Synthesis of monodisperse iron oxide and iron/iron oxide core/shell nanoparticles via iron-oleylamine complex

Monodisperse magnetic nanoparticles are of great scientific and technical interests. This paper reports a single-step synthesis of monodisperse magnetite nanoparticles with particle size of 8 nm. Iron/maghaemite core/shell nanoparticles with particle size of 11 nm were obtained by reducing the concentration of oleylamine. TEM and in-situ FTIR results suggested that iron-oleylamine intermediate was generated in-situ and decomposed at higher temperature. Oleylamine was also found on the surface of nanoparticles, indicating its role as capping agent which provided steric protection of as-synthesized nanoparticles from agglomeration. Both magnetite and iron/maghaemite core/shell nanoparticles were superparamagnetic at room temperature with a blocking temperature at 80 K and 67 K, respectively.     

Zero-valent iron nanoparticles preparation

Zero-valent iron nanoparticles were synthesized by hydrogenating [Fe[N(Si(CH₃)₃)₂]₂] at room temperature and a pressure of 3 atm. To monitor the reaction, a stainless steel pressure reactor lined with PTFE and mechanically stirred was designed. This design allowed the extraction of samples at different times, minimizing the perturbation in the system. In this way, the shape and the diameter of the nanoparticles produced during the reaction were also monitored. The results showed the production of zero-valent iron nanoparticles that were approximately 5 nm in diameter arranged in agglomerates. The agglomerates grew to 900 nm when the reaction time increased up to 12 h; however, the diameter of the individual nanoparticles remained almost the same. During the reaction, some byproducts constituted by amino species acted as surfactants; therefore, no other surfactants were necessary.     

Synthesis of monodisperse organic- and water-soluble iron oxide nanoparticles using Fe(OH)3 as precursor

The precursors used to prepare high-quality nanoparticles by high-temperature decomposition are expensive and toxic organometallic compounds. Fe(OH)₃, an inexpensive and environmentally friendly iron-containing compound, is for the first time introduced to act as an precursor to generate monodisperse iron oxide nanoparticles. The obtained nanoparticles are characterised by transmission electronic microscopy, IR, XRD and vibrating sample magnetometer. Organic-soluble ferromagnetic rod-like and superparamagnetic dot-like nanoparticles with the size ranging from 12 to 25?nm are obtained in a nonpolar solvent by adjusting reaction parameters, such as surfactant concentration and reaction time. Water-soluble nanoparticles can be synthesised when a bipolar solvent is used instead of nonpolar solvent. The results show that Fe(OH)₃ is a promising precursor for the high-temperature decomposition method.     

Synthesis and anti-ultraviolet properties of monodisperse BSA-conjugated zinc oxide nanoparticles

A three-step process was designed to fabricate bovine serum albumin (BSA)-conjugated zinc oxide nanoparticles (BZnOs) by using BSA as the structure directing agent. The morphology and crystal phase of BZnOs were characterized by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The composition and BSA content of BZnOs were measured by Fourier transform infrared spectrograph (FTIR) and thermogravimetry (TG) analysis. The ultraviolet-visible absorption property and ultraviolet blocking effects of BZnOs were also studied. The results indicated that the monodisperse BZnOs with 20.5 ± 3.5 nm in diameter had better anti-ultraviolet activities and exhibited the potential as the sunscreen.     

Nitric oxide donor superparamagnetic iron oxide nanoparticles

This work reports a new strategy for delivering nitric oxide (NO), based on magnetic nanoparticles (MNPs), with great potential for biomedical applications. Water-soluble magnetic nanoparticles were prepared through a co-precipitation method by using ferrous and ferric chlorides in acidic solution, followed by a mercaptosuccinic acid (MSA) coating. The thiolated nanoparticles (SH-NPs) were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The results showed that the SH-NPs have a mean diameter of 10 nm and display superparamagnetic behavior at room temperature. Free thiol groups on the magnetite surface were nitrosated through the addition of an acidified nitrite solution, yielding nitrosated magnetic nanoparticles (SNO-NPs). The amount of NO covalently bound to the nanoparticles surface was evaluated by chemiluminescense. The SNO-NPs spontaneously released NO in aqueous solution at levels required for biomedical applications. This new magnetic NO-delivery vehicle has a great potential to generate desired amounts of NO directed to the target location.     

