同步合成模板法制备热解炭及其电化学电容性能研究

研究制备新型炭材料是提高电化学电容器性能的有效途径。本文以二氧化硅干凝胶为模板,以合成间苯二酚-甲醛(RF)干凝胶为炭前驱体,采用同步合成模板法制得了比表面积达1100m²·g^-1,孔径分布集中,平均孔径为4.5nm的炭材料。循环伏安研究表明,与比表面积为1720m²·g^-1的活性炭相比,本研究制得的炭材料具有更优异的电化学电容性能,2mV·s^-1时比容量达195F·g^-1。     

Microporous Silica Xerogel Membrane with High Selectivity and High Permeance for Carbon Dioxide Separation

The asymmetric microporous silica xerogel membrane was prepared by sol-gel method. A multi-layer (asymmetric) structure was obtained by silica xerogel layer on top of mesoporous silica layer (mean pore diameter of 4 nm), supported by porous alumina tube (mean pore diameter of 0.1 m). The ratio of the permeances, CO₂/N₂ for this membrane attained more than 60 at 298 K. This value is considerably higher than the theoretical Knudsen value (CO₂/N₂ = 0.8). The gas permeances of this membrane were about 5–10 times higher than the previous membrane. Application of the membrane to an enrichment of CO₂ from air was also investigated. CO₂ in the air (about 300 ppm) was concentrated to more than 1000 ppm by using the membrane at 298 K.     

Extensions in the synthesis and catalytic application of titanium silicalite-1

Titanium silicalite-1 (TS-1) was prepared by microwave heating of a SiO₂–TiO₂ xerogel, which was dry-impregnated with tetrapropylammonium hydroxide (TPAOH). Highly crystalline product was obtained, with the yields higher than 90%, within 30 min after microwave irradiation. These are significant advantages over the conventional oven heating using alkoxide precursors in liquid phase, which requires 1-2 day crystallization time with low product yields. Sub-micron sized SiO₂–TiO₂ prepared by thermal plasma process and Ti-containing mesoporous silica, Ti-HMS, were also tested as the solid phase precursor for TS-1. These were found inferior as precursor due to difficulties in uniformly wetting the surface with TPAOH. It was possible to prepare TS-1 using diethoxysiloxane-ethyltitanate (DESET, 93.75 mol Si:6.25 mol Ti) as a single mixed alkoxide precursor, but titanium species in the sample were highly unstable and large fraction of them came out from the framework to form TiO₂ clusters upon calcination. In addition, TS-1 monolith was prepared utilizing polyurethane foam as an infiltration medium of the synthesis gel. The prepared TS-1 monolith exhibited properties similar to those of TS-1 powders, but the elementary unit of the former was made of 1–2 micron-sized hexagonal shaped crystals, causing diffusion problems. Catalytic activities of all the prepared catalysts were evaluated using 1-hexene epoxidation as a probe reaction, and 2,5-dihydrofuran epoxidation was also examined using TS-1 as an alternative process to make 3,4-epoxytetrahydrofuran.     

Site selection spectroscopy of SiO2:Eu3+ gels

Silica gels doped with Eu³⁺ ions were studied at temperatures between 10 K and 300 K by site selection spectroscopy in samples heated up to 200°C. The ⁵D₀ ⁷F₀ transition shows internal structures due to the different environments of the europium ions. Lifetimes, energy levels and homogeneous linewidths are site dependent. In the wet gel the Eu³⁺ ions prefer a liquid-like environment and only when the liquid is removed by heat treatment, the ion is linked more strongly to the silica network.     

Preparation of Transparent, Partially-Crystallized BaTiO3 Monolithic Xerogels by Sol-Gel Processing

Transparent, partially-crystallized nanostructured barium titanate (BaTiO3) monolithic xerogels (dried at 90°C) have been successfully synthesized via hydrolysis of Ba, Ti alkoxide precursor solutions in a concentration range of 1.0 mol/l with addition of water with a molar ratio of H2O/Ba 6.3. Transparent monolithic xerogels obtained from a precursor solution of 1.0 mol/l remained transparent even after firing at 500°C in oxygen, although the degree of their transparency was considerably decreased. Firing at temperatures above 500°C yielded translucent ceramics of BaTiO3, and ultimately, firing above 600°C resulted in normal opaque ceramic bodies. Those obtained from a more concentrated precursor solution of 1.2 mol/l were, on the other hand, still transparent after firing at 600°C in oxygen, and turned opaque at 700°C. The results demonstrate that the materials retained their transparency even after pyrolysis of organic compounds involving exothermic oxidation at temperatures in the range of 200 to 400°C. The densification behavior of transparent BaTiO3 monolithic xerogels obtained was found to be excellent; for example, those derived from a 1.0 mol/l precursor solution could be sintered to form monolithic BaTiO3 ceramics with a relative sintered density of about 94% and an average grain size of 1 m by firing at 1100°C for 2 h in oxygen.     

