Synthesis of zirconium oxide by hydrolysis of zirconium alkoxide

Submicrometre particles have been prepared from hydrolysis-polycondensation of zirconium alkoxide [Zr(n-C₃H₇O)₄] in ethanolic solution. The properties of these particles (morphology, specific surface area, S _BET, crystal phase and size distribution) after calcination at 450 °C for 5 h were found to depend on the conditions of synthesis, i.e. alkoxide concentration and mole ratio water/alkoxide.     

Synthesis and characterization of high surface area molybdenum nitride

The synthesis of high surface area γ-Mo₂N materials using the nitridation of oxide precursors MoO₃, H₂MoO₅, and H₂MoO₅·H₂O with ammonia at 650°C is described. H₂MoO₅ and its hydrated form were obtained from the reaction of MoO₃ and diluted H₂O₂. The materials were characterized by means of X-ray powder diffraction, thermal analysis and nitrogen physisorption. Directly after the preparation, the nitride materials were subjected to different processing conditions: (1) contact to air, (2) inert gas or (3) treated with 1% O₂(g)/N₂(g) gas mixture (Passivation). The synthesis and passivation conditions critically affect the specific surface area of the final product. By means of XRD a minor quantity of MoO₂ was detected in most of the products. The highest specific surface area of the nitrides was 158.4 m²/g for γ-Mo₂N materials using H₂MoO₅·H₂O as the precursor. The high specific surface area corresponds to an average particle diameter of 4 nm, assuming a cubic morphology of the nanocrystals (d_p = 6/ρS_BET, ρ = 9.5 g/cc). The nitrogen physisorption isotherms of γ-Mo₂N are of type IV, but pore sizes and diameters differ significantly depending on the synthesis conditions due to different defect structures of the intermediates generated in the course of the topotactic transformation of the oxides to nitrides.     

Synthesis of porous,high surface area MgO microspheres

Porous MgO microspheres with nanocrystallites have been prepared by a wet precipitation process using ammonium hydrogen carbonate and ammonium hydroxide as precipitants. The as-precipitated powders are composed of crystalline Mg₅(OH)₂(CO₃)₄.4H₂O microspheres with porous and hollow microstructure and are decomposed and transformed to nanocrystalline cubic MgO after being calcined at 500 °C. The average crystallite size of MgO microspheres increases from 10 nm to 31.6 nm with increasing temperature from 500 °C to 1100 °C. The surface area of the MgO powder decreases from 90.7 m²/g to 31.5 m²/g with increasing temperature from 500 °C to 1100 °C.     

Synthesis of rose-like boron nitride particles with a high specific surface area

Novel rose-like BN nanostructures were synthesized on a large scale via a two-step procedure. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometer and nitrogen porosimetry. The results show that the obtained rose-like nanostructures are composed of a large amount of h-BN crystalline flakes and have a surface area of 90.31 m²/g. A mechanism was proposed to explain the formation process of the rose-like BN nanostructures.     

Synthesis of high surface area mesoporous bioactive glass nanospheres

Mesoporous bioactive glass (MBG) nanospheres having the composition of SiO₂-CaO-P₂O₅ with both a large specific surface area (∼ 1040 m² g^− 1) and pore volume (1.54 cm³ g^− 1) were prepared using the ionic surfactant, cetyltrimethyl-ammonium bromide (CTAB), as a template. The size of the nanospheres depends on the amount of CaO that is incorporated and can be controlled over the range of diameters from 20 to 200 nm under dilute aqueous condition. In vitro bioactivity studies were carried out in simulated body fluid (SBF). Cytotoxicity tests of the MBG nanospheres were also performed by observing their influence on J774 macrophages at various concentrations.     

Synthesis of high surface area ZnO powder by continuous precipitation

Synthesis of high surface area ZnO powder was achieved by continuous precipitation using zinc ions and urea at low temperature of 90 °C. The powder precipitated resulted in high-purity single-phase ZnO powder when calcined at 280 °C for 3 h in air. The solution pH and the precipitation duration strongly affected the surface area of the calcined ZnO powder. Detailed structural characterizations demonstrated that the synthesized ZnO powder were single crystalline with wurtzite hexagonal phase. The powdered samples precipitated by homogeneous precipitation crystallized directly to hydrozincite without any intermediate phase formation.The phase structures, morphologies and properties of the final ZnO powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering particle size analysis (DLS), and nitrogen physisorption in order to determine the specific surface area (BET) and the pore size distribution (BJH).     

