Effects of metal precursor in the sol–gel synthesis on the physicochemical properties of Pd/Al2O3–CeO2 catalyst: CO oxidation

The object of this research was to investigate the effects of various precursors and different fabricating procedures of Pd/Al₂O₃–CeO₂ catalysts by the sol–gel method. The physicochemical properties and structures of catalyst were characterized with BET surface area, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The performance of the Pd/Al₂O₃–CeO₂ catalyst was also evaluated by CO oxidation tests with a continuous quartz reactor. The results indicated that the catalyst prepared with inorganometallic precursors showed a high dispersion of Pd, large surface area and pore volume, and a high activity in CO oxidation. The higher redox interaction between Pd and Ce of the support starting with inorganometallic precursors, as determined from X-ray powder diffraction, is suggested as being responsible for such a catalytic behavior.     

Preparation and optical properties of nanoscale MgAl2O4 powders doped with Co ions

Co²⁺-doped MgAl₂O₄ nanocrystalline powders were prepared by co-precipitation method. The gels and/or calcined samples were characterized by means of thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectrum and near-infrared absorption spectrum. MgAl₂O₄ nanocrystals were produced by calcining the gel above 800 °C, with the crystallite size of 10-30 nm in the temperature range of 800-1100 °C. The influence of pH value of precipitant solution on the dispersing of powders was studied and the result showed that Co:MgAl₂O₄ nanocrystalline powders exhibited good dispersion when pH = 11. The absorption spectrum of Co²⁺-doped MgAl₂O₄ exhibited a broad absorption band in the wavelength range of 1200-1600 nm, which indicated that Co²⁺ ions substituted for the tetrahedrally coordinated Mg²⁺ ions in the MgAl₂O₄ lattice.     

Influence of pulsed laser deposition rate on the microstructure and thermoelectric properties of Ca3Co4O9 thin films

The effects of deposition rate on the microstructure and thermoelectric (TE) properties of Ca₃Co₄O₉ thin films fabricated by pulsed laser deposition (PLD) technique were investigated. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) revealed that a fast deposition rate resulted in not only low crystallinity but also the existence of the Ca_xCoO₂ secondary phase. Formation of Ca_xCoO₂ was inevitable during the thin film growth, and this was discussed from both structural and compositional point of view. With longer deposition interval or with sufficient oxygen at a lower deposition rate, the Ca_xCoO₂ phase was able to transit into the desired Ca₃Co₄O₉ phase during the coalescence process. The quality of the thin films was further analyzed by electrical properties measurements. The Ca₃Co₄O₉ thin film fabricated at a slower deposition rate was found to exhibit a low electrical resistivity of 9.4 mΩ cm and high Seebeck coefficient of 240 μV/K at about 700 °C, indicating a good quality film.     

Growth mechanism of nanorods in REBa2Cu3Oy films (RE: rare-earth element)

Critical current density under magnetic fields has been improved by the introduction of artificial pinning centers. Nanorods in REBa₂Cu₃O_y films are significantly effective as c-axis-correlated pinning centers. However, nanorods sometimes tilt from the c-axis direction of superconducting films. To understand the mechanism of nanorod tilting, ErBa₂Cu₃O_y films containing Ba(Nb_0.5Er_0.5)O₃ (BNO) nanorods were deposited on a SrTiO₃ single crystal with a vicinal surface. Microstructures of the nanorods were examined by transmission electron microscopy (TEM). As a result, it was found that BNO nanorods grew diagonally from steps of the substrate surface in cross-sectional TEM images. The mechanism of the diagonal growth of nanorods can be explained by the segregation coefficient.     

Synthesis and properties of α‐Fe2O3 nanorods

We report synthesis of α‐Fe₂O₃ (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 °C. The calcined α‐Fe₂O₃ nanorods were characterized by X‐ray diffraction (XRD), high‐resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The result showed that the α‐Fe₂O₃ nanorods were hexagonal structure. The nanorods have diameter of 30‐50 nm and length of 120‐150 nm. The weak ferromagnetic behavior was observed with saturation magnetization = 0.6 emu/g, coercive force = 25 Oe and remanant magnetization = 0.03 emu/g. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-yield synthesis of single-crystal short Eu2O3 nanorods through a facile sol–gel template approach

