γ-Fe2O3 Nanocrystals Research Articles

Up-converting β-NaY0.8[Yb0.18Er0.02]F4 nanoparticles coated by superparamagnetic γ-Fe2O3 nanosatellites: elaboration, characterization and in vitro cytotoxicity.

Current biomedical imaging techniques are vital for the diagnosis of various diseases. They are related to the development of multimodal probes encompassing all the functionalities required for comprehensive imaging. In this context, we applied a simple and reproducible wet synthesis route to produce such probes. This method allowed us to prepare about 100 nm sized lanthanide-doped yttrium fluoride nanoparticles β-NaY0.8[Yb0.18Er0.02]F4, coated with about 10 nm sized iron oxide γ-Fe2O3 nanocrystals. By this way, the built granular hetero-nanostructures combine desirable up-converting photoluminescence (the core) and superparamagnetic properties (the satellites), enabling dual optical and magnetic resonance imaging applications. Through citrate ligand grafting, the designed core-satellite particles formed stable aqueous colloids, which are valuable for biomedical applications. Optical spectroscopy and confocal microscopy revealed their capability for sustained visible light emission (predominantly green) upon near-infrared excitation (980 nm). Additionally, based on XTT assays, when incubated for 24 hours with mammalian healthy or cancer cells, even at doses as high as 0.1 mg mL-1 (milligrams of particles), they did not induce significant cytotoxicity. The measured body temperature magnetization of the engineered nanoconstructs was found to be about 10 emu g-1 (grams of particles) at 1.5 T, which is high enough to use them as positive or negative contrast magnetic resonance agents in the clinic, as confirmed by relaxometry measurements in Milli-Q water. This result underscores their promising biomedical utility as bimodal probes for optical and magnetic imaging.

Amino-grafted water-soluble maghemite nanocrystals synthesized by deep eutectic solvents electrolysis: Investigation of the formation mechanism

Benefiting from the hydrophilicity and modifiability, aminated iron oxide nanoparticles play significant roles in the construction of magnetically responsive functional materials, and are then widely used in the field of biomedicine and water purification. Using the deep eutectic solvent (DES) composed of urea and choline chloride as an electrolyte, amino-grafted water-soluble maghemite (γ-Fe2O3) nanocrystals have been synthesized by organic electrolysis (DES-electrolysis). In the present work, the DES containing ferrous ions is used as the electrolyte to verify whether magnetite (Fe3O4) can be prepared by that organic electrolysis strategy. The results show that, regardless of the presence or absence of ferrous ions in the DES-based electrolyte, the resulting nanocrystals are maghemite rather than magnetite. The synthesized amino-grafted γ-Fe2O3 nanoparticles can also be highly and stably dispersed in water. The present work deepens the understanding of the formation mechanism of amino-grafted water-soluble maghemite nanocrystals synthesized by DES-electrolysis.

Wood-derived porous carbon supported γ-Fe2O3 nanoparticles as efficient catalyst for oxygen reduction reaction

The sluggish kinetics of oxygen reduction reaction at the cathode is one of the obstacles of the next-generation energy conversion system such as fuel cell and Zn-air battery. Here, a simple pyrolysis method was used to transform delignification-treated balsa wood into nitrogen-doped porous layered carbon materials. γ-Fe2O3 nanocrystals were supported on N-doped wood-derived carbon materials. The prepared Fe2O3-CW1000 catalyst exhibits superior ORR performance with a high onset potential of 0.98 VRHE in alkaline environment. This is consistent with the potential of commercial Pt/C. The superior ORR activity is attributed to the fact that γ-Fe2O3 nanoparticles promote the activity of Fe-Nx sites. And the N-enriched porous carbon matrix facilitates the faster electron movement on the catalyst surface and the full exposure of the active sites.

Magnetic Mesoporous Silica Nanorods Loaded with Ceria and Functionalized with Fluorophores for Multimodal Imaging.

