Wangjun Feng

Fabrication of 0-3 type manganite/insulator composites and manipulation of their magnetotransport properties

In order to promote the technological applications of perovskite manganites, a great fundamental interest has been devoted to tailoring and/or enhancing their magnetotransport properties. Design and fabrication of manganite-based nanocomposites offer great potential to tailor the magnetotransport properties. In this work, we illustrate the promising concept of 0-3 type manganite/insulator composites (where manganite nanoparticles are uniformly and discretely embedded in a three-dimensional-connectivity insulator matrix) through the example of the La0.67Ca0.33MnO3 (LCMO)/MgO system. We present a promising strategy, which is based on the creation of core (LCMO)–shell (MgO) composite powders, for the synthesis of 0-3 type LCMO/MgO composites. A modified polyacrylamide gel method has been developed to prepare the core-shell structured LCMO/MgO composite powders. Besides its ability to create well-defined core-shell composite structures, the present gel method also allows the production of nanopowders with uni...

Growth mechanism of Cu nanopowders prepared by anodic are plasma

Abstract Based on the thermodynamics and kinetics theory, a theoretical model was built to illuminate the formation of metal nanopowders by anodic are discharging plasma method, and the mechanism of particle nucleation and growth was investigated. In addition, the morphology, crystal structure, particle size and specific surface area of the nanopowders were characterized by X-ray diffraction(XRD), Brunauer-Emmett-Teller(BET) adsorption, transmission electron microscopy(TEM) and the corresponding selected area electron diffraction(SAED). The experimental results indicate that the nanopowders prepared by this process have uniform size, high purity, single phase and spherical shape. The crystal structure is FCC structure, the same as that of the bulk materials; the specific surface area is 12 m2/g, the particle size distribution ranges from 30 to 90 nm with an average particle size of 67 nm which is obtained from TEM and confirmed from XRD and BET results.

Characterization of carbon encapsulated Fe-nanoparticles prepared by confined arc plasma

Abstract Carbon encapsulated Fe nanoparticles were successfully prepared via confined arc plasma method. The composition, morphology, microstructure, specific surface area and particle size of the product were characterized via X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray spectrometry and Brunauer-Emmett-Teller N 2 adsorption. The experiment results show that the carbon encapsulated Fe nanoparticles have clear core-shell structure. The core of the particles is body centered cubic Fe, and the shell is disorder carbons. The particles are in spherical or ellipsoidal shapes. The particle size of the nanocapsules ranges from 15 to 40 nm, with the average value of about 30 nm. The particle diameter of the core is 18 nm, the thickness of the shells is 6-8 nm, and the specific surface area is 24 m 2 /g.

Preparation and particle size characterization of Cu nanoparticles prepared by anodic arc plasma

Copper nanoparticles were successfully prepared in large scale by means of anodic arc discharging plasma method in inert atmosphere. The particle size, specific surface area, crystal structure, and morphology of the samples were characterized by X-ray diffraction (XRD), BET equation, transmission electron microscopy (TEM), and the corresponding selected area electron diffraction (SAED). The experimental results indicate that the crystal structure of the samples is fcc structure the same as that of the bulk materials. The specific surface area is 11m^2/g, the particle size distribution is 30 to 90nm, and the average particle size is about 67nm obtained from TEM and confirmed from XRD and BET results. The nanoparticles with uniform size, high purity, narrow size distribution and spherical shape can be prepared by this convenient and effective method.

Processing parameters for Cu nanopowders prepared by anodic arc plasma

Abstract Copper nanopowders were successfully prepared by anodic arc discharging plasma method with home-made experimental apparatus. The effects of various processing parameters on the particle size of Cu nanopowders were investigated in the process, and the optimum processing parameters were obtained. In addition, the morphology, crystal structure, particle size distribution of the nanopowders were characterized via X-ray diffraction(XRD), transmission electron microscopy(TEM) and the corresponding selected area electron diffraction(SAED). The experimental results show that the crystal structure of the samples is the same fcc structure as that of the bulk materials. The processing parameters play a major role in controlling the particle size. The particle size increases with the increase of the arc current or gas pressure.

