Magnetic Properties of Annealed CoFe2O4 Nanoparticles Synthesized by the PEG-Assisted Route

Annealed cobalt inverse spinel-type ferrite nanoparticles were synthesized using polyethylene glycol assisted co-precipitation. The structure, magnetic properties and effect of annealing temperature was investigated in detail. Saturation magnetization, coercivity and remanence magnetization were observed to decrease with increasing temperature. The magnetic hysteresis curves supported the proposition that the CoFe₂O₄ nanoparticles showed ferromagnetic character from 10 to 400 K. Magnetization measurements showed the blocking temperature to be higher than 400 K. Unsaturated magnetization behavior suggested the existence of disordered spins in the surface layer of the CoFe₂O₄ nanoparticles.     

Magnetic Properties of Nickel–Zinc Ferrite Toroids Prepared from Nanoparticles

Toroids comprised of silica-coated 10 nm diameter nickel–zinc (Ni–Fe) ferrite nanoparticles (Ni_0.5Zn_0.5Fe₂O₄) have been fabricated by careful control of both the coating process and subsequent densification by viscous sintering. A narrow processing window is identified between a maximum temperature at which the nanoparticles coarsen, losing their super-paramagnetic properties, and a lower temperature required for viscous flow densification. Key to the successful fabrication was drying and cold isostatic pressing of the silica-coated nanoparticles; other routes invariably led to cracking during either drying or sintering. The super-paramagnetic blocking temperature, the coercive field, and remanent magnetization could all be controlled over a wide range by varying the thickness of the silica coating from 1 to 15 nm. The dipole–dipole coupling distance is estimated to be 4 nm. The high-frequency (1–500 MHz) properties were sensitive to the sintering temperature as well as the thickness of the silica coating. Toroids sintered at 1000°C or less exhibited no high-frequency magnetic losses and their permeability decreased with increasing temperature, suggesting that the permeability was controlled by thermally activated magnetization relaxation.     

Novel Synthesis Route for Chitosan-Coated Zinc Ferrite Nanoparticles as Potential Sorbents for Wastewater Treatment

Magnetic chitosan–zinc ferrite (ChZnF) composites were proposed as potential adsorbents due to their appropriate physical characteristics and facile separation under external magnetic fields. The magnetic component (ZnFe₂O₄) was prepared by the sol–gel autocombustion method that yields nanometric spinel compounds with narrow size distribution and with low energy consumption. A certain amount of magnetic powder was dispersed consecutively by ultrasonication in a chitosan-PEG (polyethylene glycol) mixture, in order to obtain the desired nanocomposite. The as-obtained materials were characterized by FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), TEM (transmission electron microscopy), small-angle X-ray scattering, and Brunauer–Emmett–Teller test measurements. Finally, the chitosan-ferrite nanomaterial was successfully tested in simulated wastewater treatments. Different kinetic and equilibrium models have been fitted by nonlinear regression to analyze the adsorption data.     

Composition-Size Effects in Nickel–Zinc Ferrite Nanoparticles Prepared by Aqueous Coprecipitation

Nickel–zinc ferrite nanoparticles across the solid solution range, Ni_{1− x} Zn _x Fe₂O₄, from nickel ferrite to zinc ferrite were prepared by aqueous precipitation of mixed nitrate solutions at the same pH of 12.3. There is a linear relationship between the nanoparticle diameter and composition, decreasing with increasing zinc concentration across the solid solution. The nanoparticles are highly resistant to coarsening and some of them are faceted, suggesting that they are close to thermodynamic equilibrium. Measurements of the surface charge density of the nanoparticles, based on simultaneous conductimetric and potentiometeric titration, are presented as a function of composition for the zinc-rich compositions. A trend exists between the surface charge density and the zinc concentration, suggesting that they may be stabilized by charge.     

超声雾化辅助微波法合成氧化锌纳米颗粒及其光催化性能

氧化锌(ZnO)具有宽带隙、高光催化效率和稳定的化学性质,已成为处理水体中有机污染物的常用材料.采用超声雾化辅助微波法成功合成了ZnO纳米颗粒,XRD图谱和TEM照片表明超声雾化抑制了ZnO结晶,其结构为无序状,得到的ZnO纳米颗粒为非晶态.非晶态ZnO纳米颗粒紫外最强吸收峰为300nm,紫外吸收边发生红移,禁带宽度降...     

