Synthesis of Mesoporous Silica from Sodium Silica Solutions and a Poly(ethylene oxide)Based Surfactant (original) (raw)
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Chemistry of Materials, 2005
The presence of various counteranions in the interfacial region of the silicate-surfactant mesophase introduces opportunities for manipulation of the phase structure. Well-ordered three-dimensional hexagonal P6 3 /mmc, cubic Pm3 hn, two-dimensional hexagonal p6mm, and cubic Ia3 hd mesoporous materials have been synthesized with the same surfactant (cetyltriethylammonium bromide), depending on the kind of acids. The counteranions of acidic media have resulted in increasing surfactant packing parameter g in the order SO 4 2-< Cl-< Br-< NO 3-, which leads to different formation routes to the mesostructures. It has been found that the mesophases are always transformed from the lower curvature one into the higher curvature one in the acidic synthesis gel. The combination of X-ray diffraction patterns, scanning electron microscope images, and high-resolution transmission electron microscope images presented visible evidence for the mesostructural constructions. In particular, the synthesis of a cubic Pm3 hn mesoporous molecular sieve was studied in the presence of trimethylbenzene (TMB) isomers. The rate of transformation is greatly affected by the structure of the TMB isomers and their content; 1,2,3-TMB was the most favorable to the stabilization of the p6mm hexagonal mesophase, 1,3,5-TMB was the least favorable, and 1,2,4-TMB showed intermediate behavior.
Formation Mechanism of Anionic Surfactant-Templated Mesoporous Silica
Chemistry of Materials
The synthesis mechanism of anionic surfactant-templated mesoporous silica (AMS) is described. A family of highly ordered mesoporous silica structures have been synthesized via an approach based on the self-assembly of anionic surfactants and inorganic precursors by using aminopropylsiloxane or quaternized aminopropylsiloxane as the co-structure-directing agent (CSDA), which is a different route from previous pathways. Mesophases with differing surface curvatures, varying from cage type (tetragonal P4 2 /mnm; cubic Pm3 hn with modulations; cubic Fd3 hm) to cylindrical (two-dimensional hexagonal p6mm), bicontinuous (cubic Ia3 hd and Pn3 hm), and lamellar have been obtained by controlling the charge density of the micelle surfaces by varying the degree of ionization of the carboxylate surfactants. Changing the degree of ionization of the surfactant results in changes of the surfactant packing parameter g, which leads to different mesostructures. Furthermore, variation of the charge density of positively charged amino groups of the CSDA also gives rise to different values of g. Mesoporous silicas, functionalized with amino and quaternary ammonium groups and with the various structures given above, have been obtained by extraction of the surfactant. This report leads to a deeper understanding of the interactions between the surfactant anions and the CSDA and provides a feasible and facile approach to the mesophase design of AMS materials.
2020
In this paper, a facile method for preparing sub-micron spherical mesoporous silica by the sol-gel process and cationic surfactant cetyltrimethylammonium bromide (CTAB) as a soft template was reported. Moreover, the effect of surfactant concentration on the specific surface area and the total pore volume was investigated. The specific surface area, pore characteristic, morphology, chemical composition, and structure of mesoporous silica were studied using various methods. The N2 adsorption test showed that increasing the CTAB concentration from 4.6 mM to 7.2 mM increases the specific surface area from 416.48 to 564.07 m2g-1. However, the maximum pore volume was obtained at 5.9 mM CTAB. The spherical shape of the powders was confirmed by field emission scanning electron microscopy. Besides, X-ray diffraction, fourier transform infrared spectra, and energy dispersive spectrometry analysis indicated that the synthesized samples are SiO2, with an amorphous structure. Based on the struct...
Science and Technology of Advanced Materials, 2007
A series of mesoporous silicas (MS-1-MS-9) were synthesized at different gel compositions using a triblock copolymer (TCP), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), as the surfactant. The interactive effects of acidity, the contents of tetraethyl orthosilicate (TEOS) and the surfactant, and the gelling temperature on the characteristics of the final material were simultaneously characterized. Increasing acidity favored mesopore formation. A material with a surface area of 760 m 2 /g, mostly in the mesoporous range, was obtained at 1.0(TEOS):0.017(TCP):7.3HCl:115.7H 2 O. Mesopore formation was predominantly determined by the TEOS:TCP ratio and was promoted with its increase from 1.56:1 to 2.09:1. A further increase to 2.61:1 was detrimental. Whereas increasing the TCP content to 3.5% w/w improved micellization, a further increase to 4.6% should be avoided. Mesoporous silicas showed low crystallinity but a high degree of hexagonal mesoscopic organization. The weak surface acidity was attributed to surface silanols, the number of which was proportional to mesoporosity. r
Langmuir, 2009
Hydrocarbon and fluorocarbon surfactants show highly nonideal mixing that under some conditions results in demixing of the two types of surfactants into distinct populations of fluorocarbon-rich and hydrocarbon-rich aggregates. This also occurs in materials prepared by cooperative assembly of hydrolyzed tetraethoxysilane with mixtures of cetyltrimethylammonium chloride (CTAC) and 1,1,2,2-tetrahydro-perfluorodecylpyridinium chloride (HFDePC). Here, we report conditions under which demixed micelles lead to bimodal mesoporous materials (including specific concentrations of ammonia and salt in the synthesis solution) and show that the sizes of the hydrocarbontemplated and fluorocarbon-templated pores can be finely and independently controlled by adding lipophilic or fluorophilic oils, respectively. Nitrogen sorption isotherms and transmission electron microscopy provide clear evidence for a single phase of demixed but disordered wormhole-like pores.
