One-pot polyelectrolyte assisted hydrothermal synthesis of TiO2-reduced graphene oxide nanocomposite

We demonstrated a facile and efficient strategy for the fabrication of poly(diallyldimethylammonium chloride) (PDDA)-assisted reduced graphene oxide (RGO) sheets–titanium dioxide (TiO₂) in the absence of any seeds and surfactants. PDDA is used as both a reducing agent and a stabilizer to prepare the colloidal suspension of graphene nanosheets. The incorporation of PDDA successfully turns graphene nanosheets into general platforms for in situ growth of TiO₂. The prepared TiO₂–RGO has been thoroughly characterized by spectroscopic (Fourier-transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy) and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy, atomic force microscopy and transmission electron microscopy) have been employed to probe the morphological structures as well as to investigate the exfoliation of RGO sheets. It is interesting to see that the TiO₂–RGO composites exhibited excellent photocatalytic activity to hydrogen evolution.     

Hydrothermal synthesis of magnetic reduced graphene oxide sheets

We demonstrated an environmental friendly and efficient route for preparation of magnetic reduced graphene oxide composite (MN-CCG). Glucose was used as the reducing agent in this one-step hydrothermal method. The reducing process was accompanied by generation of magnetic nanoparticles. The structure and composition of the nanocomposite was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, thermal gravimetric analysis, atomic force microscopy and transmission electron microscopy. It was found that the prepared MN-CCG is highly water suspendable and sensitive to magnetic field.     

Formation, characterization and magnetic properties of carbon-encapsulated iron carbide nanoparticles

Fe₃C nanoparticles encapsulated in carbon shell with a size range of 20–50 nm were obtained in large scale by reacting anhydrous FeCl₃, hexamethylenetetramine and metal Na in an autoclave at 650 °C. Magnetization measurements show that the as-obtained materials display superparamagnetic properties at room temperature. A possible formation mechanism of the core–shell nano-structures was discussed.     

The enhanced coercivity for the magnetite/silica nanocomposite at room temperature

Magnetite/silica nanocomposite was synthesized by a facile solvothermal processing at 150 °C for about 10 h. X-ray diffraction (XRD) analysis revealed the effect of annealing on the crystallinity of silica. Transmission electron microscopy (TEM) images showed the good dispersion of magnetite in the silica matrix. Magnetic properties of the nanocomposite were characterized by vibration sample magnetometer (VSM), and the enhanced coercivity was explained by the intrinsic anisotropy of the particles enhanced by the interparticle dipolar fields.     

Synthesis,characterization and catalytic activity studies of Pd-based supported nanoparticle catalyst anchoring on poly(N-vinyl-2-pyrrolidone) modified CMK-3

Pd nanoparticle-poly(N-vinyl-2-pyrrolidone)/CMK-3 (Pd-PVP/CMK-3) composite was prepared by in situ polymerization method which was effectively employed as a novel heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction. The physical and chemical properties of Pd nanoparticle-PVP/CMK-3 were investigated using FT-IR, XRD, BET, UV–vis, TEM and TGA techniques. The reaction was carried out between aryl halides and phenylboronic acid in the presence of water at room temperature. The stability of the catalyst was good and could be reused 10 times without much loss of activity in Suzuki–Miyaura reaction.     

Synthesis of mesoporous silica materials (MCM-41) from iron ore tailings

Highly ordered mesoporous materials were successfully synthesized by using the iron ore tailings as the silica source and n-hexadecyltrimethyl ammonium bromide as the template. The samples were detail characterized by powder X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and N₂ physisorption. The as-synthesized materials had high surface area of 527 m² g⁻¹ and the mean pore diameter of 2.65 nm with a well-ordered two-dimensional hexagonal structure. It is feasible to prepare mesoporous MCM-41 materials using the iron ore tailings as precursor.     

Microwave-hydrothermal synthesis of γ-Fe2O3 nanoparticles and their magnetic properties

Nanosized γ-Fe₂O₃ is synthesized by the microwave-hydrothermal method. Powder X-ray diffraction and transmission electron microscopic studies showed that the average particle size is 10 nm. Magnetic studies reveal that the γ-Fe₂O₃ nanoparticles are superparamagnetic at room temperature, with a superparamagnetic blocking temperature of 200 K. The magnetic characteristics of the nanoparticles indicate their strongly interacting nature.     

