Synthesis and characterization of Ni<Subscript>0.6</Subscript>Zn<Subscript>0.4</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nano-particles obtained by auto catalytic thermal decomposition of carboxylato-hydrazinate complex

Ni_0.6Zn_0.4Fe₂O₄ nano-particles have been synthesized by self-propagating auto-combustion of nickel zinc ferrous fumarato-hydrazinate complex. The precursor complex has been characterized by chemical analysis, IR, AAS, thermal analysis and isothermal mass loss studies. The precursor on ignition undergoes self-propagating auto combustion to give Ni_0.6Zn_0.4Fe₂O₄. The X-ray diffraction studies confirmed the single phase formation of nano-size ‘as synthesized’ Ni_0.6Zn_0.4Fe₂O₄. TEM observation showed the average particle size to be 20 nm. Infrared and magnetization studies were also carried out on the ‘as synthesized’ Ni_0.6Zn_0.4Fe₂O₄. The lower value of saturation magnetization and higher Curie temperature of ‘as synthesized’ ferrite also hint at the nano size nature.     

Effect of heat treatment on particle growth and magnetic properties of electrospun Sr<Subscript>0.8</Subscript>La<Subscript>0.2</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>11.8</Subscript>O<Subscript>19</Subscript> nanofibers

Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉/poly(vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol–gel assisted electrospinning. Subsequently, the M-type ferrite Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers with diameters about 120 nm were obtained by calcination of these precursors at different heat treatment conditions. The precursor and resultant Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer. With the calcination temperature increased up to 1,000 °C for 2 h or the holding time prolonged to 12 h at 900 °C, the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ particles gradually grow into a hexagonal elongated plate-like morphology due to the dimensional control along the nanofiber length. These elongated plate-like particles will be linked one by one to form the nanofiber with a necklace-like morphology. The magnetic properties of the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers are closely related to grain sizes, impurities and defects in the ferrite, which are influenced by the calcination temperature, holding time and heating rate. After calcined at 900 °C for 12 h with a heating rate of 3 °C/min, the optimized magnetic properties are achieved with the specific saturation magnetization 75.0 A m² kg⁻¹ and coercivity 426.3 kA m⁻¹ for the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers.     

Obtaining of Ni<Subscript>0.65</Subscript>Zn<Subscript>0.35</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites by thermal decomposition of complex compounds embedded in silica matrix

This article presents the results of our investigation on the obtaining of Ni_0.65Zn_0.35Fe₂O₄ ferrite nanoparticles embedded in a SiO₂ matrix using a modified sol–gel synthesis method, starting from tetraethylorthosilicate (TEOS), metal (Fe^III,Ni^II,Zn^II) nitrates and ethylene glycol (EG). This method consists in the formation of carboxylate type complexes, inside the silica matrix, used as forerunners for the ferrite/silica nanocomposites. We prepared gels with different compositions, in order to obtain, through a suitable thermal treatment, the nanocomposites (Ni_0.65Zn_0.35Fe₂O₄)_x–(SiO₂)_100–x (where x=10, 20, 30, 40, 50, 60 mass%). The synthesized gels were studied by differential thermal analysis (DTA), thermogravimetry (TG) and FTIR spectroscopy. The formation of Ni–Zn ferrite in the silica matrix and the behavior in an external magnetic field were studied by X-ray diffraction (XRD) and quasi-static magnetic measurements (50 Hz).     

Ammonia gas sensor based on a spinel semiconductor,Co<Subscript>0.8</Subscript>Ni<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanomaterial

Thick film of nanocrystalline Co_0.8Ni_0.2Fe₂O₄ was obtained by sol–gel citrate method for gas sensing application. The synthesized powder was characterized by X-ray diffraction (XRD) and transmission electron microscopy. The XRD pattern shows spinel type structure of Co_0.8Ni_0.2Fe₂O₄. XRD of Co_0.8Ni_0.2Fe₂O₄ revels formation of solid solution with average grain size of about 30 nm. From gas sensing properties it observed that nickel doping improves the sensor response and selectivity towards ammonia gas and very low response to LPG, CO, and H₂S at 280 °C. Furthermore, incorporation of Pd improves the sensor response and stability of ammonia gas and reduced the operating temperature upto 210 °C. The sensor is a promising candidate for practical detector of ammonia.     

