Preparation of mesoporous TiO2 by the sol-gel method assisted by surfactants

Mesoporous titania was obtained by gelation of tetraisopropyl orthotitanate in aqueous or alcoholic solutions with addition of a cationic or anionic surfactant. The gels were dried and calcined to obtain the oxides. The dried samples and the oxides were characterized by thermal analysis, N₂- adsorption measurements, infrared spectroscopy, X-ray diffraction and titration with n-butylamine. The effect of the type of surfactant, the chain length of the surfactant and the synthesis method on the textural and surface characteristics of the oxides obtained has been investigated. Cationic surfactants such as dodecyltrimethylammoniumbromide and cetyltrimethylammoniumbromide are effective in controlling the pore size and in increasing the pore volume and the surface area. On the contrary, the sodium dodecylsulphate employed as an anionic surfactant is not incorporated to the hydrous titanium oxide network. The use of a surfactant in the preparation enhances the acid strength of the surface sites of the titanium oxide formed.     

Synthesis and characterization of nanocrystalline mesoporous zirconia using supercritical drying

Synthesis of nano-crystalline zirconia aerogel was done by sol-gel technique and supercritical drying using n-propanol solvent at and above supercritical temperature (235-280 degrees C) and pressure (48-52 bar) of n-propanol. Zirconia xerogel samples have also been prepared by conventional thermal drying method to compare with the super critically dried samples. Crystalline phase, crystallite size, surface area, pore volume, and pore size distribution were determined for all the samples in detail to understand the effect of gel drying methods on these properties. Supercritical drying of zirconia gel was observed to give thermally stable, nano-crystalline, tetragonal zirconia aerogels having high specific surface area and porosity with narrow and uniform pore size distribution as compared to thermally dried zirconia. With supercritical drying, zirconia samples show the formation of only mesopores whereas in thermally dried samples, substantial amount of micropores are observed along with mesopores. The samples prepared using supercritical drying yield nano-crystalline zirconia with smaller crystallite size (4-6 nm) as compared to higher crystallite size (13-20 nm) observed with thermally dried zirconia.     

Control of pore size distribution of silica gel through sol-gel process using water soluble polymers as additives

To control the pore size distribution of silica gel, several kinds of water soluble polymers were added in the sol-gel process starting from tetraethyl orthosilicate. The polymers employed here were classified into three groups. The first group comprised uncharged polymers such as polyvinyl alcohol and polyethylene glycol, which affected only the amount of micropores and small mesopores (<20 nm). The second group comprised charged polymers (polyelectrolyte) such as polyacrylic acid (anionic) and a quaternary salt of polyethylene imine (cationic), which significantly increased the number of larger mesopores (>20nm). The third group comprised proteins such as lipase and albumin and decreased the number of micropore and mesopores and greatly increased the number of macropores. The results could almost be explained in terms of the principal effects of the polymers on a process of sol particle growth.     

Experimental investigation of the wetting ability of surfactants to coals dust based on physical chemistry characteristics of the different coal samples

To select suitable surfactant as water-spray additive to improve dust suppression efficiency, six types of coal sample (lignite, long flame coal, non-caking coal, gas coal, coking coal, and anthracite) were selected from some typical mining areas in China, the influence of the physical chemistry characteristics of coal samples on the wetting ability of surfactants to the coals dust was investigated. Their proximate composition, ultimate content, chemical structure, surface morphology, pore structure parameters, and contact angle were determined. Three kinds of anionic surfactants – Sodium Alcohol Ether Sulphate (AES), Sodium Alpha-Olefin Sulfonate (AOS), Fatty Acid Methyl Esters Ethoxylate Sulfonate (FMES) – and one kind of nonionic surfactant – Coco Diethanolamide (CDEA) – were selected to carry out sedimentation experiments on the coal samples dust, to explore the main factors influencing the wettability of the coal samples dust. Among these factors, pore size is the main factor determining the wettability of coal dust, the contact angle decreases linearly (R² = 0.96) with pore size increase. The experimental results demonstrate that the following factors produce correspondingly increased wettability: higher moisture content, lower carbon content, higher oxygen content, more oxygen-containing functional groups, and increased pore size. In addition, the wettability of the six types of the coal samples dust shows a high-low-high trend with metamorphic degree increase, lignite has the strongest wettability, and the coking coal with the highest degree of metamorphism in the selected bituminous coal sample has the weakest wettability. Moreover, compared with nonionic surfactants, anionic surfactants have stronger wetting ability, but the same anionic surfactants have different wetting abilities to coal dust with different metamorphic degrees. AOS has stronger wetting ability to the dust of long flame coal, non-caking coal, and anthracite; AES has stronger wetting ability to the dust of lignite and coking coal; and FMES has stronger wetting ability to the dust of gas coal. The research results provide a theoretical basis for different coal mines to select suitable surfactants as water-spray additives to improve dust suppression efficiency.     

