Efficient visible light magnetic modified iron oxide photocatalysts

Magnetite iron oxide (Fe₃O₄) nanoparticles were synthesized via simple co-precipitation method using ferrous and ferric ions salts. Fe₃O₄ nanoparticles were modified by silica and titania. Pure and modified nanoparticles were employed for dye degradation under visible light. X-ray diffraction analysis indicated inverse spinel structure of Fe₃O₄ nanoparticles. The particle size of magnetite nanoparticles is decreased due to coating of silica and titania. Scanning and transmission electron microscopy indicated the spherical morphology for all samples. The synthesized Fe₃O₄ nanoparticles were ferromagnetic in nature with highest saturation magnetization value of 1.1034 emu as compared to silica and titania coated samples. Fourier transform infra-red spectra confirmed the incorporation of magnetite nanoparticles with silica and titania. Titania modified magnetite sample showed the highest photocatalytic activity as compared to silica modified magnetite nanoparticles and bare iron oxide under visible light irradiations.     

Synthesis and encapsulation of magnetite nanoparticles in PLGA: effect of amount of PLGA on characteristics of encapsulated nanoparticles

Oleic acid-coated superparamagnetic iron oxide nanoparticles (Fe₃O₄) encapsulated within poly(d,l-lactide-co-glycolide) (PLGA) particles were prepared by the w/o/w emulsion technique using poly(vinyl alcohol) as a dispersant. The concentration of PLGA in the oil phase was varied (5, 15, 30, 45, and 60?mg/ml) at constant magnetite concentration in the oil phase (5?mg/ml) to study the properties of composite Fe₃O₄–PLGA nanoparticles. Even though PLGA concentration varied widely in the oil phase, the weight percent of 7–16?nm diameter magnetite in the particles varied only from 56 to 62?% (23–28?vol.%). The obtained composite nanoparticles were essentially spherical with magnetite spatially uniformly dispersed in individual PLGA particles, as measured by transmission electron microscopy (TEM). Also, the magnetite concentration in each particle did not vary widely as determined qualitatively via microscopy. Hydrodynamic diameters of the composite nanoparticles as measured by dynamic light scattering increased by approximately 10?% with added magnetite, with a smaller relative increase in diameter measured by TEM. The zeta potential of the particles was about ?26?mV, independent of Fe₃O₄ loading. Relatively high saturation magnetizations (36–45?emu/g) were measured for these highly loaded particles, with the latter value only 7?emu/g lower than the value measured for the oleic acid-coated particles alone.     

Adsorption of Biomineralization Protein Mms6 on Magnetite (Fe3O4) Nanoparticles

Biomineralization is an elaborate process that controls the deposition of inorganic materials in living organisms with the aid of associated proteins. Magnetotactic bacteria mineralize magnetite (Fe₃O₄) nanoparticles with finely tuned morphologies in their cells. Mms6, a magnetosome membrane specific (Mms) protein isolated from the surfaces of bacterial magnetite nanoparticles, plays an important role in regulating the magnetite crystal morphology. Although the binding ability of Mms6 to magnetite nanoparticles has been speculated, the interactions between Mms6 and magnetite crystals have not been elucidated thus far. Here, we show a direct adsorption ability of Mms6 on magnetite nanoparticles in vitro. An adsorption isotherm indicates that Mms6 has a high adsorption affinity (Kd = 9.52 µM) to magnetite nanoparticles. In addition, Mms6 also demonstrated adsorption on other inorganic nanoparticles such as titanium oxide, zinc oxide, and hydroxyapatite. Therefore, Mms6 can potentially be utilized for the bioconjugation of functional proteins to inorganic material surfaces to modulate inorganic nanoparticles for biomedical and medicinal applications.     

