Further Insights into the Porous Structure of TEOS Derived Silica Gels

The porous structure of TEOS derived silica gels was studied using nitrogen adsorption at 77 K. Silica gels were prepared using TEOS, H₂O and ethanol for different molar ratios. No catalyst was used in this study. Silica gels were also heat treated up to 1000°C. The nitrogen sorption isotherms were analyzed by two models: Fractal and Percolation Theories. Using the fractal analysis approach, the surface roughness of the porous structure of silica gels was determined. The surface fractal dimension depends on the hydrolysis conditions and heat treatment. The surface fractal dimension decreases with increasing H₂O/TEOS molar ratio or heating temperature. For the silica gels studied, the surface fractal dimension changed from 2.6 to 2.5 after heating the gels, and from 2.4 to 2.6 with decreasing H₂O/TEOS ratio.Using the Percolation theory, we have determined the connectivity of the porous structure of silica gels. The extent of sorption hysteresis of the nitrogen isotherms reflects the connectivity of the pore network. The mean coordination number (connectivity) Z, and the linear dimension of the network, L, have been calculated from the hysteresis of the isotherms. For the as-prepared silica gels, Z was about 8 and L close to 2. On heating the gels, Z decreases to 4 and L increases to 7, results which are in accordance with the collapse of the porous network.     

Effects of the Water Quantity on the Solventless TEOS Hydrolysis Under Ultrasound Stimulation

The acid hydrolysis under ultrasound stimulation of solventless tetraethoxysilane(TEOS)-water mixtures was studied at 40°C, by means of a heat flux calorimetric method, as a function of the initial water/TEOS molar ratio (r) ranging from 2 to 10. The method is based on the time record of the exothermic heat peak of hydrolysis, arising after an induction time under ultrasound stimulation, which is a measure of the reaction rate. The hydrolysed quantity was found to be approximately independent of the water/TEOS molar ratio, even for r < 4. Polycondensation reaction takes place mainly for low water/TEOS molar ratio in order to supply water to allow almost complete hydrolysis. The overall process of dissolution and hydrolysis has reasonably been described by a previous modelling. The dissolution process of water in TEOS, under ultrasound stimulation and acid conditions, was found to be rather dependent of the alcohol produced in the hydrolysis reaction instead of the initial water quantity present in the mixture.     

竹红菌素的结构修饰

竹红菌甲素(简称甲素,HA)是一种新发现的苝醌衍生物,可作光疗药物和光敏化剂。为了筛选出更好的光疗药物,我们逐步修饰了竹红菌素的结构。痂囊腔菌素1的2位和11位甲氧基可被三氯化铝选择性地脱去甲基,而6位和7位的甲氧基不变化,但反应后产物难于分离提     

Chromium(IV) Stabilisation in New Ceramic Matrices by Coprecipitation Method: Application as Ceramic Pigments

In this paper the stabilization of Cr⁴⁺ in new ceramic matrices as willemite Zn₂SiO₄ and galium‐gadolinium garnet GGG (Gd₃Ga₅O₁₂) is studied and compared with the chromium‐sphene ceramic pigment using the traditional solid reaction and an unconventional coprecipitation method.The chromate amount etched from the powders using Cr^III and Cr^VI precursors on ceramic and coprecipitation routes are analysed in order to evaluate the environmental impact on the waste water. Cr‐willemite and codoped Ca, Cr‐GGG produces solid solutions of Cr⁴⁺ ion occupying tetrahedral and dodecahedral sites, respectively, while Cr⁴⁺ into sphene lattice occupies octahedral sites. Cr‐willemite are stable when used as ceramic pigment in habitual tile glazes but Cr‐GGG unstabilses and produces green colour associated to Cr³⁺ solved in the glaze. Coprecipitate powders are more reactive than ceramic powders but in Cr‐GGG stabilizes the metastable Ca₃Cr₂O₈ oxide. Chromate amount in washing hot water are not dependent of the chromium precursor but depends of the allowed reactivity level and the reaction media.     

