Akaganeite Nanorods Research Articles

Understanding the mechanisms of anisotropic dissolution in metal oxides by applying radiolysis simulations to liquid-phase TEM

Iron-based redox-active minerals are ubiquitous in soils, sediments, and aquatic systems. Their dissolution is of great importance for microbial impacts on carbon cycling and the biogeochemistry of the lithosphere and hydrosphere. Despite its widespread significance and extensive prior study, the atomic-to-nanoscale mechanisms of dissolution remain poorly understood, particularly the interplay between acidic and reductive processes. Here, we use insitu liquid-phase-transmission electron microscopy (LP-TEM) and simulations of radiolysis to probe and control acidic versus reductive dissolution of akaganeite (β-FeOOH) nanorods. Informed by crystal structure and surface chemistry, the balance between acidic dissolution at rod tips and reductive dissolution at rod sides was systematically varied using pH buffers, background chloride anions, and electron beam dose. We find that buffers, such as bis-tris, effectively inhibited dissolution by consuming radiolytic acidic and reducing species such as superoxides and aqueous electrons. In contrast, chloride anions simultaneously suppressed dissolution at rod tips by stabilizing structural elements while promoting dissolution at rod sides through surface complexation. Dissolution behaviors were systematically varied by shifting the balance between acidic and reductive attacks. The findings show LP-TEM combined with simulations of radiolysis effects can provide a unique and versatile platform for quantitatively investigating dissolution mechanisms, with implications for understanding metal cycling in natural environments and the development of tailored nanomaterials.

Effect of small amounts of akaganeite (β-FeOOH) nanorods on the gelation, phase behaviour and injectability of thermoresponsive Pluronic F127.

Pluronic F127 (PF127) is a copolymer with an amphiphilic nature and can self-assemble to form micelles and, beyond 20% (w/v), form a thermoresponsive physical gel state. However, they are mechanically weak and easily dissolve in physiological environments, which limits their use in load-bearing in specific biomedical applications. Therefore, we propose a pluronic-based hydrogel with enhanced stability by incorporating small amounts of paramagnetic nanorods, akaganeite (β-FeOOH) nanorods (NRs) of aspect ratio ∼7, with PF127. Due to their weak magnetic properties, β-FeOOH NRs have been used as a precursor for preparing stable iron-oxide states (e.g., hematite and magnetite), and the studies on β-FeOOH NRs to be used as a primary component in hydrogels are at the nascent stage. Here we report a method to synthesize β-FeOOH NRs on a gram scale using a simple sol-gel process and characterize the NRs with various techniques. A phase diagram and thermoresponsive behaviour based on rheological experiments and visual observations are proposed for 20% (w/v) PF127 with low concentrations (0.1-1.0% (w/v)) of β-FeOOH NRs. We observe a unique non-monotonous behaviour in the gel network represented by various rheological parameters like storage modulus, yield stress, fragility, high-frequency modulus plateau, and characteristic relaxation time as a function of nanorod concentration. A plausible physical mechanism is proposed to fundamentally understand the observed phase behaviour in the composite gels. These gels show thermoresponsiveness and enhanced injectability, and could find applications in tissue engineering and drug delivery.

Magnetic properties, phase evolution, hollow structure and biomedical application of hematite (α-Fe2O3) and QUAIPH

We investigate synthesis, phase evolution, hollow and porous structure and magnetic properties of quasi-amorphous intermediate phase (QUAIPH) and hematite (α-Fe2O3) nanostructure synthesized by annealing of akaganeite (β-FeOOH) nanorods. It is found that the annealing temperature determines the phase composition of the products, the crystal structure/size dictates the magnetic properties whereas the final nanorod morphology is determined by the starting material. Annealing of β-FeOOH at ∼300 °C resulted in the formation of hollow QUAIPH nanorods. The synthesized material shows low-cytotoxicity, superparamagnetism and good transverse relaxivity, which is rarely reported for QUAIPH. The QUAIPH nanorods started to transform to porous hematite nanostructures at ∼350 °C and phase transformation was completed at 600 °C. During the annealing, the crystal structure changed from monoclinic (akaganeite) to quasi-amorphous and rhombohedral (hematite). Unusually, the crystallite size first decreased (akaganeite → QUAIPH) and then increased (QUAIPH → hematite) during annealing whereas the nanorods retained particle shape. The magnetic properties of the samples changed from antiferromagnetic (akaganeite) to superparamagnetic with blocking temperature TB = 84 K (QUAIPH) and finally to weak-ferromagnetic with the Morin transition at TM = 244 K and high coercivity HC = 1652 Oe (hematite). The low-cytotoxicity and MRI relaxivity (r2 = 5.80 mM−1 s−1 (akaganeite), r2 = 4.31 mM−1 s−1 (QUAIPH) and r2 = 5.17 mM−1 s−1 (hematite)) reveal potential for biomedical applications.