High-yield Eu₂O₃ short nanorods have been prepared by a facile sol-gel method with polystyrene/polyelectrolyte (PS/PE) microreactor as template in an aqueous solution of europium nitrate in the presence of ammonia and urea. The properties of Eu₂O₃ nanorods were characterized by powder X-ray diffraction, thermogravimetric analysis, transmission electron microscopy (TEM), high-resolution transmission electron microscopy, field emission scanning electron microscopy (FESEM), and photoluminescence spectroscopy. The particle sizes measured from TEM and FESEM are about 200 nm×500 nm (W×L). A possible mechanism for the formation of such high-yield oxide nanorods is discussed.     

Structure and morphology of [icosahedral Al62Cu25.5Fe12.5]100−x[decagonal Al70Co15Ni15]x alloys, for x=10(03 and 510)

Alloys made from mixtures of Al₆₂Cu_25.5Fe_12.5 icosahedral quasicrystal (IQC) and Al₇₀Co₁₅Ni₁₅ decagonal quasicrystal (DQC) were studied by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The transition from IQC to DQC was thus discussed by studying the evolution of their constituent phases in each alloy. Three approximant phases were found as common phases in most of the pseudo-binary alloys: λ-Al₁₃Fe₄, β-AlFe and τ3-Al₃Ni₂. It is found that, with the increment of the DQC content in the alloy, the λ phase changes from Al₁₃Fe₄ to Al₁₃Co₄ and the τ3 phase changes from Al₃Cu₂ to Al₃Ni₂. The formation of these phases were found also to follow the evolution of their corresponding e/a-constant lines in the Al–(Cu,Ni)–(Fe,Co) pseudo-ternary phase diagram. Under this framework, the roles played by the related approximants in the transition process are briefly discussed.     

A study of the growth process of Co3O4 microcrystals synthesized via a hydrothermal method

Pure Co₃O₄ microcrystals were prepared by a hydrothermal method from Co(NO₃)₂·6H₂O and urea solution, and the effect of thermal treatment time on the growth of Co₃O₄ microcrystals was studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV‐Vis absorption spectra. The results show that with the thermal treatment time increases from 2 h to 12 h, the shape of as‐prepared Co₃O₄ microcrystals changes from the hedgehog sphere‐like to the as‐cubic one that were stacked by lots of lamella, and finally cubes, and then longer time treatment will only lead to the size growth and agglomeration of particles. In conclusion, the cubic Co₃O₄ microcrystals of uniform size (∼6 μm) are synthesized via a 12‐h thermal treatment. Moreover, the synthesis mechanism has been studied.     

Study of the structural insertion of Al in the Al2O3-SiO2 and Nd2O3-Al2O3-SiO2 glass systems

Glasses in the Al₂O₃-SiO₂ and Nd₂O₃-Al₂O₃-SiO₂ systems were prepared by the sol-gel method. The gel-glass evolution was studied using near-infrared (NIR) and ultraviolet-visible (UV-VIS) spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The results obtained indicate a relationship between the sample compositions, the treatment temperature and the Al coordination. In the samples of the Nd₂O₃-Al₂O₃-SiO₂ system the densification of the structure, when the treatment temperature increases, leads to the segregation of neodymium oxide particles.     

Fabrication of cobalt ferrite nanostructures and comparison of their electrochemical properties

Cobalt Ferrite (CoFe₂O₄) nanorods and nanorings have been successfully controllable synthesized by solvothermal method. The specific characteristics were confirmed by X‐ray diffraction studies (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The measurement of their electrochemical properties as supercapacitor electrode materials indicate different morphological characterizations have various capacitive effects, and CoFe₂O₄ nanorings generally have larger specific capacitances than nanorods at different scan rates and current densities in 1.0 M KOH solution.     

Synthesis of Nb2O5·nH2O nanoparticles by water-in-oil microemulsion

Hydrous niobium oxide (Nb₂O₅·nH₂O) nanoparticles had been successfully prepared by water-in-oil microemulsion. They were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTG), Fourier transform infrared spectroscopy (FTIR), BET surface area measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the nanoparticle was exactly Nb₂O₅·nH₂O with spherical shape. Their BET surface area was 60 m² g⁻¹. XRD results showed that Nb₂O₅·nH₂O nanoparticles with crystallite size in nanometer scale were formed. The crystallinity and crystallity size increased with increasing annealing temperature. TT-phase of Nb₂O₅ was obtained when the sample is annealed at 550 °C.     