Multifunctional magnetic nanocomposites based on mesoporous silica have a wide range of potential applications in catalysis, biomedicine, or sensing. Such particles combine responsiveness to external magnetic fields with other functionalities endowed by the agents loaded inside the pores or conjugated to the particle surface. Different applications might benefit from specific particle morphologies. In the case of biomedical applications, mesoporous silica nanospheres have been extensively studied while nanorods, with a more challenging preparation, have attracted much less attention despite the positive impact on the therapeutic performance shown by seminal studies. Here, we report on a sol–gel synthesis of mesoporous rodlike silica particles of two distinct lengths (1.4 and 0.9 μm) and aspect ratios (4.7 and 2.2) using Pluronic P123 as a structure-directing template and rendering ∼1 g of rods per batch. Iron oxide nanoparticles have been synthesized within the pores yielding maghemite (γ-Fe2O3) nanocrystals of elongated shape (∼7 nm × 5 nm) with a [110] preferential orientation along the rod axis and a superparamagnetic character. The performance of the rods as T2-weighted MRI contrast agents has also been confirmed. In a subsequent step, the mesoporous silica rods were loaded with a cerium compound and their surface was functionalized with fluorophores (fluorescamine and Cyanine5) emitting at λ = 525 and 730 nm, respectively, thus highlighting the possibility of multiple imaging modalities. The biocompatibility of the rods was evaluated in vitro in a zebrafish (Danio rerio) liver cell line (ZFL), with results showing that neither long nor short rods with magnetic particles caused cytotoxicity in ZFL cells for concentrations up to 50 μg/ml. We advocate that such nanocomposites can find applications in medical imaging and therapy, where the influence of shape on performance can be also assessed.

Crystal-Phase Control of Ternary Metal Oxides by Solid-State Synthesis with Nanocrystals.

Ternary metal oxides are materials of interest for many applications, from batteries to catalysis. Their crystalline structure and composition determine their properties, and thus it is important to achieve control over these features. Here, we demonstrate that solid-state chemistry among nanocrystalline precursors is a promising approach for their synthesis. We show that the crystalline phase of nanocrystal precursors direct that of the ternary reaction product. The combination of X-ray and electron microscopy techniques reveals that the spinel and rhombohedral phases of copper iron oxide are obtained by reacting copper nanocrystals with spinel γ-Fe2O3 and corundum α-Fe2O3 nanocrystals, respectively. Considering the available library of nanocrystals with tunable crystal phases, this discovery opens up an alternative pathway toward the synthesis of a wide variety of ternary and quaternary materials, including those with metastable phases.

Facile preparation of lignosulfonate-based superparamagnetic colloidal nanocrystal clusters (CNCs)

Colloidal nanocrystal clusters (CNCs) are hierarchical nanostructure formed by clustering several nanocrystals into one nano-ensemble. In this work, novel lignosulfonate (LS)-based superparamagnetic CNCs were prepared for the first time. The strategy based on electrostatic interaction between LS, nanocrystals and charge control agent, and included multistep of surface modification, precipitation and self-assembly. With the protection of LS and blocking of CTAB, individual γ-Fe2O3 nanocrystals in the colloidal particles can keep monodisperse to form the cluster morphology. The superparamagnetic γ-Fe2O3 endowed superparamagnetic property to the CNCs, and the saturation magnetization value of CNCs increased with the increase number of nanocrystals in the LS spheres. Furthermore, the LS-based superparamagnetic CNCs showed excellent dye adsorption efficiency for different dyes, especially for positive charged cationic dyes.

Removal of Lead Contaminants with γ-Fe2O3 Nanocrystals

γ-Fe2O3 (maghemite) nanocrystals were synthesized by co-precipitation method at room temperature have been used to remove Pb+2 from aqueous solutions. The prepared of this sample was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). XRD patterns indicated the maghemite structure of average particle size of ∼12 nm, which was further confirmed by the FESEM images of the γ-Fe2O3 nanosrystals. Magnetic saturation of synthesized maghemite was found to be 68.4 emu g–1. Adsorption experiments were tested for pH of the solutions, contact time and initial concentration of metal ions. The kinetic data of adsorption of heavy metal ions on the surface of the synthesized nano-adsorbent was described by a pseudo-second order equation. The adsorption equilibrium study exhibited that the heavy metal ions adsorption of maghemite nanocrystals followed a Langmuir and Freundlich isotherm model. Pb2+ adsorption equilibrium data were best fitted to Langmuir equation and maximum adsorption capacity of 25 mg g–1 was obtained. This work demonstrates that the synthesized γ-Fe2O3 nanocrystals can be considered as prospective nano-adsorbent.

