Solvent-free preparation of copper ferrite microspheres composed of nanorods using a new coordination compound as precursor

This work presents a simple solvent-free route based on solid-state thermal decomposition approach to synthesize magnetic copper ferrite (CuFe₂O₄) microspheres and copper ferrite/metal oxide composites. For this purpose, [Cu(en)₃]₃[Fe(ox)₃]₂ complex (where en?=?ethylenediamine and ox?=?oxalate) was introduced as a new single-source precursor. Ferromagnetic property of the nanostructures was determined by alternating gradient force magnetometer. The effect of different ligands and temperatures on the morphology of the products was investigated. Solid-state thermal decomposition of the precursor at different temperatures in the range of 400–800?°C led to the fabrication of magnetic copper ferrites with various particle sizes. X-ray powder diffraction patterns and images of scanning electron microscopy showed formation of CuFe₂O₄/Fe₂O₃ microspheres with very smooth surfaces and CuFe₂O₄/CuO microspheres coated with nanorods by thermal decomposition of the precursor at 400 and 700?°C, respectively. The results confirmed that copper ferrite and CuFe₂O₄/CuO nanocomposites were suitable materials with appropriate performance in catalyst and photo-catalytic applications.     

Synthesis and characterization of KNd2Ti3O9.5 nanocrystal and its catalytic effect on decomposition of ammonium perchlorate

A novel kind of perovskite type oxide KNd₂Ti₃O_9.5 nanocrystals with an average size of 12 nm were successfully fabricated by a stearic acid sol–gel method (SAM) using Ti(OBu)₄, KOH, Nd₂O₃ and stearic acid as the raw materials. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the products. The catalytic effect of the KNd₂Ti₃O_9.5 nanoparticles on thermal decomposition of ammonium perchlorate (AP) was investigated by differential thermal analysis (DTA) and thermal gravimetry (TG) experiments. Results indicated that the obtained KNd₂Ti₃O_9.5 nanocrystals took on cubic structure and presented both good dispersibility and uniform crystallite size. Also, they have an intense catalytic effect on the thermal decomposition of AP. Adding 2% of KNd₂Ti₃O_9.5 nanoparticles to AP can obviously decrease the thermal decomposition temperature of AP by 50 °C, increase the heat of decomposition from 590 J g⁻¹ to 1659 J g⁻¹ and obviously quicken the decomposition reaction rate.     

Neodymium-doped copper ferrite: auto-combustion synthesis,characterization and photocatalytic properties

Neodymium doped copper ferrite nanoparticles were successfully synthesized by via a sol–gel auto combustion method with the aid of copper (II) nitrate, iron (III) nitrate, neodymium (III) nitrate and starch without adding external surfactant. Moreover, starch plays role as capping agent, reductant agent, and natural template in the synthesis CuFe_2?xNd_xO₄ nanoparticles. The as-synthesized CuFe_2?xNd_xO₄ nanoparticles were characterized by means of several techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis and UV–Vis diffuse reflectance spectroscopy. The magnetic properties of as-prepared CuFe_2?xNd_xO₄ nanoparticles were also investigated with vibrating sample magnetometer (VSM). To evaluate the photocatalyst properties of nanocrystalline CuFe_2?xNd_xO₄, the photocatalytic degradation of methyl orange (MO) under ultraviolet light irradiation was carried out.     

Cu/Fe hydrotalcite derived mixed oxides as new catalyst for thermal decomposition of ammonium perchlorate

Cu/Fe mixed oxides (Cu/Fe-MOs) were prepared by calcination of Cu/Fe hydrotalcite (Cu/Fe-HT) precursors. They were used as new catalyst for thermal decomposition of ammonium perchlorate (AP) and their catalytic activity was studied by thermal gravimetric and differential thermal analysis. With the addition of 4 wt.% Cu/Fe-MOs, thermal decomposition of AP was accelerated by 104 °C. Higher catalyst addition favors further decomposition of AP. The catalytic activity order is: Cu/Fe-MOs-500 > Cu/Fe-MOs-800 > CuO·Fe₂O₃. The proposed catalytic mechanism is the presence of O₂⁻ on the surface of Cu/Fe-MOs which can simplify thermal decomposition of AP.     