Synthesis and characterization of Bi3.15Nd0.85Ti3O12 nanotube arrays

Nd-substituted bismuth titanate (Bi_3.15Nd_0.85Ti₃O₁₂, BNT) nanotube arrays are fabricated by means of a sol–gel method utilizing porous anodic aluminum oxide (AAO) template. The morphologies and structures have been determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diameter and length of these nanotubes are about 200 nm and 60 μm, respectively, and their wall thickness is about 30 nm. The average grain size is around 40 nm. XRD data show that the BNT nanotubes possess bismuth-layered perovskite structure. High-resolution electron microscopy (HRTEM) image demonstrates that the BNT nanotubes are polycrystalline. Polarization–electric field (P–E) response curves of BNT nanotube arrays were measured, and a size induced polarization reduction phenomenon is observed.     

Complex crystallization mode of amorphous/nanocrystalline composite Al86Ni2Co5.8Gd5.7Si0.5

Kinetics of the first crystallization stage of Al₈₆Ni₂Co_5.8Gd_5.7Si_0.5 amorphous alloy and structure of the partially crystallized specimens were investigated by measurements of electrical resistance, X-ray diffraction and transmission electron microscopy. The presence of Al nanocrystals and eutectic colonies consisted of mutually oriented crystals of Al and metastable phase was found. The transient nucleation and slowing-down diffusion-limited growth and the interface-controlled growth of the quenched-in nuclei were identified as mechanisms of formation of the Al nanocrystals and eutectic colonies, respectively.     

Synthesis and characterization of single-crystalline PrCO3OH dodecahedral microrods and its thermal conversion to Pr6O11

Single-crystalline PrCO₃OH dodecahedral microrods with an orthorhombic structure have been successfully synthesized by the hydrothermal method used urea as the precipitator. Pr₆O₁₁ dodecahedral microrods have been obtained by thermal conversion of PrCO₃OH dodecahedral microrods at 600 °C in air for 6 h. The as-synthesized products were characterized by X-ray powder diffraction, field-emission scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectra, fourier transform infrared spectroscopy and thermogravimetry–differential thermal analysis. The effect of the reaction parameters on the morphology of the product has been investigated. The dodecahedral microrods with larger size and better crystallinity can be obtained under the higher reaction temperature. The possible formation mechanism of PrCO₃OH microrods was discussed.     

Crystalline bismuth oxide nanorods fabricated on Pt‐coated substrates using a trimethylbismuth and oxygen mixture

The current work reports the fabrication of crystalline Bi₂O₃ nanorods on Pt‐coated Si substrates using trimethylbismuth and O₂ as the bismuth and the oxygen sources, respectively, in the metalorganic chemical vapor deposition process. Their microstructures were characterized by scanning electron microscopy, X‐ray diffraction, and transmission electron microscopy. The obtained nanorods were crystalline, with their diameters in the range of 20–200 nm. The absence of tip‐nanoparticle and the presence of predeposited Bi₂O₃ layer indicated that the growth was dominated by a vapor‐solid process. The photoluminescence measurements of the Bi₂O₃ nanorods at room temperature exhibited an emission band peaked at around 422 nm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zr‐doped CeO2 Hollow slightly‐truncated nano‐octahedrons: One‐pot synthesis,characterization and their application in catalysis of CO oxidation

Zirconium‐doped ceria hollow slightly‐truncated nano‐octahedrons (HTNOs) (Ce_1‐xZr_xO₂) were synthesized by a one‐pot, facile hydrothermal method. The morphology and crystalline structure were characterized with powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and the high resolution transmission electron microscopy (HRTEM). The composition and chemical valence on the surface of the as‐prepared Ce_1‐xZr_xO₂ powders were detected by X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The surface area and pore size distribution of as‐obtained Zr‐doped ceria HTNOs were measured by N₂ adsorption‐desorption measurement. Mechanisms for the growth of Zr‐doped ceria HTNOs are proposed as both oriented attachment and Ostwald ripening process and the formation of the hollow structure is strongly dependent on the addition of Zr⁴⁺ ions. Furthermore, the as‐obtained Zr‐doped ceria HTNOs revealed superior catalytic activity and thermal stability toward CO oxidation compared to pure ceria. It may provide a new path for the fabrication of inorganic hollow structures on introducing alien metal ions.     