Preparation,spectroscopic and thermal analysis of hexa-hydrazine nickel cobalt ferrous succinate precursor and study of solid-state properties of its nanosized thermal product,Ni<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Nickel cobalt ferrite, Ni_0.5Co_0.5Fe₂O₄, has been prepared by precursor combustion technique from hexa-hydrazine nickel cobalt ferrous succinate precursor. The precursor was characterized by chemical analysis, CHNS analysis, infrared spectroscopy, TG–DTA and mass loss studies. The thermal data show how the precursor decomposes in four steps to give stable ferrite phase. The precursor decomposes autocatalytically once initially ignited, to give the ‘as-prepared’ nano-spinel ferrite. The X-ray diffraction analysis reveals single cubic spinel phase structure. The infrared measurements between 4000 and 350 cm^?1 confirmed the intrinsic cation vibrations of the spinel structure. The SEM image clearly shows the nanosized nature of the ferrite. The dielectric constant and loss tangent are found to decrease with increase in frequency which is due to Maxwell–Wagner interfacial polarization. The loss tangent shows a relaxation peak at ~1 kHz. The variation of DC electrical resistivity with temperature indicates semiconductor behaviour. The temperature- and field-dependent magnetization data of ‘as-prepared’ ferrite reveal that the lattice has either a canted or partially misaligned spin structure due to the nanosized nature of the ferrite.     

Synthesis and characterization of La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>Co<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>O<Subscript>3±δ</Subscript> nanopowders by microwave assisted sol–gel route

Nano-crystalline La_0.8Sr_0.2Co_0.5Fe_0.5O_3±δ powder has been successfully synthesized by microwave assisted sol–gel (MWSG) method. The decomposition and crystallization behavior of the gel-precursor was studied by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis. From the result of FT-IR and X-ray diffraction patterns, it is found that a perovskite La_0.8Sr_0.2Co_0.5Fe_0.5O_3±δ was formed by irradiating the precursor at 700 W for 3 min, but the well-crystalline perovskite La_0.8Sr_0.2Co_0.5Fe_0.5O_3±δ was obtained at 700 W for 35 min. Morphological and specific area analysis of the powder were done by transmission electron microscopy (TEM), scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET). The surface areas measured was 38.9 m²/g and the grain size was ∼23 nm. Electrochemical properties of pure LSCF cathode on YSZ electrolyte at intermediate temperatures were investigated by using AC impedance analyzer, which shows a low area specific resistance (0.077 Ω cm² at 1073 K and 0.672 Ω cm² at 953 K). Moreover, the synthesis period of 20 h usually observed for conventional heating mode is reduced to a few minutes. Thus, the MWSG method is proved to be a novel, extremely facile, time-saving and energy-efficient route to synthesize LSCF powders.     

Preparation and characterization of Co0.5Zn0.5Fe2(C4H2O4)3·6N2H4 A precursor to prepare Co0.5Zn0.5Fe2O4 nanoparticles

A good precursor is foremost in the preparation of nanosized metal or mixed metal oxides. In the present study a novel precursor, cobalt zinc fumarato-hydrazinate Co_0.5Zn_0.5Fe₂(C₄H₂O₄)₃·6N₂H₄ has been prepared which decompose at a much lower temperature to give nanosized mixed-metal oxides. X-ray investigations, confirms the formation of single spinel phase. The FTIR spectra show N-N stretching vibration at 965 cm⁻¹ which confirms the bidentate bridging hydrazine. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential scanning calorimetric analysis. The precursor shows two-step dehydrazination followed by decarboxylation to form Co_0.5Zn_0.5Fe₂O₄, the chemical analysis of the sample is corroborative of this.     

Synthesis and characterization of ultrafine spinel ferrite obtained by precursor combustion technique

Nanoparticles of the spinel ferrite, Co_0.6Ni_0.4Fe₂O₄ have been synthesized by the precursor combustion technique. This synthetic route makes use of a novel precursor viz. metal fumarato hydrazinate which decomposes autocatalytically after ignition to yield nanosized spinel ferrite. The X-ray powder diffraction of the ??as prepared?? oxide confirms the formation of monophasic nanocrystalline cobalt nickel ferrite. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been fixed as Co_0.6Ni_0.4Fe₂(C₄H₂O₄)₃·6N₂H₄. The Curie temperature of the ??as prepared?? oxide was determined by ac susceptibility measurements.     

Synthesis of cobalt nickel ferrite nanoparticles via autocatalytic decomposition of the precursor

The chemistry, structure, and properties of spinel ferrites are largely governed by the method of preparation. The metal carboxylato-hydrazinate precursors are known to yield nanosized oxides at a comparatively lower temperature. In this study, we are reporting the synthesis of one such precursor, cobalt nickel ferrous fumarato-hydrazinate which decomposes autocatalytically to give cobalt nickel ferrite nanoparticles. The XRD study of this decomposed product confirms the formation of single-phase spinel, i.e., Co_0.5Ni_0.5Fe₂O₄. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric (TG), and differential scanning calorimetric (DSC) analysis. The precursor has also been characterized by FTIR, EDX, and chemical analysis, and its chemical composition has been determined as Co_0.5Ni_0.5Fe₂(C₄H₂O₄)₃·6N₂H₄.     

Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Photocatalysis of cobalt zinc ferrite nanorods under solar light

Co_0.7Zn_0.3Fe₂O₄ nanorods were synthesized from hydrazine precursor by co-precipitation technique. Infrared and thermogravimetric–differential thermogravimetric curves of the precursor indicated the bridging bidentate nature of hydrazine and three-step thermal decomposition. The as-synthesized cobalt zinc ferrite nanorods were characterized by powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, vibrating sample magnetometry and UV–diffuse reflection spectroscopy which proposed the phase structure, morphology, magnetic and optical properties. Co_0.7Zn_0.3Fe₂O₄ nanorods showed a sensible photocatalytic activity on Congo red, Malachite green, Methylene blue, Methyl red, Rhodamine B and Rose bengal under solar light at different time intervals and were magnetically separated.     

Towards high-performance cathode materials for lithium-ion batteries: Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-coated LiNi<Subscript>0.8</Subscript>Co<Subscript>0.15</Subscript>Zn<Subscript>0.05</Subscript>O<Subscript>2</Subscript>

Zn-doped LiNi_0.8Co_0.2O₂ exhibits impressive electrochemical performance but suffers limited cycling stability due to the relative large size of irregular and bare particle which is prepared by conventional solid-state method usually requiring high calcination temperature and prolonged calcination time. Here, submicron LiNi_0.8Co_0.15Zn_0.05O₂ as cathode material for lithium-ion batteries is synthesized by a facile sol-gel method, which followed by coating Al₂O₃ layer of about 15 nm to enhance its electrochemistry performance. The as-prepared Al₂O₃-coated LiNi_0.8Co_0.15Zn_0.05O₂ cathode delivers a highly reversible capacity of 182 mA h g^?1 and 94% capacity retention after 100 cycles at a current rate of 0.5 C, which is much superior to that of bare LiNi_0.8Co_0.15Zn_0.05O₂ cathode. The enhanced electrochemistry performance can be attributed to the Al₂O₃-coated protective layer, which prevents the direct contact between the LiNi_0.8Co_0.15Zn_0.05O₂ and electrolyte. The escalating trend of Li-ion diffusion coefficient estimated form electrochemical impedance spectroscopic (EIS) also indicate the enhanced structural stability of Al₂O₃-coated LiNi_0.8Co_0.15Zn_0.05O₂, which rationally illuminates the protection mechanism of the Al₂O₃-coated layer.     

Photocatalytic intercalated material based on HLaNb<Subscript>2</Subscript>O<Subscript>7</Subscript> as host and Cd<Subscript>0.8</Subscript>Zn<Subscript>0.2</Subscript>S as guest

A novel photocatalytic material (Pt,Cd0.8Zn0.2S)/HLaNb2O7 was fabricated by successive intercalation and exchange reactions. The (Pt,Cd0.8Zn0.2S)/HLaNb2O7 possessed a gallery height less than 0.5 nm and showed a broad absorption with wavelength over 370-500 nm. Using (Pt,Cd0.8Zn0.2S)/HLaNb2O7 as catalyst, the photocatalytic H2 evolution was more than 160 cm3·h-1·g-1 in the presence of Na2S as a sacrificial agent under irradiation with wavelength more than 290 nm from a 100-W mercury lamp. Furthermore, the catalyst showed photocatalytic activity even under visible light irradiation.     

Phase formation in the FeVO<Subscript>4</Subscript>–Co<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> system

Phase relations in the solid state in the FeVO₄–Co₃V₂O₈ system, in the whole range of components concentration have been studied. It was found that the composition of the phase of the howardevansite type structure, formed in the investigated system, corresponds with the Co_2.616Fe_4.256V₆O₂₄ formula. The phase of the lyonsite type structure has a homogeneity range with the Co_3+1.5xFe_4–xV₆O₂₄ formula (0.476 formula (0.476<x<1.667). The melting temperature and the volume of the unit cell of the lyonsite type structure phase increases together with the rise of cobalt quantity contained in it. Basing on the results of the DTA and XRD measurements a phase diagram of the FeVO_4–Co₃V₂O₈ system up to the solidus line was constructed.     

