Effect of the reaction parameters on the particle size in the dispersion polymerization of 2‐hydroxyethyl and glycidyl methacrylate in the presence of a ferrofluid

The precipitation of Fe₃O₄ from an aqueous solution with ammonium hydroxide produced nanoparticles that were coated with a layer of oleic acid [or, in some cases, poly(ethylene oxide) or poly(vinylpyrrolidone)] before their dispersion into the organic phase. The encapsulation of magnetite nanoparticles in poly(2‐hydroxyethyl methacrylate) or poly(2‐hydroxyethyl methacrylate‐co‐glycidyl methacrylate) microparticles was achieved by dispersion polymerization in toluene/2‐methylpropan‐1‐ol. Magnetic poly(glycidyl methacrylate) microparticles were obtained in the presence of poly(ethylene oxide) at the magnetite/monomer interface. The particles containing up to 20 wt % iron maintained their discrete nature and did not aggregate. The effect of the reaction medium polarity, the concentrations of the monomer, initiator, and stabilizer, and the temperature on the particle size, particle size distribution, and iron and oxirane group contents was studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1848–1863, 2003     

Preparation of single-phase α-Fe(III) oxide nanoparticles by thermal decomposition. Influence of the precursor on properties

In this research, we present an experimental procedure to prepare single-phase α-Fe(III) oxide nanoparticles by thermal decomposition of five different precursors including: iron(III) citrate; Fe(C₆H₅O₇), iron(III) acetylacetonate; Fe(C₅H₇O₂)₃, and iron(III) oxalate; Fe(C₂O₄)₃, iron(III) acetate; Fe(C₂H₃O₂)₃, and the thermal curves obtained were analyzed. The influence of the thermal decomposition of precursors on the formation α-Fe₂O₃ was studied by differential thermal gravimetry and thermogravimetry. The synthesized powders were characterized by using X-ray diffraction and scanning electron microscopy. High quality iron oxide nanoparticles with narrow size distribution and average particle size between ca. 2 and 30 nm have been obtained. It was found that the iron precursors affect the temperatures of the pure α-Fe₂O₃ nanoparticle formation with different diameters; iron(III) citrate (29 nm), iron(III) acetylacetonate (37 nm), and iron(III) oxalate (24 nm).     

Nanostructured Iron Oxide Platform for Impedimetric Cholesterol Detection

A nanostructured iron oxide (NanoFe₃O₄, particle size ca. 25 nm and roughness ca. 21 nm) film deposited onto a hydrolyzed indium‐tin‐oxide (ITO) coated glass plate has been used to immobilize cholesterol oxidase (ChOx) to fabricate an impedimetric cholesterol sensor. Electrochemical studies reveal that surface charged Fe₃O₄ nanoparticles provide better conformation for ChOx loading resulting in enhanced electron transfer between ChOx and the electrode. Impedimetric response studies of the ChOx/NanoFe₃O₄/ITO bioelectrode exhibit improved linearity (2.5–400 mg/dL), low detection limit (0.25 mg/dL), fast response time (25 s), high sensitivity (86 Ω/mg dL^?1/cm^?2) and a low value of the Michaelis‐Menten constant (K_m, 0.8 mg/dL) with a regression coefficient of 0.997.     

Catalytic conversions of chloroolefins over iron oxide nanoparticles 2. Isomerization of dichlorobutenes over iron oxide nanoparticles stabilized on the surface of ultradispersed poly(tetrafluoroethylene)

Nanosized iron oxides stabilized on the surface of ultradispersed poly(tetrafluoroethylene) (UPTFE) granules were synthesized by the thermal destruction of iron formate in boiling bed of UPTFE on the surface of heated mineral oil. The particle size of nanoparticles (∼6 nm) containing 5, 10, and 16 wt.% Fe depends weakly on the temperature of synthesis and iron to polymer ratio. The metal state is determined by the synthesis conditions. The nanoparticles synthesized at 280 °C consist mainly of the Fe₃O₄ and Fe₂O₃ phases. The samples obtained at 320 °C also contain iron(II) oxide. The catalytic properties of the obtained samples were tested in dichlorobutene isomerization. Unlike isomerization on the iron oxide nanoparticles supported on silica gel, reaction over the UPTFE supports proceeds without an induction period. The sample with 10 wt.% Fe containing magnetically ordered γ-Fe₂O₃ nanoparticles possesses the highest catalytic activity. Fast electron exchange between the iron ions in different oxidation states and high defectiveness of the nanoparticles contribute, most likely, to the catalytic activity. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1383–1390, June, 2005.     