Combustion synthesis of CuFe2O4

Metallic ferrites are investigated as prospective materials for different applications especially as anodes in extractive metallurgy. CuFe₂O₄, one of the important ferrites, is envisaged for substituting the carbon anode in Hall-Heroult cells. A single step combustion process has been used for the synthesis of CuFe₂O₄ powder from cupric nitrate, ferric nitrate and urea. The experimental conditions for maximum conversion efficiency of the precursor powders have been optimized. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) have confirmed the formation, structure and homogeneity of the as-prepared powders. The detailed physical, electrical and structural characterization of the materials have been carried out for the specimens obtained on sintering at different temperatures up to 1000 °C.     

Catalytic Activity of the Spinel Ferrite Nanocrystals on the Growth of Carbon Nanotubes

We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe₂O₄) (ii) ferrite where cobalt was substituted by nickel (Ni _x Co_1?x Fe₂O₄, with x=0, 0.2, 0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc (Zn _y Ni_1?y Fe₂O₄ with y=1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray diffraction patterns show that the ferrite samples have been crystallized in the cubic spinel structural phase. We obtained the size of grains by field emission scanning electron microscopy images and their magnetic properties by vibrating sample magnetometer. Next, carbon nanotubes were grown on these nanocatalysts by the catalytic chemical vapor deposition method. We show that the catalytic activity of these nanocrystals on the carbon nanotube growth depend on cation distributions in the octahedral and tetrahedral sites, structural isotropy, and catalytic activity due to cations. Our study may have applications in finding a suitable candidate of doped ferrite nanocrystals as catalysts for carbon nanotube growth. More interestingly, the yield of fabrication of carbon nanotubes can be considered as an indirect tool to study catalytic activity of ferrites.     

Influence of 150 MeV Ni swift heavy ion irradiation on CuFe2O4 thin films prepared by radio frequency magnetron sputtering: Modification on structure and surface morphology

The bulk copper ferrite nanomaterials are synthesized by co-precipitation technique. The vibrating sample magnetometer measurement for bulk CuFe₂O₄ reveals its unsaturated superparamagnetic behavior. The crystallites of the synthesized nanomaterial are in cubic form having an average size of ~ 100 Å and are used as target to prepare thin films of various thicknesses (600, 900 and 1100 nm) by radio frequency magnetron sputtering technique. X-ray peaks arise only when films are annealed at 1200 °C and also they are found to be in tetragonal structure. The magnetic characteristics of 900 nm unirradiated CuFe₂O₄ thin film exhibit superparamagnetic behavior and have an unsaturated magnetic moment at high field. Magnetic force microscopy images of unirradiated CuFe₂O₄ thin films confirm the soft nature of the magnetic materials. The 150 MeV Ni¹¹⁺ swift heavy ion irradiation on these thin films at the fluence of 1 × 10¹⁴ ions/cm² modifies the polycrystalline nature due to electron-phonon coupling. Atomic force microscopy image shows that the swift heavy ion irradiation induces agglomeration of particles in 600 and 900 nm thin films and increases rms surface roughness from 33.43 to 39.65 and 69.7 to 102.46 nm respectively. However, in 1100 nm film, holes are created and channel-like structures are observed along with a decrease in the rms surface roughness from 75.12 to 24.46 nm. Magnetic force microscopy images of 900 nm irradiated thin film explain the formation of domains on irradiation and are also supported by the ferromagnetic hysteresis observed using vibrating sample magnetometer.     

Synthese de quelques ferrites par reaction de double decomposition entre le ferrite de lithium (LiFeO2) et un sel fondu

In this paper are specified the conditions of formation of pure ferrites by the double decomposition reaction between the lithium ferrite and divalent metal double salts such as chlorides. 2 LifeO₂ + K₂MCl₄ → MFe₂O₄ + 2 LiCl + 2 KCl (M=Co,Ni,Mn,Zn,Mg) These reactions can be achieved at 600°C with an excess of molten double salt in absence of oxygen and water vapor. Spinel mixed iron oxides are obtained as fine spherical particles with a narrow granulometric repartition (0,1 to 0,2 μ). The formation of pure cupric ferrite CuFe₂ O₄ is not possible because the decomposition of cupric salt in our reaction conditions cannot be avoided.     