Formation and characterization of iron oxide nanoparticles loaded on self-organized TiO2 nanotubes

The iron oxide nanoparticles were loaded onto self-organized TiO₂ nanotube layers grown by anodization of Ti in fluoride containing electrolytes. The nanoparticles were obtained by electrodepositing method in glycerol/water/FeCl₃·6H₂O electrolytes at room temperature. The X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) measurements showed that the nanoparticles consisted of iron nanocrystalline (Fe) and magnetite (Fe₃O₄). The hematite (α-Fe₂O₃) structure was obtained by annealing in air at 450 °C. The growth mechanism of the nanoparticles and their morphology were also described. Furthermore, the nanoparticles exhibited good ferromagnetic properties at room temperature.     

In Situ Mineralization of Magnetite Nanoparticles in Chitosan Hydrogel

Based on chelation effect between iron ions and amino groups of chitosan, in situ mineralization of magnetite nanoparticles in chitosan hydrogel under ambient conditions was proposed. The chelation effect between iron ions and amino groups in CS–Fe complex, which led to that chitosan hydrogel exerted a crucial control on the magnetite mineralization, was proved by X-ray photoelectron spectrum. The composition, morphology and size of the mineralized magnetite nanoparticles were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and thermal gravity. The mineralized nanoparticles were nonstoichiometric magnetite with a unit formula of Fe_2.85O₄ and coated by a thin layer of chitosan. The mineralized magnetite nanoparticles with mean diameter of 13 nm dispersed in chitosan hydrogel uniformly. Magnetization measurement indicated that superparamagnetism behavior was exhibited. These magnetite nanoparticles mineralized in chitosan hydrogel have potential applications in the field of biotechnology. Moreover, this method can also be used to synthesize other kinds of inorganic nanoparticles, such as ZnO, Fe₂O₃ and hydroxyapatite.     

Synthesis and characterization of a magnetic hybrid material consisting of iron oxide in a carboxymethyl cellulose matrix

A magnetic hybrid material (MHM), consisting of iron‐oxide nanoparticles (?4 nm) embedded in sodium carboxymethyl cellulose (Na‐CMC) matrix was synthesized. The MHM synthesis process was performed in two stages. First, a precursor hybrid material (Fe(II)‐CMC) was synthesized from two aqueous solutions: Na‐CMC solution and FeCl₂ solution. In the second stage, the precursor hybrid material was treated with H₂O₂ under alkaline conditions to obtain the MHM. The results obtained from X‐ray diffraction show that the crystalline structure of iron oxide into MHM corresponds to maghemite or magnetite phase. Conversely, the results obtained from Fourier transform infrared (FTIR) spectroscopy reveal that the polymeric matrix (Na‐CMC) preserves its chemical structure into the MHM. Furthermore, in FTIR spectra are identified two characteristic bands at 570 and 477 cm^?1 which can be associated to maghemite phase. Images obtained by high resolution transmission electron microscopy and bright field scanning transmission electron microscope show that iron‐oxide nanoparticles are embedded in the Na‐CMC. Magnetic properties were measured at room and low temperature using a quantum design MPMS SQUID‐VSM magnetometer. Diagrams of magnetization versus temperature show that iron‐oxide nanoparticles embedded in Na‐CMC have a superparamagnetic‐like behavior. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A Novel Method for Measuring Active Sites of Fe3O4 for WGS Reaction

Phase transformation among iron oxides was investigated. Pure magnetite material was obtained by reducing iron oxide with diluted hydrogen in a narrow temperature window and with steam to prevent over-reduction. A pulse chromatographic method with N₂O decomposition over magnetite surface to determine active sites of iron oxide based catalysts for water gas shift reaction has been developed. N₂O decomposes over activated Fe₃O₄ surface to N₂ and leaves oxygen species at oxygen vacancy on the catalyst surface, which is the same site for water gas shift reaction. Lower temperature for N₂O decomposition is required to avoid magnetite bulk oxidation. An oxygen coverage on the active sites θ = 1 corresponded to a surface stoichiometry of N₂O/Fe²⁺ = 0.5 was estimated. A linear correlation between water gas shift reaction rate and the quantity of decomposed N₂O over the corresponded catalysts was observed.     

