Mesoporous Silica Materials Synthesized via Sol-Gel Methods Modified with Ionic Liquid and Surfactant Molecules

Mesoporous silica materials were synthesized via a sol-gel method employing a room temperature ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4) as a new solvent medium and further modified with surfactant (hexadecyl-trimethyl-ammonium bromide, CTAB) as a pore templating material. The synthesized samples were characterized by the transmission electron microscopy, X-ray diffraction, and N2 adsorption-desorption techniques. The results indicated that the mesoporous silica synthesized by using bmimBF4 and CTAB as mixed templates showed better mesostructural order and smaller pore size, compared with mesoporous silica materials synthesized by using single bmimBF4 as template under the same conditions. This indicates that the presence of surfactant can affect the microstructures of silica prepared by the present synthesis method.     

Effect of salts on synthesis of mesoporous materials with mixed cationic and anionic surfactants as templates

Mesoporous silica materials were synthesized using tetraеthoxysilane as precursor and liquid crystals formed in aqueous mixtures of cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) as templates, without and with the addition of NaBr or Na₂SO₄. For this purpose, the formation of liquid crystals as a function of the ratio of CTAB and SDS under different conditions was studied. It was found that liquid crystals formed in the mixed system of CTAB and SDS at certain mixing ratios are well-structured templates for the synthesis of mesoporous silicas. The synthesized silica materials were characterized by transmission electron microscope and nitrogen adsorption/desorption analysis. The pore size of mesoporous silicas could be controlled between 3 to 6 nm by simply changing the concentration of NaBr in solution. The mesoporous silicas exhibited lamellar structure and the order of structural arrangement was promoted with addition of NaBr. However, addition of Na₂SO₄ led to ink-bottle type pores of mesoporous silica with a narrow pore size distribution of around 2 nm and a higher specific surface area of 610 m² g^–1.     

二元阴阳离子表面活性剂法合成介孔氧化硅囊泡

以十二烷基磺酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)为表面活性剂, 在SDS与CTAB的摩尔比为1.0~2.3时, 以正硅酸乙酯(TEOS)为硅源, 在氨水-水体系中于68℃下合成介孔氧化硅囊泡. 通过透射电子显微镜(TEM)、 X射线衍射仪(XRD)、 热重分析仪(TGA)和氮气吸附-脱附实验仪对合成的产物进行表征. 结果表明, 合成的产物为介孔氧化硅囊泡聚集体, 孔径约为4 nm, 样品的Brunauer-Emmett-Teller(BET)比表面积为826 m²/g. 对介孔氧化硅囊泡的形成机理做了初步探讨.     

Design and synthesis of ordered mesoporous silica materials with high degree of silica condensation at high temperature from a mixture of polymer surfactant with small organic ammonium

Thermal stability on a mixture of triblock polymer (P123) and fluorocarbon surfactant (FC-4) in acidic media for synthesis of ordered mesoporous materials has been carefully investigated by NMR spectroscopy at various treated temperatures (RT-180 degrees C) and the templating mechanism of the mixture on high-temperature synthesis has been proposed. Accordingly, we have designed fluorocarbon-free templates for syntheses of ordered mesoporous silica materials at high temperatures. As expected, ordered mesoporous silica materials with high degree of silica condensation are synthesized at high temperatures from these designed templates.     

Thermogravimetry applied to characterization of fly ash-based MCM-41 mesoporous materials

The thermogravimetry (TG) was used for characterization of the fly ash (FA)-based MCM-41 mesoporous materials. MCM-41 mesoporous materials were synthesized using silica extracts from different FA. The synthesis of MCM-41 from FA was carried out by the hydrothermal method using the supernatants of coal FA (in the form of sodium silicate) and cationic cetyltrimethylammonium bromide (CTAB) surfactants as the structure-directing agents. On the basis of the data obtained from the TG analysis, thermal behaviour of FA-based MCM-41 mesoporous materials was assessed. This study has established the range of temperatures corresponding to the desorption of water, decomposition of the surfactant and condensation of silanol, thereby making the overall quality assessment of FA-based MCM-41 mesoporous materials.     