Hydrophilic magnetic polymer latexes. 2. Encapsulation of adsorbed iron oxide nanoparticles

The encapsulation of seed polymer particles coated by anionic iron oxide nanoparticles has been investigated using N-isopropylacrylamide as a main monomer, N,N-methylene bisacrylamide as a crosslinking agent, itaconic acid as a functional monomer and potassium persulfate as an anionic initiator. The magnetic latexes obtained have been characterized with regard to particle size, iron oxide content and electrophoretic mobility. All these properties have been examined by varying several polymerization parameters: reaction medium, monomer(s) and crosslinking agent concentrations, nature of seed latexes and type of polymerization (batch versus shot process). The magnetic content in the polymer microspheres strongly depends on the polymerization procedure (i.e., encapsulation process) and varies between 6 and 23 wt%, and monodisperse magnetic polymer particles were obtained. Received: 28 December 1999 Accepted in revised form: 15 June 1999     

An experimental trial for the determination of the critical coagulation concentration using the sedimentation method

A method for determining the critical coagulation concentration (C _c) from the change in the transmittance of the sol with stand time after adding a coagulating agent is discussed. Potassium nitrate was used as the coagulating agent because the specific adsorption of electrolyte ions on the particle and the hydrolysis of electrolyte ions are negligible. Apparent critical coagulation concentrations,C _c ^a, of iron (III) hydroxide and silver iodide sols were obtained from the transmittance vs. potassium nitrate concentration curves for various stand times. The values ofC _c ^a decreased with increasing stand time. TheC _c ^a value obtained for the shortest stand time was closer toC _c obtained from the initial turbidity change of the sol by applying Rayleigh's law. The Hamaker constant for the particle in water was calculated from theC _c ^a value obtained at the shortest time and the experimentally determined outer Helmholtz plane potential. The calculated Hamaker constants were comparable to the theoretical values for iron (III) hydroxide and silver iodide.     

Synthesis,characterization, and properties of monodispersed magnetite coated multi‐walled carbon nanotube/polypyrrole nanocomposites synthesized by in‐situ chemical oxidative polymerization

This study describes the preparation of a nanocomposites fabricated from monodispersed 4‐nm iron oxide (Fe₃O₄) coated on the surface of carboxylic acid containing multi‐walled carbon nanotube (c‐MWCNT) and polypyrrole (PPy) by in situ chemical oxidative polymerization. High‐resolution transmission electron microscopy images and X‐ray diffraction (XRD) data indicate that the resulting Fe₃O₄ nanoparticles synthesized using the thermal decomposition are close to spherical dots with a particle size about 4 ± 0.2 nm. The resulting nanoparticles were further mixed with c‐MWCNT in an aqueous solution containing with anionic surfactant sodium bis(2‐ethylhexyl) sulfosuccinate to form one‐dimensional Fe₃O₄ coated c‐MWCNT template for further preparation of nanocomposite. Structural and morphological analysis using field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, and XRD showed that the fabricated Fe₃O₄ coated c‐MWCNT/PPy nanocomposites are one‐dimensional core (Fe₃O₄ coated c‐MWCNT)‐shell (PPy) structures. The conductivities of these Fe₃O₄ coated c‐MWCNT/PPy nanocomposites are about four times higher than those of pure PPy matrix. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 727–733, 2008     

Preparation of CuCrO2 nanoparticles with narrow size distribution by sol–gel method

Copper chromium oxide (CuCrO₂) nanoparticles were synthesized by sol–gel method. The effect of annealing temperature, duration of heat treatment and metallic ion concentration in precursor solution on the structural properties of the nanoparticles was investigated. The delafossite structure of CuCrO₂ powder was confirmed by X-ray diffractometer. It was found that the crystallite sizes as well as the size of the nanoparticles increased with annealing temperature and duration of heat treatment but decreased with metallic ion concentration. Nanoparticles’ size was obtained using particle size analyzer. The synthesized CuCrO₂ nanoparticles with 0.7 M metallic ion concentration have the lowest crystallite and particle sizes with a narrow size distribution in the range of 13.5–15.6 nm. In the presence of this metallic ion concentration, we could also produce single crystal CuCrO₂ nanoparticles. Moreover, the CuCrO₂ nanoparticles exhibit a large optical band gap that increases with metallic ion concentration. The optical band gap of the nanoparticles fabricated with 0.7 M metallic ion concentration in precursor solution is about 3.99 eV.     

