共查询到20条相似文献,搜索用时 15 毫秒
1.
《Current Opinion in Colloid & Interface Science》2002,7(1-2):107-115
Since the discovery of the organized mesoporous solids by Mobil Oil Co. scientists, numerous patents and papers dealing with the synthesis, mechanisms of formation, properties and applications of these exciting solids have been published. A better understanding in the mechanisms of formation has been achieved through the use of in situ techniques of investigation. It appears that the mechanism depends much on the experimental conditions of synthesis. Even if the interaction between the inorganic precursor and the organic template is the key factor in the control of the formation of these materials, none of the proposed mechanisms provides an exclusive and definitive answer. 相似文献
2.
We put forward a theoretical model for the morphological transitions of templated mesoporous materials. These materials consist of a mixture of surfactant molecules and inorganic compounds which evolve dynamically upon mixing to form different morphologies depending on the composition and conditions at which mixing occurs. Our theoretical analysis is based on the assumption that adsorption of the inorganic compounds onto mesoscopic assemblies of surfactant molecules changes the effective interactions between the surfactant molecules, consequently lowering the spontaneous curvature of the surfactant layer and inducing morphological changes in the system. On the basis of a mean field phase diagram, we are able to follow the trajectories of the system starting with different initial conditions, and predict the final morphology of the product. In a typical scenario, the reduction in the spontaneous curvature leads first to a smooth transition from compact spherical micelles to elongated worm-like micelles. In the second stage, the layer of inorganic material coating the micelles gives rise to attractive inter-micellar interactions that eventually induce a collapse of the system into a closely packed hexagonal array of coated cylinders. Other pathways may lead to different structures including disordered bicontinuous and ordered cubic phases. The model is in good qualitative agreement with experimental observations. 相似文献
3.
Spectroscopic monitoring for the formation of mesoporous MCM-41 materials upon microwave irradiation
Hyung Mi Sung-Suh Dae Sung Kim Yong-Ki Park Sang-Eon Park 《Research on Chemical Intermediates》2000,26(3):283-294
The mesoporous MCM-41 materials were prepared in very short crystallization time (∼40 min) upon microwave irradiation in comparison
with conventional hydrothermal heating method. With both microwave irradiation and hydrothermal heating, the MCM-41 formation
via supramolecular templating method has been monitored by fluorescence and electron spin resonance (ESR) spectroscopy. Pyrene
as a fluorescence probe and 4-(N,N-dimethyl-N-hexadecyl)ammonium-2,2,6,6-tetramethyl piperidinyloxy iodide (CAT16) as a spin probe were respectively dissolved into the micelle solutions to form
the MCM-41 precursor gels. These probes allow the monitoring of the supramolecular interaction between the anionic silicate
species and the cationic surfactant molecules during the MCM-41 formation. Analyses of fluorescence and ESR spectra indicate
that the fast increase of hydrophobicity and microviscosity at the solubilzation sites of the probes results from the accelerated
condensation of silicates onto the micelle surface upon microwave irradiation. The fluorescence change from the silicate L-center
in the MCM-41 precursor gel also probes the fast silicate condensation upon microwave irradiation. It seems that the fast
formation of MCM-41 upon microwave irradiation is ascribed to the microwave-susceptible head groups of surfactant molecules
in addition to fast dissolution of the precursor gel. 相似文献
4.
The co-condensation of tetraethoxysilane (TEOS) and organotrialkoxysilane R'Si(OEt)3 (R' group containing a phosphorus atom) in the presence of a neutral surfactant (n-C16H33NH2) template provides ordered mesoporous hybrid materials. We show that further chemical reactions (sulfuration and quaternization) at phosphorus centres do not disrupt the ordered structure and the textural characteristics of the materials. 相似文献
5.