Growth of BiFeO 3 microcylinders under a hydrothermal condition

BiFeO3 microcylinders were synthesized via a hydrothermal condition. SEM observation reveals that with increasing the hydrothermal reaction time from 6 to 15 h, the microcylinders grow from ∼0.7 to ∼4.1 µm in height, whereas their diameter remains to be 3.7-3.8 µm with a minor change. The microcylinders are mainly made up of sphere-like grains of 100-150nm in size. A possible growth mechanism of the BiFeO3 microcylinders is proposed. The photocatalytic activity of the as-prepared BiFeO3 samples was evaluated by the degradation of acid orange 7 under simulated sunlight irradiation, revealing that they possess an appreciable photocatalytic activity. Magnetic hysteresis loop measurement shows that the BiFeO3 microcylinders exhibit a typical antiferromagnetic behavior at room temperature.

Polyacrylamide Gel Preparation, Photocatalytic Properties, and Mechanism of BiVO 4 Particles: Polyacrylamide Gel Preparation, Photocatalytic Properties, and Mechanism of BiVO 4 Particles

BiVO4 particles were prepared by a polyacrylamide gel method and characterized by X-ray diffraction, scanning electron micros- copy, and ultraviolet-visible diffuse reflectance spectroscopy.The results demonstrate that the as-prepared BiVO4 particles crystallize in a monoclinic scheelite-type structure, are regularly shaped like spheres with a uniform size of ～400 nm, and have a bandgap energy of 2.49 eV. The photocatalytic activity of BiVO4 particles was evaluated by the degradation of methylene blue under simulated sunlight irradiation. The effects of O2, N2, ethanol, and KI on the photocatalytic efficiency were investigated. Hydroxyl radicals (·OH) formed on the catalyst under simulated sunlight irradiation were detected by photoluminescence spectroscopy using terephthalic acid as a probe molecule. The photocatalytic degradation mechanism involved is discussed in detail. Based on the photocatalytic results, hydroxyl radicals and photogenerated h+ are suggested to be the two main active species toward the photocatalytic degradation of methylene blue by BiVO4.

Preparation of bismuth ferrite nanoparticles and their photocatalytic activity for MO degradation

A modified polyacrylamide gel method was used to fabricate Bi<inf>2</inf>Fe<inf>4</inf>O<inf>9</inf> nanoparticles. Thermogravimetric (TG) analysis, differential scanning calorimetry (DSC) analysis, fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) were used in combination to investigate the thermal decomposition process of xerogels and the formation of Bi<inf>2</inf>Fe<inf>4</inf>O<inf>9</inf> phase. It is demonstrated that high-phase-purity Bi<inf>2</inf>Fe<inf>4</inf>O<inf>9</inf> nanoparticles can be prepared at a calcining temperature of 750 °C. Scanning electron microscope (SEM) observation reveals that the prepared Bi<inf>2</inf>Fe<inf>4</inf>O<inf>9</inf> nanoparticles are nearly spherical in shape, exhibit a smooth surface, feature no agglomeration character, and have an average diameter of about 220 nm. Ultraviolet-visible diffuse reflectance spectroscopy was used to investigate the light-absorbing properties of Bi<inf>2</inf>Fe<inf>4</inf>O<inf>9</inf> nanoparticles, and the value of the optical bandgap energy is obtained to be 2.08 eV. The photocatalytic activity of Bi<inf>2</inf>Fe<inf>4</inf>O<inf>9</inf> nanoparticles was evaluated by the degradation of methyl orange (MO), a typical azo dye. The experimental results reveal that the product exhibits a pronounced photocatalytic activity for the MO decomposition under ultraviolet and visible-light irradiation.