嵌段共聚物与阳离子表面活性剂混合模板合成介孔SiO_2

利用三嵌段共聚物EO_(20)PO_(70)EO_(20)与阳离子表面活性剂CTAB作为混合 模板合成了内部孔结构与外观形貌同时受到调控的介孔氧化硅。与使用单一共聚物 模板制备的介孔氧化硅相比，在混合模板作用下得到的介孔氧化硅的孔结构有序度 降低，而孔径则随混合模板中共聚物的质量分数的降低而减小。在EO_(20)PO_(70) EO_(20)与CTAB质量比为1:1时可得到形貌完好、表面光滑的介孔氧化硅微米球，其 平均孔径为3.2nm，比表面积为972m~2/g。     

Engineering macroporous composite materials using competitive adsorption in particle-stabilized foams

Slow crystallization and growth rate at room temperature in the presence of surfactant micelles is a new strategy used to synthesize hierarchical Na-A zeolites. The observed structure of the hierarchical materials was consistent with a two stage growth mechanism. During the early stage of the gel evolution, miniature zeolite gel particles were formed and assembled around surfactant (cetyltrimethylammonium bromide - CTAB) micelles. In a second stage, the slow mass transformation into crystalline phase and the low growth rate of the formed crystallites retained the CTAB micelles within the crystallization domain. After the removal of CTAB templates, the products showed large mesopores which were attributed to the interstitial voids between the aggregated zeolite nanocrystallites. The size of the mesopores can be further expanded by using linear hydrocarbons as swelling agents. The influences of the added amount of the hydrocarbons and the length of the hydrocarbon chains on the mesopore size were examined. The effects of the aging period and the concentration of CTAB in the synthesis mixture on the pore size distribution were also investigated. The colloidal suspension of the synthesized zeolite showed negative zeta potential throughout the entire range of pH. The mesoporous Na-A zeolite synthesized in this work showed higher ethylene adsorption capacity as compared to the conventional microporous Na-A zeolite. XRD, DLS, SEM, N(2) adsorption-desorption at 77K, TEM, (29)Si NMR and FTIR techniques were used to characterize the hierarchical Na-A zeolite.     

Adsorption behavior of hydrophobin and hydrophobin/surfactant mixtures at the air-water interface

The adsorption of the surface-active protein hydrophobin, HFBII, and the competitive adsorption of HFBII with the cationic, anionic, and nonionic surfactants hexadecyltrimethylammonium bromide, CTAB, sodium dodecyl sulfate, SDS, and hexaethylene monododecyl ether, C(12)E(6), has been studied using neutron reflectivity, NR. HFBII adsorbs strongly at the air-water interface to form a dense monolayer ～30 ? thick, with a mean area per molecule of ～400 ?(2) and a volume fraction of ～0.7, for concentrations greater than 0.01 g/L, and the adsorption is independent of the solution pH. In competition with the conventional surfactants CTAB, SDS, and C(12)E(6) at pH 7, the HFBII adsorption totally dominates the surface for surfactant concentrations less than the critical micellar concentration, cmc. Above the cmc of the conventional surfactants, HFBII is displaced by the surfactant (CTAB, SDS, or C(12)E(6)). For C(12)E(6) this displacement is only partial, and some HFBII remains at the surface for concentrations greater than the C(12)E(6) cmc. At low pH (pH 3) the patterns of adsorption for HFBII/SDS and HFBII/C(12)E(6) are different. At concentrations just below the surfactant cmc there is now mixed HFBII/surfactant adsorption for both SDS and C(12)E(6). For the HFBII/SDS mixture the structure of the adsorbed layer is more complex in the region immediately below the SDS cmc, resulting from the HFBII/SDS complex formation at the interface.     

