Iron Oxide Shell Research Articles

Graphene oxide-induced formation of a boron-doped iron oxide shell on the surface of NZVI for enhancing nitrate removal

The surface products have a significant influence on the reactivity of zero-valent iron-based materials. Although the enhancing effect of graphene on the reactivity of nanoscale zero-valent iron (NZVI)/graphene composites have been confirmed, the effect of graphene on the formation of surface products of NZVI is not well understood. In order to assess the effect of graphene on the structural of the outer iron oxide layers of NZVI, the NZVI was pre-oxidized by graphene oxide (ONZVI-GO). Compared with the NZVI oxidized by O2 (ONZVI-O2), ONZVI-GO was shown to be effective at NO3− removal with a high efficiency over a wide range of initial pH values. The results from characterization showed that GO could induce the formation of a tight iron oxide shell with dense spinel structures. The boron introduced during the preparation of NZVI was doped into iron oxides on the surface of ONZVI-GO. The B–O in adsorbed borate was transformed to B–B/B–Fe in the lattice structure of iron oxides, causing the formation of highly electron-deficient Lewis acid sites on the surface of ONZVI-GO, which could effectively gather NO3− and OH−, leading to the higher efficiency removal of NO3− than ONZVI-O2 over a wide range of initial pH values. This study provides new insight into the interaction between graphene and the surface species of NZVI.

Magnetic core\u2013shell nanowires as MRI contrast agents for cell tracking

BackgroundIdentifying the precise location of cells and their migration dynamics is of utmost importance for achieving the therapeutic potential of cells after implantation into a host. Magnetic resonance imaging is a suitable, non-invasive technique for cell monitoring when used in combination with contrast agents.ResultsThis work shows that nanowires with an iron core and an iron oxide shell are excellent materials for this application, due to their customizable magnetic properties and biocompatibility. The longitudinal and transverse magnetic relaxivities of the core–shell nanowires were evaluated at 1.5 T, revealing a high performance as T2 contrast agents. Different levels of oxidation and various surface coatings were tested at 7 T. Their effects on the T2 contrast were reflected in the tailored transverse relaxivities. Finally, the detection of nanowire-labeled breast cancer cells was demonstrated in T2-weighted images of cells implanted in both, in vitro in tissue-mimicking phantoms and in vivo in mouse brain. Labeling the cells with a nanowire concentration of 0.8 μg of Fe/mL allowed the detection of 25 cells/µL in vitro, diminishing the possibility of side effects. This performance enabled an efficient labelling for high-resolution cell detection after in vivo implantation (~ 10 nanowire-labeled cells) over a minimum of 40 days.ConclusionsIron-iron oxide core–shell nanowires enabled the efficient and longitudinal cellular detection through magnetic resonance imaging acting as T2 contrast agents. Combined with the possibility of magnetic guidance as well as triggering of cellular responses, for instance by the recently discovered strong photothermal response, opens the door to new horizons in cell therapy and make iron-iron oxide core–shell nanowires a promising theranostic platform.

Relative contribution of ferryl ion species (Fe(IV)) and sulfate radical formed in nanoscale zero valent iron activated peroxydisulfate and peroxymonosulfate processes

Activation of persulfates (i.e., peroxydisulfate (PDS) and peroxymonosulfate (PMS)) by nanoscale zero-valent iron (nZVI) is reported to be effective in oxidative treatment of environmental contaminants. It has been widely accepted in numerous literature that sulfate radical (SO4•-) formed from the decomposition of persulfates activated by aqueous Fe(II) released from nZVI corrosion is responsible for the oxidative performance in nZVI/persulfates systems. In this work, by employing methyl phenyl sulfoxide (PMSO) as a probe, we demonstrated that the activation of persulfates by nZVI through electron transfer led to SO4•- formation, while the homogeneous activation of persulfate by the released Fe(II) resulted in ferryl ion species (Fe(IV)) generation in nZVI/persulfates systems. Similarly, nanoscale zero-valent aluminum (nZVAl) and zinc (nZVZn) were also demonstrated to be able to donate electron to persulfates leading to SO4•- formation. However, the insulative aluminum oxide shell hindered the electron transfer leading to the poor persulfates decomposition, while the conductive iron and zinc oxide shell enabled the electron transfer process resulting in a continuous generation of SO4•-. Further, it was obtained that the relative contribution of SO4•- and Fe(IV) in nZVI/persulfates systems was independent of the initial concentration of nZVI and PDS, but was positively correlated with PMS concentration. In addition, the increase of pH from 3 to 7 led to the decrease of the relative contribution of Fe(IV), which was rationalized by the decrease of availability of aqueous Fe(II) at higher pH. Our findings not only shed lights on the nature of the reactive intermediate formed in the nZVI/persulfates systems, but also unprecedentedly distinguished the surface activation of persulfates from the homogeneous catalysis process.