Synthesis of magnetic Cu/CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite as a highly efficient Fenton-like catalyst for methylene blue degradation

A magnetic Cu/CuFe₂O₄ nanocomposite was synthesized by a facile one-pot solvothermal method and characterized as an excellent Fenton-like catalyst for methylene blue (MB) degradation. The content of zero-valent copper (Cu⁰) in Cu/CuFe₂O₄ composite could be simply controlled by changing the dosage of sodium acetate in the synthetic process, and the Fenton-like catalytic performance of Cu/CuFe₂O₄ composite enhanced with increasing the Cu⁰ content. In the presence of H₂O₂ (15 mM), the as-synthesized 3-Cu/CuFe₂O₄ nanocomposite could remove 99% of MB (50 mg/L) after only 4 min at pH 2.50, greatly higher than that of pure CuFe₂O₄ and Cu⁰ under the same condition. The enhancement activity of Cu/CuFe₂O₄ nanocomposite was due to the synergistic effect between Cu⁰ and CuFe₂O₄. The radical capture experiments and coumarin fluorescent probe technique confirmed that MB was degraded mainly by the attack of OH^· radicals in Cu/CuFe₂O₄–H₂O₂ system.     

Synthesis of nanocrystalline xCuFe2O4-(1 − x)BiFeO3 magnetoelectric composite by chemical method

xCuFe₂O₄-(1 − x)BiFeO₃ spinel-perovskite nanocomposites with x = 0.1, 0.2, 0.3 and 0.4 were prepared using citrate precursor method. X-ray diffraction (XRD) analysis showed phase formation of xCuFe₂O₄-(1 − x)BiFeO₃ calcined at 500 °C. Transmission electron microscopy (TEM) shows formation of nanocrystallites of xCuFe₂O₄-(1 − x)BiFeO₃ with an average particle size of 40 nm. Variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Coercivity, saturation magnetization and squareness have been found to vary with concentration of ferrite phase and annealing temperature due to the increase in crystallite size. Squareness and coercivity increased with an increase in annealing temperature up to 500 °C and then decreased with a further increase in temperature to 600 °C. Magnetoelectric effect of the nanocomposites was found to be strongly depending on the magnetic bias and magnetic field frequency.     

Template synthesis of magnetic one-dimensional nanostructured spinel MFe2O4 (M = Ni, Mg, Co)

The iron nitrate and suitable salt of nickel, cobalt, or magnesium with molar ratio of 2:1 were introduced into the pores of mesoporous silica SBA-15 via two-solvent method. The thermal decomposition of the precursors and the formation of one-dimensional nanostructured spinel ferrite in SBA-15 pores were monitored by XRD, TG-DTA, N₂ adsorption-desorption, and TEM. The pure spinel MFe₂O₄ nanowires obtained through complete removal of the silica template with aqueous NaOH solution were confirmed by TEM and HRTEM. The spinel MFe₂O₄ nanowires showed increasing normal configuration and exhibited superparamagnetism in comparison with the bulk ones.     

D-xylose-derived carbon microspheres modified by CuFe2O4 nanoparticles with excellent microwave absorption properties

In this work, we studied the preparation and microwave absorption properties of D-xylose-derived carbon materials modified by CuFe₂O₄ nanoparticles and discussed the influence of the addition amount of carbon materials. It was prepared with a simple hydrothermal method, and various methods are used to characterize its microscopic morphology, chemical structure and microwave absorption properties.Results show that the modification of copper ferrite nanoparticles is effective in mitigating polarization and magnetic losses, enhancing the microwave absorption properties of the samples and absorption curves of the composite materials change from a single peak to double peaks. Comparing all samples it can be concluded that the effective absorption bandwidth of CuFe₂O₄ composite materials containing carbon microspheres (CuFe₂O₄/CMs-0.3) is 6.24 GHz. The minimum reflection loss (RL) is???50.4 dB at 14.64 GHz. The thickness of the above corresponds to 2.5 mm. This work not only provides a reference method for the preparation of microwave absorbing materials but also contributes to the understanding of absorption mechanisms.