Protective Effect of Polyoxometalates in {Mo132}/Maghemite Binary Superlattices Under Annealing.

The binary assembly DDA-{Mo132}/OA-γ-Fe2O3 (DDA = didodecyldimethylammonium, {Mo132} = [Mo132O372(CH3COO)30(H2O)72]42−, OA = oleic acid) constitutes one of the two examples in the literature of binary superlattices made of a mixing of nanocrystals and oxo-clusters. In a precedent work, we reported in details the preparation of such magnetic binary systems and studied the effect of the nature of the polyoxometalates (POMs) on the magnetic properties. In the present paper, we study the stability of this model binary assembly under heating at various temperatures. Indeed, especially if magnetic and/or transport properties are targeted, an annealing can be essential to change the phase of the nanocrystals in a more magnetic one and/or to desorb the organic capping of the nano-objects that can constitute an obstacle to the electronic communication between the nano-objects. We gave evidence that the maghemite organization in the binary assembly is maintained until 370°C under vacuum thanks to the presence of the POMs. This latter evolve in the phase MoO3, but still permits to avoid the aggregation of the nanocrystals as well as preserve their periodical arrangement. On the contrary, an assembly made of pure γ-Fe2O3 nanocrystals displays a clear aggregation of the nano-objects from 370°C, as attested by transmission and scanning electronic microscopies and confirmed by magnetic measurements. The stability of the magnetic nanocrystals in such POMs/nanocrystals assemblies opens the way to (i) the elaboration of new binary assemblies from POMs and numerous kinds of nanocrystals with a good control on the magnetic properties and to (ii) the investigation of new physical properties as exchange coupling, or magneto-transport in such systems.

Facile preparation of N-doped corncob-derived carbon nanofiber efficiently encapsulating Fe2O3 nanocrystals towards high ORR electrocatalytic activity

Abstract Facile preparation of cost-effective and durable porous carbon-supported non-precious-metal/nitrogen electrocatalysts for oxygen reduction reaction (ORR) is extremely important for promoting the commercialized applications of such catalysts. In this work, the FeCl3-containing porphyrinato iron-based covalent porous polymer (FeCl3·FePor-CPP) was fabricated in-situ onto porous corncob biomass supports via a simple one-pot method. Subsequent thermal-reduction pyrolysis at 700 °C–900 °C with CO2 gas as an activating agent resulted in Fe2O3-decorated and N-doped graphitic carbon composite Fe2O3@NCb NC = N-doped graphene analog; bio-C = the corncob-derived hierarchically porous graphitic biomass carbon framework). The derived α-Fe2O3 and γ-Fe2O3 nanocrystals (5–10 nm particle diameter) were all immobilized on the N-doped bio-C micro/nanofibers. Notably, the Fe2O3@NC&bio-C obtained at the pyrolysis temperature of 800 °C (Fe2O3@NC&bio-C-800), exhibited unusual ORR catalytic efficiency via a 4-electron pathway with the onset and half-wave potentials of 0.96 V and 0.85 V vs. RHE, respectively. In addition, Fe2O3@NC&bio-C-800 also exhibited a high and stable limiting current density of -6.0 mA cm−2, remarkably stability (larger than 91% retention after 10000s), and good methanol tolerance. The present work represents one of the best results for iron-based biomass material ORR catalysts reported to date. The high ORR activity is attributed to the uniformly distributed α-Fe2O3 and γ-Fe2O3 nanoparticles on the N-enriched carbon matrix with a large specific surface area of 772.6 m2 g−1. This facilitates favor faster electron movement and better adsorption of oxygen molecules on the surface of the catalyst. Nevertheless, comparative studies on the structure and ORR catalytic activity of Fe2O3@NC&bio-C-800 with Fe2O3@bio-C-800 and NC&bio-C-800 clearly highlight the synergistic effect of the coexisting Fe2O3 nanocrystals, NC, and bio-C on the ORR performance.