Modification of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes by magnetite nanoparticles

The magnetite nanoparticles and nanocomposite “Nanotube of hydrosilicate Mg—magnetite nanoparticles—Mg-ChR-NT/Fe₃O₄-NP” were obtained by coprecipitation. The composition of the synthesized samples has been established by X-ray diffraction. Using transmission electron microscopy, the presence of magnetite nanoparticles has been detected both inside the NTs and at the external surface of the NT walls. The specific surface of the NTs, nanoparticles, and composite is determined.     

The anodic oxide film on iron in neutral solution

The composition of the anodic passive oxide film on iron in neutral solution has been investigated by cathodic reduction, chemical analysis and ellipsometry. The cathodic reduction using a borate solution of pH 6·35 containing arsenic trioxide as inhibitor estimates iron in the film to be all iron (III), indicating that no magnetite layer is present. Oxygen in the film is estimated from the ellipsometric thickness to be in excess of the stoichiometric ferric oxide, suggesting the presence of bound water. The average composition is represented as Fe₂O₃.0·4H₂O, in which hydrogen may be replaced partly with iron-ion vacancy. The anodic oxide film is composed of an inner anhydrous ferric oxide layer, which thickens with the potential and an outer layer of hydrous ferric oxide whose thickness depends on the condition of passivation and environment.     

Mössbauer analysis of iron phases in brown coal ash and fireside deposits

The iron phases present in an electrostatic precipitator ash, an uncooled ash deposit and a cooled superheater ash deposit from Hazelwood Power Station, Australia, burning Morwell brown coal has been examined using Mössbauer spectroscopy. The principal iron phase in the precipitator ash and the uncooled ash deposit from a hot gas offtake was calcium aluminoferrite (Ca₂Fe_{2 ? x}Al_xO₅). Minor amounts of hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) were also detected in the precipitator ash. The cooled superheater ash deposit contained a (Mg, Fe, Al) oxide spinel as the primary iron phase; small quantities of hematite were also detected in this deposit close to the heat exchanger interface. The formation of these iron phases has been rationalized on the basis of the average composition of coal delivered to the power station and supplementary ash chemistry data obtained from other techniques. The evidence suggests that the calcium aluminoferrite in the precipitator ash is derived from inorganic constituents (distributed throughout the coal organic matrix) and the hematite and magnetite are of mineral origin (discrete particles).     

Using a bifunctional polymer for the functionalization of Fe3O4 nanoparticles

A bifunctional maleimido-tetra(ethylene glycol)-poly(glycerol monoacrylate) (MAL-TEG-PGA) polymer was synthesized and used as a linker to couple functional biomolecules to iron oxide nanoparticles. The cell-penetrating peptide Tat was chosen as a model ligand and successfully conjugated to the surface of Fe₃O₄ nanoparticles using MAL-TEG-PGA. The Tat-conjugated Fe₃O₄ nanoparticles can be prepared simply by applying the linker to the iron oxide nanoparticles and then coupling the Tat peptide to the maleimide terminus or by coating the nanoparticles with a pre-coupled linker. Cell-uptake studies demonstrated that the Tat peptide was an efficient functional biomolecule to translocate iron oxide nanoparticles into the cell nucleus. Tat-conjugated nanoparticles thus prepared may be useful for drug or gene delivery.     

Low-temperature sol–gel synthesis of magnetite superparamagnetic nanoparticles: Influence of heat treatment and citrate–nitrate equivalence ratio