Influence of Perfluorinated End Groups on the SFRD of [Pt(cod)Me(CnF2n+1)] onto Porous Al2O3 in CO2 under Reductive Conditions

The optimized synthesis of a range of cyclooctadiene‐stabilized Pt complexes that contained different perfluoro‐alkane chains, [Pt(cod)Me(C_nF_2n+1)], is presented. These metal–organic compounds were employed in the so‐called supercritical fluid reactive deposition (SFRD) in CO₂ under reductive conditions to generate metallic nanoparticles on aluminum oxide as a porous support. Thus, Al₂O₃‐supported Pt nanoparticles with a narrow particle‐size distribution were obtained. At a reduction pressure of 15.5 MPa and a temperature of 353 K, particle diameters of d₅₀=2.3–2.8 nm were generated. Decreasing the pressure during the reduction reaction led to slightly larger particles whilst decreasing the amount of organometallic precursor in CO₂ yielded a decrease in the particle size from x₅₀=3.2 nm to 2.6 nm and a particle‐size distribution of 2.2 nm. Furthermore, substitution of the CH₃ end group by the C_nF_2n+1 end groups led to a significant drop in Pt loading of about 50 %. Within the series of perfluorinated end groups that were considered, the Pt complex that contained a branched perfluoro‐isopropyl group showed the most‐interesting results when compared to the control precursor, [Pt(cod)Me₂] ( 1 ).     

Diene‐based polymer nanoparticles: Preparation and direct catalytic latex hydrogenation

The diene‐based polymer nanoparticles represented by poly(butadiene‐co‐acrylonitrile) were prepared in the semibatch emulsion polymerization system using Gemini surfactant (GS) trimethylene‐1,3‐bis(dodecyldimethylammonium bromide) as the emulsifier. The nanoparticles within the range of 17–54 nm were achieved with narrow molecular weight and particle size distributions. A spherical morphology was observed for the produced nanoparticles. The effects of GS concentration on the particle size, molecular weight, polymerization conversion and solid content, and composition of copolymer were investigated. The semibatch process using monomeric and conventional surfactant sodium dodecyl sulfate (SDS) was compared. At the second stage of this study, the prepared unsaturated nanoparticles were employed as the substrates for the latex hydrogenation in the presence of Wilkinson's catalyst, that is, RhCl(P(C₆H₅)₃)₃. The effects of the particle size and catalyst concentration on the latex hydrogenation rate were investigated. The particle size is found to have a significant effect on the reaction rate. When the 17‐nm nanoparticles were used as the substrates, a high conversion of 95 mol % was obtained within 18 h using only 0.1 wt % RhCl(P(C₆H₅)₃)₃. The latex hydrogenation process was completely free of organic solvents. The present synthesis and following “green” hydrogenation process can be extended to latices made from semibatch emulsion containing other diene‐based polymers. This study shows great promise for decreasing the demanded quantity of expensive catalyst and eliminating the organic solvent in the hydrogenation process. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Magnetic poly(N‐propargylacrylamide) microspheres: Preparation by precipitation polymerization and use in model click reactions

Magnetic poly(N‐propargylacrylamide) (PPRAAm) microspheres were prepared by the precipitation polymerization of N‐propargylacrylamide (PRAAm) in a toluene/propan‐2‐ol medium in the presence of magnetic nanoparticles (oleic acid‐coated Fe₃O₄). The effects of several polymerization parameters, including the polarity of the medium, polymerization temperature, the concentration of monomer, and the amount of magnetite (Fe₃O₄) in the polymerization feed, were examined. The microspheres were characterized in terms of their morphology, size, particle‐size distribution, and iron content using transmission and scanning electron microscopies (TEM and SEM) and atomic absorption spectroscopy (AAS). A medium polarity was identified in which magnetic particles with a narrow size distribution were formed. As expected, oleic acid‐coated Fe₃O₄ nanoparticles contributed to the stabilization of the polymerized magnetic microspheres. Alkyne groups in magnetic PPRAAm microspheres were detected by infrared spectroscopy. Magnetic PPRAAm microspheres were successfully used as the anchor to enable a “click” reaction with an azido‐end‐functionalized model peptide (radiolabeled azidopentanoyl‐GGGRGDSGGGY(¹²⁵I)‐NH₂) and 4‐azidophenylalanine using a Cu(I)‐catalyzed 1,3‐dipolar azide‐alkyne cycloaddition reaction in water. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

A molecularly imprinted polymer-coated nanocomposite of magnetic nanoparticles for estrone recognition

In this study, we synthesized Fe₃O₄ magnetic nanoparticles coated estrone-imprinted polymer with controlled size using a semi-covalent imprinting strategy. In this protocol, the estrone-silica monomer complex (EstSi) was synthesized by the reaction 3-(triethoxysilyl)propyl isocyanate with estrone, where the template was linked to the silica coating on the iron oxide core via a thermally reversible bond. The removal of the template by a simple thermal reaction produced specific estrone recognition sites on the surface of silica shell.The resulting estrone-imprinted polymer coating Fe₃O₄ magnetic hybrid nanoparticles exhibit a much higher specific recognition and saturation magnetization. The hybrid nanoparticles have been used for biochemical separation of estrone.     