In-situ formation of durable akaganeite (β-FeOOH) nanorods on sulfonate-modified poly(ethylene terephthalate) fabric for dual-functional wastewater treatment

Industrial oily wastewater with dye-pollution is a critical environmental issue for water purification. However, the fabrication of effective and stable materials for oil-water separation and simultaneous degradation of organic contaminants remains a critical challenge. Herein, we report a new process for in-situ formation of akaganeite (β-FeOOH) nanorods layer on the surface of poly(ethylene terephthalate) (PET) fabric via radiation-induced graft polymerization of glycidyl methacrylate, which is then sulfonated and mineralized. The resultant product is labeled as β-FeOOH@PET, which exhibits dual purification by demonstrating an effective oil-water separation and organic dyes photodegradation under the illumination of visible light. It provides stable performance even after 1000 wash cycles. The sulfonated layer acts as not only an electronic transport layer to prevent electron-hole recombination, but also as an anchored interface for immobilizing β-FeOOH nanorods on the sulfonated layer via strong covalent bonds. Overall, the superhydrophilicity and underwater superoleophobicity of β-FeOOH@PET fabric, along with its robustness with a flexible organic substrate and its dual purification function, provide a new insight toward oily wastewater remediation and water purification in large-scale applications.

Three-Dimensional Macroporous Alginate Scaffolds Embedded with Akaganeite Nanorods for the Filter-Based High-Speed Preparation of Arsenic-Free Drinking Water

Separation of arsenic from water is an urgent worldwide issue because of its serious toxic effect on human health and aquatic life. In this study, a filter device composed of three-dimensional (3D) macroporous alginate/akaganeite composite (MAAC) scaffolds is proposed for the convenient separation of arsenic from contaminated water. Akaganeite nanorods with superior arsenic adsorption capability are incorporated and distributed within the macroporous alginate scaffold, without significant aggregation. The micron-sized pores and oxygen functional groups in the MAAC scaffold offer enhanced mass transport of the contaminated water throughout the scaffold without the need for input of any force and allow easy contact of arsenic with the active adsorption sites of the scaffold. The high mechanical strength of the MAAC facilitates structural stability of the materials in aqueous solutions. Moreover, the scaffold is capable of excellent arsenic adsorption and can reduce the concentration of arsenic in contaminat...

Green Synthesis of Single-Crystalline Akaganeite Nanorods for Peroxidase Mimic Colorimetric Sensing of Ultralow-Level Vitamin B1 and Sulfide Ions

Development of low-cost nanomaterials for ultralow-level molecular sensing applications is drawing significant attention. In this report, single-crystalline akaganeite (β-FeOOH) nanorods were synthesized at room temperature in aqueous medium by green protocol using tea extract for sensing applications. Microscopic investigation revealed the dimensions of nanorods are 150 ± 20 nm in length and 35 ± 10 nm in diameter. The concentration of tea extract plays a crucial role on the final shape of the nanostructure. As-synthesized β-FeOOH nanorods exhibit good peroxidase-like activity in the presence of H2O2. The synthesized β-FeOOH nanorods were tested for a rapid colorimetric detection of thiamine (vitamin B1), H2O2, and S2– ions in the aqueous solutions. The sensitivity of this colorimetric probe to thiamine and S2– ions was excellent with a limit of detection as low as 44 nM and 2.19 μM, respectively. This work provides an efficient, green, reproducible, and economical approach to synthesize rodlike β-FeOOH ...

