Fabrication and characteristic of conductive and ferromagnetic hollow composite microcapsules

The fabrication of conductive and ferromagnetic hollow composite microcapsules with polypyrrole (PPy) shell and Fe₃O₄ inner-wall was successfully accomplished via a sequential processes of electrostatic attraction between negatively charged polystyrene (PS) latex and Fe₃O₄ nanoparticles, the polymerization of pyrrole and the dissolution of PS core. The morphology of the hollow composite microcapsules was testified by TEM and XRD. The hollow microcapsules possessed a conductivity of 10^− 2 S/cm, and their ferromagnetic property was attributed to the presence of magnetic Fe₃O₄ nanoparticles on the inner-wall. The improved thermal stability of the hollow microcapsules could be interpreted due to the interaction between Fe₃O₄ nanoparticles and PPy chains.     

Characterization of interface of Al2O3–304 stainless steel braze joint

Sintered Al₂O₃ is brazed with 304 stainless steel (SS) using 97(Ag28Cu)3Ti active filler alloy at 900 and 1000 °C. The interfaces developed during brazing have been systematically characterized and the results show that the thickness of the interfaces is 15–20 μm and 10–15 μm on SS side and Al₂O₃ side respectively. The presence of TiO, Cu₃Ti₃O and FeTi phases at the Al₂O₃ interface and FeTi, and Fe₃₅Cr₁₃Ni₃Ti₇ phases at the SS interface have been confirmed through XRD and TEM studies. Microhardness analysis across the brazed interfaces suggest that the SS interface (300–600 Hv) is harder than that of the SS substrate (200–250 Hv) whereas alumina interface (550–900 Hv) is softer than that of the alumina substrate (∼ 1900 Hv). It is concluded that the various new phases that are formed during brazing are responsible for the variation in the hardness values.     

Conductive polyaniline capped Fe2O3 composite anode for high rate lithium ion batteries

A composite of Fe₂O₃ capped by conductive polyaniline (PANI) was synthesized by a facile two-step method through combining homogeneous Fe₂O₃ suspension prepared by a hydrothermal method and in-situ polymerization of aniline. As anode material for lithium ion batteries, the Fe₂O₃/PANI composite manifests very large discharge capacities of 1635 mAh g⁻¹, 1480 mAh g⁻¹ at large currents of 1.0 and 2.0 A g⁻¹ (1C and 2C), respectively, as well as good cycling performance and rate capacity. The enhancement of electrochemical performance is attributed to the improved electrical conductivity and effective ion transportation of the composite electrode, in that, PANI keeps the Fe₂O₃ nanorods uniformly connected and offers conductive contact between the electrolyte and the active electrode materials.     

One-step solution auto-combustion process for the rapid synthesis of crystalline phase iron oxide nanoparticles with improved magnetic and photocatalytic properties

We report the solution auto-combustion (AC) process for the rapid synthesis of Fe₃O₄ nanoparticles derived from the sol–gel (SG) process. The citric acid (CA) and tartaric acid (TA) is used as gelling agents in the SG process, where the citric acid turns into a fuel that combusts the gel and yields a highly magnetic crystalline phase Fe₃O₄ nanoparticles in one step with an average particle size of 50 nm. In contrast, the citric acid at different concentrations and tartaric acid at any concentrations do not lead to any combustion process and yield amorphous iron oxides. Upon annealing, these CA and TA derived iron oxide samples are turned to crystalline phase α-Fe₂O₃ particles. In contrast, the as-synthesized AC sample (i.e. Fe₃O₄) is oxidized to γ-Fe₂O₃ phase, which is confirmed from their respective XRD, Rietveld refinement and XPS studies. All the synthesized iron oxide phases showed broad visible light absorption. The room temperature M?H hysteresis curves obtained from VSM revealed that the Fe₃O₄ and α-Fe₂O₃/γ-Fe₂O₃ phases exhibit super-paramagnetic and ferromagnetic properties, respectively. The photocatalytic efficiencies of the samples are found to be in the order of Fe₃O₄ > γ-Fe₂O₃ > α-Fe₂O₃ with 98, 87, 79/73% degradation of rhodamine B dye at the end of 3 h and H₂ evolution rate over these systems is found to be 2.1, 1.3 and 0.92/0.89 mmol/h/g, respectively under simulated solar light irradiation. The photocatalytic recycle studies demonstrated that all the synthesized photocatalysts possess excellent chemical and photo-stabilities.     