     

Nanostructured ZnO network films deposited on Al2O3 substrates by chemical bath deposition

Nanostructured ZnO network films have been fabricated on Al₂O₃ substrates by the combination of chemical bath deposition and thermal decomposition process. Layered basic zinc nitrate (LBZN) network films were deposited on the Al₂O₃ substrates with LBZN crystal seeds in methanol solution of zinc nitrate hexahydrate and hexamethylenetetramine. The LBZN precursor films were then transformed into nanostructured ZnO films by heating at 260 °C in air. During the thermal decomposition process abnormal exothermic heat effect was observed at 200-210 °C and CH₃ groups were found in the as-deposited films. We propose that methanol molecules are integrated in the LBZN films forming LBZN-CH₃OH complex and that the heat effect comes from the exothermic release of the methanol.     

Crystallographic and low frequency conductivity studies of the spinel systems CuFe2O4 and Cu1?xZnxGa0.1Fe1.9O4; (0.0 ≤ x ≤ 0.5)

Spinel solid solutions of CuFe₂O₄ and Cu_1−xZn_xGa_0.1Fe_1.9O₄ with (0.0 ≤ x ≤ 0.5) are synthesized. Crystallographic phase transformation from tetragonal-to-cubic occurred at x = 0.2. The derived structural parameters manifest that Zn occupies the tetrahedral A-site while Cu and Ga occupy the octahedral B-site and Fe distributes among A- and B-sites. Electrical conductivity measurements of these materials as a function of temperature and frequency revealed semiconducting behavior except CuFe₂O₄ sample, which has a metallic behavior at low frequency and at high frequency, semiconductor-to-metallic transition occurred as temperature increases. The metallic behavior in this sample is attributed to cation-cation interactions at B-site while, the semiconductor behavior in Cu_1−xZn_xGa_0.1Fe_1.9O₄ compounds is due to the cation–anion–cation interactions at the same site in the spinel lattice. All compositions exhibit transition with change in the slope of conductivity versus temperature curve. This transition temperature (T_c) decreases linearly with increasing Zn content x. The relation of the universal exponent s with temperature gives evidence that over large polaron OLP and correlated barrier hopping CBH conduction mechanisms are presented in CuFe₂O₄ and Cu_1−xZn_xGa_0.1Fe_1.9O₄ compounds respectively.     

Surface and catalytic properties of MoO3/Al2O3 system doped with Co3O4

Thermal solid-solid interactions in cobalt treated MoO₃/Al₂O₃ system were investigated using X-ray powder diffraction. The solids were prepared by wet impregnation method using Al(OH)₃, ammonium molybdate and cobalt nitrate solutions, drying at 100 °C then calcination at 300, 500, 750 and 1000 °C. The amount of MoO₃, was fixed at 16.67 mol% and those of cobalt oxide were varied between 2.04 and 14.29 mol% Co₃O₄. Surface and catalytic properties of various solid samples precalcined at 300 and 500 °C were studied using nitrogen adsorption at −196 °C, conversion of isopropanol at 200-500 °C and decomposition of H₂O₂ at 30-50 °C.The results obtained revealed that pure mixed solids precalcined at 300 °C consisted of AlOOH and MoO₃ phases. Cobalt oxide-doped samples calcined at the same temperature consisted also of AlOOH, MoO₃ and CoMoO₄ compounds. The rise in calcination temperature to 500 °C resulted in complete conversion of AlOOH into very poorly crystalline γ-Al₂O₃. The further increase in precalcination temperature to 750 °C led to the formation of Al₂(MoO₄)₃, κ-Al₂O₃ besides CoMoO₄ and un-reacted portion of Co₃O₄ in the samples rich in cobalt oxide. Pure MoO₃/Al₂O₃ preheated at 1000 °C composed of MoO₃-αAl₂O₃ solid solution (acquired grey colour). The doped samples consisted of the same solid solution together with CoMoO₄ and CoAl₂O₄ compounds.The increase in calcination temperature of pure and variously doped solids from 300 to 500 °C increased their specific surface areas and total pore volume which suffered a drastic decrease upon heating at 750 °C. Doping the investigated system with small amounts of cobalt oxide (2.04 and 4 mol%) followed by heating at 300 and 500 °C increased its catalytic activity in H₂O₂ decomposition. This increase, measured at 300 °C, attained 25.4- and 12.9-fold for the solids precalcined at 300 and 500 °C, respectively. The increase in the amount of dopant added above this limit decreased the catalytic activity which remained bigger than those of un-treated catalysts. On the other hand, the doping process decreased the catalytic activity of treated solids in isopropanol conversion especially the catalysts precalcined at 300 °C. This treatment modified the selectivities of treated solids towards dehydration and dehydrogenation of reacted alcohol.The activation energies of H₂O₂ decomposition were determined for pure and variously doped solids. The results obtained were discussed in light of induced changes in chemical composition and surface properties of the investigated system due to doping with cobalt oxide.     