One-Pot Method for Preparation of Magnetic Multi-Core Nanocarriers for Drug Delivery.

The development of various magnetically-responsive nanostructures is of great importance in biomedicine. The controlled assembly of many small superparamagnetic nanocrystals into large multi-core clusters is needed for effective magnetic drug delivery. Here, we present a novel one-pot method for the preparation of multi-core clusters for drug delivery (i.e., magnetic nanocarriers). The method is based on hot homogenization of a hydrophobic phase containing a nonpolar surfactant into an aqueous phase, using ultrasonication. The solvent-free hydrophobic phase that contained tetradecan-1-ol, γ-Fe2O3 nanocrystals, orlistat, and surfactant was dispersed into a warm aqueous surfactant solution, with the formation of small droplets. Then, a pre-cooled aqueous phase was added for rapid cooling and the formation of solid magnetic nanocarriers. Two different nonpolar surfactants, polyethylene glycol dodecyl ether (B4) and our own N1,N1-dimethyl-N2-(tricosan-12-yl)ethane-1,2-diamine (SP11), were investigated for the preparation of MC-B4 and MC-SP11 magnetic nanocarriers, respectively. The nanocarriers formed were of spherical shape, with mean hydrodynamic sizes <160 nm, good colloidal stability, and high drug loading (7.65 wt.%). The MC-B4 nanocarriers showed prolonged drug release, while no drug release was seen for the MC-SP11 nanocarriers over the same time frame. Thus, the selection of a nonpolar surfactant for preparation of magnetic nanocarriers is crucial to enable drug release from nanocarrier.

Flame synthesis of gamma-iron-oxide (γ-Fe2O3) nanocrystal films and carbon nanotubes on stainless-steel substrates

Using a rapid, open-atmosphere flame synthesis technique, iron-oxide nanoparticles (α-Fe2O3) and nanocrystals (γ-Fe2O3) and carbon nanotubes (CNTs) are grown directly on stainless steel substrates. Multiple inverse-diffusion flames provide both oxide species (H2O and CO2) and carbon species (CH4, CO, C2H2), at elevated temperature, conducive for the growths of iron-oxide nanoparticles/nanocrystals and CNTs. The growth of α-Fe2O3 nanoparticles occurs at 500 °C. At a temperature of 850 °C, the growth of CNTs occurs on type 304 stainless steel, while γ-Fe2O nanocrystal films are grown on 304 L and 316 L stainless steels with relatively lower innate carbon content. Interestingly, a temperature-step process, where 304 stainless steel substrate is initially at 500 °C and then increased to 850 °C, distinctly converts the “seed” α-Fe2O3 nanoparticles into larger γ-Fe2O3 nanocrystals, with some scattered CNTs. Strategically time-varied local conditions should produce different compositional ratios of iron-oxide/CNT hybrid films, as well as targeted functionally-graded nanostructures and nanocomposites.

The surface chemistry of iron oxide nanocrystals: surface reduction of γ-Fe2O3 to Fe3O4 by redox-active catechol surface ligands

The effect of surface functionalization on the structural and magnetic properties of catechol-functionalized iron oxide magnetic (γ-Fe2O3) nanocrystals was investigated.