Effect of growth temperature on the structural and transport properties of magnetite thin films prepared by pulse laser deposition on single crystal Si substrate

Magnetite (Fe₃O₄) thin films are prepared by pulsed laser deposition using an α-Fe₂O₃ target on silicon (111) substrate in the substrate temperature range of 350 °C to 550 °C. X-ray diffraction (XRD) measurement shows that the film deposited at 450 °C is a single phase Fe₃O₄ film oriented along [111] direction. However, the film grown at 350 °C reveals mixed oxide phases (FeO and Fe₃O₄), while the film deposited at 550 °C is a polycrystalline Fe₃O₄. X-ray photoelectron spectroscopy study confirms the XRD findings. Raman measurements reveal identical spectra for all the films deposited at different substrate temperatures. We observe abrupt increase in the resistivity behavior of all the films around Verwey transition temperature (T_V) (125 K-120 K) though the transition is broader in the film deposited at 350 °C. We observe that the optimized temperature for the growth of Fe₃O₄ film on Si is 450 °C. The electrical transport behavior follows Shklovskii and Efros variable range hopping type conduction mechanism below T_V for the film deposited at 450 °C possibly due to the granular growth of the film.     

Preparation of pH-responsive Fe3O4/Poly (acrylic acid-stat-methyl methacrylate-block-(2-dimethylamino) ethyl methacrylate) magnetic composite microspheres and its application in controlled release of drug

Controlled radical polymerization based on 1, 1-diphenylethylene (DPE method) was used to prepare pH-responsive magnetic composite microspheres. By this method, Fe₃O₄/Poly (acrylic acid-stat-methyl methacrylate-block-(2-dimethylamino) ethyl methacrylate) (Fe₃O₄/P(AA-MMA-DMA)) microspheres were prepared via emulsifier free emulsion polymerization of acrylic acid (AA), methyl methacrylate (MMA) and (2-dimethylamino) ethyl methacrylate (DMA) using 1, 1-diphenylethylene (DPE) as radical control agent in the presence of Fe₃O₄ nanoparticles. The structure and properties of Fe₃O₄/P (AA-MMA-DMA) microspheres were characterized by IR, ¹H NMR, SEC-MALLS, TEM, TGA, VSM and DLS. The application of Fe₃O₄/P (AA-MMA-DMA) microspheres in controlled release of drug was also investigated. It was found that the DPE method allowed the preparation of pH-responsive magnetic composite microspheres, and Fe₃O₄/P (AA-MMA-DMA) microspheres obtained were pH-responsive, perfect sphere-shaped morphologies, superparamagnetism with a saturation magnetization of 14.36 emu/g, and high magnetic content with a value of 29%. Moreover, Fe₃O₄/P (AA-MMA-DMA) microspheres could control the release of phenolphthalein in a buffer solution by adjusting the pH value.     

Self-controlled growth of Fe3BO6 crystallites in shape of nanorods from iron-borate glass of small templates

Fe₃BO₆ can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe₃BO₆ growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B₂O₃ − xFe₂O₃, x = 40–50 mol%. B₂O₃ as a strong glass former co-bridges the Fe³⁺ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe³⁺ species in form of a compound Fe₃BO₆, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B₂O₃ layer (15–25 nm thickness) has grown on the Fe₃BO₆ of the nanorods in situ in a specific structure. XPS bands in the Fe³⁺, B³⁺ and O²⁻ species confer this model structure. A local BO₃ → BO₄ conversion has incurred in the boroxol (B₃O_4.5)_n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm⁻¹.     