Preparation of molybdenum-doped akaganeite nano-rods and their catalytic effect on the viscosity reduction of extra heavy crude oil

Abstract Molybdenum-doped akaganeite nano-rods were prepared by one step facile synthesis. The formation of akaganeite depends on the molar ratio of hexaammonium molybdate to ferric chloride hexahydrate. The nano-rods have an average particle size of ca. 30 nm and disperse uniformly. As a catalyst, the nano-rods can effectively increase the viscosity reduction rate of Shengli Oilfield extra heavy crude oil (175000 mPa s at 50 °C), especially combined with tetralin (a hydrogen donor). The results of SARA analysis, elemental analysis, and 1H NMR spectra indicate that the increase of light component caused by the denitrification and desulfuration of the catalyst plus tetralin as well as the loosening of heavy component molecules can be responsible for the viscosity reduction of the heavy oil.

Akaganeite nanorods decorated graphene oxide sheets for removal and recovery of aqueous phosphate

The increased amount of phosphate in water results in the depletion of dissolved oxygen levels and becomes detrimental to aquatic organism. The waste generated from industries contains large quantity of phosphates and needed effective treatment before reaching to the fresh water. In this study we report synthesis of a nanocomposite containing akaganeite nanorods (β-FeOOH) and graphene oxide sheets (GO) via chemical route and used as a low-cost potential adsorbent for removal of phosphate dissolved in the water. In the presence of graphene oxide β-FeOOH nanorods showed enhanced aspect ratio of rods from 5 to 7. The influence of adsorbent dose, adsorption time, solution pH, and initial phosphate concentration on the phosphate removal capacity were studied. The second order kinetics model fitted better compare to the first and solid diffusion model. The adsorption isotherm was best fitted with Langmuir model compare to Freundlich isotherm indicates formation of monolayer of phosphate on the surface of adsorbent. The β-FeOOH nanorods/GO nanocomposite showed maximum phosphate adsorption capacity 45.2mg/g at pH 7 and room temperature 30°C.

Photocatalytic degradation of phenanthrene in the presence of akaganeite nano-rods and the identification of degradation products

The spiked samples of phenanthrene on the soil surfaces were irradiated in presence of akaganeite nano-rods.

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., ...

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.

Hydrothermal Synthesis of Akaganeite Nanorods and Their Supercapacitance Property

In this study, rod-shaped akaganeite nanostructures were successfully synthesized via a facile hydrothermal process using polyvinylpyrrolidone as the soft template and NaAc as the precipitation agent. The electrochemical properties of the as-prepared akaganeite nanorods were investigated by cyclic voltammetry, galvanostatic charge–discharge, and constant current discharge. The results reveal that the as-prepared akaganeite nanorods exhibit high specific supercapacitance of 1,140 F g−1. Rod-shaped akaganeite (FeOOH) nanostructures, synthesized via a facile hydrothermal process, show very high supercapacitance.

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[...

Size-controlled synthesis of uniform akaganeite nanorods and their encapsulation in alginate microbeads for arsenic removal

Alginate microbeads encapsulating the uniform akaganeite nanorods were used for quick, easy arsenic removal from highly contaminated water.

Growth kinetics evaluation of hydrothermally synthesized β-FeOOH nanorods

Based on the proposition that a quantitative and qualitative relationship between alcohol surface tension and particle growth exists, the effect of four different organic solvents on the growth kinetics of β-FeOOH (akaganeite) nanorods have been evaluated in this study. Two-stage growth of akaganeite nanorods have been observed in the presence of butanol and propanol as solvents. The first growth stage follows a typical power law representing Ostwald Ripening (OR) kinetic. The second stage of growth was found to be asymptotic and was fitted by the Oriented Attachment (OA) kinetics. HRTEM images of the synthesized nanoparticles also showed crystallographically specific oriented attachment based growth of the nanocrystals. Signs of OA mechanism was not observed from the TEM images of the particles synthesized using ethanol and methanol as solvents. The rate constants for each kinetic was evaluated and the rate constant for OR kinetics, kOR, was found to be significantly higher than the rate constant for OA kinetics, kOA, under the reported conditions for the four different solvents used. The rate constants were related to the surface tension of alcohol. A factorial trial was used to evaluate the significance of interaction effects of process parameters. By correlating the surface tension of solvents with different process parameters a generalized correlation has been developed to predict β-FeOOH aspect ratios for the first time. This correlation was validated by an independent study. This correlation takes three different process parameters into consideration in conjunction with the solvent surface tension to predict particle aspect ratios with acceptable confidence.