The effect of Cu content on the structure of Ni1−xCuxFe2O4 spinels

A series of Ni_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 °C. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 °C to 350 °C. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu²⁺ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe₂O₄, showing different surface oxygen species from the spinel and CuO. Cu²⁺ substitution favors the occupancy of A-sites by Fe³⁺.     

Temperature-dependent oxygen release, intercalation behaviour and catalytic properties of V2O5·xNb2O5 compounds

In order to investigate the catalytic properties, V_2,38Nb_10,7O_32,7, VNb₉O₂₅ and solid solutions of V₂O₅ in TT-Nb₂O₅ were prepared by thermal decomposition of freeze-dried oxalate precursors. The samples were characterised by X-ray diffraction and surface area determination. The crystalline samples are capable of the intercalation of sodium and lithium ions from solution. Above a temperature of about 500 °C, in dependence on the oxygen partial pressure a reversible release and uptake of oxygen without a structural variation takes place. The catalytic properties have been evaluated for the oxidative dehydrogenation (ODH) of propane and propene. There are only small differences in the catalytic activity of the different crystalline samples. Because of the relative high starting temperature, a selective catalytic oxidation of propane to propene is hardly observed.     

Preparation and characterization of hollow glass microspheres coated by CoFe2O4 nanoparticles using urea as precipitator via coprecipitation method

The composite of hollow glass microspheres coated by CoFe₂O₄ nanoparticles has been successfully prepared using urea as precipitator via coprecipitation method. The resultant composites were characterized by X-ray diffraction, field emission scanning electron microscope and vibrating sample magnetometer. The results showed that the slow decomposition of urea could be beneficial to form uniform and entire cobalt ferrite coating layer on the surface of hollow glass microspheres. The smoothest morphology was obtained for the sample prepared from 0.7 M urea, while the sample prepared from 1.0 M urea had the thickest shell. This indicated that there was a competition between the morphology and thickness of the coated microspheres. A possible formation mechanism of hollow glass microspheres coated with cobalt ferrite was proposed. The magnetic properties of the samples were also investigated.     

Synthesis of the nanocrystalline CoFe2O4 ferrite thin films by a novel sol-gel method using glucose as an additional agent

Polycrystalline and nanometer-sized CoFe₂O₄ ferrite thin films are successfully synthesized using glucose as an addition agent. The thermal gravimetric/differential thermal analyzer, X-ray diffractometer, electron diffraction, scanning electron microscope, atomic force microscope and vibrating sample magnetometer are used to characterize the effects of the calcination temperature on the crystalline structure, morphology and magnetic properties of the Co-ferrite thin films. CoFe₂O₄ ferrite thin films have a single phase inverse spinel structure and are crystallized at and above 300 °C which is much lower than the required temperature in the traditional ceramic method (about 500-600 °C). Co-ferrite thin films annealed at relative low temperature of 400 °C show very small particle size with average of 32 nm and excellent magnetic properties for information storage applications.