Spinel ferrite nanoparticles are a remarkably versatile group of metal oxides with unique magnetic and electronic properties, making them promising candidates for certain electronic, biomedical, and environmental applications. Magnetite nanoparticles are obtained using complex synthesis methodologies that require inert atmospheres, additives to induce pH changes, expensive or toxic reagents, or complex equipment. In this work, a new approach to obtain superparamagnetic magnetite nanoparticles using citrate–nitrate sol–gel synthesis followed by heat treatment is presented. Iron nitrate and citric acid were added in different equivalence ratios (χ) (citrate/nitrate = 0.30, 0.85, and 1.40). The thermal behaviour of the xerogels was evaluated using thermal analysis techniques, and the results indicated that decreasing the equivalence ratio decreased the temperature required for magnetite formation, and the different release rates of reducing gases influenced the properties of the final material formed. The heat-treatment temperatures for the synthesis with the optimal χ were 130, 150, and 170 °C for 2, 4, and 8 h. Each condition was characterised in terms of the structure and magnetic properties of the product. The results showed that the prepared iron oxide nanoparticles were in the magnetite phase (Fe₃O₄) and possessed a crystallite size of 4.5–6.0 nm and average particle size of <10 nm. The magnetite nanoparticles displayed superparamagnetic behaviour, with a saturation magnetisation of up to 26.24 emu/g and remanent magnetisation of almost zero. Therefore, these superparamagnetic magnetite nanoparticles have excellent potential for biomedical and environmental applications.     

Residual oil cracking combined with hydrogen production by steam-iron reaction

A new residual oil upgrading process has been developed. Residual oils were cracked over an iron oxide catalyst with simultaneous generation of hydrogen. The newly-developed iron oxide catalyst containing CaO and Cr₂O₃ was found to be a good catalyst for this process because it exhibited stable activity in the steam-iron reaction in the laboratory experiment and also in a large scale pilot plant. Effects of these foreign oxides on redox cycles were investigated. The catalyst was designed so as to maintain the stoichiometric balance between the reduction of magnetite and the oxidation of wustite by adding CaO and Cr₂O₃.     

Contributions of TMAH Surfactant on Hierarchical Structures of PVA/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–TMAH Ferrogels by Using SAXS Instrument

The magnetic hydrogels combining polyvinyl-alcohol (PVA) and Fe₃O₄ (magnetite)–TMAH (tetra-methyl ammonium hydroxide) have been successfully fabricated via a Freezing-thawing route. The magnetite nanoparticles were prepared from iron sands by using coprecipitation method. The transmission electron microscopy image revealed that the magnetite nanoparticles with a reaction temperature of 30 °C had the average particle size of 12 nm in clusters of aggregation. The result was similar to the particle size obtained from X-ray diffraction data analyzed by Scherer equation. Furthermore, synchrotron small angle X-ray scattering data were analyzed by using two lognormal distributions to calculate the distribution of the individual magnetite particles. Meanwhile, Teubner-Strey and Beaucage models were employed to observe the distribution of magnetite particles coated by TMAH as a surfactant. The data analysis showed that the magnetite particles within the magnetic hydrogels formed aggregations with diameters of cluster particles in the range from 13.1 to 31.8 nm. Interestingly, the diameter of clusters particle increased from 13.1 to 31.8 nm along with the increasing concentration of ferrofluids from 1 to 15 wt%. This phenomenon was predicted to result from the effect of TMAH as a surface reactant agent that prevented the aggregation by coating the surface of the magnetite nanoparticles.     

Pullulan: A versatile coating agent for superparamagnetic iron oxide nanoparticles

Ultrasmall superparamagnetic iron oxide (Fe₃O₄) nanoparticles coated by biocompatible pullulan (Pu‐USPIO) with sizes below 10 nm and having a magnetite core and a hydrophilic outer shell of pullulan were prepared. The formed Pu‐USPIOs were thoroughly characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, atomic force microscopy, and small‐angle X‐ray scattering experiments. The content of magnetic nanoparticles embedded into the pullulan matrix was determined by thermogravimetric analysis. Vibrating sample magnetometry analysis was used to evaluate the magnetic properties of the Pu‐USPIO samples. Because of the presence of pullulan, these nanoparticles could be conditioned in many versatile forms, from a clear solution to magnetic films, for potential applications, including magnetic hyperthermia mediators. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42926.     

