Nguyen Viet Long

Controlled Synthesis and Magnetic Properties of Uniform Hierarchical Polyhedral α-Fe2O3 Particles

The controlled synthesis of uniform hierarchical polyhedral iron (Fe) micro-/nanoscale oxide particles with the α-Fe2O3 structure is presented. The hierarchical polyhedral iron oxide particles were synthesized by modified polyol methods with sodium borohydride as a powerful and efficient reducing agent. A critical heat treatment process used during the synthesis allowed for the interesting formation of α-Fe2O3 hematite with a micro-/nanoscale structure. The structure and weak ferromagnetism of the α-Fe2O3 particles were investigated by x-ray diffraction with whole pattern fitting and Rietveld refinement, scanning electron microscopy, and by vibrating sample magnetometry. The as-prepared α-Fe2O3 particles and the three dimensional models presented have promising practical applications for energy storage and conversion in batteries, capacitors, and fuel cells, and related spintronic devices and technologies.

Fabrication of Semiconductor ZnO Nanostructures for Versatile SERS Application

Since the initial discovery of surface-enhanced Raman scattering (SERS) in the 1970s, it has exhibited a huge potential application in many fields due to its outstanding advantages. Since the ultra-sensitive noble metallic nanostructures have increasingly exposed themselves as having some problems during application, semiconductors have been gradually exploited as one of the critical SERS substrate materials due to their distinctive advantages when compared with noble metals. ZnO is one of the most representative metallic oxide semiconductors with an abundant reserve, various and cost-effective fabrication techniques, as well as special physical and chemical properties. Thanks to the varied morphologies, size-dependent exciton, good chemical stability, a tunable band gap, carrier concentration, and stoichiometry, ZnO nanostructures have the potential to be exploited as SERS substrates. Moreover, other distinctive properties possessed by ZnO such as biocompatibility, photocatcalysis and self-cleaning, and gas- and chemo-sensitivity can be synergistically integrated and exerted with SERS activity to realize the multifunctional potential of ZnO substrates. In this review, we discuss the inevitable development trend of exploiting the potential semiconductor ZnO as a SERS substrate. After clarifying the root cause of the great disparity between the enhancement factor (EF) of noble metals and that of ZnO nanostructures, two specific methods are put forward to improve the SERS activity of ZnO, namely: elemental doping and combination of ZnO with noble metals. Then, we introduce a distinctive advantage of ZnO as SERS substrate and illustrate the necessity of reporting a meaningful average EF. We also summarize some fabrication methods for ZnO nanostructures with varied dimensions (0–3 dimensions). Finally, we present an overview of ZnO nanostructures for the versatile SERS application.

Polyol-Mediated Synthesis, Microstructure and Magnetic Properties of Hierarchical Sphere, Rod, and Polyhedral α -Fe 2 O 3 Oxide Particles

In this research, the synthesis of hierarchical sphere, rod, and polyhedral α-Fe2O3 particles by a modified polyol method is presented. Hybrid micro/ nanoscale α-Fe2O3 particles with grain and grain boundary textures were found as a result of the heat treatment added to the synthesis process. The magnetic properties of the particles are investigated to assess their use in practical applications in the fields of energy, environment, and biology. The heat-treatment step at high temperature was found to strengthen the durability and stability of the Fe-oxide micro/nanoscale particles, enabling the final formation of the Fe-oxide grain and grain boundary structure on their surface and inside the particles. The mechanism behind the formation mainly focused on the ideas of atomic deformation at the micro/nanoscale and particle deformation at microscale. Finally, the hierarchical hybrid micro/nanoscale structures were identified as the challenges and opportunities for research on the micro/nanoscale Fe alloys and oxides particles with grain and grain boundary textures. The large Fe oxide particles with MS about 2.9xa0emu/g, and the advantages of high durability, stability, and the good ferromagnetic properties can be promising potential candidates for energy materials in the easy reuse due to their relative large sizes in a range of 10xa0μm.

Synthesis of Pt–Pd Bimetallic Porous Nanostructures as Electrocatalysts for the Methanol Oxidation Reaction

Pt-based bimetallic nanostructures have attracted a great deal of attention due to their unique nanostructures and excellent catalytic properties. In this study, we prepared porous Pt–Pd nanoparticles using an efficient, one-pot co-reduction process without using any templates or toxic reactants. In this process, Pt–Pd nanoparticles with different nanostructures were obtained by adjusting the temperature and ratio of the two precursors; and their catalytic properties for the oxidation of methanol were studied. The porous Pt–Pd nanostructures showed better electrocatalytic activity for the oxidation of methanol with a higher current density (0.67 mA/cm2), compared with the commercial Pt/C catalyst (0.31 mA/cm2). This method provides one easy pathway to economically prepare different alloy nanostructures for various applications.

Controlled Synthesis and Ferrimagnetism of Homogeneous Hierarchical CoFe 2 O 4 Particles

Uniform, large, spherical, hierarchical CoFe2O4 spinel particles have been successfully prepared by a modified polyol method using NaBH4 and NaOH, revealing controlled size, shape, and morphology with high crystallinity in a certain microscale range. Their inverse AB2O4-type crystal structure was intensively studied by x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Using stock solutions of CoCl2 and FeCl3 precursors in 1:2 ratio, CoFe2O4 particles were formed well with high crystallinity in the best inverse spinel structure in space group Fd-3m. The fascinating ferrimagnetic and hysteretic properties of the as-prepared hierarchical CoFe2O4 spinel particles were investigated by vibrating-sample magnetometry (VSM) at room temperature (RT). The results confirm formation of hierarchical CoFe2O4 microscale particles with inverse-spinel AB2O4-type structure and high magnetization by modified polyol method with heat treatment.