Catalytic Oxidation of CO Over Synthesized Nickel Ferrite Nanoparticles from Fly Ash

Catalytic oxidation of carbon monoxide (CO) gas over nanosized nickel ferrites prepared from fly ash has been investigated. X-ray diffraction analyses showed that pure crystalline nickel ferrite, NiFe₂O₄, phase can be obtained by thermal treatment of the precursors at temperature >800 °C for 120 min in the studied pH range, from 7 (neutral) to 12 (highly alkaline). In the temperature range 500 ≤ T ≤ 800 °C, impure low crystalline NiFe₂O₄ phase formed. The main impurities are FeO (OH) and Fe₂O₃ · H₂O phases. Higher magnetization (32 emu/g) is obtained for a precursor precipitated at pH 10 and thermally treated at 1,200 °C for 120 min. The catalytic oxidation of CO over nanocrystalline NiFe₂O₄ powders was studied using quadrupole mass gas analyzer system. The main parameters as crystal size, surface area and firing temperature are used to clarify the efficiency of using NiFe₂O₄ powders in catalytic oxidation of CO. It was found that the efficiency of catalytic oxidation decreased by increasing firing temperature and crystallite size of the samples. The lower crystal size (2–8.5 nm), the higher surface area (25–55 m²/g) and the presence of impurities FeO(OH) phase enhanced CO adsorption and consequently its oxidation.     

塑料用铁酸锌黄颜料性能的研究

采用混合、煅烧-研磨法制备耐高温颜料铁酸锌黄。测试了不同改性剂制备的颜料对颜色的影响,通过CIE测色系统对添加有耐高温颜料铁酸锌黄的通用塑料外观颜色进行表征。结果表明:选用氧化铝作改性剂时,生产出的颜料着色力高、颜色鲜艳。     

Size and Shape Tailoring of Titania Nanoparticles Synthesized by Solvothermal Route in Different Solvents

A simple solvothermal low‐temperature synthesis process of TiO₂ nanoparticles was investigated in different solvents [Octanol (Oc), Ethanolamine (Am) and Terathane (Tr)] with titanium (IV) chloride (TiCl₄) as precursor. The samples were characterized by X‐Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). XRD showed the crystallite size ranging from 4 to 12 nm, which were calculated using Debye–Scherrer's equation. The existence of poor or high crystalline anatase phases and high crystalline anatase/rutile mixture was also shown. TEM images displayed variations in the morphological behavior depending on the synthesis condition. Particles of irregular morphology with high irregular agglomeration up to well‐defined particles can be observed, which are self‐assembled by oriented attachment (OA). This self‐assembly led to TiO₂ microparticles with 3‐D Wulff shape for anatase and 1‐D shape for rutile. The results showed that the TiO₂ nanopowder could be easily engineered and adapted by the solvent type, the TiCl₄ concentration and the synthesis time.     

Electrical Properties and Phase Stability of a Zinc Ferrite

The electrical conductivity and theromoelectric power of a zinc ferrite of nominal composition 0.46ZnO·0.54Fe₂O₃ were examined as a function of oxygen partial pressure under equilibrium conditions at elevated temperatures. The isothermal variations of both transport properties were found to be closely correlated with P _O2-induced phase transitions from wustite to ferrite spinel to hematite with successively increasing P _O2's. The region of thermodynamic stability of each phase was determined from either of the two property isotherms. Within the single-phase field of the spinel ferrite, both properties are P _O2 dependent. Applying the small polaron hopping model to these results, the P _O2 and temperature dependencies of the octahedral ferrous and ferric ion concentrations were extracted and interpreted in terms of the buffering capability of the nominal A-site cation and the variability of the partial molar enthalpy of oxygen with the progress of the oxidation reaction of Fe²⁺ to Fe³⁺.     