Seed-mediated synthesis of iron oxide and gold/iron oxide nanoparticles

In this study, we prepared magnetic iron oxide and gold/iron oxide nanoparticles (NPs) and characterized their morphologies and properties by XRD, TEM, EDX, VSM and UV-vis measurements. The magnetite iron oxide NPs of 10 nm were synthesized by coprecipitation of Fe2+ and Fe+3 in the solution of NH4OH and then they were used as seed particles for the subsequent growth to prepare the magnetite NPs of different particle sizes and also to prepare gold/iron oxide composite NPs. All those magnetite NPs are superparamagnetic and the gold/iron oxide composite NPs combine the optical and magnetic properties, which are contributed by gold and iron oxide components, respectively.     

The preparation of iron (III) oxide nanoparticles using W/O microemulsion

Iron (III) oxide, Fe₂O₃, nanoparticles were prepared using W/O microemulsion as the reactor. W/O microemulsion was formed using n-heptane as oil phase, water and AOT as the surfactant under the specific composition. Iron (III) Chloride was used as a starting material and Ammonium hydroxide was a precipitating agent. Fe₂O₃, nanoparticles were then produced in situ the water core. Size of particles could be adjusted by the water content of the mixtures. The higher the water content, the bigger the particle size. The average size of the nanoparticles obtained was smaller than 100 nm. Moreover, Fe₂O₃ produced by this method was hematite with hexagonal in structure.     

Multifunctional iron and iron oxide nanoparticles in silica

Iron and iron oxide nanoparticles in silica layers deposited by sol–gel techniques on Si wafers were formed and studied. It was shown that multifunctional nanoparticles of different iron oxides possessing various physical properties can be fabricated by means of post-growth annealing of (SiO₂:Fe)/SiO₂/Si samples in various atmospheres. The hematite, maghemite, and iron nanoparticles were found to be dominant upon annealing the samples in air, argon, and hydrogen atmosphere, respectively. The physical properties of produced hybrid structures were studied by Raman and FT-IR spectroscopy, spectroscopic ellipsometry, AFM, and magnetic measurements. The sol–gel technique with subsequent annealing procedure is demonstrated to be an effective method for the formation of multifunctional hybrid structures composed of iron or iron oxide nanoparticles in silica matrix.     

A new two-phase system for the preparation of nearly monodisperse silver nanoparticles

Nearly monodisperse silver nanoparticles were prepared in a two-phase water-cyclohexane system. Aqueous silver nitrate was reduced by the product of the reaction of aqueous hydrazine with benzyl aldehyde in cyclohexane to form, in the presence of oleic acid, cyclohexane-soluble silver nanoparticles. The silver nanoparticles were examined by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The nanoparticles are relatively monodisperse (diameter less than 6 nm) and have good stability in cyclohexane due to the oleic acid adsorbed on their surfaces. These silver nanoparticles were successfully assembled into a powder with a face-centered-cubic structure by slow evaporation of the solvent. With some change in particle size, these silver nanoparticles could be transferred from cyclohexane to water by the addition of cetyltrimethylammonium bromide.     

Novel phase-transfer preparation of monodisperse silver and gold nanoparticles at room temperature

In a novel water-cyclohexane two-phase system, the aqueous formaldehyde is transferred to cyclohexane phase via reaction with dodecylamine to form reductive intermediates in cyclohexane; the intermediates are capable of reducing silver or gold ions in aqueous solution to form dodecylamine protected silver and gold nanoparticles in cyclohexane solution at room temperature. The prepared silver and gold nanoparticles are examined by transmission electron microscopy (TEM), UV-Visible spectroscopy (UV-vis), X-photon electron spectroscopy (XPS) and Fourier transfer infrared spectroscopy (FT-IR). It is found that these nanoparticles are monodisperse in size of less than 10 nm and have good stability in cyclohexane due to the adsorbed dodecylamine on nanoparticle surface. Moreover, the synthesis mechanism is revealed via gas chromatography (GC), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR) analyses of the solutions during the preparation process.     