Functionalized and postfunctionalizable porous polymeric films through evaporation-induced phase separation using mixed solvents

Condensation of water droplets during rapid evaporation of a polymer solution, under humid conditions, has been known to generate uniformly porous polymer films. Similar porous films are also formed when a solution of the polymer in THF containing small amounts of water, is allowed to evaporate rapidly under air flow; this suggests that water droplets may be formed during the final stages of film formation. In the presence of added surfactants, the interface of water droplets could become lined with the surfactants and consequently the internal walls of the pores generated, upon removal of the water, could become decorated with the hydrophilic head groups of the surfactant molecules. In a series of carefully designed experiments, we have examined the effect of added surfactants, both anionic and cationic, on the formation of porous PMMA films; the films were prepared by evaporating a solution of the polymer in THF containing controlled amounts of aqueous surfactant solutions. We observed that the average size of the pores decreases with increasing surfactant concentration, while it increases with increasing amounts of added water. The size of the pores and their distribution were examined using AFM and IR imaging methods. Although IR imaging possessed inadequate resolution to confirm the presence of surfactants at the pore surface, exchange of the inorganic counterion, such as the sodium-ion of SDS, with suitable ionic organic dyes permitted the unequivocal demonstration of the presence of the surfactants at the interface by the use of confocal fluorescence microscopy.     

机械制粉工艺粉状乳化炸药防结块研究

机械制粉工艺是制造粉状乳化炸药的有效技术途径之一,但产品易吸湿、结块。为改善其抗结块性,分别研究了表面活性剂、无机盐、固体粉末的影响效果。结果表明,水相中添加无机盐是最有效的抗结块方法,尤其是添加复合无机盐与阴离子型表面活性剂的产品具有良好的储存性能与热安定性,并且爆炸性能与喷雾制粉工艺产品接近,优于二号岩石铵锑炸药。     

Geotechnical properties of some organoclays

The engineering characteristics of clay are dependant on its mineral and chemical structure. When the clay soils interacted with water, their volume and shear strength and compressibility properties change gradually. Large amount of decrease in terms of the shear strength of clay soils due to swelling is observed. In order to solve these problems, the stabilization of clay soils using chemical additives is a prevalent subject of research. In view of this, previous research studies have employed surface active surfactants to modify the fundamental properties of soft clays. In this study, surfactant–clay complexes (organoclays) were developed using a raw clay modification with four surfactants and their geotechnical properties were determined in laboratory conditions. Two of the surfactants are cationic (cetyl trimethyl ammonium chloride, denoted as CTAC and quaternised ethoxylated fatty amine, denoted as QEFA) and the others are anionic (linear alkylbenzene sulphonic acid, denoted as LABSA and sodium lauryl ether sulfate, denoted as SLES). The experimental results indicated that the geotechnical properties of organoclays show significant change when compared to those of natural clay. The specific gravities, unconfined compression strengths and maximum dry densities of all organoclays were decreased. Optimum moisture content and swelling pressure values were decreased in cationic surfactant modified clays. However, the optimum moisture content and swelling pressure values of anionic surfactant clays are increased. A direct shear test was performed to determine the shear strength of organoclays. The test results also showed that the internal friction angles of organoclays were increased. Additionally, the change in the hydraulic conductivity was found to be insignificant.     