Synthesis of MCM-41 frameworks incorporating oxygen-sulphur derivates of molybdenum and tungsten

The first examples of mesostructured materials containing Mo- and W-oxo-sulphur species incorporated into a poorly ordered MCM-41 framework have been prepared under hydrothermal condition and alkaline medium. The incorporation of oxygen-sulphur derivates of molybdenum and tungsten not only increases significantly the pore diameter, but also improves the thermal stability of the MCM-41-related mesoporous material.     

A comprehensive study of soft magnetic materials based on FeSi spheres and polymeric resin modified by silica nanorods

A novel soft magnetic composite (SMC) based on spherical FeSi particles precisely covered by hybrid phenolic resin was designed. The hybrid resin including silica nano-rods chemically incorporated into the phenolic polymer matrix was prepared by the modified sol–gel method. A chemical bridge connecting silica nano-rods with the base polymeric net was verified by FTIR, ¹³C and ²⁹Si NMR spectroscopy, whereas the shape and size of silica nano-rods were determined by TEM. It is shown that the modification of polymeric resin by silica nano-rods generally leads to the improved thermal and mechanical properties of the final samples. The hybrid resin serves as a perfect insulating coating deposited on FeSi particles and the core–shell particles can be further compacted by standard powder metallurgy methods in order to prepare final samples for mechanical, electric and magnetic testing. SEM images evidence negligible porosity, uniform distribution of the hybrid resin around FeSi particles, as well as, dimensional shape stability of the final samples after thermal treatment. The hardness, flexural strength and density of the final samples are comparable to the sintered SMCs, but they simultaneously exhibit much higher specific resistivity along with only slightly lower coercivity and permeability.     

One-pot syntheses of Li3V2(PO4)3/C cathode material for lithium ion batteries via ascorbic acid reduction approach

Monoclinic Li₃V₂(PO₄)₃/C composite synthesized by ascorbic acid reduction method is examined as a cathode material for Li-ion batteries. Transmission electron microscopy (TEM) images show that the nano-size particles are obtained. The reversible capacity of Li₃V₂(PO₄)₃/C prepared with LiOH and H₃PO₄ is 141.2 mAh g⁻¹ after 100 cycles at 1C discharge rate between 3 V and 4.8 V, and the retention rates of discharge capacity is 93.4%. Ascorbic acid plays not only as reduction reagent, but also as carbon sources. This strategy shortens the time of solid state reaction and facilitates the procedure of synthesis. Effects of different precursors materials on the performance of the Li₃V₂(PO₄)₃/C are investigated.     

Preparation and magnetic properties of spindle porous iron nanoparticles

Spindle porous iron nanoparticles were firstly synthesized by reducing the pre-synthesized hematite (α-Fe₂O₃) spindle particles with hydrogen gas. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms and vibrating sample magnetometry (VSM). A lattice shrinkage mechanism was employed to explain the formation process of the porous structure, and the adsorbed phosphate was proposed as a protective shell in the reduction process. N₂ adsorption/desorption result showed a Brunauer-Emmett-Teller (BET) surface area of 29.7 m²/g and a continuous pore size distribution from 2 nm to 100 nm. The magnetic hysteresis loop of the synthesized iron particles showed a saturation magnetization of 84.65 emu/g and a coercivity of 442.36 Oe at room temperature.     

Controllable synthesis and magnetic property of BiMn2O5 crystals

Uniform submicron BiMn₂O₅ particles were prepared via a facile one-step hydrothermal route at low temperature. Bi(NO₃)₃, MnCl₂·4H₂O and KMnO₄ were used as starting materials; KOH as a pH adjustor and also as a mineralizer. Single-crystalline orthorhombic BiMn₂O₅ sample with controllable morphology was obtained. The microstructure strongly depends on the molar ratio of the starting materials, KOH concentration and reaction temperature. X-ray photoelectron spectroscopy shows the existence of Mn⁴⁺ state. Magnetic measurement indicates Néel temperature T_N at 44 K. The susceptibility above T_N obeys the Curie-Weiss law, χ = C/(T − θ), with θ = −350 K. The effective paramagnetic moment μ_eff = 4.66 μ_B/Mn, demonstrating the coexistence of mixed Mn³⁺ and Mn⁴⁺ valences.     