Enhanced sunlight-absorption of Fe2O3 covered by PANI for the photodegradation of organic pollutants and antimicrobial inactivation

The current study focused on preparing S-scheme heterojunction Fe₂O₃-PANI nanocomposite and pristine Fe₂O₃ using surfactant-assisted sol–gel and polymerization routes. The structural conformation was assessed through XRD diffractograms that confirmed the Fe₂O₃ phase in both samples. FTIR data traces the metal–oxygen and carbon-related bonds. PL results showed that the recombination rate is retarded in nanocomposite. TEM images confirmed the covering of PANI over Fe₂O₃. EDX mapping showed that Fe, C, N, and O were present in the grown nanocomposite. XPS study revealed the binding energies of constituent atoms. The optical energy bandgap 2.8 and 2.7 eV for Fe₂O₃ and Fe₂O₃-PANI was observed through UV–Vis analysis. The photocatalytic test against methyl blue (MB), eosin yellow (EY), and methyl red (MR) dyes were executed for 50 min under direct sunlight. The Fe₂O₃-PANI showed 99.8, 98.5, and 99.6% degradation efficiency against MB, EY, and MR dyes, respectively, which was higher than Fe₂O₃. The recyclability assessment confirmed the reusability upto four cycles. The antimicrobial property against E. coli, P-aeruginosa, K-pneumoniae, S. aureus, and P. vulgaris bacterial strains revealed a higher response for Fe₂O₃-PANI with the zone of inhibition 30, 31, 31, 30, and 30 nm, respectively. The enhanced performance of Fe₂O₃-PANI is being credited to S-scheme heterostructure supported with PANI, which can hinder the recombination process and support electron/hole separation. The results indicated that the as-grown nanocomposite could be a promising candidate against bacterial disinfection and an excellent stable photocatalyst.     

Chemical and structural properties of the system Fe2O3-In2O3

The system Fe₂O₃-In₂O₃ was studied using X-ray diffraction,⁵⁷Fe Mössbauer spectroscopy and infrared spectroscopy. The samples were prepared by chemical coprecipitation and thermal treatment of the hydroxide coprecipitates. For samples heated at 600 °C, a phase, α- (Fe_1?x In _x )₂O₃, isostructural with α-Fe₂O₃, exists for 0?x?0.8, and a phase C-(Fe_1?x In _x )₂O₃, isostructural with cubic In₂O₃, exists for 0.3?x?/1. In the two-phase region these two phases are poorly crystallized. An amorphous phase is also observed for 0.3?x?0.7. For samples heated at 900 °C the two-phase region is wider and exists for 0.1?x?0.8 with the two phases well crystallized. In these samples an amorphous phase is not observed.⁵⁷Fe Mössbauer spectroscopy of samples prepared at 600 °C indicated a general tendency of the broadening of spectral lines and the decrease of numerical values of the hyperfine magnetic field (HMF) with increasing molar fraction In₂O₃ in the system Fe₂O₃-In₂O₃. The samples prepared at 900 °C, in the two-phase region, are characterized by a constant HMF value of 510 kOe at room temperature. Infrared spectroscopy was also used to follow the changes in the infrared spectra of the system Fe₂O₃-In₂O₃ with gradual increase of molar fraction of In₂O₃. A correlation between X-ray diffraction, Mössbauer spectroscopic and infrared spectroscopic results was obtained.     

Structural characterization and catalytic activities of titania supported iron (III) oxide catalysts: Effect of Li+ impregnation

Pure Fe₂O₃/TiO₂ catalysts (1–35 wt.% Fe₂O₃) and Li-impregnated Fe₂O₃/TiO₂ catalysts (1–10 wt.% Li₂O) were prepared. The structural characteristics of pre-calcined samples were examined by using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and ESR techniques. The surface acidity was measured by the adsorption of n-butylamine in non-aqueous media. The catalytic conversion of 2-propanol at 320–360 °C using the microcatalytic pulse technique was studied.XRD of 650 °C-calcination products showed the existence of pure oxide phases as well as other spinels depending on the chemical composition. ESR spectra indicated the existence of Fe(III) in α-Fe₂O₃ phase and in spinel phase. The chemical composition, surface acidity of the catalyst and reaction temperature affect the catalytic conversion of 2-propanol.     

