Adsorption Properties of Silica Gel Prepared from a Decationized Sol

In accordance with the IUPAC classification, the shape of the capillary condensation hysteresis and type of the sorption isotherms of the vapors of water and tetrachloromethane by silica gel are identified, the latter being prepared from a decationized silica sol in the presence of aluminum chloride. It is found that the adsorption and structural properties of the silica gel depend on the concentration of silicon(IV) oxide and Al/Si molar ratio, as well as on the type of the adsorbate used. It is shown that the effect of aluminum chloride is manifested mainly in the spatial rearrangement of the particles of silicon(IV) oxide into dense agglomerates followed by their aggregation with the conservation of internal porosity. This leads to the appearance of narrow slitlike mesopores and to a decrease in or the stabilization of the average pore radius.     

Luminescence Properties of Tb-Doped Yttrium Disilicate Prepared by the Sol–Gel Method

A sol–gel method for the synthesis of nanosized powders of yttrium disilicate doped with Tb^{3 +} is presented. The influence of grain size and annealing temperature on the structure and luminescence properties of the materials obtained has been investigated. The preparation of glass-ceramic composite has been also described. The effect of incorporating the nanocrystals into sol–gel silica glasses on their physicochemical properties has been shown and discussed. A lack of influence of the annealing above 1300°C on the lifetimes measured for the nanocrystals embedded in the glass, as compared to the Y₂Si₂O₇:Tb^{3 +} powders, has been observed.     

Preparation and Characterization of CdTe Nanoparticles in Zirconia Films Prepared by the Sol Gel Method

Two methods for the synthesis of CdTe nanoparticles in zirconia sol-gel films are demonstrated. The nanoparticles were obtained by chemical reduction of Te(IV) using reducing agent (hydrazine) or tin chloride. Particle sizes ranging from 6 to 20 nm in diameter could be prepared by varying the experimetal parameters. The size and crystalline structure of the particles were characterized by optical absorption, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The film morphology was characterized by scanning force microscopy.The film obtained by SnCl₂ method is smooth and homogeneous. The dense structure of CdTe nanoparticles of a few nm in diameter is revealed. The films prepared with hydrazine are porous as a result of evolution of the decomposition gaseous products during the reduction.Advantages and disadvantages of the two methods are discussed.     

Structural Features of Phosphate and Sulfate Modified Zirconia Prepared by Sol–Gel Route

This paper describes the effect of sulfate, phosphate and nitrate complexing ligands on the structural features of amorphous xerogels and on the crystallization of metastable zirconia phases during the xerogel-ceramic conversion. Powdered samples were prepared by a sol–gel route using zirconyl chloride precursors chemically modified by complexing ligands. The structural evolution of ZrO₂ phases as function of firing temperature was analyzed by XRPD, EXAFS and ³¹P NMR/MAS. The experimental results show the formation of metastable t-ZrO₂ during the low firing temperature of xerogels modified by sulfate or phosphate groups. The martensitic tetragonal-monoclinic transformation occurs during desorption of sulfate groups. The largest temperature interval of stability of metastable tetragonal zirconia was observed for phosphate-modified xerogels.     

Synthesis of Nano Silica Particles for Polishing Prepared by Sol–Gel Method

In order to produce an excellent abrasive, a fabrication method for cocoon shaped silica particles has been studied. The particles are prepared from TMOS, water, ammonia and methanol by a sol–gel method. The method is to add the methanol solution of TMOS at a constant supply rate to a mixture of water, ammonia and methanol. Effects of various reaction conditions such as temperatures, supply rates of TMOS, and amounts of TMOS are studied on the diameter and shape of the particles. The diameter and shape are resulted in depending strongly on temperatures. High temperature makes particles with the high aspect ratio and the small diameter. And the mechanism of forming the cocoon shaped particle is also discussed. It is concluded that the primary particles are generated at the beginning stage of reaction and two of them become the cocoon shaped particle. For the polishing efficiency, particles have high polishing efficiency with the diameter between 40 nm and 210 nm. As a result, best diameter of particles for abrasive is 40–100 nm with respect to polishing efficiency and surface finish.     

