after field removal. This work illustrates the interest, for such problems, of considering the field-induced alignment of anisotropic nanoparticles in the isotropic phase, an approach that is effective at low filler content, that avoids the need of controlling the nematic texture, and that allows tuning of the orientation level of the particles at will simply by adjusting the field intensity.

Surfactant-assisted nanorod synthesis of α-FeOOH and its adsorption characteristics for methylene blue

Abstract

Facile fabrication of α-FeOOH nanorod/RGO composite: a robust photocatalyst for reduction of Cr(vi) under visible light irradiation

In situ fabrication and deposition of α-FeOOH nanorods over RGO sheets for the photoreduction of Cr(vi) under visible light irradiation.

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.

Low temperature preparation of α-FeOOH/reduced graphene oxide and its catalytic activity for the photodegradation of an organic dye

A new approach to prepare α-FeOOH/reduced graphene oxide (RGO) at room temperature has been developed. Instead of reducing graphene oxide (GO) with the most commonly used reagents, which are highly toxic or explosive, Fe2+ was used as the reducing reagent. Fe2+ efficiently reduced GO under mild conditions to form α-FeOOH/RGO via spontaneous in situ deposition of α-FeOOH nanorods onto the RGO surfaces. The resulting α-FeOOH/RGO was characterized by transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, x-ray photoelectron spectroscopy, x-ray diffraction analysis and infrared spectroscopy. The α-FeOOH/RGO was then applied as a photocatalyst for the degradation of the azo dye, methyl orange.

Synthesis of monodispersed α-FeOOH nanorods with a high content of surface hydroxyl groups and enhanced ion-exchange properties towards As(v)

Monodispersed α-FeOOH nanorods, with a high content of surface hydroxyl groups, were synthesized using a simple solution method at room temperature. The obtained α-FeOOH nanorods were characterized by field emission scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, nitrogen adsorption–desorption isotherms and X-ray diffraction. The presence of cetyltrimethylammonium bromide (CTAB) successfully avoids the congregation of the α-FeOOH nanorods, which resulted in the formation of the monodispersed α-FeOOH nanorods and the increase of the surface hydroxyl groups. The adsorption properties of the nanorods towards toxic As(V) ions were investigated. The results suggest that the adsorption properties of the monodispersed α-FeOOH nanorods were also improved compared with the congregated ones synthesized without CTAB or surfactant instead of pure water. The enhanced adsorption properties were attributed to the high content of the surface hydroxyl groups, which were revealed by X-ray photoelectron spectrometer and Fourier transform infrared absorption spectroscopy.

Synthesis of a multifunctional graphene–carbon nanotube aerogel and its strong adsorption of lead from aqueous solution

Mechanically enhanced aerogels of graphene sheets and carbon nanotubes (CNTs) were prepared via hydrothermal reduction of graphene oxide and CNTs in the presence of ferrous ions (FeSO4 solution). The resultant graphene–CNT aerogels possess a 3-D network of carbon structures containing micro-sized pores and α-FeOOH nanorods within the matrix. The CNTs may act as a scaffold in the aerogels to resist compressive stress and prevent them from collapse. The aerogels have very low density (0.011–0.087 g cm−3), depending on the amount of ferrous ions used in the synthesis. In addition, the aerogels also have excellent mechanical properties with elastic modulus between 0.011 and 0.29 MPa. Because of their porous structures, the graphene–CNTs aerogels showed excellent removal ability to aqueous lead with rates between 230 and 451 mg g−1 and thus could be potentially used as a promising adsorbent for many environmental applications.

Controlled synthesis of α-FeOOH nanorods and their transformation to mesoporous α-Fe2O3, Fe3O4@C nanorods as anodes for lithium ion batteries

α-FeOOH nanorods with varying lengths of 200–500 nm and axis ratios of 2–8 have been successfully synthesized by a simple hydrothermal method with different amounts of hydrazine. Hierarchical nanostructured mesoporous α-Fe2O3 and Fe3O4@C, which combined both mesoporosity and carbon coating, were fabricated by transformation of these α-FeOOH nanorods. The mechanism of formation has been described in detail. The α-FeOOH, mesoporous α-Fe2O3 and Fe3O4@C samples with the longest nanorods exhibited excellent cycle and rate performance, as the long nanorods could ensure many fast and convenient electron transport pathways, thus enhancing the electronic conductivity. The as-synthesized mesoporous α-Fe2O3 and Fe3O4@C nanorods showed large specific surface area and porosity due to the inner mesoporous structure, effectively increasing the contact area between the electrode materials and electrolyte, shortening the diffusion length of Li+ and alleviating the stress from volume changes during the charge–discharge process. Mesoporous Fe3O4@C nanorods exhibit high reversible capacities of 1072 mAh g−1 after 50 cycles, demonstrating the superior electron transport and fast Li+ diffusion ability combination of outer carbon layer and mesoporous microstructure.