Highly (100)-oriented Ce1 − xFexO2 − δ solid solution films prepared by laser chemical vapor deposition

Ce_1 − xFe_xO_2 − δ solid solution films were prepared on amorphous silica substrates by laser chemical vapor deposition using metal dipivaloylmethanate precursors and a semiconductor InGaAlAs (808 nm in wavelength) laser. X-ray diffraction revealed the formation of single Ce_1 − xFe_xO_2 − δ phase at x ≤ 0.15, while CeO₂ and Fe₂O₃ phases were found for higher Fe content. Highly (100)-oriented Ce_1 − xFe_xO_2 − δ (x = 0.02) films were obtained at laser power, P_L = 50-200 W and deposition temperature, T_dep = 800-1063 K. Lotgering factor (200) was calculated to be above 0.8 for films prepared at P_L = 50-150 W. X-ray photoelectron spectroscopy revealed the presence of Fe³⁺, Ce⁴⁺ and Ce³⁺ on solid solution films. Cross-sectional transmission electron microscope images disclosed a film columnar feather-like structure with a large number of nano-scale interspaces. Deposition rates were 2 or 3 orders of magnitude higher than those reported for conventional metal organic chemical vapor deposition of CeO₂.     

Physicochemical properties of solid-solid interactions in nanosized NiO-substituted Fe2O3/TiO2 system at 1200 °C

The solid-solid interactions between nanosized pure and NiO-substituted ferric and titanium(IV) oxides have been investigated using XRD technique and microstructure studies, also magnetic properties were studied using vibrating samples magnetometer (VSM). The amounts of substituting Ni²⁺ were x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mole. A mixture equimolar proportions of finely powdered Fe₂O₃ and TiO₂ were mixed with NiO, ball milled, compressed at 250 kg/cm² and fired at 1200 °C for 4 h.The obtained results showed that with substituting Ni²⁺ concentration x = 0 only Fe₂TiO₅ phase is present (∼80 nm) which showed a very small saturation magnetic flux density (B_s), remnant magnetic flux density (B_r) and the maximum energy product (BH)_max. By the addition of x = 0.2 NiO, new phases were observed NiTiO₃ and NiFe₂O₄ of crystallite sizes 160 and 110 nm, respectively. By the increase of substituting Ni²⁺ concentration the NiTiO₃ and NiFe₂O₄ phases increased on the expense of Fe₂TiO₅ up to x = 0.4, then the increase in substituting Ni²⁺ concentration led to a decrease in Fe₂TiO₅ and NiTiO₃ while NiFe₂O₄ increases which results in a great improvement of magnetic properties.All samples exhibit a catalytic activity towards H₂O₂ decomposition and the values of rate constant increase with increasing amount of Ni²⁺ substituting. The most acidic active sites are shown by specimens substituted with x = 0 this concludes that H₂O₂ decomposition is not favored on acidic active sites.     

Growth of nano-particles of Al2O3, AlN and iron oxide with different crystalline phases in a thermal plasma reactor

The paper presents the experimental results showing that the crystalline phase of the nano-particles, synthesized in a DC transferred arc thermal plasma reactor, critically depend on the operating pressure in the reaction zone. The paper reports about the changes in crystalline phases of three different compounds namely: aluminium oxide (Al₂O₃), aluminium nitride (AlN) and iron oxide (Fe_xO_y) synthesized at 760 Torr and 500 Torr of operating pressures. The major outcome of the present work is that the phases having higher defect densities are more probable to form at the sub-atmospheric operating pressures. The variations in the crystalline structures are discussed on the basis of the change in the temperature during the nucleation process, prevailing at the boundary of the plasma, on account of the ambient pressures. The as-synthesized nano-particles were examined by X-ray diffraction analysis and transmission electron microscopy. In addition, the confirmatory analysis of the crystalline phases of iron oxides was carried out with the help of Mössbauer spectroscopy.     