Preparation and magnetization of hematite nanocrystals with amorphous iron oxide layers by hydrothermal conditions

Hematite nanocrystals modified with surface layers of amorphous hydrous iron oxides were prepared by hydrothermal conditions in the absence of alkali. The formation temperature was found to be ca. 130°C. When the temperature was lower than 130°C, no product was formed, while above this temperature, the amount of amorphous hydrous iron oxides at the surface of hematite nanocrystals was drastically decreased. The amorphous layers on the hematite nanocrystals obtained at 130°C were determined to be Fe₂O₃·1.64H₂O. The coercivity for the hematite nanocrystals with modified layers was 0.534 kOe, which is slightly larger than the values for hematite nanocrystals with few agglomerations.     

Synthesis and characterizations of Ni-Fe@spinel oxide core-shell nanoparticles

Core-shell Ni-Fe@ferrite nanoparticles with an average diameter of 14 nm and shell thickness of 3 nm were synthesized through a redox-transmetalation process. The alloy core and spinel oxide shell were verified by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. The hydrophobic oleylamine molecules on the surface were replaced by hydrophilic meso-2,3-Dimercaptosuccinic acid to make the nanoparticles to be water-soluble. X-ray diffraction study of the as-prepared core-shell nanoparticles indicates that they remained face centered cubic alloy core and spinel shell form in air. Magnetic measurements indicate that the core-shell nanoparticles exhibit superparamagnetic and exchange bias characteristics at 300 K and 5 K, respectively.     

Effect of PbO-SiO2 and PbO-B2O3 flux systems on the crystalline and magnetic properties of Ni0.5Zn0.5Fe2O4 ferrite prepared from the mixed powders

Lead borate and lead silicate were added to lower the sintering temperature of a Ni_0.5Zn_0.5Fe₂O₄ ferrite prepared from the blend of two types of powders and to homogenize the grain size. 5PbO·SiO₂ and 5PbO·B₂O₃ flux systems were added to lower the sintering temperature and diminish the magnetic loss at high frequencies. The ferrites were studied by bulk density, scanning electron microscopy and impedance analysis. It was found that the addition of PbO markedly accelerated the grain growth, while SiO₂ and B₂O₃ were found to be effective to obstruct the movement of grain boundaries and to minimize the grain size. Doping with PbO in the mixed powders appropriately increased the densification and initial permeability. The ferrite doped with 1% of 5PbO·SiO₂ possessed the lowest loss tangent (tgδ) in the range of 5 M-40 MHz and the highest threshold frequency.     

The effect of calcining temperature on the magnetic properties of the ultra-fine NiCuZn-ferrites

In this study, the ultra-fine NiCuZn-ferrite was prepared by a coprecipitation method. The magnetic properties were investigated in terms of calcining temperature. The ferrite powders, Ni_0.206Cu_0.206Zn_0.618Fe_1.94O_4−δ, were initially heat treated at various temperatures of 300-750 °C, and then sintered at the final temperature of 900 °C. The average particle size calculated by a XRD pattern and confirmed by a transmission electron microscope (TEM) micrograph was 7.5 nm. The calcining temperature was an important factor for microstructures and magnetic properties of the sintered ferrite. Scanning electron microscope (SEM) micrographs showed a uniform grain growth with small pores and high densification at the calcining temperature of 450 °C. From the results of magnetic property measurements, the ferrite calcined at 450 °C showed higher initial permeability (170) and quality factor (72) than those of other calcining temperatures.     