Vanapalli SA Iacovella CR Sung KE Mukhija D Millunchick JM Burns MA Glotzer SC Solomon MJ 《Langmuir : the ACS journal of surfaces and colloids》2008,24(7):3661-3670
We study fluidic assembly and packing of spherical particles in rectilinear microchannels that are terminated by a flow constriction. First, we introduce a method for active assembly of particles in the confined microchannels by triggering a local constriction in the fluid channel using a partially closed membrane valve. This microfluidic valve allows active, on-demand particle assembly as opposed to previous passive assembly methods based on terminal channels and weirs. Second, we study the three-dimensional assembly and packing of particles against a weir in confined rectilinear microchannels. The packings result in achiral particle chains with alternating (zigzag) structure. This structure is characterized by a single, repeated bond angle whose components projected into the frame of the channel are quantified by confocal microscopy and image processing. Brownian dynamics simulation of the packing comprehensively delineates the range of bond angles possible in narrow, rectilinear microchannels as well as the complex dependence of these angles on the relative dimensions of the channel and particles. The simulations of the three-dimensional packings are accurately modeled by a compact theory based on trigonometric relationships. The experimentally measured bond angles show excellent agreement with the simulations, thereby validating the functional dependence of the achiral packing bond angles on channel dimensions. This functional relationship is immediately useful for the design of anisotropic particles by microfluidic synthesis. 相似文献
6.
A. Yu. Myshastyi A. V. Shvets V. S. Dyadyun O. M. Zhigalina V. G. Il’in 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(3):357-359
The influence of synthesis conditions and Mg2+, Co2+, and Zn2+ admixtures on the formation of lamellar, cubic, and hexagonal mesophases was studied. After calcining at 653 K in an argon flow, the mesophases transformed into mesoporous materials with D pore = 27–80 Å, V pore = 0.10–0.30 cm3/g, and s BET = 80–200 m2g. Nanotubes based on mesostructural lamellar vanadium oxide with inside diameters of from 100 to 500 Å were obtained in the presence of several amines as templates. 相似文献
7.
A coordination cage with an elusive icosahedral geometry was obtained by K+-induced rearrangement of a hexanuclear [(cymene)Ru(pyridine-3,5-dicarboxylate)]6 complex. 相似文献
8.
Che S Lim S Kaneda M Yoshitake H Terasaki O Tatsumi T 《Journal of the American Chemical Society》2002,124(47):13962-13963
The presence of various counteranions at the interfacial region of the silicate-surfactant mesophase introduces opportunities for manipulation of the phase structure. Well-ordered 3D-hexagonal P63/mmc, cubic Pmn, 2D-hexagonal p6mm, and cubic Iad mesoporous materials have been synthesized with the same surfactant, cetyltriethylammonium bromide, in the presence of various acids. The counteranions of acidic media have resulted in increasing the surfactant packing parameter g in the order SO42- < Cl- < Br- < NO3-, which leads to the different time course of formation of mesostructures. The effect of counteranions on the formation of mesostructures is explained in terms of not only the adsorption strength on the headgroups of the surfactant micelle but also the rate of silica condensation affecting the charge density matching between the surfactant and silica. It has been found that the mesophase is always transformed from the larger g parameter into the smaller one. The distinct morphologies of the 3D-hexagonal P63/mmc mesophases have been rationally explained by supposing this particular mesostructure. The cubic Iad phase has been first synthesized under acidic conditions. 相似文献
9.
Felinger A 《Journal of chromatography. A》2011,1218(15):1939-1941
The recently developed pellicular packing materials show high efficiency and have attracted great interest. The improved mass-transfer kinetics of the core-shell particles is due to the shorter diffusion path of the molecules within the stationary phase. In this study we show how the diffusion time of the molecules visiting the stationary phase depends on the geometry of the porous shell stationary phase. The mean escape time of diffusion is calculated on the basis of a random walk model. 相似文献
10.
Despite great efforts, the development of a reliable way to assemble mesoporous metal-organic frameworks (mesoMOFs) remains a challenge. In this work, we have designed a cooperative template system, comprising a surfactant (cetyltrimethylammonium bromide) and a chelating agent (citric acid), for the generation of a mesoMOF containing a hierarchical system of mesopores interconnected with microspores. The surfactant molecules form micelles and the chelating agent bridges the MOF and the micelles, making self-assembly and crystal growth proceed under the direction of the cooperative template. However, when the surfactant or the chelating agent was applied individually, no mesoMOF was obtained. 相似文献
11.