Investigation on the mechanical strength of magnetic hollow silica prepared from Pickering emulsion route

In this paper, a one-pot sol–gel method was used to synthesize magnetic hollow silica through Pickering emulsion route. The mechanical strength of as-prepared magnetic hollow silica was adjusted and investigated. It was found that the emulsion droplet in Pickering emulsion was solely stabilized by cetrltrimethylammionium bromide (CTAB)-modified Fe₃O₄ particles while the silica source originally dispersed in oil phase was hydrolyzed at the emulsion droplet interface. This led to the formation of silica that then coated on the interface of the emulsion droplet to create magnetic hollow silica after being washed and dried. Controlling the hydrolyzing rate and degree of silica source and enhancing the binding force between silica and Fe₃O₄ nano particles can improve the mechanical strength of magnetic hollow silica.     

Synthesis and characterization of Bi2Fe4O9 powders

Bi₂Fe₄O₉ have been successfully prepared using ethylenediaminetetraacetic (EDTA) acid as a chelating agent and ethylene glycol as an esterification agent. Heating of a mixed solution of EDTA, ethylene glycol, and nitrates of iron and bismuth at 140 °C produced a transparent polymeric resin without any precipitation, which after pyrolysis at 250 °C was converted to a powder precursor for Bi₂Fe₄O₉. The precursors were heated at 400–800 °C in air to obtain Bi₂Fe₄O₉ powder and differential scanning calorimetry (DSC), thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques were used to characterize the precursors and the derived oxide powders. XRD analysis showed that well-crystallized and single-phase Bi₂Fe₄O₉ with orthorhombic symmetry was obtained at 700 °C for 2 h and BiFeO₃ and Fe₂O₃/FeCO₃ were intermediate phases before the formation of Bi₂Fe₄O₉. Bi₂Fe₄O₉ powders show weak ferromagnetism at room temperature.     

Spinel Phase Relations in the Fe3O4–CuFe2O4 System

Phase equilibria involving spinel solid solutions, delafossite, and hematite in the Fe–Cu–O system are studied by emf measurements in solid-electrolyte galvanic cells. The results demonstrate that, above 1250 K, Fe₃O₄ and CuFe₂O₄ form a continuous series of solid solutions. At lower temperatures, the solid solution disproportionates with the formation of delafossite and Fe₂O₃, and two spinel solid solutions appear: one based on Fe₃O₄ and the other based on Cu₂FeO₄. The compositions of the spinel phases in equilibrium with delafossite and Fe₂O₃ are determined in the range 1100–1250 K.     

The origin of hematite nanowire growth during the thermal oxidation of iron

The oxidation of Fe in pure oxygen between 400 °C and 600 °C has been investigated in order to obtain insight into the mechanism of the spontaneous formation of α-Fe₂O₃ nanowires. By varying the oxidation temperature, Fe can be oxidized to form Fe₂O₃/Fe₃O₄/FeO/Fe or Fe₂O₃/Fe₃O₄/Fe layered structure, followed by hematite nanowire growth on the outer layer of hematite (Fe₂O₃). It is observed that Fe₂O₃ nanowires have a bicrystal structure and form directly on the top of the underlying Fe₂O₃ grains. It is shown that the compressive stresses generated by the volume change accompanying the Fe₂O₃/Fe₃O₄ interface reaction stimulate Fe₂O₃ nanowire formation and that the Fe₂O₃ nanowire growth is via surface diffusion of Fe cations supplied from the outward grain boundary diffusion through the Fe₂O₃ layer. This principle of nanowire formation may have broader applicability in layered systems, where the stress gradient in thin layers can be introduced via solid-state interfacial reaction or other means.     