Structural behavior of laser-irradiated γ-Fe2O3 nanocrystals dispersed in porous silica matrix : γ-Fe2O3 to α-Fe2O3 phase transition and formation of ε-Fe2O3

The effects of laser irradiation on γ-Fe2O3 4 ± 1 nm diameter maghemite nanocrystals synthesized by co-precipitation and dispersed into an amorphous silica matrix by sol-gel methods have been investigated as function of iron oxide mass fraction. The structural properties of γ-Fe2O3 phase were carefully examined by X-ray diffraction and transmission electron microscopy. It has been shown that γ-Fe2O3 nanocrystals are isolated from each other and uniformly dispersed in silica matrix. The phase stability of maghemite nanocrystals was examined in situ under laser irradiation by Raman spectroscopy and compared with that resulting from heat treatment by X-ray diffraction. It was concluded that ε-Fe2O3 is an intermediate phase between γ-Fe2O3 and α-Fe2O3 and a series of distinct Raman vibrational bands were identified with the ε-Fe2O3 phase. The structural transformation of γ-Fe2O3 into α-Fe2O3 occurs either directly or via ε-Fe2O3, depending on the rate of nanocrystal agglomeration, the concentration of iron oxide in the nanocomposite and the properties of silica matrix. A phase diagram is established as a function of laser power density and concentration.

Binary Superlattices from {Mo132} Polyoxometalates and Maghemite Nanocrystals: Long-Range Ordering and Fine-Tuning of Dipole Interactions.

In the present article, the successful coassembly of spherical 6.2 nm maghemite (γ-Fe2O3) nanocrystals and giant polyoxometalates (POMs) such as 2.9 nm {Mo132} is demonstrated. To do so, colloidal solutions of oleic acid-capped γ-Fe2O3 and long-chain alkylammonium-encapsulated {Mo132 } dispersed in chloroform are mixed together and supported self-organized binary superlattices are obtained upon the solvent evaporation on immersed substrates. Both electronic microscopy and small angles X-ray scattering data reveal an AB-type structure and an enhanced structuration of the magnetic nanocrystals (MNCs) assembly with POMs in octahedral interstices. Therefore, {Mo132} acts as an efficient binder constituent for improving the nanocrystals ordering in 3D films. Interestingly, in the case of didodecyldimethylammonium (C12)-encapsulated POMs, the long-range ordered binary assemblies are obtained while preserving the nanocrystals magnetic properties due to weak POMs-MNCs interactions. On the other hand, POMs of larger effective diameter can be employed as spacer blocks for MNCs as shown by using {Mo132} capped with dioctadecyldimethylammonium (C18) displaying longer chains. In that case, it is shown that POMs can also be used for fine-tuning the dipolar interactions in γ-Fe2O3 nanocrystal assemblies.

Improved Transversal Relaxivity for Highly Crystalline Nanoparticles of Pure γ‐Fe2O3 Phase

Pure and highly crystalline γ-Fe2O3 nanocrystals (NCs) are obtained when hydrolysis and oxidation of a Fe(II) organometallic precursor are performed in successive steps. Their synthesis in pure alkylamine leads to NCs of about 6 nm. In aqueous solutions of poly(vinyl)pyrrolidone, such pristine NCs form aggregates of about 150 nm that exhibit a high transversal relaxivity (r2 =466 mM(-1) s(-1)) about four times higher than that of a commercial Feridex magnetic resonance imaging (MRI) contrast agent. Consequently, they provide a significant decrease in the NMR signal at very short echo time (8 ms), which is of paramount importance in clinical practice because of the reduced duration of MRI measurements.

Improving Magnetooptical Faraday Effect of maghemite/silica nanocomposites

The present work is focused on the evaluation and characterization of the Magnetooptical Faraday Effect (MOFE) of sol–gel processed composites consisting of maghemite iron oxide nanoparticles embedded in a silica xerogel matrix. These materials are of great interest mainly for magnetic-field sensing applications because of their high MOFE response, even at low magnetic fields. We have implemented an in-situ approach for the composite processing in which nanoparticles precursor are formed while host matrix polymerization and subsequent annealing steps leads to γ-Fe2O3 nanocrystals growth inside the porous xerogel framework. The samples thus obtained are reddish monoliths showing convenient mechanical properties. This method allows obtaining, with carefully controlled preparation conditions, materials with reproducible mechanical, magnetic and optical properties. It is shown that an additional processing step in which the samples were subjected to thermal oxidation treatment in air, leads to an enhancement more than 10 times in the sample optical transmittance, in comparison with the values of the untreated samples. The study of the magnetooptical behavior of these materials reveals a rather high Faraday rotation, as well as a reproducible and practically reversible linear range at low magnetic fields.