Magnetic poly(glycidyl methacrylate) microspheres prepared by dispersion polymerization in the presence of electrostatically stabilized ferrofluids

Fine magnetite nanoparticles, both electrostatically stabilized and nonstabilized, were synthesized in situ by precipitation of Fe(II) and Fe(III) salts in alkaline medium. Magnetic poly(glycidyl methacrylate) (PGMA) microspheres with core‐shell structure, where Fe₃O₄ is the magnetic core and PGMA is the shell, were obtained by dispersion polymerization initiated with 2,2′‐azobisisobutyronitrile (AIBN), 4,4′‐azobis(4‐cyanovaleric acid) (ACVA), or ammonium persulfate (APS) in ethanol containing poly(vinylpyrrolidone) or ethylcellulose stabilizer in the presence of iron oxide ferrofluid. The average microsphere size ranged from 100 nm to 2 μm. The effects of the nature of ferrofluid, polymerization temperature, monomer, initiator, and stabilizer concentration on the PGMA particle size and polydispersity were studied. The particles contained 2–24 wt % of iron. AIBN produced larger microspheres than APS or ACVA. Polymers encapsulating electrostatically stabilized iron oxide particles contained lower amounts of oxirane groups compared with those obtained with untreated ferrofluid. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5827–5837, 2004     

Manganese-Zinc Ferrites: Safe and Efficient Nanolabels for Cell Imaging and Tracking In Vivo

Manganese-zinc ferrite nanoparticles were synthesized by using a hydrothermal treatment, coated with silica, and then tested as efficient cellular labels for cell tracking, using magnetic resonance imaging (MRI) in vivo. A toxicity study was performed on rat mesenchymal stem cells and C6 glioblastoma cells. Adverse effects on viability and cell proliferation were observed at the highest concentration (0.55 mM) only; cell viability was not compromised at lower concentrations. Nanoparticle internalization was confirmed by transmission electron microscopy. The particles were found in membranous vesicles inside the cytoplasm. Although the metal content (0.42 pg Fe/cell) was lower compared to commercially available iron oxide nanoparticles, labeled cells reached a comparable relaxation rate R₂, owing to higher nanoparticle relaxivity. Cells from transgenic luciferase-positive rats were used for in vivo experiments. Labeled cells were transplanted into the muscles of non-bioluminescent rats and visualized by MRI. The cells produced a distinct hypointense signal in T₂- or T₂*-weighted MR images in vivo. Cell viability in vivo was verified by bioluminescence.     

Green and one‐pot surface coating of iron oxide magnetic nanoparticles with natural amino acids and biocompatibility investigation

We report the synthesis of iron oxide magnetic nanoparticles (IONPs) coated with various natural amino acids (AAs) using a one‐pot reaction in an aqueous medium. Several AAs, which contained hydrophilic and hydrophobic groups, were selected to study their effects on size, morphology and toxicity of IONPs. Functionalized IONPs were characterized using X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning and transmission electron microscopies. Furthermore, vibrating sample magnetometry analysis shows these nanoparticles have excellent magnetic properties. Cellular toxicity of IONPs was also investigated on HFF2 cell lines. The AA‐coated IONPs are non‐toxic and biocompatible. Natural AA‐coated IONPs show a potential for their development in in vitro and in vivo biomedical fields due to their non‐toxicity, good ζ‐potential and related small size and narrow size distribution.     