Effect of solvent type on polycondensation of TEOS catalyzed by DBTL as used for stone consolidation

We have investigated the effect of solvent in the sol–gel process of tetraethylorthosilicate (TEOS) when di-n-butyltin dilaurate (DBTL) is used as polycondensation catalyst. Two sets of materials similar to those employed in the field of stone consolidation were prepared in the laboratory by using either protic or aprotic solvents: (1) xerogels from TEOS/DBTL, and (2) composites from TEOS/colloidal silica particles/DBTL. The results have shown that the solvent directly influences the aggregation pathway of the condensates. For a mixture of methyl ethyl ketone/acetone (aprotic solvents), gels with a higher degree of condensation were obtained. In the case of TEOS xerogels, the materials are essentially non-porous. Additionally, the incorporation of colloidal silica particles induces an important increase in porosity, which is even more dramatic when ethanol is used as solvent, through the formation of micro and mesoporous materials as the concentration of particles is increased. A TEOS polymerization pathway is suggested depending on which system of solvents is used. Various analytical techniques were used to characterize the materials obtained.     

Kinetics of O2 + TEOS gas-phase chemical reactions in a remote RF plasma reactor with electron spin resonance

Kinetics of the reaction O+TEOS (tetraethoxysilane) was studied by means of the ESR method. Molecular oxygen was partially atomized by a 13.56-MHz discharge in the quartz tube that passed inside an ESR cavity. TEOS vapors were injected between the discharge and ESR cavity. O-atom loss occurring due to the reaction of atomic oxygen with TEOS molecules was measured and the rate coefficient k, of the reaction of O atoms with TEOS molecules was determined. The obtained results could be used for deposition process simulations.     

The Chemistry of Rose Pigments

In this article we present a survey of the pigments found in the flowers and fruits of old and modern varieties of roses. The yellow colors are produced by carotenoids, the reds by anthocyanins, and the modern oranges by a mixture of the two. The great structural diversity of the carotenoids contrasts with a surprisingly small number of anthocyanins. For the carotenoids found in roses, a clear correspondence exists between the structure and the breeding partners used; the old yellow roses, which arose from crosses with Chinese varieties, mainly contain carotenoids from early stages in the biosynthesis, while in the modern yellow roses, which are descended from Central Asian foetida types, hydroxylations, epoxidations, and epoxide transformations readily occur. A recently elucidated carotenoid degradation sequence follows the scheme C₄₀ → C₁₃ + C₂₇ → C₁₃ + C₁₄. The C₁₃ compounds are odoriferous substances that contribute to the scent of roses. In the physiological pH region, copigmentation with flavonol glycosides is crucial for stabilization of the anthocyanin chromophores. Many roses, including the “apothecary's rose”, which was once used medicinally, contain large amounts of strongly astringent ellagitannins, monosaccharide esters of gallic acid.     

Formation of Silica Nanoparticles by Hydrolysis of TEOS Using a Mixed Semi-Batch/Batch Method

A new method for preparing silica nanoparticles, which consists of a two-stage semi-batch/batch hydrolysis reaction of tetraethylorthosilicate (TEOS), is presented. A relatively slow rate of hydrolysis of the TEOS occurred during the semi-batch process, which resulted in larger silica particles with a narrower size distribution. This was in direct contrast to the batch process. An example of reduction in particle size for an initial semi-batch and subsequent batch reaction is shown. On completion of the initial semi-batch step, the silica particles had a diameter of 106 nm. As the subsequent batch reaction proceeded, the mean size of the particles decreased to 23 nm. In this work, it was found that the optimal conditions for the silica nanoparticles using this mixed method were as follows; (TEOS: 0.5 M, H₂O: 6.0 M, NH₄OH: 0.2 M, feed rate: 5.0 ml/min, temperature: 42.5°C). In conclusion, a mixedsemi-batch/batch system suggested a new probability for the synthesis of nanoparticles.     