Structure and surface chemistry in crystalline mesoporous (CeO(2-δ))-YSZ

Mesoporous metal oxides (CeO(2-δ))-YSZ have been synthesized by a versatile direct synthesis method using ionic cetyltrimethylammonium bromide (CTAB) and different nonionic (block copolymers) as surfactants and urea as hydrolyzing agent. The synthesis was realized at pH=9 using tetraethylammonium hydroxide (TEAOH) as pH mediator. Calcination at 550 °C led to the formation of crystalline metal oxides with uniform mesoporosity. The obtained materials have been characterized by thermogravimetric analysis (TG-DTG), wide and small-angle X-ray diffraction (XRD), Raman spectroscopy, Brunauer, Emmett and Teller (BET) surface area analysis, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). All the obtained materials exhibits mesoporous structure, crystalline structure indexed in a cubic symmetry, showing a high surface area, a uniform and narrow pore size distribution, spherical morphology typical for the mesoporous materials. The crystalline and mesoporous structures, surface chemistry and stoichiometry for the samples synthesized using ionic and nonionic surfactants have been discussed.     

In Situ and Post Reaction Cobalt-Incorporation into Periodic Mesoporous Ethanesilica Materials

Cobalt incorporated periodic mesoporous organosilica materials were synthesized in situ by condensation of 1,2-bistrimethoxysilylethane (BTME) in the presence of cetyltrimethylammonium bromide (CTAB) and cobalt nitrate and by incipient wetness addition of Co to BTME mesoporous silica. BET and pore measurements as well as DTA and TGA analysis of the materials revealed that the mesoporous structure is retained under the synthetic conditions used, after solvent extraction and importantly to temperatures of ca. 400°C under N₂. Raman spectroscopy also revealed the presence of the ethane moiety in the Co materials and that the surfactant was removed by solvent extraction. BET and pore measurement studies revealed that the surface area and pore volume of the materials decreased with increasing cobalt loading. The studies indicate that the new Co materials have potential as Fischer-Tropsch catalysts.     

Oligomeric polymer surfactant driven self-assembly of phenylene-bridged mesoporous materials and their physicochemical properties

The detailed synthesis of highly hydrophobic average pore benzene-bridged hybrid mesoporous silicas under an acidic medium is described. With the use of a 1,4-bis(triethoxysilane)benzene silsesquioxane precursor and biodegradable alkyl polyoxyethylene (Brij-56 or Brij-76) nonionic surfactant oligomers as supramolecular templates, no molecular scale periodicity was observed. The well-defined mesoporous materials could be synthesized with two-dimensional hexagonal (p6mm) symmetries. The textural and surface properties (adsorption isotherms of water and benzene vapors) were estimated and were compared to the analogous benzene-bridged mesoporous silica with molecular scale periodicity which was prepared using cationic surfactant under basic conditions. Different textural properties resulted for the two kinds of materials and revealed some important insights regarding the structure and nature of the materials.     

Electrochemical Characteristics of Discrete,Uniform, and Monodispersed Hollow Mesoporous Carbon Spheres in Double‐Layered Supercapacitors

Core–shell‐structured mesoporous silica spheres were prepared by using n‐octadecyltrimethoxysilane (C18TMS) as the surfactant. Hollow mesoporous carbon spheres with controllable diameters were fabricated from core–shell‐structured mesoporous silica sphere templates by chemical vapor deposition (CVD). By controlling the thickness of the silica shell, hollow carbon spheres (HCSs) with different diameters can be obtained. The use of ethylene as the carbon precursor in the CVD process produces the materials in a single step without the need to remove the surfactant. The mechanism of formation and the role played by the surfactant, C18TMS, are investigated. The materials have large potential in double‐layer supercapacitors, and their electrochemical properties were determined. HCSs with thicker mesoporous shells possess a larger surface area, which in turn increases their electrochemical capacitance. The samples prepared at a lower temperature also exhibit increased capacitance as a result of the Brunauer–Emmett–Teller (BET) area and larger pore size.     

Preparation of ordered mesoporous SiC from preceramic polymer templated by nanoporous silica

Highly ordered mesoporous SiC materials were prepared by infiltrating viscous liquid preceramic polymer, allylhydridopolycarbosilane, into two types of surface modified nanoporous silica templates: mesoporous silica SBA-15 and mesocellular siliceous foam. The silica templates were subsequently etched off after pyrolysis at 1000 degrees C under nitrogen atmosphere with the resultant formation of ordered mesoporous structures. The mesoporous SiC materials, synthesized from both types of templates possessed high Brunauer-Emmett-Teller (BET) surface areas in the range of 250-260 m(2)/g with pore sizes of 3.4-3.6 nm. The ordered structures of mesoporous SiC were exact inverse replicas of their respective silica templates, as characterized by small angle X-ray diffraction (XRD), transmission electron microscope (TEM) images, and the adsorption-desorption isotherm of nitrogen.     