Synthesis and Characterization of ZrO2-CaSO4 Materials Prepared by the Sol–Gel Method

Mixtures of ZrO₂-CaSO₄ in different molar ratio were prepared by the sol–gel method. The precursors were anhydrous calcium sulfate (CaSO₄) and zirconium n-butoxide in ethanol. Sulfuric acid was used as a hydrolysis catalyst to carry out the reaction at pH 3. The samples were thermally annealed and characterized by X-ray powder diffraction (XRD). Crystalline structure for selected samples (100, 90, 80% molar ZrO₂), were refined by the Rietveld method. Tetragonal zirconia and anhydrite were obtained in all compositions ranges, from 400 up to 800°C, although baddeyelite appears in the zirconia rich end (98% molar) from 600°C. Towards high calcium content, different nanostructured calcium sulfates as gypsum, bassanite and anhydrite were obtained.     

溶胶凝胶法制氧化铝负载铜基超细粒子催化剂的研究

采用溶胶凝胶法制氧化铝负载铜基超细粒子催化剂的制备了氧化铝负载的铜基超细粒子催化剂，用ＴＧ－ＤＴＡ，ＸＲＤ，ＢＥＴ以及ＴＥＭ等技术手段，对催化剂的物相结构，表面孔结构，粒子形貌以及催化性能等进行了研究。结果表明，利用溶胶凝胶法，可以直接帛备出高比表面积，低堆积密度的纤维状纳米级负载型Ｃｕ／Ａｌ２Ｏ３超细粒子；活性组分以远低于纳米级的微晶粒子簇状态，均匀地分散在纳米级氧化铝载体表面上，而且在低于５０     

钛凝胶的光致变色和电致变色特性

Titania gel is very sensitive to change of color to blue-purple by UV irradiation and to brown color under extra electric field polarzation. The UV absorption spectra of the photochromic (PC) and electrochromic(EC) titania gel are different to that of the nanocrystalline TiO_2 which changes to blue color by UV irradiation or under extra electric field polarization. The steady-state ESR measurements at room temperature indicate that ESR signals of Ti3+ appeared in PC and EC titania gel with the g values corresponding to 1.9505 and 1.9512, respectively.     

Electrochemical and Electrochromic Properties of Ni Oxide Thin Films Prepared by a Sol–Gel Method

Nickel oxide thin films, which are well known anodic coloration materials that are used in electrochromic devices, were prepared by a sol–gel method, and their electrochemical and electrochromic properties were investigated. The sol was prepared from Ni(OH)₂ powder with an average size of 7 nm, in a mixture of ethylene glycol and absolute ethanol. The films were coated on an ITO substrate using the powder, dispersed in the solution. When additive materials, acetyl acetone and glycerol, were added to the sol its hardness and adhesion properties were improved. The optimized thin film formed an amorphous, porous structure, and showed a large current density during continuous potential and pulse potential cycling. The film also was transparent and had a high coloration efficiency (33.5 cm²/C) and a rapid response time (1.0–2.5 s) during the coloring/bleaching process.     

Morphology and Texture of Silica Prepared by Sol–Gel Synthesis on the Surface of Fibrous Carbon Materials

Silica materials are synthesized by the sol–gel method including the deposition of tetraethoxysilane on various micro- and nanocarbon fibers. The use of nanofibrous carbon as a template makes it possible to prepare thermally stable mesoporous SiO₂ samples with unusually high surface areas (up to 1255 m²/g) and high porosity (up to 5.6 cm³/g). These silica materials and aerogels prepared by supercritical drying have comparable pore volumes. It is found by high-resolution electron microscopy that a thin-wall matrix permeated by channels is a prevailing structure of silica materials. When some catalytic fibrous carbons are used as templates, silica nanotubes can be prepared.     