无机颜料合成的探究及社会调研

无机颜料是多种日用品常用的着色剂,厦门大学本科生社会实践小组在查阅文献的基础上,在实验室小量合成了部分无机颜料,对合成方法进行了总结、讨论;同时进行了问卷调查,到相关企业进行了参观、学习。     

食品中7种常见的非食用色素检测研究进展

食用色素可以明显改善食品外观,激发食欲,在食品行业有着广泛的应用,但若向食品中添加非食用色素来代替食用色素,则会对人体存在致癌风险。食品中常见的非食用色素有以下7种:碱性嫩黄O、碱性橙Ⅱ、酸性橙Ⅱ、苏丹红、若丹明B、美术绿和孔雀石绿,而目前对这7种非食用色素检测的国家标准还未全部建立。本文综述了近3年来食品行业中针对这7种非食用色素的各种检验方法,以期为食品安全监督检测提供参考。     

Formation of fractal porous silica by hydrolysis of TEOS in a bicontinuous microemulsion

Mesoporous silica particles have been prepared by hydrolysis of TEOS (Si(OC₂H₅)₄) in bicontinuous microemulsions containing polyoxyethylene (POE) dodecylether, isooctane and water. TEOS was dissolved in a continuous water phase and hydrolyzed by the dispersed water at around the phase inversion temperature (60°C). Undulating solid materials with layered mesostructures were produced from middle-phase microemulsions in the three phase region (o/w=0.2–0.7). On the other hand, the solids obtained from the lower aqueous phase in the three phase region were found to have a heterogeneous disordered structure. Measurements of the fractal dimensions were performed in the macropore region using a box-counting method for the outline of the SEM texture. We found that the macropore size distribution in the particles prepared from the middle-phase microemulsion follows the fractal rule with a dimension of 1.7. From the results of nitrogen adsorption/desorption curves on the silica, a steep increase in the adsorption amounts was observed at a relative pressure below 0.2, and adsorption/desorption hysteresis was also observed at a relative pressure between 0.3 and 0.5. These studies suggest that the silica synthesized in the bicontinuous microemulsion mesostructure has a very broad size range from micro to macropores with a fractal distribution.     

火焰原子吸收法测定三种天然色素中的八种无机元素

用火焰原子吸收光谱法测定了三种色素中常见的八种微量无机元素Zn、Fe、Ca、Cu、K、Na、Mn、Mg的含量。结果表明，三种色素中K、Mg、Ca含量较高，Cu含量较低。讨论了几种无机元素与健康的关系，对开发这三种天然色素提供了有用的参考数据。     

Surface Energy Changes of Heat Treated TEOS Derived Silica Xerogels

The surface energy of monolithic silica xerogels was examined by measuring the interaction of organic probes with xerogels heated at temperatures close to the gel-to-glass transition temperature. Values of the dispersive component of the surface energy, , between 60 and 80 mJ m^-2 have been observed using n-alkanes for silica xerogels heated at 700, 800 and 900°C. At 1000°C, decreases to 8.37 mJ · m^-2. Also the differential heat of adsorption, variation of standard free energy and entropy of adsorption decrease when the silica xerogel is heated at 1000°C, showing a lower interaction potential of the organic probes with the silica surface. For the silica xerogels heated between 700 and 900°C, the acid character varies in accordance with the variation of the chemical nature of the silica. Upon heating at 1000°C, both acid and base characters are very close in accordance with a neutral surface. Within the experimental conditions used in this work, the surface of the obtained monolithic silica xerogels behaves as a glass surface when the treating temperature is 1000°C.     

Thin-Layer Chromatographic Separation of the Chloroplast Pigments

Abstract

The separation of the chloroplast pigments is achieved by two-way chromatography on cellulose sheets. The chromatographic system employed is superior to any other thin-layer or paper system yet found.     