Permalloy/alumina soft magnetic composite compacts obtained by reaction of Al-permalloy with Fe2O3 nanoparticles upon spark plasma sintering

Composite sintered soft magnetic materials of permalloy/alumina type have been obtained by reactive spark plasma sintering. The composite compacts have been obtained by sintering of Ni71.25Fe23.75Al5 alloy with 3 and 5% (wt.) Fe₂O₃ nanoparticles. The Ni based alloy with large particles (up to hundreds of μm) have been covered by a thin layer of iron ferric oxide nanoparticles (20–40 nm). The as obtained composite particles have been subjected to sintering process using a homemade installation at 900 °C for 10 min. Upon sintering process several reactions between Ni-based alloy and iron oxide are induced, the main phase resulting from reaction is alumina-Al₂O₃ as it results by X-ray diffraction investigations. According to the scanning electron microscopy and energy dispersive X-ray spectroscopy investigations, alumina forms a matrix embedding the Ni-based particles. The alumina matrix is continuous, but the layer has large variation in width, and offers a high electrical resistivity. A mechanism of formation is proposed for the alumina matrix composite compacts when using Al-permalloy powder and iron oxide. The compacts have been tested in DC and AC for magnetic characteristics.     

Functional acrylic acid as stabilizer for synthesis of smart hydrogel particles containing a magnetic Fe3O4 core

This paper reports a novel method to synthesize magnetic, stimuli-sensitive latex nanoparticles made with magnetite/poly(N-isopropylacrylamide-co-acrylic acid) (Fe₃O₄/P(NIPAAm-co-AAc)). To form a stabilized suspended core, iron oxide (Fe₃O₄) was functionalized with AAc such that further polymerization with NIPAAm and AAc monomers could occur. The P(NIPAAm-co-AAc) shell layer exhibited thermosensitive properties. The inclusion of Fe₃O₄ into the latex nanoparticles was confirmed using transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, thermogravimetric analyzer (TGA), and superconducting quantum interference device magnetometer. The NIP–(AAc2.6–Fe) latex nanoparticles contained 2.25% Fe₃O₄ (by weight), as determined by TGA analysis. The particle diameters measured approximately 160–240 nm with a lower critical solution temperature of 35 °C. These novel magnetic stimuli-responsive latex nanoparticles have potential applications in numerous fields, such as catalyst supports, protein immobilization, cancer therapy, target drug delivery systems, and other biomedical applications.     

Cytotoxic effect of functionalized superparamagnetic samarium doped iron oxide nanoparticles for hyperthermia application

Magnetic Fluid Hyperthermia (MFH) is an emerging and safe technique for cancer treatment. Radiotherapy and Chemotherapy are widely adopted techniques for treating cancer but cause damage to the nearby healthy tissue. This paves the way for hyperthermia treatment for cancer. Since healthy cells are more heat-tolerant than malignant cells, magnetic nanoparticles with superparamagnetic properties were used in hyperthermia treatment. Surface modified magnetite (Fe₃O₄) iron oxide nanoparticles with enhanced stability, solubility, bio-compatibility and magnetic property were employed in hyperthermia treatment. In the present study, Superparamagnetic Samarium doped magnetite (Fe₃O₄:Sm) nanoparticles were functionalized with Oleylamine (OAm) and polyvinyl alcohol (PVA) by the sol-gel process. The obtained nanoparticles were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Transmission Electron Microscopy (TEM), and UV–Visible diffuse reflectance spectroscopy (UV-DRS), Thermogravimetric analysis (TGA) and Vibrating Sample Magnetometer (VSM). From XRD data, the crystallite size of oleylamine coated samarium doped magnetite (OAm–Fe₃O₄:Sm) and PVA-coated samarium doped Fe₃O₄ (PVA- Fe₃O₄:Sm) were found to be 9.5 nm and 10.9 nm, respectively. TEM images of the functionalized nanoparticles were visualized as a spherical structure with reduced agglomeration. UV-DRS gives the bandgap value of OAm–Fe₃O₄:Sm and PVA- Fe₃O₄:Sm coated samarium doped magnetite to be 2.3 eV and 2 eV respectively. VSM measurement of OAm-Fe₃O₄:Sm and PVA- Fe₃O₄:Sm coated, showed superparamagnetic behaviour. The cytotoxicity study on the L929 cell line shows that both oleylamine and PVA-coated samarium doped magnetite were less toxic and biocompatible compared to the uncoated Fe₃O₄:Sm. The hyperthermia study reveals a rise in temperature within a few seconds with a high Specific Absorption Rate (SAR) value, confirming that the functionalized Samarium doped Fe₃O₄ was an effective nanomaterial for hyperthermia application.     