聚合物泡孔材料为模板的溶胶－凝胶法制备大孔结构二氧化钛陶瓷

Macroporous titania monoliths were prepared via sol-gel method using polymer foam as templates.The poly-mer foam polymerized via concentrated emulsion polymerization was immerged in a solution of titanium(IV)iso-propoxide in 2-propanol,which underwent a sol-gel process.The organic components were subsequently removedby calcination.The effects of various parameters,including the nature of the monomer,the volume fraction of dis-persed phase of the concentrated emulsion,and concentration of the sol-gel solution were investigated.The SEMmicrographs of the macroporous titania monoliths thus obtained showed that the porous structure of the final mate-rial was effectively controllable.     

钛凝胶的光致变色和电致变色特性

过渡金属氧化物光致变色［１,２］和电致变色［３－７］材料在图象显示、信息存储以及做为调节光线强弱的“灵巧窗”等方面有着潜在的应用．国内外广大的科研工作者,在新型光电变色材料的寻找和光电变色机理等方面开展了较广泛而深入的研究．目前普遍认为变色机理为双注...     

Vanadium Pentoxide Sol and Gel Mesophases

Colloidal suspensions of V₂O₅ ribbon-like particles display optical textures typical of lyotropic nematic phases. Tactoids (small nematic droplets) and then isotropic phases are formed as these systems are diluted. Nematic suspensions can be oriented by applying a magnetic or an electric field. Such a liquid crystal behavior is mainly due to the highly anisotropic shape of vanadium oxide colloidal particles. Acid dissociation at the oxide/water interface gives rise to surface electrical charges and electrostatic repulsion should also be responsible for the stabilization of the nematic phases. Anisotropic xerogel layers are formed when these gels are deposited and dried onto flat substrates. X-ray diffraction patterns of such coatings exhibit a series of 00l harmonics due to the turbostratic stacking of the oxide particles. Dehydration is reversible and fluid mesophases are again obtained via a swelling process when water is added to the xerogel.     

Visible Up-Conversion Luminescence in Ho3+: BaTiO3 Nano-Crystals Prepared by Sol Gel Technique

Visible up-conversion emissions at (435, 545, 580, 675 and 690 nm) and (437, 547 575 and 675 nm) have been observed from the sol-gel derived nano-crystalline Ho³⁺: BaTiO₃ powders and thin films respectively, under 808 nm laser diode excitation emissions. Combined with the energy level structure of Ho³⁺ ions and the kinetics of the visible emissions, the up-conversion mechanism has been analyzed and explained. The blue, green and red emissions of both samples has been attributed to the ground state-directed transition from (⁵F₁), (⁵S₂) and (⁵F₅), which are populated through excited state absorption (ESA) for 808 nm excitation. Nano-structure pure barium titanate and doped with different concentrations of Ho³⁺ ions in the from of powder and thin film have been prepared by sol-gel technique, using barium acetate (Ba(Ac)₂), and titanium butoxide (Ti(C₄H₉O)₄), as precursors. The thin films were prepared by sol-gel spin coating method. The as-grown thin films and powders were found to be amorphous, which crystallized to the tetragonal phase after heating at 750°C in air for 30 minutes. The crystallite sizes of the thin film and powder both doped with 4% Ho³⁺ ions was found to be equal to 11 and 16 nm, respectvely.     

溶胶—凝胶工艺制备TiO2薄膜的表面组成和价态研究

通过Ｘ射线光电子能谱（ＸＰＳ）和电子自旋共振谱（ＥＳＲ）,确定了采用溶胶－凝胶工艺制备的ＴｉＯ２光催化纳米薄膜中元素的化学组成和价态。实验结果表明,薄膜中除含有钛和氧元素外,还有一定量的来自有机前驱物中未完全燃烧的残余碳和少量从玻璃表面扩散到薄膜中的钠和钙离子;Ｔｉ除了以Ｔｉ＾４＋价形态存在外,还有一定量的Ｔｉ以Ｔｉ＾３＋和Ｔｉ＾２＋形式存在,这种情况主要是由于有机基团的燃烧,来自玻璃基体中钠与钙     