Surfactant Templated Silica Xerogels as Adsorbents for Rhodamine 6G

A series of silica xerogels was synthesized by using TEOS as the silica precursor and a non ionic surfactant Triton X100 (TX100) and a cationic surfactant Hexadecyltrimethylammonium Bromide (CTAB) as templates. The xerogels were synthesized through 2‐way catalysis using ultrasonic radiations for homogeneous mixing of the precursors and template. The surfactant template was later removed through calcination at 550 °C. It was found out that gels having CTAB as the template had higher surface area (612.08 m²/g) than the gels templated by TX100 (539.6 m²/g). High surface area xerogels were used in adsorption experiments for aqueous solutions of Rhodamine 6G (R6G). UV visible spectroscopy was used to find out the concentrations of dye solutions. The adsorption data of both the types of xerogels was found to follow Freundlich's adsorption model pointing towards the possibility of adsorption of the dye molecules on the heterogeneous surface of the adsorbent.     

Dual latex/surfactant templating of hollow spherical silica particles with ordered mesoporous shells

Hollow spherical silica particles with hexagonally ordered mesoporous shells are synthesized with the dual use of cetyltrimethylammonium bromide (CTAB) and unmodified polystyrene latex microspheres as templates in concentrated aqueous ammonia. In most of the hollow mesoporous particles, cylindrical pores run parallel to the hollow core due to interactions of CTAB/silica aggregates with the latices. Effects on the product structure of the CTAB:latex ratio, the amount of aqueous ammonia, and the latex size are studied. Hollow particles with hexagonally patterned mesoporous shells are obtained at moderate CTAB:latex ratios. Too little CTAB causes silica shell growth without surfactant templating, and too much induces nucleation of new mesoporous silica particles without latex cores. The concentration of ammonia must be large to induce co-assembly of CTAB, silica, and latex into dispersed particles. The results are consistent with the formation of particles by addition of CTAB/silica aggregates to the surface of latex microspheres. When the size and number density of the latex microspheres are changed, the size of the hollow core and the shell thickness can be controlled. However, if the microspheres are too small (50 nm in this case), agglomerated particles with many hollow voids are obtained, most likely due to colloidal instability.     

Functionalized mesoporous materials for adsorption and release of different drug molecules: A comparative study

The adsorption capacity and release properties of mesoporous materials for drug molecules can be improved by functionalizing their surfaces with judiciously chosen organic groups. Functionalized ordered mesoporous materials containing various types of organic groups via a co-condensation synthetic method from 15% organosilane and by post-grafting organosilanes onto a pre-made mesoporous silica were synthesized. Comparative studies of their adsorption and release properties for various model drug molecules were then conducted. Functional groups including 3-aminopropyl, 3-mercaptopropyl, vinyl, and secondary amine groups were used to functionalize the mesoporous materials while rhodamine 6G and ibuprofen were utilized to investigate the materials’ relative adsorption and release properties. The self-assembly of the mesoporous materials was carried out in the presence of cetyltrimethylammonium bromide (CTAB) surfactant, which produced MCM-41 type materials with pore diameters of ∼2.7-3.3 nm and moderate to high surface areas up to ∼1000 m²/g. The different functional groups introduced into the materials dictated their adsorption capacity and release properties. While mercaptopropyl and vinyl functionalized samples showed high adsorption capacity for rhodamine 6G, amine functionalized samples exhibited higher adsorption capacity for ibuprofen. While the diffusional release of ibuprofen was fitted on the Fickian diffusion model, the release of rhodamine 6G followed Super Case-II transport model.     