Zero valent iron core-iron oxide shell nanoparticles as small magnetic particle imaging tracers.

Nanoparticle tracers with small sizes and large magnetization are critical for biomedical imaging and especially for magnetic particle imaging (MPI). Small size is important for accessing future intracellular and neurological in vivo applications Here, we show <15 nm nanoparticles made of zero valent iron cores, iron oxide shells and coated with a strongly binding brush co-polymer are effective MPI tracers. The small nanoparticle cores create a hydrodynamic diameter that is half of the state-of-the-art iron oxide tracers while the strongly magnetic zero valent iron maintains similar MPI signal magnitude and resolution.

Engineering of Ruthenium-Iron Oxide Colloidal Heterostructures: Improved Yields in CO2 Hydrogenation to Hydrocarbons.

Catalytic CO2 reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. One approach utilizes the reverse water-gas shift reaction, followed by Fischer-Tropsch synthesis, and iron is a well-known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium-iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium-iron core-shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO2 conversion processes.

Engineering of Ruthenium–Iron Oxide Colloidal Heterostructures: Improved Yields in CO2 Hydrogenation to Hydrocarbons

AbstractCatalytic CO2 reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. One approach utilizes the reverse water‐gas shift reaction, followed by Fischer–Tropsch synthesis, and iron is a well‐known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium–iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium–iron core–shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO2 conversion processes.

Regeneration of zero-valent iron powder by the cocatalytic effect of WS2 in the environmental applications

One of the biggest problems of microsized iron powder (mZVI) is that with the occurrence of redox reactions, a compact iron oxide shell can be formed on the surface of mZVI, which eventually leads to the catalyst poisoning and inactivation. Here, commercial WS2 is employed for accelerating Fe3+/Fe2+ cycle and foreclosing passivation of mZVI to achieve the regeneration of mZVI for the first time. After 10 cycles oxidation, WS2 cocatalytic effect can make the mZVI/H2O2 maintain the degradation rate of 99% for the remediation of organic pollutants. Moreover, it is found that WS2 can realize the regeneration of mZVI after the reduction of heavy metal ions (Cr6+, Cu2+ and Ni2+), especially, the removal rate of Ni2+ can be recovered from 9.2% back to 30.8%. The enhanced activity and stability can be ascribed to the double active sites on WS2 and mZVI surfaces. The exposed active W4+ sites on WS2 surface can accelerate the Fe3+/Fe2+ cycling reaction, and the active Fe0 active sites can increase the circulation of iron and tungsten ions simultaneously. This research provides a new approach for the regeneration of mZVI during the redox reaction in environmental application, which makes it possible to use mZVI to treat sewage on a large scale.

Trapping and electrical characterization of single core/shell iron-based nanoparticles in self-aligned nanogaps

We report on the fabrication and measurements of platinum-self-aligned nanogap devices containing cubed iron (core)/iron oxide (shell) nanoparticles (NPs) with two average different sizes (13 and 17 nm). The nanoparticles are deposited by means of a cluster gun technique. Their trapping across the nanogap is demonstrated by comparing the current vs voltage characteristics (I-Vs) before and after the deposition. At low temperature, the I-Vs can be well fitted to the Korotkov and Nazarov Coulomb blockade model, which captures the coexistence of single-electron tunneling and tunnel barrier suppression upon a bias voltage increase. The measurements thus show that Coulomb-blockaded devices can be made with a nanoparticle cluster source, which extends the existing possibilities to fabricate such devices to those in which it is very challenging to reduce the usual NP agglomeration given by a solution method.

Liquid Nitrogen Activation of Zero-Valent Iron and Its Enhanced Cr(VI) Removal Performance.

In this study, we report that liquid nitrogen treatment is a promising zero-valent iron activation method that does not remove the iron oxide shell; this can improve the apparent Cr(VI) removal rate constant of zero-valent iron by about 4-120 times, depending on the particle sizes and the suppliers of zero-valent iron. It was found that liquid nitrogen, with its low temperature of 77 K, could crack the iron oxide shell of zero-valent iron to produce abundant fractures because of the different thermal expansion coefficients of iron oxide and iron. These fractures provided suitable mass transfer channels for the inward transfer of water/oxygen molecules to the iron core and the subsequent in situ generation of Fe(II) for the reduction of Cr(VI) to Cr(III). More importantly, systematic characterizations confirmed the generation of an Fe(III)/Cr(III)/Cr(VI) composite on the surface of zero-valent iron during the removal, suggesting its environmental benignancy. This study provides a novel physical zero-valent iron activation method, sheds light on the importance of the iron oxide shell of zero-valent iron on Cr(VI) removal, and clarifies the intrinsic Cr(VI) removal mechanism of zero-valent iron.