Preparation of Composite Iron Oxides via Hydrothermal Process

Composite iron oxides are very important advanced materials. In this paper different types of iron oxides α-FeOOH, α-Fe2O3 and composite oxide NiFe2O4 were synthesized via a simple hydrothermal method at 180°C for 10 h. The phases and morphologies of the products were characterized by X-ray diffractometer and high-resolution transmission electron microscopy. The results indicated that α-FeOOH nanorods were prepared when mole concentration of NaOH solution was 3M. By increasing the concentration of NaOH to 5M and 8M, we obtained qusi-fusiform α-Fe2O3 single-crystallines and composite oxide NiFe2O4 nanocrystals, respectively. Our experiments showed that both the concentration of NaOH solution and existence of sulphate ions affect the formation of varying morphologies of the products.

Core–shell Fe@Fe3C/C nanocomposites as anode materials for Li ion batteries

Core–shell Fe@Fe3C/C nanocomposites were prepared by adopting α-FeOOH nanorods as the Fe precursor though a simple and green route. The obtained core–shell nanospheres consisted of single crystalline Fe cores (20–50nm) coated with well-proportioned Fe3C shell (∼8nm) in amorphous carbon. The composites delivered a reversible capacity of ∼500mAh g−1 after 30 cycles. However, no obvious changes were observed in the XRD patterns of Fe@Fe3C/C electrodes before and after the discharge process, indicating that Fe and Fe3C are inactive for lithium storage. Many characterizations were performed to propose a reasonable explanation about the Li storage capacity.

Effect of Ionic Strength on the Kinetics of Crystal Growth by Oriented Aggregation

Oriented aggregation is an important, nonclassical crystal growth mechanism that occurs in a wide array of materials, often producing nanoparticles with unique, anisotropic, and symmetry-defying morphologies. The growth of acicular goethite (α-FeOOH) nanorods from ellipsoidal ferrihydrite (Fe5HO8·4H2O) nanoparticles was used as a model system to study the effects of sodium nitrate concentration on product crystal morphology and the kinetics of growth by oriented aggregation. Time-resolved sampling and transmission electron microscopy were employed with semi-automated image analysis to quantify the growth rate constant of oriented aggregation. Results are discussed in the context of Derjaguin and Landau, Verwey and Overbeek (DLVO) theory through the use of quantitative statistical comparisons and modeling of rate constants. Increasing the concentration of sodium nitrate results in an increasing second-order growth rate constant. The magnitude of increase depends on the primary particle size; however, the magnitude and trend in size dependence did not follow predictions based on DLVO theory.

Proton-promoted dissolution of α-FeOOH nanorods and microrods: Size dependence, anion effects (carbonate and phosphate), aggregation and surface adsorption

Iron-containing oxide nanoparticles are of great interest from a number of technological perspectives and they are also present in the natural environment. Although recent evidence suggests that particle size plays an important role in the dissolution of metal oxides, a detailed fundamental understanding of the influence of particle size is just beginning to emerge. In the current study, we investigate whether nanoscale size-effects are observed for the dissolution of iron oxyhydroxide under different conditions. The dissolution of two particle sizes of goethite, α-FeOOH in the nanoscale and microscale size regimes (herein referred to as nanorods and microrods), in aqueous suspensions at pH 2 is investigated. It is shown here that in the presence of nitrate, nanorods shows greater dissolution on both a per mass and per surface area basis relative to microrods, in agreement with earlier studies. In the presence of carbonate and phosphate, however, dissolution of α-FeOOH nanorods at pH 2 is significantly inhibited, despite the fact that these anions result in a three- to fivefold enhancement of the dissolution of microrods relative to the nitrate anion. Light scattering techniques and electron microscopy show that nanorod suspensions are less stable compared to microrod suspensions resulting in nanorod aggregation under conditions where microrods stay more dispersed. Furthermore, spectroscopic studies using ATR–FTIR spectroscopy show distinct differences in phosphate and carbonate adsorption on nanorods compared to microrods. These results demonstrate that aggregation and the details of surface adsorption are important in the dissolution behavior of nanoscale materials.

