Investigation of acrylonitrile polymerization on the surface of porous microspherical silica gel

The kinetics of acrylonitrile polymerization on the surface of porous microspherical silica gel (PMSS) was studied and some kinetic parameters were determined. The structure of PMSS-based sorbents was analyzed by FTIR-spectroscopy, XRD and sorption analysis before and after microcapsulation with polyacrylonitrile.     

A fundamental study on recovery of copper with a cation exchange membrane: Part 1 — Ion exchange equilibria between cupric and hydrogen ions

It is possible to concentrate metal ion against the gradient of its concentration through a cation exchange membrane. The membrane has a high ion exchange capacity and is hydrophilic, therefore a rapid transfer rate of ions is expected. Ion exchange equilibrium data between cupric and hydrogen ions for sulfuric and nitric acid systems are obtained and analyzed quantitatively for concentrations of dissociated cupric and hydrogen ions.     

Modified silica gel with 5-amino-1,3,4-thiadiazole-2-thiol for heavy metal ions removal

A two sorbents was to synthesize for heavy metals removal: silica gel modified with 5-amino-1,3,4-thiadiazole-2-thiol (S5A) and pure silica gel. Modification of silica gel is achieved by tetraethyl orthosilicate (TEOS) preliminary hydrolyzed at room temperature. 5-Amino-1,3,4-thiadiazole-2-thiol is added, with continuous stirring with a magnetic stirrer, to the hydrolyzed TEOS. Pure silica gel (sample SG) is obtained by the classical sol–gel method using the same conditions and initial component ratios. The sorbents have been characterized as to their surface area, pore volumes, content of the functional groups, IR spectra, sulfur and nitrogen content. Their sorption properties to heavy (Cu(II), Co(II), Ni(II), Cd(II), Pb(II) and Hg(II) metals are investigated. The investigations indicate that modified silica gel is characterized by a relatively higher sorption capacity than is the unmodified one. The highest sorption capacity belongs to Hg(II) in presence of unmodified silica gel due to which this sorbent can be used for selective extraction of mercury ions from aqueous solutions.     

Extraction of metal ions from water with tetrapyrazolic macrocycles bound to Merrifield resin and silica gel

Two macrocyclic tetrapyrazolic compounds having internal cavities of different sizes of were covalently bound both to a porous silica gel and to a Merrifield resin. The ability of these sorbents to extract heavy and akali metal ion from water by a solid–liquid extraction process was studied and compared to results of classical liquid–liquid extraction with the unbound pyrazole compounds. The grafting at the surface of silica does not affect the complexing properties of the ligands. However, the hydrophobic nature of the Merrifield resin has a marked effect, especially on the selectivity of extraction between the alkali metals. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2495–2499, 2000     

Effect of cupric ions on serum and liver cholesterol metabolism

Cupric ions were administered subcutaneously to male Sprague-Dawley rats at a single dose of 200 μmol/kg. At 24 hr after administration, a remarkable increase of total and free cholesterol was seen in the rat serum. Also, when lecithin-cholesterol acyltransferase (LCAT) (E.C. 2.3.1.43) activity was expressed as the percentage of the total serum that free cholesterol esterified, the acyltransferase activity in rats treated with cupric ions showed a slight decrease while the triglyceride content in rat serum and liver decreased by 54% and 61%, respectively. However, the content of hepatic cholesterol in rats treated with cupric ions did not show such a marked change. On the other hand, acid cholesteryl ester hydrolase activity (Acid CEH) (E.C. 3.1.1.14) in liver lysosomes of rats treated with cupric ions showed a marked decrease with increasing cupric ion concentration both in vivo and in vitro. Furthermore, cupric ions caused a marked release of the lysosomal enzymes cathepsin D and β-glucuronidase into the cytosolic fraction. The changes in acid cholesteryl ester hydrolase activity induced by cupric ions appear to be a direct effect of cupric ions on the enzyme. These results suggest that excessive cupric ion concentrations could cause various disorders in lipid metabolism.     