Spin filter effect in iron oxide nanocrystal arrays

Integrating nanocrystals (NCs) into magnetic tunnel structures is of considerable interest due to expectation of novel properties from their spin selective transport and single electron features. Superstructures by colloidal NCs having translational and orientational order and interesting collective magnetic properties can be prepd. by soln. casting through sensitive interparticle and particle-substrate interactions. In this work, we discuss the study on magnetic field induced assembly of mono-dispersed iron oxide NCs to obtain spin filter effect across the superlattice array, when sandwiched between gold electrodes. The deposition of mixed phase Fe3O4@γ-Fe2O3 NCs on SiO2/Au surface proceeds through slow solvent evapn. and are studied for controlled interparticle spacing. For specific NC concn., the ordering depends on the substrate chem. and the ligands passivating NC surface, which affects the concn. of cluster nuclei formed. In presence of a magnetic field, the tunnel structure exhibits enhanced pos. tunnel magnetoresistance at low temps., which could be related to their ferromagnetism and the attempts by electrons to percolate NC superlattice with preserved spin. A sign reversal for magnetoresistance is exhibited by the vertical tunnel junctions on raising the temp.

Multiwalled carbon nanotubes anchored with maghemite nanocrystals for high-performance lithium storage

In this paper, we have anchored maghemite (γ-Fe2O3) nanocrystals compactly and uniformly on multiwalled carbon nanotubes (MWCNT) via a polyelectrolyte-assisted layer-by-layer assembly approach based on electrostatic attraction. When evaluated as an anode for lithium-ion batteries (LIBs), the as-synthesized MWCNT-γ-Fe2O3 nanohybrid displays high reversible capacities, remarkable cycling stability, and magnificent high rate capability, facilitating its application as an advanced anode for high-energy, long-life, and high-power LIBs.

γ-Fe2O3/graphene nanocomposites as a stable high performance anode material for neutral aqueous supercapacitors

γ-Fe2O3/graphene nanocomposites were developed as a high performance anode material for environmentally friendly neutral aqueous supercapacitors. This composite electrode, in addition to its good capacitive characteristics, exhibited outstanding rate capability and cycling stability. γ-Fe2O3 nanocrystals of 5 nm in size were potentiostatically deposited onto a hosting porous graphene film to form the γ-Fe2O3/graphene nanocomposite. The porous graphene film provided a highly conductive network to enhance the charge transport/transfer involved in the capacitance generation process and helped disperse the γ-Fe2O3 nanocrystals within the graphene network to promote better utilization of the γ-Fe2O3 nanocrystals for capacitance generation. The capacitive performances of the γ-Fe2O3/graphene composite electrode were investigated by cyclic voltammetry and galvanostatic charging/discharging analyses in 1 M Na2SO3 over a potential window of 0 to −0.8 V (vs. Ag/AgCl). A high specific capacitance of 224 F gFe2O3−1 was achieved for the γ-Fe2O3/graphene composite electrode at 25 mV s−1, 2.4 fold that of the plain γ-Fe2O3 electrode. The outstanding rate capability of the composite electrode was demonstrated with a high capacitance retention rate of 91% when the charging/discharging current density increased from 1 to 20 A g−1. At the high charging/discharging current density of 20 A g−1, the Coulombic efficiency remained high at 95%. The composite electrode experienced an electrochemical activation and its specific capacitance remained high above the starting specific capacitance after 40 000 cycles at 500 mV s−1, exhibiting outstanding cycling stability.

Multi-Functional Silica Nanoparticles Based on Metal Atom Clusters: From Design to Toxicological Studies

We report on the interest of luminescent and nanosized metal atom clusters for the development of functional silica nanoparticles. Furthermore, multi-functional hybrid nanoparticles have been achieved by associating these luminescent clusters with magnetic γ-Fe2O3 nanocrystals and plasmonic gold nanocrystals. In addition, as part of the risk evaluation before potential applications, the toxicity of the nanoparticles was evaluated both on plants and on human cells.