Surface Chemistry of α-FeOOH Nanorods and Microrods with Gas-Phase Nitric Acid and Water Vapor: Insights into the Role of Particle Size, Surface Structure, and Surface Hydroxyl Groups in the Adsorption and Reactivity of α-FeOOH with Atmospheric Gases

In this study, heterogeneous interactions of H2O and HNO3 on goethite, α-FeOOH, a component of mineral dust aerosol, are investigated with simultaneous QCM measurements and ATR-FTIR spectroscopy. Laboratory synthesized α-FeOOH of varying sizes (microrods and nanorods) when exposed to gas phase H2O and HNO3 results in the uptake of these gases. This combined approach of QCM measurements and ATR-FTIR spectroscopy allows for both quantification of the amount of uptake and spectroscopic data that provides information on speciation of adsorbed products. The results show that, in the case of H2O, both microrods and nanorods take up water and that the total amounts of water, when normalized to surface area, are similar. However, for HNO3 uptake, the saturation coverage of total and irreversibly bound HNO3 on microrods was observed to be higher than that on nanorods, a size effect which is attributed to surface structural changes that occur as a function of particle size. Furthermore, an investigation of the beha...

Size-controlled synthesis of Rod-like α-FeOOH nanostructure

One-dimensional goethite (α-FeOOH) nanorods were successfully fabricated by a hydrothermal route without any template. Experimental results reveal that concentrations of Fe3+ and ethylenediaminetetraacetic disodium salt (Na2EDTA) affect the phase composition and size of the as-synthesized products. The size of the rod-like α-FeOOH increased when the concentration of Na2EDTA was increased, where Na2EDTA acts as a nucleation inhibitor. α-Fe2O3 nanoparticles were produced when the concentration of Fe3+ was increased from 0.02 to 0.08 and 0.40M. A possible formation mechanism was proposed based on the results of the time dependent experiments. Different electrolytes and surfactants can affect the size and the aspect ratio of the as-prepared nanorod-like α-FeOOH. Na2SO4 induced the decreasing of the size of the as-prepared sample. KCl and PVP affected the aspect ratio of the nanorods.

Macroscopic Multifunctional Graphene-Based Hydrogels and Aerogels by a Metal Ion Induced Self-Assembly Process

We report a one-step fabrication of macroscopic multifunctional graphene-based hydrogels with robust interconnected networks under the synergistic effects of the reduction of graphene oxide sheets by ferrous ions and in situ simultaneous deposition of nanoparticles on graphene sheets. The functional components, such as α-FeOOH nanorods and magnetic Fe(3)O(4) nanoparticles, can be easily incorporated with graphene sheets to assemble macroscopic graphene monoliths just by control of pH value under mild conditions. Such functional graphene-based hydrogels exhibit excellent capability for removal of pollutants and, thus, could be used as promising adsorbents for water purification. The method presented here is proved to be versatile to induce macroscopic assembly of reduced graphene sheets with other functional metal oxides and thus to access a variety of graphene-based multifunctional nanocomposites in the form of macroscopic hydrogels or aerogels.

Facile synthesis of single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods as anode materials for lithium-ion batteries

In this work, single-crystalline α-FeOOH nanorods with a length of 400–700 nm and a diameter of 20–80 nm were successfully synthesized via a facile template-free hydrothermal method. Single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods could be obtained from these α-FeOOH precursors after calcining at 350 °C in air and 500 °C in nitrogen, respectively. The as-prepared single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods exhibited a large specific surface area and porosity, effectively enhancing the electrochemical reaction area and accommodate the strain during the charge–discharge cycling process.

Synthesis and characterization of a nanocomposite of goethite nanorods and reduced graphene oxide for electrochemical capacitors

We report a one-step synthesis of a nanocomposite of goethite (α-FeOOH) nanorods and reduced graphene oxide (RGO) using a solution method in which ferrous cations serve as a reducing agent of graphite oxide (GO) to graphene and a precursor to grow goethite nanorods. As-prepared goethite nanorods have an average length of 200nm and a diameter of 30nm and are densely attached on both sides of the RGO sheets. The electrochemical properties of the nanocomposite were characterized by cyclic voltammetry (CV) and chronopotentiometry (CP) charge–discharge tests. The results showed that goethite/RGO composites have a high electrochemical capacitance of 165.5Fg−1 with an excellent recycling capability making the material promising for electrochemical capacitors.

Single-Crystalline Porous Hematite Nanorods: Photocatalytic and Magnetic Properties

Single-crystalline hematite nanorods with void pores were synthesized by a facile hydrothermal process and subsequent heat treatment in air. The pores were formed by removal of released H2O in α-FeOOH nanorods and ionic liquids. The ionic liquids were adsorbed on the surface of O-terminated α-FeOOH nanorods by electrostatic force, and hydrogen bonds formed between the hydrogen atom at the C2 position of the imidazole ring and the oxygen atom of O–Fe. The proposed formation mechanism has been investigated on the basis of the TEM image and SAED pattern. Hematite with a different porosity and degree of crystallinity has a different photocatalytic property for the photodegradation of methyl orange. The temperature-dependent magnetization and magnetic hysteresis of samples indicate the interesting magnetic property evolution, which is attributed to the finite size and surface effect of the pore–solid architecture created by void pores in the rods.