Adsorption and oxidation of PCP on the surface of magnetite: Kinetic experiments and spectroscopic investigations

The oxidation of pentachlorophenol (PCP) on the surface of magnetite used as heterogeneous catalyst has been investigated under various experimental conditions (initial substrate concentration, H₂O₂ dose, solid loading and temperature) at neutral pH and correlated with the adsorption behavior. The surface reactivity of magnetite was evaluated by conducting the kinetic study of both H₂O₂ decomposition and PCP oxidation experiments. The occurrence of the optimum values of H₂O₂ and magnetite concentrations for the effective degradation of PCP could be explained by the scavenging reactions with H₂O₂ or iron oxide surface. The surface interactions with PCP in the absence and the presence of oxidant can be well described by Langmuir and Langmuir–Hinshelwood models, respectively. All batch experiments indicate that Fenton-like oxidation of PCP was controlled by surface mechanism reaction and the species compete with each other for adsorption on a fixed number of surface active sites. The apparent degradation rate was dominated by the rate of intrinsic chemical reactions on the oxide surface rather than the rate of mass transfer. Raman analysis suggested that the sorbed PCP was removed form magnetite surface at the first stage of oxidation reaction. The mineralization determined by TOC abatement was completed after 7 d, while total dechlorination was achieved at 4 d treatment time. The first reaction of PCP oxidation should be the dechlorination since 90% of chloride was formed at the first 30 h corresponding to the total disappearance of parent compound. All X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and chemical analyses showed that the magnetite catalyst exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle.     

Chemical and Textural Characterization of Iron Oxide Nanoparticles and Their Effect on the Thermal Decomposition of Ammonium Perchlorate

Metal oxide nanoparticles have been used as burning rate catalysts for ammonium perchlorate (AP) decomposition in composite solid propellants. Though most papers point to the efficiency of different sizes, shapes and compositions, the texture of the agglomerated particles plays an important role in the catalytic efficiency, but this aspect is not always discussed. In this paper, iron oxide and composite iron oxide/silica powders were synthesized in microemulsion systems and their effect on the decomposition of AP was investigated. X‐ray diffraction (XRD) analysis and Fourier transformed infrared spectroscopy (FT‐IR) showed that the synthesized powders have an amorphous to nanocrystalline pattern, with Fe₂O₃ composition. The use of different FT‐IR spectroscopic techniques – transmission, diffuse reflectance (DRIFT) and universal attenuated total reflectance (UATR) – allied to electron microscopy analysis allowed the characterization of the samples’ surface, indicating that silicon oxide forms a thick matrix that covers the iron oxide nanoparticles. Adsorption of N₂, light scattering and electron microscopy pointed that all samples are formed by mesoporous agglomerated nanoparticles containing micropores indicating that silicon oxide forms a thick matrix that covers the iron oxide nanoparticles. Adsorption of N₂, pointed that all samples show different microstructures and light scattering indicated results refer to agglomerated particles. Finally, the catalytic effect of the samples on the decomposition of AP was evaluated by thermogravimetric analysis coupled to differential thermal analysis (TG/DTA), showing that only the high temperature decomposition step of AP was affected by the catalyst, shifting to lower temperatures the higher the surface area of the synthesized iron oxide sample, regardless of the presence of the silica matrix.