Crystalline-Amorphous Permalloy@Iron Oxide Core-Shell Nanoparticles Decorated on Graphene as High-Efficiency, Lightweight, and Hydrophobic Microwave Absorbents.

The exploration of high-efficiency microwave absorption materials with lightweight and hydrophobic features is highly expected to reduce or eliminate the electromagnetic pollution. Graphene-based nanocomposites are universally acknowledged as promising candidates for absorbing microwaves due to their remarkable dielectric properties and lightweight characteristic. However, the hydrophilicity of graphene may reduce their stability and restrict the applications in moist environment. Herein, a well-designed heterostructure composed of crystalline permalloy core and amorphous iron oxide shell was uniformly adhered on oleylamine-modified graphene nanosheets by a one-pot thermal decomposition method. Compared with the recognized hydrophilic graphene-based hybrid materials, the permalloy@iron oxide/graphene nanocomposites show excellent hydrophobic and water-resistant features with a water contact angle of 136.5°. Besides, the nanocomposites show high-efficiency microwave absorption performance, benefiting from the tunneling effect, polarization, interface interaction, impedance matching condition, and synergistic effect between core-shell permalloy@iron oxide nanoparticles and graphene nanosheets. A broad effective absorption bandwidth with reflection loss (RL) value exceeding -10 dB can be obtained from 4.25 to 18 GHz, covering about 86% measured frequency range when the absorber thickness is 2.0-5.0 mm. Also, the microwave absorption performance of nanocomposites can be tuned by changing the amount of graphene. More importantly, a greatly improved microwave absorption effectiveness of -71.1 dB can be achieved for the nanocomposites in comparison with the bare permalloy@iron oxide nanoparticles (-5.6 dB) and oleylamine-modified GO nanosheets (-3.56 dB). The lightweight and hydrophobic permalloy@iron oxide/graphene nanocomposites with high-efficiency microwave absorption performance are highly promising to improve the environmental adaptability of electric devices, especially in the wet environment.

Hexavalent chromium removal by a new composite system of dissimilatory iron reduction bacteria Aeromonas hydrophila and nanoscale zero-valent iron

Core-shell Fe@Fe2O3 nanowire is one special nanoscale zero-valent iron (NZVI) with an iron core and an outside shell of iron oxide containing the surface bound ferrous ions, which has been used to remove various pollutants including Cr(VI). However, it can be easily oxidized to accumulate iron oxides on the shell, resulting in the loss of reactive activity during its long-term application. Therefore, the dissolution of iron oxides by reduction is required to maintain NZVI reactivity. In this study, we combine NZVI and a dissimilatory iron reduction bacteria (DIRB), Aeromonas hydrophila HS01, to establish a composite system for a sustainable anoxic reduction of Cr(VI). HS01 can stably coexist with NZVI, reduce the oxidized Fe on NZVI and generate more dissolved Fe(II) under anoxic conditions. This presence of HS01 can maintain the core-shell structured morphology and relatively more Fe0 and Fe(II) on NZVI surface, and enhance the reactivity in Cr(VI) removal. Our results indicated that a suitable DIRB can be used to prolong the reactivity of NZVI, and their combination is an efficient method for anoxic Cr(VI) removal.

Nanoencapsulation of arsenate with nanoscale zero-valent iron (nZVI): A 3D perspective

The principal forces driving the efficient enrichment and encapsulation of arsenic (As) into nanoscale zero-valent iron (nZVI) are the disordered arrangement of the atoms and the gradient chemical potentials within the core-shell interface. The chemical compositions and the fine structure of nZVI are characterized with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), X-ray energy-dispersive spectroscopy (XEDS), electron energy loss spectroscopy (EELS), and high-resolution X-ray photoelectron spectroscopy (HR-XPS). Atomically resolved EELS at the oxygen K-edge unfolds that the Fe species in nZVI are well stratified from Fe(III) oxides in the outermost periphery to a mixed Fe(III)/Fe(II) interlayer, then Fe(II) oxide and the pure Fe(0) phase. Reactions between As(V) and nZVI suggest that a well-structured local redox gradient exists within the shell layer, which serves as a thermodynamically favorable conduit for electron transfer from the iron core to the surface-bound As(V). HR-XPS with ion sputtering shows that arsenic species shift from As(V), As(III)/As(V) to As(V)/As(III)/As(0) from the iron oxide shell–water interface to the Fe(0) core. Results reinforce previous work on the efficacy of nZVI for removing and remediating arsenic while the analytical TEM methods are also applicable to the study of environmental interfaces and surface chemistry.