Methanogenesis Facilitated by Geobiochemical Iron Cycle in a Novel Syntrophic Methanogenic Microbial Community

Production and emission of methane have been increasing concerns due to its significant effect on global climate change and the carbon cycle. Here we report facilitated methane production from acetate by a novel community of methanogens and acetate oxidizing bacteria in the presence of poorly crystalline akaganeite slurry. Comparative analyses showed that methanogenesis was significantly enhanced by added akaganeite and acetate was mostly stoichiometrically converted to methane. Electrons produced from anaerobic acetate oxidation are transferred to akaganeite nanorods that likely prompt the transformation into goethite nanofibers through a series of biogeochemical processes of soluble Fe(II) readsorption and Fe(III) reprecipitation. The methanogenic archaea likely harness the biotransformation of akaganeite to goethite by the Fe(III)-Fe(II) cycle to facilitate production of methane. These results provide new insights into biogeochemistry of iron minerals and methanogenesis in the environment, as well as the development of sustainable methods for microbial methane production.

Experimental and theoretical study on the β-FeOOH nanorods: growth and conversion

This study presents an experimental and theoretical study on the growth of monodispersed akaganeite (β-FeOOH) nanorods with tunable aspect ratios (longitudinal to transversal) under mild conditions (80 °C, aqueous solution). The synthesis of β-FeOOH nanorods is highly influenced by the presence of salt ions, and thus, the effect of various anions (e.g., NO3 −, SO4 2−, F−, Cl−, and Br−) were investigated on the microstructure, morphology, and size of the nanoparticles. It was found that these anions could interact strongly or weakly with the FeO6 octahedral unit in the ferric oxyhydroxides, hence greatly affect the morphology, crystallization, and structure of the iron oxide/oxyhydroxide nanoparticles under the reported conditions. Moreover, these nanorods could be converted into magnetite (Fe3O4) through the reduction of hydrazine, which provides a new template approach to prepare magnetite nanorods with shape and size control at ambient conditions. The microstructure, composition, and structural transformation of the as-synthesized nanoparticles were characterized by various techniques, such as transmission electron microscopy (TEM and HRTEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The possible formation and growth mechanism of akaganeite nanorods were discussed. Finally, the influence of anions on the β-FeOOH(100), (110), and (001) surfaces was further understood by theoretical simulations (e.g., molecular dynamics method).

Controlled synthesis, magnetic and sensing properties of hematite nanorods and microcapsules

Hematite microcapsules with and without etching are fabricated controllably through adjusting the synthesis temperature via a 3,3-thiodipropionic acid (TPA)-assisted hydrothermal synthesis method. Hematite nanorods can be obtained after the calcination of akaganeite nanorods which were prepared at a low synthesis temperature. Based on the experimental results, it is suggested that at the early stage the synthesis of akaganeite and hematite samples involves the hydrolysis of ferric chloride to promote nucleation in the presence of TPA and subsequently experiences the coordination-assisted growth guided by the ligand of TPA. Magnetic hysteresis measurements show that the size and shape of the hematite micro-/nanostructures have important effects on their magnetic properties. Furthermore, hematite nanorods display the best electrochemical sensing behavior toward the reduction of H 2O 2 among these hematite samples.

Design of magnetic akaganeite-cyanobacteria hybrid biofilms

Common Anabaena cyanobacteria are shown to form intra-cellularly akaganeite β-FeOOH nanorods of well-controlled size and unusual morphology at room temperature. High-resolution transmission electron microscopy showed that these nanorods present a complex arrangement of pores forming a spongelike structure. These hybrid akaganeite-cyanobacteria were used to form “one-pot” hybrid biofilms. The hybrid biofilm presents higher coercivity ( H c = 44.6 kA m − 1 (560 Oe)) when compared to lyophilized akaganeite-cyanobacteria powder ( H c = 0.8 kA m − 1 (10 Oe)) due to the quasi-assembly of the cells on the glass substrate compared to the lyophilized randomly akaganeite-cyanobacteria powder.

Photosynthetic Microorganism-Mediated Synthesis of Akaganeite (β-FeOOH) Nanorods

Common Anabaena and Calothrix cyanobacteria and Klebsormidium green algae are shown to form intracellularly akaganeite beta-FeOOH nanorods of well-controlled size and unusual morphology at room temperature. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy X-ray energy dispersive spectrometry (SEM-EDS) analyses are used to investigate particle structure, size, and morphology. A mechanism involving iron-siderophore complex formation is proposed and compared with iron biomineralization in magnetotactic bacteria.