Facile one-pot preparation, surface functionalization, and toxicity assay of APTS-coated iron oxide nanoparticles

We report a facile approach to synthesizing 3-aminopropyltrimethoxysilane (APTS)-coated magnetic iron oxide (Fe(3)O(4)@APTS) nanoparticles (NPs) with tunable surface functional groups for potential biomedical applications. The Fe(3)O(4) NPs with a mean diameter of 6.5?nm were synthesized by a hydrothermal route in the presence of APTS. The formed amine-surfaced Fe(3)O(4)@APTS NPs were further chemically modified with acetic anhydride and succinic anhydride to generate neutral (Fe(3)O(4)@APTS?Ac) and negatively charged (Fe(3)O(4)@APTS?SAH) NPs. These differently functionalized NPs were extensively characterized by x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry analysis, zeta potential measurements, and T(2) relaxometry. The cytotoxicity of the particles was evaluated by in vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric viability assay of cells along with microscopic observation of cell morphology. The hemocompatibility of the particles was assessed by in vitro hemolysis assay. We show that the hydrothermal approach enables an efficient modification of APTS onto the Fe(3)O(4) NP surfaces and the formed NPs with different surface charge polarities are water-dispersible and colloidally stable. The acetylated Fe(3)O(4)@APTS?Ac NPs displayed good biocompatibility and hemocompatibility in the concentration range of 0-100?μg?ml(-1), while the pristine Fe(3)O(4)@APTS and Fe(3)O(4)@APTS?SAH particles started to display slight cytotoxicity at a concentration of 10?μg?ml(-1). The findings from this study suggest that the Fe(3)O(4)@APTS NPs synthesized by the one-pot hydrothermal route can be surface modified for various potential biomedical applications.     

Abrasive properties of aluminum iron oxide nanoparticles

Aluminum iron oxide nanoparticles have been prepared by heat-treating ammonium hydroxycarbonate complexes with the general formula NH₄Al₂Fe(OH)₅(CO₃) · nH₂O and have been characterized by X-ray diffraction, IR spectroscopy, differential thermal analysis, scanning electron microscopy, and particle size analysis. The mixed oxide α-Al_{2 − x} Fe _x O₃ with x = 0.30−0.37 prepared from hydroxy complexes ensures surface roughness values R _a = 0.005−0.02 μm in polishing of the ShKh15 quenched steel with an austenite/martensite structure and offers high abrasion rate owing to its enhanced tribochemical activity and the presence of particles in the size range 1–10 nm.     

Hydrothermal synthesis of surface-modified iron oxide nanoparticles

We synthesized surface-modified iron oxide nanoparticles in aqueous phase by heating an aqueous solution of iron sulfate (FeSO₄) at 473 K with a small amount of either n-decanoic acid (C₉H₁₉COOH) or n-decylamine (C₁₀H₂₁NH₂), which is not miscible with water at room temperature. Transmission electron microscopy showed that the addition of n-decanoic acid or decylamine changed the shape of the obtained nanoparticles. X-ray diffraction spectra revealed that the synthesized nanoparticles were in α-Fe₂O₃ or Fe₃O₄ phase while Fourier transform infrared spectroscopy and thermogravimetry indicated the existence of an organic layer on the surface of the nanoparticles. In the synthetic condition, decreased dielectric constant of water at higher temperature increased the solubility of n-decanoic acid or n-decylamine in water to promote the reaction between the surface of iron oxide nanoparticles and the organic reagents. After the synthesis, the used organic modifiers separated from the aqueous phase at room temperature, which may help the environmentally benign synthesis of surface-modified metal oxide nanoparticles.     

Biological crystallization of self-aligned iron oxide nanoparticles

Crystal growth and magnetic behavior of iron oxide nanoparticles assembled with biomolecules have been investigated. The nanoparticles assembled with trypsin molecules exhibit superparamagnetism at room temperature with blocking temperature ($sim$80 K) significantly lower than those without trypsin ($sim$140 K). This is attributed to reduced magnetostatic couplings between particles due to increased distance between particles separated by trypsin molecules. Moreover, the synthesized nanoparticle–biomolecule assemblies consist of a unique one-dimensional self-assembled arrays of nanoparticles found by structural analysis using transmission electron microscopy. The moirÉ fringes observed from the particle arrays indicate that the particles are aligned with slight misorientation of their crystallographic axes. Such an unusual formation of nanoparticle arrays may be relevant to specific ligand sites in trypsin molecules and the magnetostatic interparticle couplings.     

Template synthesis of highly crystalline and monodisperse iron oxide pigments of nanosize

Synthesis of highly crystalline and monodisperse iron oxide nanoparticles is reported. The separation of Fe centers through site-specific binding to a polysaccharide–alginate matrix enables the generation of particles with a monodisperse or narrow size distribution character, resulting in transparent pigments. Site-specific interactions coupled with gel like character of alginate is proposed as the mechanism behind generation of lower particle sizes. Alginate-Fe complexes developed were subjected to heat treatment to provide for crystalline character and development of hematite (α-Fe₂O₃). Conditions most ideal for achieving monodispersity and lower sizes have been optimized and confirmed through microscopic and photon correlation spectroscopic measurements.     