Synthesis and characterization of ordered mesoporous silicon carbide with high specific surface area

Ordered mesoporous silicon carbide with a high specific surface area was prepared using poly(methlysilylene)ethynylene by utilizing mesoporous silica SBA-15 as a template which was etched off after pyrolysis in an argon atmosphere. The obtained sample is mainly composed of randomly oriented β-SiC crystallites, and it exhibits an ordered mesoporous structure, a high surface area of 511 m²/g, a large pore volume of 0.61 cm³/g, and narrow pore-size distributions of 4 nm. The rough surface and high order of the material that result from the strong interconnections of the SiC products are the main reasons for such high surface areas. The mesoporous ceramics have stability even after re-treatment at 900 °C for 2 h under an air atmosphere.     

Synthesis of lanthanum zirconium oxide nanomaterials through composite-hydroxide-mediated approach

A novel thermal barrier coating material, lanthanum zirconium oxide (La₂Zr₂O₇) has been synthesized through the composite-hydroxide-mediated method at low temperature. The phase structures, morphology, thermal stability and thermal conductivity of the as-synthesized La₂Zr₂O₇ were investigated systematically. The X-ray diffraction (XRD) patterns revealed a single phase with cubic pyrochlore structure for La₂Zr₂O₇ after treated at 1300 °C for 100 h. The transmission electron microscope (TEM) and scanning electron microscope (SEM) analyses showed that the sample was made up of sphere-like nanoparticles with the size between 50 and 100 nm. Furthermore, the thermal analysis result demonstrated the La₂Zr₂O₇ sample had high thermal stability even at 1300 °C. As the temperature increased to 1200 °C, the thermal conductivity value could be as low as 1.75 W m^?1 K^?1. Due to the high-temperature stability and lower thermal conductivity, the La₂Zr₂O₇ material is expected to be a promising candidate for the use of thermal barrier coatings.     

Synthesis and characterization of metal ions containing hydroxyapatite microparticles with high specific surface area

Zinc and/or iron ions containing hydroxyapatite (HA) microparticles, which had twice as high specific surface area and higher pore volumes compared with the pure HA, were fabricated by a spray drying method; the zinc and/or iron ions were incorporated into the constitutional nanocrystals with below 20 nm in size in preparing. The small amount of carbonate ions was substituted in the phosphate group. The particle sizes were distributed in the range of 1 to 20 microm in diameter and its averaged size was approximately 6 microm. The microparticles with a spherical shape showed a single phase of HA and, after treated at higher temperature than 800 degrees C, had the high crystallite HA and the other phase of metal oxide such as ZnO or Fe2O3. The microparticles with higher specific surface area will be applicable for the drug delivery carriers of proteins.     

Synthesis of high surface area mesoporous carbonates in novel ionic liquid

High surface area mesoporous SrCO₃, CaCO₃ and MnCO₃ with straw-like bundles morphology were synthesized in a novel imidazolium pyruvate ionic liquid. These carbonates were characterized by X-ray diffraction, Fourier transform infrared spectra and transmission electron microscopy. The results revealed that these carbonates have pure orthorhombic and rhombohedral structures, respectively, and the prepared products all show the unique straw-like morphology. Mesoporous properties and high surface areas of SrCO₃(118 m²/g), CaCO₃(43 m²/g) and MnCO₃ (122 m²/g) were also confirmed by the corresponding N₂ sorption analyses.     

Nanocrystalline tetragonal zirconium oxide stabilization at low temperatures by using rare earth ions: Sm and Tb

Zirconium oxide was synthesized by the sol–gel method and the tetragonal structure was stabilized up to 1000 °C by doping with different rare earth ions. The evolution of the crystalline structure as a function of the annealing temperature and rare earth concentration of doped and undoped samples were investigated by X-ray diffraction. Our experimental results show that it is possible to obtain up to 73 wt.% of tetragonal content by doping the ZrO₂ with 2 mol% of Sm₂O₃ or Tb₂O₃ and annealing at 1000 °C. Variations in the lattice parameters and nanocrystallite size were also obtained. Our results suggest that the stabilization of tetragonal structure can be obtained with other rare earth ions.     

高比表面积纳米氧化锆的制备及应用

氧化锆是一种重要的催化剂及载体.它具有酸碱双功能表面性质,尤其是它优良的耐热性能在材料领域得到了广泛应用.本文介绍了几种高比表面积纳米氧化锆的制备方法以及在各种新材料领域的应用.     