Supercritical hydrothermal synthesis of Cu2O(SeO3): Structural characterization, thermal, spectroscopic and magnetic studies

Cu₂O(SeO₃) has been synthesized in supercritical hydrothermal conditions, using an externally heated steel reactor with coupled hydraulic pump for the application of high pressure. The compound crystallizes in the P2₁3 cubic space group. The unit cell parameter is a = 9.930(1) Å with Z = 12. The crystal structure has been refined by the Rietveld method. The limit of thermal stability is, approximately, 490 °C. Above this temperature the compound decomposes to SeO₂(g) and CuO(s). The IR spectrum shows the characteristic bands of the (SeO₃)²⁻ oxoanion. In the diffuse reflectance spectrum two intense absorptions characteristic of the Cu(II) cations in five-coordination are observed. The ESR spectra are isotropic from room temperature to 5 K, with g = 2.11(2). The thermal evolution of the intensity and line width of the signals suggest a ferromagnetic transition in the 50-45 K range. Magnetic measurements, at low temperatures, confirm the existence of a ferromagnetic transition with a critical temperature of 55 K.     

Characterization and magnetic properties of Sm- and Gd-substituted CoFe2O4 nanoparticles prepared by forced hydrolysis in polyol

Pure nanoparticles of the CoFe_2−xRE_xO₄ (RE = Gd, Sm; x = 0.0, 0.1) system have been prepared by forced hydrolysis in polyol. The insertion of Sm³⁺ and Gd³⁺ cations into the cobalt ferrite structure has been investigated. X-ray micro-analysis (EDX) shows that the RE contents are close to the nominal ones. X-ray diffraction (XRD) evidences a cell size increase with slight distortions in the spinel-like lattice indicating the entrance of RE³⁺ ions. Micro-Raman spectroscopy confirms the cubic inverse-spinel structure and rules out the existence of impurities like hematite. Magnetic measurements (SQUID) show important differences in the magnetic properties of the unsubstituted and substituted particles. All the particles are superparamagnetic at room temperature and ferrimagnetic at low temperature. However, their main magnetic characteristics appear to be directly dependent on the RE content.     

Catalytic activity and magnetic properties of barium hexaferrite prepared from barite ore

Barium hexaferrite (BaFe₁₂O₁₉) has traditionally been used in permanent magnets and more recently used for high density magnetic recording. The classical ceramic method for the preparation of barium hexaferrite consists of firing mixture of chemical grade iron oxide and barium carbonate at high temperature. In this paper a mixture of chemical grade hematite, barium oxide and predetermined mixtures of iron oxide ore and barite ore containing variable amounts of coke were used to prepare barium hexaferrite (BaFe₁₂O₁₉) as a permanent magnetic material. The mixtures were mixed in a ball mill and fired for 20 h in a tube furnace at different temperatures (1100, 1150, 1200 and 1250 °C). XRD, magnetic properties, porosity measurements and catalytic activity were used for characterization of the produced ferrite. The results of experiments showed that the optimum conditions for the preparation of barium hexaferrite are found at 1200 °C for the mixture of chemical grade hematite and barium oxide. It was also found that the barium hexaferrite can be prepared from the iron and barite ores at 1200 °C. The addition of coke enhanced the yield of barium hexaferrite and improved its physicochemical properties. Samples prepared from ores with coke% = 0 show the most acidic active sites, they show a higher catalytic activity towards H₂O₂ decomposition. With addition of coke the catalytic activity decreases due to the poisoning effect of carbon on the available active site.     

SiC-dopped MCM-41 materials with enhanced thermal and hydrothermal stabilities

SiC-dopped MCM-41 mesoporous materials were synthesized by the in situ hydrothermal synthesis, in which a small amount of SiC was added in the precursor solvent of molecular sieve before the hydrothermal treatment. The materials were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N₂ physical adsorption and thermogravimetric analysis, respectively. The results show that the thermal and hydrothermal stabilities of MCM-41 materials can be improved obviously by incorporating a small amount of SiC. The structure collapse temperature of SiC-dopped MCM-41 materials is 100 °C higher than that of pure MCM-41 according to the differential scanning calorimetry analysis. Hydrothermal treatment experiments also show that the pure MCM-41 will losses it's ordered mesoporous structure in boiling water for 24 h while the SiC-dopped MCM-41 materials still keep partial porous structure.