Synthesis of eco-compatible bimetallic silver/iron nanoparticles for water remediation and reactivity assessment on bromophenol blue

In the last decade, zero-valent iron nanoparticles (nZVI) have been applied for groundwater remediation and they proved to be effective towards a wide range of contaminants, both organic and inorganic. One of the critical aspects related to the synthesis of this material concerns the use of borohydride, which increases the cost of the final product and generates toxic borates. In this paper, a new synthesis method of bimetallic nanoscale zero-valent silver/iron (nZVSI), its properties and its reactivity towards a model compound are presented. The novel synthesis protocol employs benign hydrosulfite as reducing agent and it is of easy implementation and scalability. The resulting nanoparticles have narrow size distribution and show appropriate colloidal stability. They consist of a core of zerovalent iron and a thin shell of iron oxide, while silver is homogeneously distributed within the material. The nanoparticles showed effective reactivity, able to degrade bromophenol blue with suitable kinetics and using a low amount of material. Additionally, the bimetallic nanomaterial significantly outperformed nanometric zero-valent silver (nZVS) and nZVI obtained with the same protocol. The proposed synthesis would allow to significantly reduce the environmental and health impact of the stage prior to product application via injection in the subsoil. Also, the simplicity and the safety of the proposed synthesis procedure would allow the production of the bimetallic reactant directly on-site, thus streamlining the remediation process and maximizing its efficiency.

Preparation of core-shell Pt@Fe3O4@SiO2 nanostructures by oxidation of core-shell FePt@SiO2 nanoflowers and their performance in preferential CO oxidation reaction

Core–shell Pt@Fe3O4@SiO2 nanostructures were successfully prepared in three step procedure. FePt nanoflowers were first prepared by an oleylamine-mediated chemical synthetic route, and then coated with thin silica (SiO2) layer (∼5 nm) by a method based in microemulsion. Then, the core–shell Pt@Fe3O4@SiO2 nanostructures were prepared thorough the calcination step at 550 °C in air static of FePt nanoflowers (FePt@SiO2) samples. The silica layer played an important role to avoid nanoparticles agglomeration during the heat treatment. Iron oxide (Fe3O4) shell grown on Pt nanoparticle surface showed able to act as promoter for CO conversion in Preferential Reaction of Oxidation of CO (PROX-CO).

Tuning the Core–Shell Structure of Au144@Fe2O3 for Optimal Catalytic Activity for CO Oxidation

Core–shell heterostructures have been utilized as a catalyst that is thermally stable and exhibits a synergistic effect between core and shell, resulting in increased catalytic activity. Here we report on the synthetic procedure involving a Au144 core with an iron oxide shell which can be varied in thickness. The Au144@Fe2O3 particles with Au:Fe mass ratios of 1:2, 1:4, and 1:6 were synthesized and then deposited onto silica via colloidal deposition. Using CO oxidation, each Au144@Fe2O3/SiO2 catalyst gave varying degrees of full CO conversion depending on the thickness of the iron oxide layer. The 1:4 Au144@Fe2O3/SiO2 catalyst produced the best catalytic activity and was further investigated via thermal treatments, where calcination at 300 °C presented the best results, and the 1:4 ratio was still active at 100 °C after thermal treatments.

Efficient catalytic degradation of bisphenol A by novel Fe0- vermiculite composite in photo-Fenton system: Mechanism and effect of iron oxide shell

Novel Fe0-vermiculite (Fe-Ver-C-H2) composite was synthesized by thermal reduction and acted as catalysts to remove bisphenol A (BPA) in photo-Fenton system. In term of activation ability toward H2O2, separation ability and stability, Fe-Ver-C-H2 presented obvious advantages over other kinds of Fe0-vermiculite composite (Fe-Ver-NaBH4), which obtained by traditional liquid reduction. The reason was that iron oxide shells on the surface of Fe0 were α-Fe2O3 and Fe3O4 for Fe-Ver-NaBH4 and Fe-Ver-C-H2, respectively. And for Fe-Ver-C-H2, the synergistic effect between iron core (Fe0) and iron oxide shell (Fe3O4) is beneficial to catalytic performance. The mechanism and plausible pathway of BPA degradation were also proposed according to the results of radical scavenger studies and gas chromatography-mass spectrometry (GC-MS), respectively. In addition, factorial effects for Fe-Ver-C-H2 in photo-Fenton system were also investigated and optimized as: pH of 5, dosage of 0.2 g L−1 and H2O2 concentration of 20 mM. This study presented a facile method to synthesize novel Fe0-vermiculite composite and provided a new sight to investigate the effect of iron oxide shell on the catalytic performance when Fe0-vermiculite composite acted as catalyst to remove contaminants from the environment in photo-Fenton system.