This article reviews the recent progress made in asymmetric catalysis in the nanopores of mesoporous materials and periodic mesoporous organosilicas (PMOs). Some examples of chiral catalysts within the nanopores show improved catalytic performance compared to homogeneous catalysts. The factors including the confinement effect, the properties of the linkages and the microenvironment in nanopores, which affect the activity and enantioselectivity of asymmetric catalysis in nanopores, are discussed. 相似文献
12.
Vrålstad T Glomm WR Rønning M Dathe H Jentys A Lercher JA Oye G Stöcker M Sjöblom J 《The journal of physical chemistry. B》2006,110(11):5386-5394
Cobalt-containing mesoporous materials that have been prepared using different procedures have been comparatively characterized by transmission electron microscopy/energy-dispersive X-ray spectroscopy (TEM/EDS), extended X-ray absorption fine structure spectroscopy (EXAFS), X-ray absorption near edge spectroscopy (XANES), and ultraviolet-visible (UV-vis), near-infrared (NIR), and mid-infrared (mid-IR) spectroscopies, and the results provide new insights into the local environment and properties of cobalt in this type of material. TEM/EDS analyses have shown that tetraethyl orthosilicate (TEOS) may be less appropriate as a silicon source during the syntheses of cobalt-containing mesoporous materials, because the distribution of cobalt throughout the framework may become uneven. EXAFS has been determined to be the most suitable method for direct verification of framework incorporation, by identifying silicon as the backscatterer in the second shell. Such a direct verification may not be obtained using UV-vis spectroscopy. From EXAFS analyses, it is also possible to distinguish between surface-bound and framework-incorporated cobalt. There is a good agreement between the results obtained from XANES and UV-vis regarding the coordination symmetry of cobalt in the samples. The presence of cobalt in the silica framework has been determined to create Lewis acid sites, and these acid sites are suggested to be located at tetrahedral cobalt sites at the surface. 相似文献
13.
Surfactant-directed assembly of mesoporous metal-organic framework nanoplates in ionic liquids 总被引:1,自引:0,他引:1
L Peng J Zhang J Li B Han Z Xue G Yang 《Chemical communications (Cambridge, England)》2012,48(69):8688-8690
Mesoporous MOF nanoplates were formed in surfactant-IL solutions. This method is simple, requires less energy, and is environmental friendly, and can be easily applied to the synthesis of other MOFs with different morphologies and porosities. 相似文献
14.
Dong Chencheng Liu Jun Xing Mingyang Zhang Jinlong 《Research on Chemical Intermediates》2018,44(11):7079-7091
Research on Chemical Intermediates - With the prevalence of green chemistry and the concept of a harmonious society, humans have much greater environmental awareness than ever before. Mesoporous... 相似文献
15.
Mesoporous material incorporating zinc with different Si/Zn ratios = 95, 65, and 20 have been synthesized by intercalating kanemite using cetyltrimethylammonium bromide as the intercalating agent and zinc nitrate. The resulting materials were characterized by different techniques such as: inductively coupled plasma technique, XRD, Brunauer-Emmett-Teller, and a temperature-programmed-desorption of pyridine. The catalytic performance was studied in the vapor phase tert-butylation of anisole with tert-butanol at different temperatures under atmospheric pressure. The results indicate that Zn-FSM-16 (20) was found to be more active than its relatives. The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4-DTBA). 相似文献
16.
Summary This paper demonstrates the possibilities in transfering HPLC methods from porous to non-porous stationary phases. The procedures
are transferred from 125 or 250 mm columns packed with porous stationary phases to 33 mm columns packed with non-porous particles.
It is demonstrated that fast HPLC using non-porous columns reduces analysis times by a factor four to eight. Precision is
comparable to HPLC with porous stationary phases. The costs for HPLC with porous and with nonporous packing materials are
similar. The implementation of these fast HPLC columns is easy because standard equipment can be used. 相似文献
17.