Peculiarities of polythermic decomposition of iron,cobalt and nickel oxalates within pores of photonic crystals based on SiO<Subscript>2</Subscript> in atmosphere with oxygen lack

Iron(II), cobalt(II) and nickel(II) oxalates were synthesized as nanofractals inside the voids of the photonic crystals based on SiO₂. Guest substances undergone polythermic decomposition within the pores of the photonic crystals in helium atmosphere containing of oxygen traces (∼1 Pa) under static conditions. Pyrolysis of Fe(COO)₂·2H₂O, Co(COO)₂·2H₂O and Ni(COO)₂·2H₂O studied by TG and DSC techniques results in the formation of the metal oxides. The nanoparticles of Fe₂O₃, CoO (Co₃O₄) and NiO populated the interspheric voids of the photonic crystals exhibited no ferromagnetic effects indicating that no metallic inclusions were formed in helium in the presence of O₂ traces. The exothermic effect was observed by the thermal decomposition of the cobalt(II) oxalate only under oxygen lack.     

The microstructure and magnetic properties of Ni<Subscript>0.4</Subscript>Zn<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> films prepared by spin-coating method

Nickel zinc ferrite (Ni_0.4Zn_0.6Fe₂O₄) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni_0.4Zn_0.6Fe₂O₄ films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M _s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H _c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M _s of 349 emu/cc and low coercivity H _c of 66 Oe. The M _s is higher than others which prepared by this method, however, the H _c is lower. The M _s of Ni_0.4Zn_0.6Fe₂O₄ films annealed at 700 °C increases with increasing annealing time and the H _c changes slightly.     

Non-isothermal kinetics of the thermal decomposition of sodium oxalate Na<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The thermal transformation of Na₂C₂O₄ was studied in N₂ atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na₂C₂O₄ and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS) methods. The activation energies (E _α) of Na₂C₂O₄ decomposition were found to be consistent. Decreasing E _α at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated through the Liqing–Donghua method was ‘cylindrical symmetry (R₂ or F_1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy pathway and revealed a very hard mechanism.     

Synthesis of Mg(Fe<Subscript>0.8</Subscript>Ga<Subscript>0.2</Subscript>)<Subscript>2</Subscript>O<Subscript>4</Subscript> by Gel Combustion Using Glycine and Starch

A powdery material Mg(Fe_0.8Ga_0.2)₂O₄ has been prepared by combusting a gel containing magnesium(II), iron(III), and gallium(III) nitrates and a glycine–starch mixture. The gel produced during the synthesis has been studied by thermal analysis (TGA/DSC) and IR spectroscopy. This mixture has been shown to be efficient to produce a homogeneous nanosized powderlike material Mg(Fe_0.8Ga_0.2)₂O₄. The morphology and properties of ceramic samples are characterized by scanning electron microscopy, X-ray powder diffraction, neutron diffraction, and vibrational magnetometry.     

Nonstoichiometric Zn Ferrite and ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Spheres: Preparation,Magnetic Properties,and Chromium Removal

Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe₂O₄/Fe₂O₃ composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe₂O₄/Fe₂O₃ composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe₂O₄/Fe₂O₃ composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe₂O₄/Fe₂O₃ composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe₂O₃,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr⁶⁺ adsorption property than ZnFe₂O₄/Fe₂O₃ composites.     

Study on the obtaining of cobalt oxides by thermal decomposition of some complex combinations,undispersed and dispersed in SiO<Subscript>2</Subscript> matrix

In order to obtain cobalt oxides nanoparticles we have used the thermal decomposition of some carboxylate type precursors. These precursors were obtained by the redox reaction between cobalt nitrate and ethylene glycol, either bulk or dispersed in silica matrix. The redox reaction takes place by heating the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution or the Si(OC₂H₅)₄-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels. Thermal analysis of the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution and Si(OC₂H₅)-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels allowed us to establish the optimal value for the synthesis temperature of the carboxylate precursors. By fast heating of the solution Co(NO₃)₂·6H₂O-C₂H₆O₂, the redox reaction is immediately followed by the decomposition of the precursor, which represents an autocombustion process. The product of this combustion contains CoO as unique phase. We have obtained a mixture of CoO and Co₃O₄ by annealing the synthesized carboxylate compounds for 2 h at 400°C. With longer annealing time (6 h), we have obtained Co₃O₄ as unique phase. The XRD study of the crystalline phases resulted by thermal decomposition of the precursors embedded in silica matrix, showed that the formation of Co₂SiO₄ and Co₃O₄, as unique phases, depends on the thermal treatment.