Magnetic field induced ferroelectric and dielectric properties in Pb(Zr0.5Ti0.5)O3 films containing Fe3O4 nanoparticles

About 1.05 µm-thick Pb(Zr_0.5Ti_0.5)O₃ (PZT) films containing Fe₃O₄ nanoparticles were deposited on LaNiO₃-coated silicon substrates through a sol-gel technique. Fe₃O₄ nanoparticles were effectively dispersed into PZT solution under the involvement of polyvinylpyrrolidone. X-ray diffraction confirmed the coexistence of PZT and Fe₃O₄ phases without other impurity phases. Scanning electron microscope revealed that the thick composite films possess well-defined and crack-free microstructure. The composite films exhibit good ferroelectric and ferromagnetic properties at room temperature. An obvious magnetodielectric effect has been demonstrated in the Pb(Zr_0.5Ti_0.5)O₃/Fe₃O₄ composite films. Magnetic field induced change in ferroelectric polarization loop may support the possible magnetoelectric coupling between PZT and Fe₃O₄ phases.     

Lubrication mechanisms of C‐MoS2‐Fe2O3 (Fe3O4) nano‐composite lubricants at the rubbing interfaces of non‐copper coated solid wires against the contact tube

Graphite‐MoS₂‐Fe₂O₃ (Fe₃O₄) nano‐composite lubricating coatings were prepared on the surfaces of non‐copper coated solid wires by a mechanical coating technique. The tribological behaviours of graphite‐MoS₂‐Fe₂O₃ (Fe₃O₄) coatings at the rubbing interfaces of welding wires against the contact tube were investigated. The results demonstrate that the lubricating properties of graphite‐Fe₃O₄ coatings outperform the lubricating properties of graphite‐Fe₂O₃ coatings. The anti‐wear performance of the contact tube is strengthened with increasing nano‐MoS₂ contents. Layers of protective tribofilms are formed at the rubbing interfaces of welding wires against a contact tube by tribochemical reaction among lubricants. The tribofilms are composed of FeO, MoO₃ and FeMoO₄ with excellent lubricating properties. They can avoid direct contact of welding wires against the contact tube, thus decreasing contact tube wear. With the transition of the contact tube wear from mild to severe, the dominant wear mechanisms of contact tube change from fatigue peeling and oxidative wear to abrasive wear and arc ablation.     

Physicochemical properties and operational stability of Taguchi design-optimized Candida rugosa lipase supported on biogenic silica/magnetite/graphene oxide for ethyl valerate synthesis

Biobased ternary nanocomposites can stabilize enzymes for greater stability, catalytic activity and easy recovery. This study aimed to optimize biogenic silica/magnetite/graphene oxide nanocomposite supported Candida rugosa lipase (CRL/SiO₂/Fe₃O₄/GO) for ethyl valerate (EV) synthesis and characterize the biocatalysts’ physicochemical properties and operational stability. CRL conjugated-oil palm leaves-derived biogenic SiO₂/Fe₃O₄/GO nanocomposite showed a maximum immobilized protein of 44.13 ± 2.1 mg/g with a specific activity (534.87 ± 9.5 U/mg), than free CRL (≥700 U/mg). GL-A-SiO₂/Fe₃O₄/GO exhibited the highest surface area (260.87 m²/g) alongside superior thermal stability in TGA/DTG. XRD revealed an amorphous SiO₂ (crystallinity = 26.7%), while Fe₃O₄ existed as cubic spinel crystal (crystallinity = 90.2%). Taguchi Design-optimization found that CRL/SiO₂/Fe₃O₄/GO best catalyzed the EV synthesis (90.4% in 3 h) at 40 ℃ using 3 mg/mL of biocatalyst, valeric acid/ethanol molar ratio of 1:2, in 10% (m/v) molecular sieves with stirring in heptane at 200 rpm. EV production was confirmed by FTIR- (C=O: 1738 cm^?1 and C–O–C: 1174 cm^?1) and GC–MS ([M]⁺ m/z = 130, C₇H₁₄O₂). CRL/SiO₂/Fe₃O₄/GO’s reusability for 11 successive esterification cycles demonstrated the SiO₂/Fe₃O₄/GO’s exceptional hyperactivation and stabilization properties on immobilized CRL. These findings conveyed the SiO₂/Fe₃O₄/GO’s efficacy to alter CRL's physicochemical properties and operational stability for catalyzing higher yields EV.