Preparation of a large Mesoporous CeO2 with crystalline walls using PMMA colloidal crystal templates

Inverse opals of crystalline CeO₂ were synthesized by using close-packed poly(methyl methacrylate) (PMMA) latex spheres of various sizes as templates, resulting in pore sizes, which could be scaled down even to the mesopore region (30–40 nm). The latex spheres were synthesized by emulsion polymerization, and the PMMA particle size could be substantially decreased by addition of sodium dodecyl sulfate (SDS) as surfactant. Owing to the larger pore wall thickness, the CeO₂ with large mesopores preserves an intact porosity to higher temperatures than previously reported mesoporous CeO₂ obtained from surfactant templates. The porosity and crystallinity were studied by microscopic techniques, wide angle X-ray diffraction (XRD), N₂ sorption, and Hg porosimetry. The evolution of crystallinity (crystallite size and lattice parameters) was determined for different annealing temperatures by means of Rietveld refinements of the XRD data. Thereby, our study allowed getting general insights into the crystallization behavior of sol–gel derived porous CeO₂ frameworks.     

Poly(ethylene oxide)-based surfactants as templates for the synthesis of mesoporous silica materials

Various mesoporous silica solids were prepared by using poly(ethylene oxide)-based surfactants as templates in a neutral, fluoride, or moderately acidic medium, and their properties examined by different physical techniques. Precipitation in an acid or neutral medium provided materials of pore size in between those of micropores and mesopores irrespective of the molecular size of the surfactant. On the other hand, syntheses in a fluoride-containing medium yielded mesoporous materials with pore diameters over the range 36-84 A that increased with increasing surfactant size. All materials possessed specific surface areas above 650 m(2)g(-1) and high pore volumes-particularly those obtained in a fluorinated medium. The conditions used in the syntheses and the fact that all produced highly disordered porous materials suggest that their mechanism of formation is essentially of the N(0)I(0) neutral type. The materials obtained in the presence of fluoride ion, which promote the condensation of siliceous species, retain greater amounts of surfactant and exhibit increased cross-linking and decreased particle sizes, which results in textural mesoporosity.     

Understanding surfactant aided aqueous dispersion of multi-walled carbon nanotubes

Dispersions of multi-walled carbon nanotubes (MWNTs) assisted by surfactant adsorption were prepared for a number of ionic and non-ionic surfactants including sodium 4-dodecylbenzenesulfonate (NaDDBS), hexadecyl(trimethyl)azanium bromide (CTAB), sodium dodecane-1-sulfonate (SDS), Pluronic? F68, Pluronic? F127, and Triton? X-100 to examine the effects of nanotube diameter, surfactant concentration, and pH on nanotube dispersability. Nanotube diameter was found to be an important role in surfactant adsorption rendering single-walled carbon nanotube studies as unreliable in predicting MWNT dispersive behavior. Similar to other reports, increasing surfactant concentrations resulted in a solubility plateau. Quantification of nanotube solubility at these plateaus demonstrated that CTAB is the best surfactant for MWNTs at neutral pH conditions. Deviations from neutral pH demonstrated negligible influence on non-ionic surfactant adsorption. In contrast, both cationic and anionic surfactants were found to be poor dispersing aids for highly acidic solutions while, CTAB remained a good surfactant under strongly basic conditions. These pH dependent results were explained in the context of nanotube surface ionization and Debye length variation.     

MCM-41介孔材料负载金属的一步法合成及其对酯化反应的催化作用

以增溶了茂金属的十六烷基三甲基溴化铵(CTAB)胶束为模板, 采用一步法合成了介孔表面负载有金属(铁、钛和锆)的介孔材料MCM-41, 通过等离子体电感耦合发射光谱仪(ICP-AES)测定铁、钛和锆负载量(质量分数)分别为1.71%、0.95%和0.81%. 通过X射线衍射(XRD)图谱和N₂吸脱附等温线可知, 负载金属的介孔材料M-MCM-41(T) 仍具有较高的比表面以及规整的六方有序孔道结构, 去除模板剂的焙烧温度对孔道结构有一定影响. 由一步法合成的金属负载介孔材料对乙酸正丁酯的酯化反应具有很高的催化活性, 其中Fe-MCM-41在单位时间单位金属催化生成的产物量(TOF)为55643 g·h^-1·g^-1, 而Zr-MCM-41的TOF高达125320 g·h^-1·g^-1. 与纯茂金属相比, 由茂金属合成的金属负载介孔材料可显著提高酯化反应的催化活性.