Specific peptides as alternative to antibody ligands for biomagnetic separation of Clostridium tyrobutyricum spores

Nowadays, the reference method for the detection of Clostridium tyrobutyricum in milk is the most-probable-number method, a very time-consuming and non-specific method. In this work, the suitability of the use of superparamagnetic beads coated with specific antibodies and peptides for bioseparation and concentration of spores of C. tyrobutyricum has been assessed. Peptide or antibody functionalized nanoparticles were able to specifically bind C. tyrobutyricum spores and concentrate them up to detectable levels. Moreover, several factors, such as particle size (200 nm and 1 μm), particle derivatization (aminated and carboxylated beads), coating method, and type of ligand have been studied in order to establish the most appropriate conditions for spore separation. Results show that concentration of spore is favored by a smaller bead size due to the wider surface of interaction in relation to particle volume. Antibody orientation, related to the binding method, is also critical in spore recovery. However, specific peptides seem to be a better ligand than antibodies, not only due to the higher recovery ratio of spores obtained but also due to the prolonged stability over time, allowing an optimal recovery of spores up to 3 weeks after bead coating. These results demonstrate that specific peptides bound to magnetic nanoparticles can be used instead of traditional antibodies to specifically bind C. tyrobutyricum spores being a potential basis for a rapid method to detect this bacterial target.     

Chitosan-mediated synthesis of mesoporous α-Fe2O3 nanoparticles and their applications in catalyzing selective oxidation of cyclohexane

This paper reports the chitosan-mediated synthesis of porous hematite nanoparticles with FeCl₃ as the precursor via a hydrothermal approach at 160 °C. A series of porous chitosan/iron oxide hybrid nanoparticles were obtained via changing the ratio of chitosan to FeCl₃, FeCl₃ concentration and pH value of the reaction solution, and producing porous iron oxide nanoparticles after calcination. The as-prepared samples were characterized by means of X-ray diffraction, transmission electron microscopy, thermal gravimetric analysis, Fourier transform infrared, and N₂ sorption. The particle sizes of these metal oxides were less than 100 nm, and the pore sizes were in the range of 2–16 nm. It was demonstrated that chitosan played a key role in the formation of the porous structures. The resultant α-Fe₂O₃ nanoparticles were used as the support to immobilize Au or Pd nanoparticles, producing Au/α-Fe₂O₃ or Pd/α-Fe₂O₃ nanoparticles. The as-prepared α-Fe₂O₃ nanocatalyst exhibited high selectivity towards cyclohexanone and cyclohexanol for catalyzing cyclohexane oxidation with O₂ at 150°C.     

Surfactant-assisted low-temperature thermal decomposition route to spherical NiO nanoparticles

Thermal decomposition has been employed to access spherical nickel oxide (NiO) nanoparticles from a new precursor, nickel-salicylate, [Ni(C₇H₅O₃)₂(H₂O)₄]. Surfactants, triphenylphosphine ((C₆H₅)₃P), and oleylamine (C₁₈H₃₅NH₂) were added to control the particle size. The products were characterized by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and thermogravimetric analysis. TEM images showed particles nearly spherical having sizes 5–15?nm. The magnetism of NiO nanoparticles was studied with a vibrating sample magnetometer. Due to smaller particle size and increased surface uncompensated spins, a superparamagnetic behavior is observed. The synthetic process is simple and affords high-purity material at a relatively lower calcination temperature.     

Control of structure and particle size of iron oxide on carrier oxide by the sol-gel method using organic polydentate ligands

It was tried to control the structure and particle size of iron oxide supported on a carrier by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands. The iron oxide/carrier composites were prepared by calcining carrier oxides impregnated with organic ligands and Fe(NO₃)₃·9H₂O. When ligands were diacetone alcohol and ethanol, the structure of the iron oxide was exclusively corundum. But, with ligands such as ethylene glycol, citric acid and galacturonic acid, the structure of the iron oxide changed from corundum to spinel as the amount of ligands used increased. With both series of ring and straight chain saccharides, size of the iron oxide particles changed depending on saccharides used. It was thus concluded that the structure and particle size of iron oxide supported on a carrier can be regulated by using organic polydentate ligands.     

Mechanism of Iron Oxide Formation from Iron Pentacarbonyl‐Doped Low‐Pressure Hydrogen/Oxygen Flames

A chemical reaction mechanism was developed for the formation of iron oxide (Fe₂O₃) from iron pentacarbonyl (Fe(CO)₅) in a low‐pressure hydrogen–oxygen flame reactor. In this paper, we describe an extensive approach for the flame‐precursor chemistry and the development of a novel model for the formation of Fe₂O₃ from the gas phase. The detailed reaction mechanism is reduced for the implementation in two‐dimensional, reacting flow simulations. The comprehensive simulation approach is completed by a model for the formation and growth of the iron oxide nanoparticles. The exhaustive and compact reaction mechanism is validated using experimental data from iron‐atom laser‐induced fluorescence imaging. The particle formation and growth model are verified with new measurements from particle mass spectrometry.