Lattice Expansion and Saturation Magnetization of Nickel–Zinc Ferrite Nanoparticles Prepared by Aqueous Precipitation

Nanoparticles of nickel–zinc ferrite prepared across the solid solution compositional range by aqueous precipitation at 100°C are all found to have both a larger lattice parameter and a lower saturation magnetization than bulk forms of the same compositions. The lower saturation magnetization is attributed to a combination of the larger lattice parameter, decreasing the super-exchange interactions between the Ni²⁺ and Fe³⁺ ions, and incomplete ordering of the cations between the octahedral and tetrahedral sites in the spinel structure. Annealing experiments suggest that the lattice expansion is probably due to the incorporation of OH⁻groups during synthesis. Characterization of the nanoparticles indicates that the saturation magnetization can be restored while preserving their super-paramagnetic behavior by heating to temperatures below which they coarsen, typically 900°C.     

纳米ZnO的水热合成及性能研究

采用简单的水热方法制备出纯净且粒径均匀的纳米Zn O粒子,借助于X射线粉末衍射仪(XRD)和扫描电子显微镜(SEM)对其物相组成及表面形貌进行了表征,通过日光下亚甲基蓝的降解研究了其光催化性能。将获得的ZnO纳米粒子沉积成膜,经表面修饰低表面能物质1H,1H,2H,2H-全氟辛基三氯硅烷(CAS)后,采用接触角测量仪研究了其润湿性能。结果表明,反应时间为20 h的ZnO纳米粒子在日光照射20 min后,亚甲基蓝的降解率达到90%以上;经表面修饰CAS后,Zn O膜呈现良好的疏水性能;经紫外光照射后,疏水性ZnO膜转换为亲水性,实现了润湿性的转换。     

掺杂对锌铁氧体吸波性能影响研究

实验采溶胶-凝胶法制备锌铁氧体前驱体,煅烧前驱体,用X射线衍射仪(XRD)、微波分光仪对煅烧后产物的物相、微波吸收性能进行研究。结果表明用溶胶-凝胶法制备了锌铁氧体;在11GHz,锌铁氧体和掺杂钴和镍的锌铁氧体的反射损耗分别为-11·55dB和-13·01dB。     

Optical and Photocatalytic Properties of Spinel ZnCr2O4 Nanoparticles Synthesized by a Hydrothermal Route

In this paper, a simple hydrothermal route has been developed to synthesize ZnCr₂O₄ nanoparticles. Experimental results show that the as-prepared ZnCr₂O₄ nanoparticles have an average particle size of <5 nm. The ZnCr₂O₄ nanoparticles have a direct band gap about 3.46 eV and exhibit blue emission in the range of 300–430 nm, centered at 358 nm when excited at 220 nm. Furthermore, the nanoparticles show apparent photocatalytic activities for the degradation of methylene blue under UV light irradiation.     

Synthesis, Properties, and Formation Mechanism of Zinc Ferrite Hollow Spheres

Hollow spheres of zinc ferrite were prepared via a surfactant-assisted hydrothermal approach. The morphology and composition of the final products were characterized by X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy. It was observed from the microscope images that the final products were composed of spherical nanostructures about 70–100 nm in diameter. Anti-ferromagnetic transition at the temperature of about 18.06 K was observed from the temperature–magnetic susceptibility curve of the ZnFe₂O₄ hollow spheres. Possible formation mechanism of the hollow sphere has been discussed. This work may provide us a new synthesis route for the preparation and fabrication of other ferrite nanostructures.     

Geometry and Electrical Properties of Grain Boundaries in Manganese Zinc Ferrite Ceramics

For large-grained manganese zinc (MnZn) ferrite ceramics, grain misorientation determined by electron backscatter diffractions and grain-boundary resistance measured using microcontact impedance spectroscopy have been correlated. The degree of oxidation of grain boundaries and, hence, the barrier height depends on the overall grain-boundary network as well as on the individual boundary structure; therefore, a statistical analysis has been performed based on several hundreds of local measurements. When the boundaries are divided into low- and high-resistance groups, statistically significant differences in rotation axis and angle distributions are found. The misorientation distribution of the low-resistance boundary group is suggested to reflect the low-energy configurations of boundary planes in MnZn ferrites.     