Calcium hydroxide coating on highly reactive nanoscale zero-valent iron for in situ remediation application

Nano scale zero-valent iron (nZVI), a promising engineering technology for in situ remediation, has been greatly limited by quick self-corrosion and low mobility in porous media. Highly reactive nZVI particles produced from the borohydride reduction method were enclosed in a releasable Ca(OH)2 layer by the chemical deposition method. The amount of Ca(OH)2 coated on nZVI surface were well controlled by the precursor dosage. At moderate Ca(OH)2 dosage (RCa/TFe = 0.25) condition, the increment of Fe0 content for the obtained nZVI/Ca-0.25 sample was observed. The interfacial reactions between the iron oxide shell and the Ca(OH)2 saturated environment were delicately elucidated by the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectrum. And the coverage of Ca(OH)2 shell on spherical nZVI surface was found more complete and uniform for the nZVI/Ca sample obtained from the moderate precursor dosage condition (RCa/TFe = 0.25). The Ca(OH)2 shell before dissolution was demonstrated owning the anti-corrosion capability to slow down the oxidation of Fe0 core in air, during ethanol storage and in aqueous environment. The mechanism of anti-corrosion capability for nZVI/Ca-0.25 particle was interestingly found to be attributed to the Ca(OH)2 shell isolation and also be potentially due to the iron oxide shell phase transformation mediated by the outer Ca(OH)2 shell. An improved trichloroethylene reduction performance was observed for nZVI/Ca-0.25 than bare nZVI. The mobility of nZVI/Ca particles in water-saturated porous media was moderately improved before shell dissolution.

Plantain Peel Mediated Green Synthesis Iron Oxide Nanoparticles, Surface Functionalization, and Them Performance towards Methylene Blue and Methyl Orange Dye Removal

Currently, green synthesis approach is used as the biocompatible, eco-friendly, and sustainable alternative of conventional approaches to synthesize iron oxide nanoparticles. In this work, magnetic iron oxide nanoparticles were synthesized by using plantain peel extract via green and biogenic approach. The surface of green synthesized iron oxide nanoparticles was functionalized to increase the stability of the nanoparticles and maintain the coexisting of both magnetic and catalytic property of the nanoparticles at the same time. Two kinds of surface functionalization structures were synthesized in this study, included silica core-iron oxide shell nanoparticles and silica core-PDDA polymerized iron oxide shell nanoparticles. The main concern of this study is the performance of bare and surface functionalized green synthesized nanoparticles. Methylene blue and methyl orange dyes were used as the model of dye removal test to indicate the feasibility of the synthesized nanocomposites. In summary, surface functionalized nanocomposites achieved higher dye removal efficiency than bare green synthesized iron oxide nanoparticles in both the methylene blue and methyl orange degradation test. Methylene blue dye was removed in higher rate than methyl orange dye due to the presence of negatively charged iron oxide nanoparticles with both the adsorptive and catalytic properties. At last, the components present in plantain peel extract were confirmed by using Fourier Transform Infrared Spectroscopy.

Magneto-Fluorescent Yolk–Shell Nanoparticles

We present a new strategy for the fabrication of magneto-fluorescent nanoparticles designed for bimodal imaging. These hybrid nanostructures comprise an optically active semiconductor nanoparticle quantum dot core with tunable fluorescence, encapsulated within a hollow paramagnetic iron oxide shell that serves as an MRI contrast agent. The yolk–shell morphology enables incorporation of the semiconductor and magnetic domains into a single structure, while avoiding direct contact between them, which typically results in quenching of the desired optical fluorescence. We successfully demonstrate utilization of the ultrasmall (15 nm hydrodynamic size) magneto-fluorescent CdSe@CdS@Hollow-Fe2O3 nanoparticles for multimodal imaging of cells at the intracellular level.

Colloidal Au/iron oxide nanocrystal heterostructures: magnetic, plasmonic and magnetic hyperthermia properties

Interface and morphology determine the magnetic, plasmonic and magnetic hyperthermia properties of Au/iron oxide nanocrystal heterostructures.