Controllable synthesis and field emission properties of In2O3 nanostructures

Large‐scale In₂O₃ nanorods, nanocubes and nanowires have been successfully synthesized by chemical vapor deposition route under atmospheric pressure. The structures and morphologies were characterized by x‐ray diffraction (XRD), scanning election microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM). The growth mechanisms of these In₂O₃ nanostructures were analyzed in detail based on the experimental results. Field‐emission measurements of these nanostructures demonstrated that nanorods with rectangular cross‐section possessed good performance with a turn‐on field of 2.47 Vμm^–1 and a field enhancement factor of 4597. The room‐temperature photoluminescence (PL) spectrum of the In₂O₃ nanostructure showed UV emission centered at about 396 nm and visible emissions located at 541 and 623 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Glass formation in the MoO3–Nd2O3–La2O3–B2O3 system

In MoO₃–Nd₂O₃–B₂O₃ and MoO₃–Nd₂O₃–La₂O₃–B₂O₃ systems, glasses were obtained in the region between 20 and 30 mol% Ln₂O₃. A liquid-phase separation region was observed near the MoO₃–B₂O₃ side up to 20 mol% Ln₂O₃ (La, Nd). The amorphous phases were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), UV–VIS and infrared spectroscopy (IR). According to DTA data B₂O₃-rich glasses are stable up to 630 °C while glasses rich in MoO₃ are stable up to 430 °C. The glasses are transparent in the visible region. Structural models for the glasses network were suggested on the basis of IR spectral investigations. It was established that BO₃ (1380 cm⁻¹), BO₄ (1100–950 cm⁻¹) and MoO₄ (860 cm⁻¹) groups build up the glass network. MoO₆ units (band at 880 cm⁻¹) together with BO₃ units participate in the formation of the glass network with a high MoO₃ content (80–90 mol%).     

CeO2-Bi2O3 nanocomposite: Two step synthesis, microstructure and photocatalytic activity

CeO₂-Bi₂O₃ composite was synthesized via a two-stage process. The precursors were prepared from Ce(NO₃)₃·6H₂O, Bi(NO₃)₃·5H₂O and CO(NH₂)₂ with different molar ratio through the hydrothermal process, and then was completed by carrying out the precursors for 4 h at 600 °C under flowing air atmosphere. Techniques of X-ray diffraction (XRD), transmission electron microscopic (TEM) and diffuse reflectance ultraviolet-vis spectra (UV-DRS) were employed to characterize the as-synthesized materials. The results showed that the microstructure and morphology of CeO₂-Bi₂O₃ composite were similar in spite of different inverse proportion. We also investigated improved photocatalytic activity in the case of CeO₂-Bi₂O₃ composite catalyst compared to the catalytic activity of pure Bi₂O₃ or CeO₂ powder. The suppression of charge recombination in the composite CeO₂-Bi₂O₃ catalyst led to higher catalytic activity for the degradation of RhB. The CeO₂ 10%/Bi₂O₃ photocatalyst exhibited maximum photocatalytic activity. The photocatalytic activity is in close relation with the inverse proportion between reactants.     

Synthesis and microstructural properties of ZnO nanorods on Ti-buffer layers

This study examined the structural properties of ZnO nanorods grown on Ti-buffer layers with different surface roughnesses of 1.5 and 4.0 nm. Vertically aligned ZnO nanorods were synthesized on Al₂O₃ substrates with a Ti-buffer layer by metal-organic chemical vapor deposition. X-ray diffraction revealed the ZnO nanorods grown on a smooth surface to have higher quality and better alignment in the ab-plane than those grown on the rough surface. Field-emission transmission electron microscopy (FE-TEM) measurements revealed a disordered layer at the ZnO/Ti interface. FE-TEM demonstrated that the Ti-buffer layer contained a mixture of ordered and amorphous phases. Energy dispersive spectroscopy (EDS) analysis revealed the Ti-buffer layers to be entirely oxides.