Ammoniothermal treatment of silica gel and simultaneous changes in surface area

A high surface area silica gel was structurally modified by autoclaving in ammonium hydroxide solutions with pH values of 9–12, at temperatures of 100–180°C, and for periods up to 5 h. Drastic variations in the texture of the xerogel took place leading to a considerable decrease in the specific surface, and to an accompanying increase in the mean particle diameter, pore radius, and number of OH groups per unit area. The extent of change depends generally on the temperature, duration of treatment, and pH of solution, although the last factor seems to be the most prominent. Such variation is ascribed to the enhanced dissolution of silica in the alkaline solution. Activation energies of hydrolysis of the siloxane bond were calculated as 17.2–19.0 kJ/mol, from a relationship correlating change in surface area with time.     

Effects of decomposition-treatment temperature on infiltration pressure of a surface modified nanoporous silica gel

When a nanoporous silica gel surface modified by silyl groups is decomposition-treated at a relatively low temperature, while the network is stable, the organic surface layers can be deactivated. As a result, the degree of hydrophobicity, which can be measured by the liquid infiltration pressure, is lowered. The infiltration and defiltration behaviors of liquid are dependent on the controlled decomposition-treatment time, the liquid composition, as well as the testing temperature. By adding electrolyte or using higher testing temperature, the infiltration pressure can be increased and the defiltration can be promoted.     

Adsorption characteristics of Cr(III) ionic imprinting polyamine on silica gel surface

In this paper, a kind of ionic imprinting polyamine (IIP) was prepared through an advanced approach. Firstly, functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles, and the PEI/SiO₂ was formed. Secondly, the ionic imprinting process was carried out using Cr³⁺ ion as a template, and epichlorohydrin (ECH) as a crosslinking agent, and Cr³⁺ ionic imprinting polyamine IIP-PEI/SiO₂ was prepared. The adsorption properties of IIP-PEI/SiO₂ for Cr³⁺ ion were studied in details by adopting both static and dynamic methods, and the effects of main imprinting conditions, such as the concentrations of Cr(III) ion and the amount of ECH, on the adsorption property of the imprinted material IIP-PEI/SiO₂ were examined. The experimental results show that the IIP-PEI/SiO₂ has high affinity and excellent selectivity for the template ion. Its adsorption amounts for template ion enhances nearly two times compared to PEI/SiO₂, and its relative selectivity coefficients relative to Zn²⁺ and Pb²⁺ are 24.63 and 59.32 respectively. Besides, the IIP-PEI/SiO₂ has a fine elution property using HCl solution as eluent.     

磷脂酰胆碱在硅胶上吸附特性的研究

为了研究硅胶对磷脂酰胆碱(PC)的吸附特性,通过分析不同吸附等温线和PC质量浓度随时间变化曲线,筛选出等温吸附模型和动力学模型并对其进行验证,求取了吸附热力学参数。结果表明:Langmuir等温吸附模型拟合结果良好,相关系数R2均在0.99以上,Lagergren拟一级动力学模型求出的平衡吸附量Qe更接近实验值。所以,这2种模型能更好地描述整个吸附过程,相对误差均在5%以内,可信度较高。此外,整个吸附过程主要受液膜扩散控制,热力学参数ΔH为-18.51—-3.79 k J/mol,该吸附为放热过程;ΔG恒负,吸附过程自发进行;ΔS在低浓度范围内恒负,高浓度范围内恒正,主要是PC与氯仿在硅胶吸附位点存在竞争关系所导致。     

Morphology of titania coatings on silica gel

Control of the hydrolysis and condensation of soluble precursors of titanium is shown to yield oxide coatings of well-defined morphology. A ``smooth' coating, consisting of patches of titania on silica, causes only a small increase in the surface area, from 130 m<sup>2</sup>/g for the uncoated silica gel to 154 m<sup>2</sup>/g. On the other hand, the ``rough' coating, which consists of 3 nm diameter titania particles dispersed over the silica surface, results in an increase in the BET surface area to 350 m²/g. The specific titania surface area was determined via isopropanol dehydration activity and was found to be comparable to the BET surface area indicating that the titania phase is responsible for the increase in surface area. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) provide definitive evidence for the coating morphology while X-ray photoelectron spectroscopy (XPS) was used to determine the dispersion of the titania. The supported titania maintains its surface area upon calcination at temperatures up to 873 K while unsupported titania looses much of its surface area. Also demonstrated in this work is a novel preparation method using titanium bis-ammonium lactato dihydroxide (TALH), a water soluble precursor. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flame retardant mechanism of silica gel/silica