The behavior of a packing material (Luna C18 from Phenomenex, Torrance, CA, USA) was studied during the consolidation of a column bed under axial compression stress. The kinetics of this consolidation, the permeability and efficiency of the columns obtained, and the reproducibility of these column properties were measured under different conditions. The consolidation process and the column properties are considerably affected by the friction between the packing material in the bed and the column wall. Clear evidence of this wall effect was demonstrated. The apparent permeability of columns consolidated under the same axial stress increases with increasing column length. The apparent modulus of elasticity of the beds increases with increasing column length. The shear resistance between the packed bed and the column wall was measured for columns of different lengths. It increases rapidly with increasing bed length. The column efficiency for thiourea (unretained) and phenyloctane (retention factor, k' approximately 1) was much poorer after recompression than after the first compression. It depended little on the compression stress. The effect of the column length was small. 相似文献
18.
Hudson S Magner E Cooney J Hodnett BK 《The journal of physical chemistry. B》2005,109(41):19496-19506
Cytochrome c and xylanase were adsorbed onto two mesoporous materials, SBA-15 (a pure silicate) and MSE (an organosilicate), with very similar physical properties but differing chemical compositions. A methodical order was developed whereby the influences of surface area, pore size, extent of order, particle size, surface potentials, isoelectric points, pH, and ionic strength on immobilization were explored. In silico studies of cytochrome c and xylanase were conducted before any immobilization experiments were carried out in order to select compatible materials and probe the interactions between the adsorbents and the mesoporous silicates. The stabilities of the mesoporous materials at different pH values and their isoelectric points and zeta potentials were determined. Electrostatic attraction dominated protein interactions with SBA-15, while weaker hydrophobic interactions are more prominent with MSE for both cytochrome c and xylanase. The ability of the immobilized protein/enzyme to withstand leaching was measured, and activity tests and thermostability experiments were conducted. Cytochrome c immobilized onto SBA-15 showed resistance to leaching and an enhanced activity compared to free protein. The immobilized cytochrome c was shown to have higher intrinsic activity but lower thermostability than free cytochrome c. From an extensive characterization of the surface properties of the silicates and proteins, we describe a systematic methodology for the adsorption of proteins onto mesoporous silicates. This approach can be utilized in the design of a solid support for any protein. 相似文献
19.
Matsumoto A Misran H Tsutsumi K 《Langmuir : the ACS journal of surfaces and colloids》2004,20(17):7139-7145
Hybrid organosilica mesoporous materials with pores of ordered three-dimensional hexagonal structure were prepared by the hydrolysis and co-condensation of 1,2-bis(triethoxysilyl)ethane with various concentrations of a surfactant as structure directing agents. The materials had high pore volume of 1-1.5 mL/g and high surface area from 1057 to 1445 m(2)/g. Adsorption measurement and adsorption calorimetry revealed that the prepared materials exhibited high hydrophobicity and high affinity toward nonpolar organic vapor such as n-hexane. The dynamic adsorption properties of the materials for n-hexane in the presence of water vapor showed that these hybrid organosilica materials preferentially adsorbed n-hexane vapor and were stable in the presence of water compared to the siliceous MCM48. 相似文献
20.
Tanaka T Ogino H Iwamoto M 《Langmuir : the ACS journal of surfaces and colloids》2007,23(23):11417-11420
Azobenzene (Az) groups were planted on the pore wall of mesoporous silica MCM-41 (M41) by silylation of triethoxy[4-phenylazo(phenyl)]silane. The optimal surface density of Az groups was 0.9 group nm-2, and too much loading of Az induced the lowering of the efficiency of the trans-cis isomerization due to the congestion of the groups. The reversible change in the pore diameters upon UV-vis irradiation could not be confirmed by N2 adsorption at 77 K but was revealed to be ca. 1.0 nm by the shift of the UV-vis absorption band of p-N,N-dimethylaminobenzylidenemalononitrile introduced into the Az-modified pores. 相似文献