Utilization of Derivatograph for Study of Synthesis of New Inorganic Pigments

In our laboratory, the synthesis of new inorganic pigments is followed by thermal analysis using a Derivatograph apparatus. The first information about the temperature region of the formation of the pigments investigated is provided by thermal analysis. The main attention is directed to the preparation of high-temperature colour pigments, lightfastness colour pigments, anticorrosive pigments, new ecological inorganic pigments and luminescent pigments. All inorganic pigments are useful for colouring of ceramic glazes, enamels, plastics, paints, cements and other building systems. The synthesis of all these pigments is based on temperature calcination of starting materials. Tens of new inorganic pigments have been prepared thanks to methods of thermal analysis. These synthesis are described in more than 100 Czech patents. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of High NIR-Reflective Red Li2MnO3 Pigments

In this work, the development of a novel class of eco-friendly red pigments based on doped Li₂MnO₃ is reported. These new compounds offer red color values of a* > 34, which are recognizably higher than the red value provided by the commonly used red pigment iron oxide Bayferrox 4130. However, the real outstanding attribute of these novel substances is their strikingly high NIR-reflectance that gives promise for a new class of materials for the practical utilization as cool pigments in building components and ceramics. We have synthesized the inorganic pigments by conventional solid-state reactions at 900 °C and subsequently carried out the structural characterizations by X-ray powder diffraction (XRPD) and Rietveld analysis. We recorded the diffuse reflectance spectra of the obtained powders and determined the color properties by means of CIE L*a*b* coordinates. Finally, we measured the NIR reflectance and calculated the NIR solar reflection of these compounds affording values above 85 % in the range from 700 to 2500 nm.     

Studies on Pigments of Life: Novel Porphyrinoids from Bacteria

A number of bacterial heme prosthetic groups whose structures deviate significantly from theubiquitous protoheme have been discovered recently. These new pigments contain dramatic modifica-tions in the aromatic core and/or side chains. Examples include heme d and heme o as well as hemed_1. Synthetic approaches of these macrocycles and their possible biosynthetic pathways will be dis-cussed.     

Immobilization and Characterization of Lactate Dehydrogenase on TEOS Derived Sol-Gel Films

Physical adsorption and physical entrapment techniques have been utilized for the immobilization of lactate dehydrogenase (LDH) on tetraethylorthosilicate (TEOS) derived sol-gel films. The enzyme (LDH) activity has been assayed as a function of time, temperature, pH and pyruvate concentration. The results of photometric measurements used for monitoring the reaction yield a response time of about 1 min, linearity over a concentration range of 0–1.5 × 10^-3 M and detection limit of 5 × 10^-5 M. The TEOS sol-gel films containing LDH have been found to be stable for about 30 days at temperatures 4 to 10°C.     

Method for Determining Color Characteristics of Plant Pigments

Pigments from petals ofRanunculus repensL. andCalendula officinalisL. are used to describe a method for determining color characteristics of pigments that is based on scanning the studied object on a flat scanner and defining the colors using Adobe Photoshop 5.0. Ten yellow pigments were found inR. Repens; 15 yellow and orange, inC. Officinalis     

Catalytic Performance and Texture of TEOS Based Cu/SiO2 Catalysts for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Highly active and selective Cu/SiO₂ catalysts for hydrogenation of dimethyl oxalate(DMO) to ethylene glycol(EG) were successfully prepared by means of a convenient one-pot synthetic method with tetraethoxysilane( TEOS) as the source of silica. XRD, H₂-TPR, SEM, TEM, XRF and N₂ physisorption measurements were performed to characterize the texture and structure of Cu/SiO2 catalysts with different copper loadings. The active components were highly dispersed on SiO₂ supports. Furthermore, the coexistence of Cu⁰ and Cu⁺ contributed a lot to the excellent performance of Cu-TEOS catalysts. The DMO conversion reached 100% and the EG selectivity reached 95% at 498 K and 2 MPa with a high liquid hourly space velocity over the 27-Cu-TEOS catalyst with an actual copper loading of 19.0%(mass fraction).