Surfactant-Templated Synthesis of Ordered Silicas with Closed Cylindrical Mesopores
Chemistry of Materials, 2012
Ordered mesoporous silicas with 2-dimensional hexagonal arrays of closed cylindrical pores were synthesized via templating with block copolymer surfactant followed by calcination at appropriately high temperatures. Precursors to closed-pore silicas, including SBA-15 silicas and organosilicas, were selected based on the existence of narrow passages to the mesopores. The increase in calcination temperature to 800−950°C led to a dramatic decrease in nitrogen uptake by the materials, indicating the loss of accessible mesopores, whereas small-angle X-ray scattering (SAXS) indicated no major structural changes other than the framework shrinkage. Since SAXS patterns for ordered mesoporous materials are related to periodic arrays of mesopores, the existence of closed mesopores was evident, as additionally confirmed by TEM. The formation of closed-pore silicas was demonstrated for ultralarge-pore SBA-15 and large-pore phenylene-bridged periodic mesoporous organosilicas. The increase in the amount of tetraethyl orthosilicate in standard SBA-15 synthesis also allowed us to observe the thermally induced pore closing. It is hypothesized that the presence of porous plugs in the cylindrical mesopores and/or caps at their ends was responsible for the propensity to the pore closing at sufficiently high temperatures. The observed behavior is likely to be relevant to a variety of silicas and organosilicas with cylindrical mesopores.
Angewandte Chemie, 2003
The hydrothermal stability of mesoporous materials is currently of great interest because of this requirement for potential applications. A number of successful examples of mesoporous materials with good hydrothermal stability were reported recently, [7] for example, an ordered hexagonal SBA-15 with thicker pore walls, vesicle-like MSU-G materials with a high SiO 4 cross-linking, disordered KIT-1, and stable mesoporous aluminosilicates from a grafting route and from a preformed solution of "zeolite seeds". [7] Notably, these mesostructured materials are prepared at room temperature or relatively low temperatures (80-150 8C). This is quite different from the higher temperatures (150-220 8C) used for the syntheses of many microporous zeolites or phosphates because the surfactant molecules are not able to direct the mesoporous structure formation due to the unfavorable conditions for micelle formation at the higher temperatures. In some cases, the large-chain surfactants will even decompose at temperatures greater than 150 8C. As with silica-based materials, a critical factor in increasing hydrothermal stability is to have more silica condensation on the pore walls, but low synthetic temperatures result in imperfectly condensed mesoporous walls with large amounts of terminal hydroxyl groups that make the mesostructure unstable, especially under hydrothermal or steam conditions. It can be expected that the level of silica condensation will be enhanced by increasing the crystallization temperature. As suggested above, the strategy of using higher crystallization temperature for the synthesis of mesoporous materials may require special surfactants that can be used as template at high temperature. Fluorocarbon surfactants are a kind of stable surfactant, which are widely used at high temperatures (> 200 8C). However, due to the rigidity and strong hydrophobicity of the fluorocarbon chains, fluorocarbon surfactants are not suitable as templates for the preparation of well-ordered mesoporous mateials. We demonstrate herein that when a fluorocarbon surfactant
American Journal of Analytical Chemistry, 2021
In recent days, the applications of silica-based nanoparticles have gained much attention. The preparation of mesoporous silicas is usually achieved via the modified Stöber method, the reaction attained by the hydrolysis and condensation of silica precursors present within a medium containing template, solvent, deionized water (DI-W) and base. Therefore, the current study aimed to prepare and characterize mesoporous silicas by using tetramethoxysilane (TMOS) as silica precursor and ethylene glycol (Et-G) as solvent. The study was based on the template dodecyltrimethylammonium bromide (C 12 TMABr) and sodium hydroxide used as an alkaline agent. Mesoporous silicas were prepared in various batches based on TMOS molar concentration, ionized water, NaOH, and other solvents. The characterization of mesoporous silicas was achieved based on their specific surface area, pore size distribution and morphology using different instruments: Brunauer, Emmett & Teller (BET), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and thermalgravimetric analysis (TGA). The study revealed that shape, average particle sizes "35 to 550 nm", average pore radius "1.62-4.5 nm" and surface area "350-1204 m 2 •g −1 " of obtained mesoporous silica particles were altered based on precursor concentration and other factors. Therefore, it is important to get the most suitable concentration of all chemicals in the preparation of mesoporous silicas to control the particle characteristics to use them upon their further applications. This is the baseline study that provides details regarding prepared silica particles with controlled characteristics, and more studies related to its applications are still in process. How to cite this paper: Algaradah, M.M.
Microporous and Mesoporous Materials, 2000
Isometric particles of mesoporous silica could be synthesized between 25°C and 45°C from reaction mixtures containing silicic acids, sodium chloride and a non-ionic surfactant (Triton X100). The size decreases from some tens of micrometers to less than 1 lm when the pH increases from 1.85 to 6. At pH lower than 3.5, glassy material forms a cement between the particles. The particle size distribution narrows at higher pH and at long reaction times (several days). A spheroidal shape is favored by low pH and high temperature, and a more polyhedral shape appears at high pH whatever the temperature. This behavior could be related to the polycondensation rate of the silicic acids, to the lifetime and disorder of the micelles and to the micelles±silicic acid interactions. Ó 2000 Elsevier Science B.V. All rights reserved.