Synthesis of silica xerogels with highly distinct morphologies in the presence of imidazolium ionic liquids

This article describes the preparation of silica xerogels by the sol–gel technique, using tetraethoxysilane as precursor and hydrofluoric acid as catalyst, in the presence of imidazolium ionic liquids (ILs). The applied ILs 1–3 contained the 1-monoethylene glycol monomethyl ether-3-methylimidazolium cation in combination with the methanesulfonate (1), tetrafluoroborate (2) and hexafluorophosphate (3) anions, respectively. Characterization of these materials was performed by photography, scanning electron microscopy, atomic force microscopy, X-ray diffraction, thermogravimetric analysis and nitrogen adsorption-desorption isotherms. The IL anion was identified as a powerful morphology controller. The methanesulfonate anion of IL 1 induced the formation of a compact lamellar monolith with an interlamellar distance of 1.5 nm and a flat surface. A free flowing powder of aggregated spherical particles was obtained in the presence of tetrafluoroborate IL 2, and the hexafluorophosphate anion of IL 3 induced the formation of porcelain like aggregates with honeycomb shapes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

表面活性物质对SiO2干凝胶中甲基橙变色反应的影响

掺杂;表面活性物质对SiO2干凝胶中甲基橙变色反应的影响     

Influence of fluorination of xerogels on the intensity of photoluminescence of gamma-irradiated sol-gel quartz glasses

We investigated the influence of fluorination of xerogel on the intensity of luminescence with a maximum at 1.9 eV attributable to nonbridging oxygen atoms in gamma-quanta irradiated sol-gel quartzglasses. It is established that in samples with a high content of hydroxyl groups (more than 8 ppm) the intensity of this luminescence correlates with the content of hydroxyl in the initial samples. Fluorination of gels at the technological stage before sintering substantially reduces the number of silanol groups, improves the quality of glass, and increases their radiative-optical stability. Translated from Zhurnal Priklandoi Spektroskopii, Vol. 67, No. 2, pp. 266–268, March–April, 2000. This work was carried out with financial support from the Belarusian Republican Foundation for Fundamental Research, project F98-139.     

Removal of rhodamine B from aqueous solutions using vanadium pentoxide/titanium butyl oxide hybrid xerogels

A stable and insoluble V_2O_5·n H_2O/tetra-n-butyl titanate(TBO) hybrid xerogel was synthesized by the sol–gel method. This novel material proved to be an efficient absorbent with an absorption capacity of 179 mg·g~(-1)for Rhodamine B(Rh B) in water due to its unique layered structure, which can effectively accommodate Rh B molecules between its layers as demonstrated by XRD and FTIR spectroscopic analyses.     

Spectral and nonlinear optical properties of metal complexes with 1,2-naphthalocyanine in silicate gel matrices

We have studied the influence of the method for embedding metal (Yb or Zn) complexes with 1,2-naphthalocyanine into nanoporous silicate xerogels (directly during sol-gel synthesis or by impregnation of the xerogel) and the nature of the Yb³⁺ exoligand (anionic Cl⁻ or acetylacetone) on the spectral properties and structure of impurity molecular centers. It is shown that the degree of protonation and/or aggregation of the studied metal complexes is determined by the average surface concentration of HO-Si≡ silanol groups of the gel-matrix nanopores. It is established that the Yb complex with 1,2-naphthalocyanine and the anionic ligand Cl⁻ penetrates to the greatest extent from solution into the inner cavities of the xerogel (degree of impregnation). This is due to quasichemical interaction of pigment molecules with the dehydroxylated nanopore surface containing ≡Si-O-Si≡ siloxane bridges. It is shown that the investigated metal complexes in both liquid solutions and solid-state silicate gel-matrices have a limiting effect on powerful optical radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 439–446, July–August, 2007.