Various types of silica, silica gel, fumed silicas and fused silica were added to polypropylene and polyethylene oxide to determine their flame retardant effectiveness and mechanisms. Polypropylene was chosen as a non‐char‐forming thermoplastic and polyethylene oxide was chosen as a polar char‐forming (slight) thermoplastic. Flammability properties were measured in the cone calorimeter and the mass loss rate was measured in our radiative gasification device in nitrogen to exclude any gas phase oxidation reactions. The addition of low density, large surface area silicas, such as fumed silicas and silica gel to polypropylene and polyethylene oxide significantly reduced the heat release rate and mass loss rate. However, the addition of fused silica did not reduce the flammability properties as much as other silicas. The mechanism of reduction in flammability properties is based on the physical processes in the condensed phase instead of chemical reactions. The balance between the density and the surface area of the additive and polymer melt viscosity determines whether the additive accumulates near the sample surface or sinks through the polymer melt layer. Fumed silicas and silica gel used in this study accumulated near the surface to act as a thermal insulation layer and also to reduce the polymer concentration near the surface. However, fused silica used in this study mainly sank through the polymer melt layer and did not accumulate near the surface. The heat release and the mass loss rate of polypropylene decreased nearly proportionally with an increase in mass loading level of silica gel up to 20% mass fraction. Polyethylene oxide samples with fumed silicas and silica gel formed physically strong char/silica surface layers. This layer acted not only as thermal insulation to protect virgin polymer but also acted as a barrier against the migration of the thermal degradation products to the surface. Published in 2000 by John Wiley & Sons, Ltd.     

Cation effect on gel – sol transition of kappa carrageenan

The steady state fluorescence (SSF) technique was employed to study gel – sol transitions of kappa carrageenan in NaCl, KCl and CaCl₂ solutions. Pyranine was used as a fluorescence probe for monitoring these transitions. Scattered light, I_sc and fluorescence intensity, I was monitored against temperature to determine the gel - sol (T_gs) transition temperatures and exponents. It was observed that T_gs values are strongly correlated to the NaCl, KCl and CaCl₂ contents. The weight average degree of polymerization, DP_w and gel fraction G, exponents (γ and β) were measured and found to be in accord with the classical Flory–Stockmayer Model.     

氯铬酸甲铵/硅胶对苯偶姻的氧化研究

介绍了氯铬酸甲铵／硅胶对苯偶姻体系的氧化反应合成相应的苯偶酰类化合物。反应条件为：反应时间１４ｈ,反应温度５５～６０℃,收率７８％～９４％。     

Studies of the fluorescent products of lipid oxidation in aqueous emulsion with glycine and on the surface of silica gel

The formation of fluorescent products in the reaction of methyl linoleate hydroperoxide with glycine in aqueous emulsions correlated directly with the decrease in diene conjugation and the increase in thiobarbituric acid (TBA) reactive substances. These correlations also were reflected in the course of the oxidation of methyl linoleate in aqueous emulsions with glycine and indicated that glycine reacted with products of peroxide decomposition as opposed to intermediates of autoxidation in hydroperoxide formation. Thin layer chromatography (TLC) and selective solvent extraction demonstrated that the products of the reaction contained many substances with a fluorescent spectrum similar to those of lipofuscin pigments. When methyl esters of polyunsaturated fatty acids or other polyunsaturated lipids underwent oxidation adsorbed on silica gel particles, products with similar fluorescent spectral properties were formed illustrating that fluorescent substances were formed in a variety of reactions associated with the oxidation of unsaturated lipids.     

Lipase ofGeotrichum candidum immobilized on silica gel

Silica gel is a useful support for the lipases ofGeotrichum candidum. Esterification of selected fatty acids and alcohols proceeded to 85–92% conversion in hydrocarbon solvents, and the degree of esterification was increased to 96–98% by adding 4Å molecular sieves at later stages of reaction. The equilibrium ratio of ester to fatty acid (butyl oleate to oleic) was determined for the supported lipase in a number of solvents and ranged from 92∶8 in hexane and isooctane to 16∶84 int-butanol. The essential character of the enzyme seemed unimpaired by deposition onto silica gel as judged by fatty acid selectivity and stereoselectivity.     