Al3+掺杂对硅胶吸附材料性能的影响

将陶瓷纤维纸用水玻璃和铝盐溶液等浸渍制备出新型Al3 掺杂硅胶吸附材料,研究了Al3 掺杂对硅胶吸附材料性能的影响.傅立叶变换红外谱、扫描电子显微镜及X射线能谱(SEM-EDS)揭示吸附材料中掺杂Al3 的存在及其含量;多孔介质孔隙分析显示,一定程度的Al3 掺杂可提高材料的比表面积和孔容,影响其孔径结构及分布,增加活性吸附位,从而提高了材料的吸附性能,在材料表面形成的Al-O-Si键增强了材料表面孔道骨架支撑力,提高了表面导热性,使其耐热性能、耐破指数和裂断长显著提高.     

The control of porosity at nano scale in resorcinol formaldehyde carbon aerogels

Organic aerogels were synthesized by sol–gel polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate (C) followed by vacuum drying. The influence of the resorcinol/sodium carbonate ratio (R/C) on the porous structure of the resultant aerogels was investigated. The nitrogen adsorption–desorption measurements show that the aerogels possess a well developed porous structure and mesoporosity was found to increase with increasing the R/C ratio. Carbon aerogels were obtained by carbonization of RF aerogels. The carbonization temperature impacts the microstructure of the aerogels by pore transformations during carbonization probably due to the formation of micropores and shrinkage of the gel structure. The results showed that a temperature of 1073 K is more effective in the development of the pore structure of the gel. Activated carbon aerogels were obtained from the CO₂ activation of carbon aerogels. Activation results in an increase in the number of both micropores and mesopores, indicative of pore creation in the structure of the carbon. Activation at higher temperatures results in a higher degree of burn off and increases the pore volume and the surface area remarkably without change of the basic porous structure, pore size, and pore size distribution.     

中孔活性炭材料的研究进展

综述了国内外在中孔活性炭材料开发方面的研究进展。着重介绍了催化活化、界面活化、混合聚合物炭化、有机凝胶炭化、铸型炭化等孔径调控方法及其中孔形成机理。为控制活性炭材料孔径大小和分布，提高其中孔容积和吸附性能提供了参考。     

A facile synthesis strategy for structural property control of mesoporous alumina and its effect on catalysis for biodiesel production

A facile synthesis route for the production of mesoporous alumina (MA) with tuneable structural properties including BET surface area, pore volume and pore size was systematically investigated by tailoring the amount of template P123 used in the synthesis. The general synthesis strategy was based on a sol–gel process by hydrolysis of aluminium isopropoxide associated with nonionic block copolymer (P123) as the template in a water system. The results showed that the addition of P123 played a crucial role in the synthesis process, leading to very regular variations in the surface area (146.6–261.6 m²/g), pore volume (0.164–2.152 cm³/g) and pore size (3.5–29.9 nm). MA-supported K species (MA-K) were prepared using KNO₃ as the potassium precursor and adopted as the catalysts for biodiesel production. The introduction of K species to MA caused a reduction in the BET surface area and pore volume, but gave rise to a significant increase in pore size, especially when the K species was higher than 10%. K incorporation resulted in the formation of disordered, but significantly larger mesopores. In catalysis, by introducing 20% molar fraction of K species to MA, very high yield of biodiesel was achieved (92.2%) and further increased to 94.4% with 25% K. Based on the control of structural properties of MA, a series of MA-20K catalysts with the same K loading (20%) but different structural properties were prepared by varying P123 addition and were further tested in biodiesel synthesis. Higher biodiesel yields were obtained over the MAs with higher surface area, pore volume and bigger pore size, which were attributed to the reduced mass transfer limitation in catalysis.     

Mesoporous silica obtained by polycondensation of octahydridooctasilsesquioxane

Mesoporous silica, due to its porosity and morphological features, have been considered a fascinating material for many technological applications. In this report, we describe the preparation of a structurally stable mesoporous silica material using octahydridooctasilsesquioxane (T₈ ^H). The structure and properties of final samples were determined by XRD, FT-IR, and TEM methods. Structural analysis has shown that the siliceous material is amorphous but mesoporous. BET surface area, pore volumes, and pore size distribution were measured using nitrogen sorption methods—data were collected from the adsorption branch using BJH method for mesopores and t-plot method for micropores. It was found that the cage-type structure of T₈ ^H molecules and the process conditions determine the specific morphology of the cross-linked products. Completely inorganic, mesoporous silica of a narrow pore distribution was obtained. It was found that the materials have large surface area and pores in the meso range (2–5 nm). The amount of mesopores and the characteristic surface area of the prepared samples strongly depended on the reaction conditions.     