Ce掺杂对SnO2薄膜电学及气敏性能的影响

以无机盐ＳｎＣｌ２．２Ｈ２Ｏ（Ｎ４）３Ｃｅ（ＮＯ３）６为原料，无水乙醇为溶剂，采用溶胶－凝胶工艺制备了纯ＳｎＯ２及ＳｎＯ２：Ｃｅ薄膜。研究了ＳｎＯ２：Ｃｅ薄膜的热分解晶化过程和Ｃｅ掺杂和ＳｎＯ２薄膜的及气敏性能的影响，发现ＳｎＯ２：Ｃｅ薄膜在常温下对Ｈ２Ｓ气体具有较妇的敢敏性能，对ＳｎＯ２：Ｃｅ薄膜的结构进行了表征。     

Titania on Silica. A Comparison of Sol-Gel Routes and Traditional Methods

Titania on silica samples have been prepared by: i) precipitation-deposition from a solution of TiCl₃ onto the surface of a commercial silica, and ii) base catalysed hydrolysis-condensation of TEOS followed by reaction with Ti isopropoxide. These samples were characterised by nitrogen and hydrogen adsorption, X-ray diffraction, FTIR, temperature programmed reduction, transmission electron microscopy and catalytic activity in butane-hydrogen conversion. The sol-gel preparation produced a better titania dispersion due to the formation of stabilising Ti-O-Si bonds. Upon these samples was then introduced Ir. Strong metal-support interactions between Ir and titania have been observed after high temperature reduction, causing a significantincrease in butane dehydrogenation activity relative to hydrogenolysis.It appears that using sol-gel chemistry useful supports for catalytic metals containing Si-O-Ti linkages can be produced and in future may be optimised for other metal-oxygen metal pairs.     

TEMPO Containing Polynorbornene Block Copolymers Prepared via ROMP and Their use as Scaffolds in Sol/Gel-Process

Summary: Block copolymers ( B ₅₀ T ₃₀ and B ₂₁ T ₃₀) containing free nitroxide-radicals with two different chain lengths derived from the monomers (+/−) endo,exo-bicyclo[2,2,1]-hept-5-ene-2,3-dicarboxylic acid-bis-O-tert.-butyl ester ( monomer B ) and (+/−)endo,exo-bicyclo[2,2,1]-hept-5-ene-2,3-dicarboxylic acid-bis-O-2,2,6,6-piperidinoxyl-ester ( monomer T ) were polymerized via ring opening metathesis polymerization (ROMP). The ter.-butyl-moiety in block B could then be hydrolyzed to obtain amphiphilic block copolymers which were used as scaffolds in subsequent sol/gel-process. The resulting block copolymers were analyzed via small angle X-Ray scattering (SAXS) to investigate microphase separation and the sol/gel products were analyzed by X-Ray Diffraction (XRD) to prove the formation of ordered TiO₂ crystals.     

Nitrifying and Denitrifying Microbiological Mud Encapsulated by the Sol–Gel Method

The aquatic underground mantle in the Peninsula of Yucatan (Mexico) represents the only source of water supply for domestic consumption. Nevertheless, this mantle is extremely vulnerable to infiltration of pollutants as nitrates due to the karstic layer. Nitrates are inorganic pollutants, whose mobility and stability make them highly dangerous in aerobic systems such as underground water. This contaminant has been found at up to 223 mg/L in artesian wells, whereas the maximum limit permitted by the World Health Organization is 45 mg/L. The development of innovative biomaterials, as nitrifying and denitrifying microbiological mud encapsulated in an inert matrix using the sol–gel technique, represents a possible alternative to eliminate nitrates in situ from the underground water of Merida in the state of Yucatan, Mexico. The sol–gel method has been extensively used for the preparation of such materials permitting a higher stability and viability of useful organisms. In this work the thermal properties of nitrifying and denitrifying mud encapsulated in silica gel derived from tetraethoxysilane are presented as a function of temperature. The photopyroelectric technique was used to study how different types of mud interchanges heat with the environment. The specific surface area of the nitrified mud was determined by analyzing the pore size distribution.