苯基键合硅胶萃取黄酮化合物的性能研究

以苯基三氯硅烷和硅胶为原料制得苯基键合硅胶固相萃取材料,采用扫描电镜、元素分析、比表面积/孔径分析、红外光谱等对其进行了结构表征。装填固相萃取小柱,以4个黄酮模型化合物为目标分析物,研究苯基键合硅胶的萃取性能。对上样体积、上样速度、上样pH、洗脱剂类型、洗脱体积、洗脱速度等萃取参数进行了优化,并建立了苯基键合硅胶富集萃取黄酮化合物的高效液相色谱分析检测方法。实验证实该方法具有宽的线性范围(1~200μg/L)、低的检出限(0.25μg/L),并成功应用于2种实际样品中黄酮化合物的富集检测。上述结果说明苯基键合硅胶是一种对黄酮化合物具有良好萃取性能的固相萃取材料。     

Cation exchange finishing of nonwoven polyester with polycarboxylic acids and cyclodextrins

We describe a chemical method for the finishing of polyester nonwoven fabrics that aimed to obtain ion exchange textiles. This approach was based on the use of polycarboxylic acids (PCA) and cyclodextrins as carbohydrate compounds and finishing agents, respectively. It was observed that the reaction between these reactants yielded a crosslinked polymer that was physically anchored onto the fibers. This polymer can be considered as a resin issued from the esterification between the COOH groups of the PCA with the OH groups of the carbohydrate. As the esterification reaction was not complete, many free carboxylic groups remained on the surface of the coating polymer. This feature offered the ion exchange properties to the textile support. In this article, we described the pad‐dry‐cure process and showed the influence of the curing parameters (time and temperature), the nature, and the concentration of the components and the pH of the impregnating bath. The grafting rate (in wt %) and the ion exchange capacity (IEC) were observed in parallel. First, it was observed that the best IEC capacity (that could reach 1 mmol/g) was obtained when an ideal compromise was applied between time and temperature of curing. We also evidenced that IEC depended on the nature and on the concentration of the PCA (chosen among citric acid, 1,2,3,4‐butanetetracarboxylic acid, and polyacrylic acid) and on the pH of the impregnating bath. Finally, it was observed that cyclodextrins were more appropriate than starch as finishing coreactants. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3730–3738, 2007     

Preparation,characterization, and properties of polyacrylonitrile–silica gel anion exchange composite fibers

This article reports the preparation of new anion exchange composite fibers (AECFs). These AECFs were prepared by simple stirring of polyacrylonitrile (PAN) and silica gel in different stoichiometric ratios. The physicochemical characterization of the prepared AECFs was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction analysis, thermogravimetric analysis (TGA, differential thermal analysis, and differential thermal gravimetry), and elemental analysis (CHNS/O). Ion‐exchange behavior was also observed. The results indicate that addition of silica gel affects the structure and properties of the composite fibers. The addition of silica gel also changes the thermal stability of PAN–silica gel AECFs. The ion‐exchange capacity of the resulting AECFs was found to be 1.98 mequiv/g. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

陶瓷基硅胶吸附材料的实验研究

采用浸渍法制得陶瓷基硅胶吸附材料,探讨了水玻璃质量分数、絮凝剂质量分数、盐酸浓度等条件对硅胶吸附性能的影响,采用扫描电镜(SEM)和孔隙分析仪揭示吸附材料的表面形貌及结构,结果显示,当水玻璃质量分数为26. 67 %、絮凝剂质量分数为15%,盐酸浓度为0. 5mol/L时,吸附剂具有较好的吸附性能,硅胶能均匀覆盖在纤维表面及其空隙中,其孔径落在纳米尺度范围内。     

溶胶凝胶一步溶剂交换与表面改性制备疏水硅气凝胶

以正硅酸乙酯为硅源,采用酸碱两步催化的溶胶-凝胶法,以无水乙醇/六甲基二硅氮烷/正己烷为溶剂交换与表面改性试剂,通过一步溶剂交换与表面改性和常压干燥工艺制备疏水SiO2气凝胶。用傅立叶变换红外光谱(FTIR)、X射线衍射(XRD)、热重-差示(TG-DSC)、场发射扫描电镜(F-SEM)和比表面积(BET)等检测手段对样品的结构、形貌和性能进行了表征。结果表明,将传统的溶剂交换与表面改性由多个步骤改为一步完成,使制备周期从原来的6d缩减到3d,不仅缩短了周期,而且使所得的SiO2气凝胶样品具有842.63m2/g的高比表面积、130kg/m3的低密度、15nm的超细颗粒、2～170nm的孔洞结构和良好的疏水性能。