Synthesis of nanocrystalline photocatalytic TiO2 thin films and particles using sol–gel method modified with nonionic surfactants

A simple sol–gel route has been developed for the preparation of nanocrystalline photocatalytic TiO₂ thin films and particles at 500 °C. The synthesis involved a novel chemistry method employing nonionic surfactant molecules as a pore directing agent along with acetic acid-based sol–gel route without direct addition of water molecules. This study investigated the effect of surfactant type and concentration on the homogeneity, morphology, light absorption, dye adsorption and degradation, and hydrophilicity of TiO₂ films as well as on the structural properties of the corresponding TiO₂ particles. The method resulted in the synthesis of mesoporous TiO₂ material with enhanced structural and catalytic properties including high surface area, large pore volume, pore size controllability, small crystallite size, enhanced crystallinity, and active anatase crystal phase. The prepared TiO₂ thin films were super-hydrophilic and possessed thermally stable spherical bicontinuous mesopore structure with highly interconnected network. Highly porous TiO₂ films prepared with polyethylene glycol sorbitan monooleate surfactant exhibited four times higher photocatalytic activity for the decoloration of methylene blue dye than the nonporous control TiO₂ films prepared without the surfactant. This sol–gel method modified with surfactant templates is useful in the preparation of nanostructured anatase TiO₂ thin films with high photocatalytic activity and desired pore structure.     

Influence of surfactant interaction on ultrafine copper powder electrodeposition

Ultrafine copper powder with uniform morphology and size was synthesized by electrodeposition. By using the Box‐Behnken design of response surface methodology, to study the interaction between anionic surfactants and nonionic surfactants at different concentrations of copper sulfate pentahydrate. The resulting copper powder was characterized by scanning electron microscopy. The results show that it is difficult to obtain uniform copper powder by using a single anionic surfactant. The staggered adsorption mechanism of the non‐ionic surfactant and the anionic surfactant at the interface disperses and stabilizes the micellar interface and prevents continued growth of the copper powder. The resulting copper powder is nearly spherical with uniform morphology and particle size. Through the optimization of the response surface methodology, a nearly spherical copper powder with an average particle size of 0.61 μm and uniform shape was finally obtained.     

Templated pores in hydrogels for improved size selectivity in gel permeation chromatography

The pore structures of cross-linked polyacrylamide gels can be altered by polymerizing in the presence of high concentrations of unreactive, micellar surfactant cosolutes which act as "templates". Removal of surfactant after polymerization is expected to leave pores with the approximate shape and dimensions of the surfactant micelles. A simple model was developed to simulate gel permeation chromatography (GPC) separations of globular proteins on templated gels. The model assumes that the partition coefficient for sieving of a protein is equal to the fraction of gel volume accessible to a sphere with a radius equal to the protein Stokes radius. The total gel volume is considered to include a fraction that is a conventional, random gel matrix and a remaining fraction contributed by templated pores. The pore size distribution of the conventional gel was estimated using the Ogston equation, which approximates the matrix as a random collection of long, thin, rigid fibers. Templated pores were assumed to have a Gaussian distribution of radii centered about some mean determined by the micelle radius. In comparison to conventional media, gels with templated pores are predicted to exhibit more sharply defined exclusion limits and improved resolution over a narrow size range centered on the mean templated pore size. Selectivity and resolution are expected to increase as the volume fraction of templated pores is increased and as the dispersion of templated pore radius is decreased. Small changes in template radius lead to large changes in the molecular weight range of optimal separation of globular proteins. It should be possible to create a series of GPC media that collectively offer high resolution over the molecular weight range of most globular proteins of interest.     