Formation of Cobalt Ferrite Nanoparticles via Glycine-Nitrate Combustion and Their Magnetic Properties

Cobalt ferrite nanoparticles, whose degree of crystallinity and particle size depends on the molar ratio of glycine to cobalt and iron nitrates, are produced by the glycine-nitrate combustion method. The highest values of the particles’ degree of crystallinity (94%) and size (77–79 nm) are observed in samples produced at a molar ratio of 0.84 of glycine to nitrates. The values of the coercive force and residual magnetization increased, together with the glycine to nitrate ratio: at 1.12, they reached 33.8 emu/g and 1350 Oe, respectively. The saturation magnetization attained the maximal value (80 emu/g) at the molar ratio of glycine to nitrates of 0.56.     

Well-aligned Nickel Nanochains Synthesized by a Template-free Route

Highly uniform and well-aligned one-dimensional Ni nanochains with controllable diameters, including 33, 78, and 120 nm, have been synthesized by applying an external magnetic field without any surface modifying agent. The formation can be explained by the interactions of magnetic dipoles in the presence of applied magnetic field. Magnetic measurements demonstrate that the shape anisotropy dominates the magnetic anisotropy. The demagnetization factor, ∆N, is in the range of 0.23–0.36.     

Photocatalytic Activity of Pure and Zinc Doped Tin Oxide Nanoparticles Synthesized by One Step Direct Injection Flame Synthesis

A very simple and rapid Direct Injection Flame Synthesis (DIFS) method is effectively used to synthesize pure tin oxide (SnO₂) and zinc doped tin oxide (Zn:SnO₂) nanoparticles from the metallic tin (Sn) and zinc (Zn) powders for the photocatalytic degradation of methylene blue (MB) dye. The DIFS nanoparticles were characterized using XRD, Raman, UV–Vis, FESEM, PL and EDX studies. The X-ray diffraction analysis indicated that the synthesized SnO₂ and Zn:SnO₂ nanoparticles have pure tetragonal phases and their average crystallite size decreases when Zn was doped with SnO₂. Raman study confirmed the various mode of vibrations and the crystal structure of the synthesized nanoparticles. Purity, atomic percentage and chemical composition were analysed using Energy dispersive X-ray analysis and found to be free from impurities. The band gap energy increases from 3.5 to 3.6 eV upon doping which was revealed from the UV–Visible spectroscopic analysis. Photoluminescence analysis confirms the red shifted emission for Zn:SnO₂ due to the oxygen deficiency. The CIE chromaticity (x,y) for SnO₂ and Zn:SnO₂ was calculated from the emission spectra and the co-ordinates represents blue and violet region respectively. Field Emission Scanning Electron Microscopy analysis showed that the pure SnO₂ nanoparticles have irregular, agglomerated, nanoflowered and nanoclustered formation whereas Zn:SnO₂ nanoparticles has more crystalline, cubical and nanoflake structure. The photocatalytic activity was enhanced due to the presence of Zn in SnO₂ under UV light irradiation. The efficiency of MB degradation by SnO₂ was found to be 82% and enhanced to 88% upon doping. Thus the Zn doped SnO₂ nanoparticles synthesized by DIFS was found to be an effective photocatalyst than the pure SnO₂.

     

WO3 Nanoparticles Synthesized Through Ion Exchange Route as Pt Electrocatalyst Support for Alcohol Oxidation

Tungsten oxide (WO₃) nanocrystals with the diameter <5 nm supported on porous carbonized resin (denoted as C‐WO₃) are synthesized. The WO₃ precursors are dispersed at ion level through ion exchange route, then reduced to WO₃ nanocrystals. Pt nanoparticles are loaded on the porous C‐WO₃ matrix (denoted as Pt/C‐WO₃) and used as electrocatalyst in fuel cell for alcohol oxidation, in which WO₃ is found efficient promotion effect on Pt electrocatalyst in the electrochemical activity and stability. Thereinto, Pt/C‐WO₃ gives 1.63 times higher current densities than the commercial Pt/C (TKK) for methanol oxidation at the same Pt loadings. Moreover, Pt/C‐WO₃ electrocatalyst shows excellent properties in mass transfer than Pt/C (TKK). The present method can be readily scaled up for the production of other nanomaterials as well as WO₃.