高比表面积AlN粉末的制备

以硝酸铝和蔗糖为原料,采用溶胶-凝胶法制备碳铝干凝胶,通过碳热还原反应制备了高比表面积的AlN粉末,探讨了反应温度,硝酸镍的添加量对合成AlN粉末的影响.用XRD,SEM和低温N2物理吸附等手段表征发现,制备的AlN球形粒子粒径均一,约40～50nm左右,具有规则形貌,高比表面积和狭窄的孔径分布;镍盐的掺杂可以显著提升生成AlN的速率,使AlN球形粒子形貌发生很大的改变,其粒子变得粗大,甚至发生了部分团聚.     

Microwave-assisted rapid synthesis of platinum nanoclusters with high surface area

Synthesis of platinum nanoclusters (PNCs), with its advantages of high surface area and reduced materials costs, represents a greatly interesting class of nanomaterials. In this paper, a one-step, rapid and efficient aqueous-phase reaction to straightforwardly produce PNCs in high yield is proposed without the need for any organic solvent, template or ion replacement, which is carried out simply by microwave-assisted heat-treatment of an aqueous solution containing K2PtCl4 and 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonicacid (HEPES) within 12 s. As-prepared platinum nanoclusters are porous interconnected nanostructures and possess very high surface area (41 m2 g(-1)). The combination of high surface area with the nanoarchitectures consisting of pores of the product is advantageous for catalytic applications.     

Synthesis and characterization of high surface area silicon carbide by dynamic vacuum carbothermal reduction

Silicon carbide (SiC) precursor was obtained by sol–gel used tetraethoxysilane as silicon source and saccharose as carbon source, and then the precursor was used to prepare SiC by carbothermal reduction under dynamic vacuum condition. The samples were characterized by X-ray diffraction, scanning electron microscope, and low-temperature nitrogen adsorption–desorption measurement. The results showed that the carbothermal temperature for synthesizing SiC needed to be at 1,100 °C under dynamic vacuum. At this temperature, the obtained sample is composed of agglomerated regular grains with size ranging from 20 to 40 nm and has a high surface area of 167 m²/g and the main pore size center at 5.3 nm.

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The preparation of tungsten oxide powders with high specific surface areas

Tungsten oxide powders with high specific surface areas (50 m²g^–1) are prepared by using a variation on the hot kerosene drying technique. It is also shown that the use of a water in oil emulsion in the hot kerosene drying technique has no effect on the specific surface areas of the resultant powders. The reason for the absence of any effect is explained. The difference between the powders prepared by the hot kerosene drying technique and the variation of this, is the high specific surface area due to the porous structure of the powders prepared by the latter method.     

Chemical solution deposited lanthanum zirconium oxide thin films: Synthesis and chemistry

Pyrochlore lanthanum zirconium oxide (LZO) thin films textured along 〈4 0 0〉 are synthesized using lanthanum acetate hydrate, zirconium propoxide, propionic acid, acetic acid glacial, and methanol as precursors. The materials growth and chemistry are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA). The formation of inkjet printed LZO films on Ni-5%W tape is found to be based on the decomposition of the LZO precursor solution. In the annealing process, Zr metal–oxides bonds are first eliminated between 150 and 250 °C, while carboxylates from precursors remain in LZO after the annealing carried out at 900 °C for an hour. Annealed LZO films have dense and smooth structure that are composed of nanoparticles sizing 10–15 nm and some pinholes sizing 25–35 nm accounted for less than 0.1% of the area are observed.     

Synthesis and photocatalytic activity of stable nanocrystalline TiO(2) with high crystallinity and large surface area

Superior photoactive TiO(2) nanopowders with high crystallinity and large surface area were synthesized by a hydrothermal process in the presence of cetyltrimethylammonium bromide and a post-treatment with ammonia. The prepared photocatalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, N(2) adsorption-desorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectra (DRS) and surface photovoltage spectroscopy (SPS). The prepared nanocrystallites were highly resistant to thermal sintering, and the calcinations up to 900 degrees C were shown to enhance the crystallinity of the anatase phase without any rutile phase and the separation rate of photoinduced charges of TiO(2) particles. It remained as large as 196 and 125 m(2)/g even after calcinations at 700 and 800 degrees C, respectively. The photocatalytic activity of prepared photocatalysts was obviously higher than that of commercial Degussa P25 on the photodegradation of methylene blue and phenol in water under ultraviolet-light irradiation, and the sample calcined at 800 degrees C afforded the highest photocatalytic activity.