表面活性剂助剂对水性基墨性能的影响

目的通过研究表面活性剂对水性基墨干燥性能、颜色性能和流变性的影响规律,得到选择表面活性剂助剂的理论基础。方法选用阴离子、非离子和阴/非三类6种表面活性剂助剂,利用流变仪和表面张力仪等测量助剂加入前后水性基墨粘度、表面张力、接触角、色密度、光泽度等的变化规律。结果6种助剂加入后对水性基墨在薄膜上的润湿性影响较小;阴离子表面活性剂能够降低水性基墨的动态表面张力和粘度,降低色密度,提高稳定性;非离子表面活性剂可以提高水性基墨的干燥速率;阴/非复合助剂和阴离子表面活性剂有利于提高水性基墨的综合性能。结论助剂对水性基墨性能影响复杂,要考虑综合效果选择使用。     

The State of Research Regarding Ordered Mesoporous Materials in Batteries

Ordered mesoporous materials, porous materials with a pore size of 2–50 nm which are prepared via the sol–gel process using surfactant molecular aggregates as a template to assemble channels through the interfacial action of organic and inorganic substances, have recently triggered a heated debate. In addition to applications in the catalytic cracking of heavy oils and residues, the manufacturing of graft materials, the purification of water, the conversion of automobile exhaust, biochips, and the treatment of environmental pollutants via photocatalysts, ordered mesoporous materials have drawn substantial attention in the field of electrochemical energy storage due to advantages such as large specific surface area, uniform and continuously adjustable pore size, and orderly arrangement. Here, a general summary and appraisal of the study of ordered mesoporous materials for batteries in recent years is given, including the synthesis methods, meso/nanostructural features, and electrochemical capabilities of such materials.     

Fabrication of a magnetic helical mesostructured silica rod

We report a one-step synthesis of magnetic helical mesostructured silica (MHMS) by self-assembly of an achiral surfactant, magnetic nanocrystals with stearic acid ligands and silicate. This core-shell structured material consists of an Fe(3)O(4) superparamagnetic nanocrystal core and a highly ordered periodic helical mesoporous silica shell. We propose that the formation of the helical structure is induced by the interaction between the surfactant and dissociated stearic acid ligands. The MHMS obtained possesses superparamagnetism, uniform mesostructure, narrow pore size distribution, high surface area, and large pore volume. Furthermore, the drug release process is demonstrated using aspirin as a drug model and MHMS as a drug carrier in a sodium phosphate buffer solution.     

Microtexture and electrical properties of PAN-ACF

Microstructure and electric conductivity of PAN-based activated carbon fibers (PAN-ACF) were investigated using tension and KOH activation. The application of tension during stabilization decreased pore volume as well as specific surface area. Increase of KOH solution concentration caused serious damage to the surface of PAN-ACF. This surface damage of PAN-ACF resulted in increase of specific surface, pore volume and wider pore size distribution. PAN-ACF with higher tension showed higher electric conductivity. However, the electric conductivity was decreased by the increased BET surface area.     

EFFECT OF SURFACTANT ADDITION ON THE MICROSTRUCTURE OF COAL FILTER CAKES

Currently, water removal from fine coal fractions is affected by vacuum filtration of a coal slurry followed by thermal drying. Due to high operating costs and the potentially hazardous nature of the drying operation, alternate methods are sought.

This work investigated the change of filter cake microstructure resulting from one such method, namely, surfactant addition to the coal slurry. By impregnating a coal filter cake with an epoxy resin, micrographic analysis of the cake structure could be made by using an image analyzer with the aid of quantitative stereology. This analysis provided a particle and pore size distribution of the filter cake which is fundamental to the understanding of the dewatering mechanism.

Three surfactants were investigated in this work: non-ionic Triton X-114, anionic Aerosol-OT, and cationic dodecyl pyrindinium chloride. The behavior of Triton X-114 and DPC was similar; they both enhanced dewatering by reducing the amount of particle segregation while increasing the pore size of the cake. Conversely, Aerosol-OT, while exhibiting enhanced dewatering characteristics, did not significantly alter the filter cake structure. At low concentrations all three surfactants exhibited little change in particle and pore size distributions when compared to a filter cake formed at the same conditions without surfactant.

Additionally, a linear relationship was shown to exist between the volume-surface mean diameters of the particles and that of the pores. Similar relationships are also presented for the geometric mean diameter and the geometric deviation. The best correlation between particles and pores was obtained from coal cakes formed with Aerosol-OT.