Ultrasonic-assisted synthesis and magnetic studies of iron oxide/MCM-41 nanocomposite

Iron oxide nanoparticles were stabilized within the pores of mesoporous silica MCM-41 amino-functionalized by a sonochemical method. Formation of iron oxide nanoparticles inside the mesoporous channels of amino-functionalized MCM-41 was realized by wet impregnation using iron nitrate, followed by calcinations at 550 °C in air. The effect of functionalization level on structural and magnetic properties of obtained nanocomposites was studied. The resulting materials were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy and selected area electron diffraction (HRTEM and SAED), vibrating sample and superconducting quantum interface magnetometers (VSM and SQUID) and nitrogen adsorption–desorption isotherms measurements. The HRTEM images reveal that the most of the iron oxide nanoparticles were dispersed inside the mesopores of silica matrix and the pore diameter of the amino-functionalized MCM-41 matrix dictates the particle size of iron oxide nanoparticles. The obtained material possesses mesoporous structure and interesting magnetic properties. Saturation magnetization value of magnetic iron oxide nanopatricles stabilized in MCM-41 amino-functionalized by in situ sonochemical synthesis was 1.84 emu g⁻¹. An important finding is that obtained magnetic nanocomposite materials exhibit enhanced magnetic properties than those of iron oxide/MCM-41 nanocomposite obtained by conventional method. The described method is providing a rather short preparation time and a narrow size distribution of iron oxide nanoparticles.     

Stable water-soluble iron oxide nanoparticles using Tiron

Success in biological and nanomaterial applications that rely on magnetic iron oxide nanoparticles (IONPs) often depends on monodispersity, size, and aqueous stability of the synthesized particles. Here we report a simple and efficient strategy to prepare monodisperse, ultrasmall, water dispersible superparamagnetic IONPs. Monodisperse IONPs are initially synthesized in organic solvents using oleic acid as a dispersant. The subsequent ligand exchange of oleic acid for dopamine and Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) allows for superior colloidal stability in aqueous media. Zeta potential measurements confirm the stability of the nanoparticles upon redispersal in water or biologically relevant buffers. The synthesized particles also preserve their general shape, size, and crystallinity after ligand exchange as evidenced by TEM and SAED measurements. Magnetic properties are also maintained after the ligand exchange as verified by magnetometry and magnetic force microscopy (MFM). An analysis of potential issues regarding this and other prior ligand exchanges is also highlighted, which may aid others in future investigations.     

Synthesis and characterization of multifunctional iron oxide nanoparticles

In order to get high water solubility, monodisperse, superparamagnetic nanoparticles, poly (acrylic acid) was employed to modify Fe3O4 by a high-temperature solution-phase hydrolysis approach. Then, folic acid (FA) and fluorescein isothiocyanate were successively conjugated with prepared magnetic nanoparticles (MNPs). The functional MNPs were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS), transmission electron microscope (TEM), inductively coupled plasma-atomic emission spectrometer (ICP-AES), and vibrating sample magnetometer (VSM), respectively. The toxicity of the materials was evaluated by selecting NIH/3T3 fibroblast cells and no toxic effect was observed. The fluorescent imaging and targeting property of the MNPs were also realized in vitro and in vivo experiments by confocal laser scanning microscopy (CLSM) and Kodak In-Vivo FX Professional Imaging System, respectively. The results indicated that the final products exhibited interesting magnetic, optical and targeting properties for further potential applications in biological and biomedical fields.     

Formation of water-soluble iron oxide nanoparticles derived from iron storage protein

This paper reports novel findings of an investigation of the formation of water-soluble iron oxide nanoparticles from iron-storage protein ferritin. The strategy couples thermal removal of the protein shell on a planar substrate and subsequent sonication in aqueous solution under controlled temperature. Advantages of using ferritin as a precursor include well-defined core size, core composition, water-solubility and processibility. The formation of the nanoparticles was characterized using TEM, UV-Vis and FTIR techniques. Iron oxide nanoparticles in the size range of 5-20 nm diameters were produced. In addition to thermal treatment conditions, the sonication temperature of the nanoparticles in water was found to play an important role in determining the resulting particle size. This simple and effective route has important implications to the design of composite nanoparticles for potential magnetic, catalytic, biomedical sensing and other nanotechnological applications.