Organic Mesoporous Silica Research Articles

Nanostuctured mesoporous materials from different silica sources using fluorinated surfactants as templates

We report here the synthesis of mesoporous silica materials from various fluorinated-based systems using as the inorganic precursor either sodium silicate solution or silicate ions produced from the dissolution of silica under basic conditions. The properties of the materials are compared with the ones of the mesostructures prepared from tetramethoxysilane as silica source. Results show that whatever the silica source, well-ordered hexagonal materials with a narrow pore size distribution are obtained. Nevertheless, the pH has a great influence on the properties of the recovered materials since it governs the interactions between the surfactant and the inorganic precursor and the pH range for which the hexagonal mesopore ordering is obtained, depends on the silica source. Using sodium silicate, hexagonal mesostructured materials with high specific surface area (≥800m2/g) and narrow pore size distribution (4nm) are recovered for pH from 0.3 to 5. It should be noted that the formation of organized mesoporous silica under acidic conditions with this precursor is barely reported in literature. Replacing sodium silicate by silica fumed, the pH range leading to a hexagonal mesopore ordering is reduced to 0.3–1.5. When the organosilane is used the ordered mesoporous materials are recovered regardless the pH. In addition in that case a better control of the self assembly between the surfactant and the silica species allows tuning the particles’ morphology. Under acidic conditions tetramethoxysilane gives rise to gyroids or toroids and favors the formation of submicrometer particles, while irregularly shaped particles are produced with sodium silicate or silica fumed under alkaline conditions. Results also show that neither the specific surface area, nor the cell parameter strongly depend on the silica precursor as long as the hexagonal structure is kept.

Highly active and stable Ni/SBA-15 catalysts prepared by a “two solvents” method for dry reforming of methane

Two series of Ni (2.5–7.5 wt%) and Ce (6 wt%) containing SBA-15 catalysts were prepared and tested in dry reforming of methane, a promising route for the production of syngas. Both Ni and Ce species were introduced in the organized mesoporous silica support in the form of nitrate salts using the “two solvents” procedure that is known to favor metal dispersion inside the porosity. Samples characterizations by N2 sorption, SAXS, XRD, SEM and TEM indicate good preservation of the porosities after Ni deposition and calcination as well as formation of NiO nanoparticles entrapped in the porous channels. In the cerium-enriched samples, the CeO2 nanoparticles are also highly dispersed. After reduction, all the catalysts show high activity and selectivity towards H2 and CO at atmospheric pressure with full CH4 conversion below 650 °C. In these conditions, there is no significant promotional effect by ceria. Moreover, prolonged tests performed at 500 °C for 12 h reveal a high stability of the catalysts. The absence of deactivation throughout the catalytic run at this temperature agrees with the low carbon amount detected after test and with the limited sintering of the Ni nanoparticles in the used catalysts. The positive effect of the SBA-15 mesoporous channels towards stabilization of the supported particles is discussed.

CuO/SBA-15 materials synthesized by solid state grinding: Influence of CuO dispersion and multicycle operation on DeSOX performances

In this study, copper oxide (CuO) has been dispersed into an organized mesoporous silica (SBA-15) using the solid state grinding method. The resulting CuO/SBA-15 materials were evaluated as SOx adsorbents and were fully characterized before and after sulfation. The influence of the calcination conditions on the copper dispersion was studied. Results show that the textural properties of the materials and the formed copper species are closely related to the calcination procedure. The adsorption performances increase with the copper dispersion. It was found that despite the high GHSV value used in this work (25,000h−1), the highly dispersed copper species confer a high efficiency to the adsorbent. Cyclic adsorption/regeneration experiments show a surprising but explainable increase in the adsorption efficiency in the second cycle followed by a slight but monotonic deactivation in the subsequent cycles, as a result of the progressive sintering of the copper species.

Effects of framework structure and coupling modification on the properties of mesoporous silica/poly(methyl methacrylate) composites

Mesoporous silicas (MPSs) with two-dimensional (2D) hexagonal framework (SBA-15) and worm-hole framework (MSU-J) were synthesized with poly(ethylene oxide- b-propylene oxide- b-ethylene oxide) (P123) and α,ω-polyoxypropylene diamine (D2000) as templates, respectively. Both SBA-15 and MSU-J were further modified with γ-(methacryloyloxy) propyl trimethoxy silane (MAPTS) via post-grafting to prepare organic mesoporous silicas (denoted SBA-15-G and MSU-J-G, respectively) with –C = C groups on the surface of mesopores. All mesoporous silicas were employed as filler to prepare improved poly(methyl methacrylate) (PMMA) composites with lower dielectric constant, higher thermal, and mechanical properties. It was found that all mesoporous silicas retained their mesostructure in MPS/PMMA composites to introduce a lot of voids into the composites. So, the dielectric constant of composites decreased with the loading of mesoporous silica and their organic derivatives increased. Also, all composites exhibited stabilized dielectric constant with lower value in comparison to pure PMMA over the whole frequency from 1 to 160 MHz. Specifically, with the addition of MPS to PMMA, the dielectric constants of the composite can be reduced from 2.91 of the pure PMMA to 2.73 and 2.64 by incorporating 4 wt% SBA-15 and 7 wt% MSU-J, respectively. All the composites exhibited improved mechanical properties, glass transmission temperature ( Tg), and thermal stability in comparison to PMMA. All these differences in macro-properties are attributed to the different structure between MPS/PMMA composites and PMMA. MSU-J silica with the larger framework pore size provides the composite with the best improvement in dielectric, thermal, and mechanical properties.

A comprehensive study of the reaction parameters involved in the synthesis of Silica thin films with well-ordered uni-directional mesopores

Ordered mesoporous thin films with well-orientated channels are an important feature in a series of applications including sensors, optics, photocatalysis, and solar cells. However, their preparation remains a great challenge. The structural optimization of highly organized mesoporous silica thin films, with channels perpendicularly orientated to the surface and prepared by a spin-coating technique, is reported. A large series of reaction parameters were revisited with a deep investigation such as the template, solvent, aging time, pH, rotation speed, and duration of spin-coating. The best conditions for each of these different parameters were subsequently used together to control the pore size and channel orientation of the well-organized films. Characterization of the films performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the films had homogeneous pores with a uni-directional orientation. Atomic force microscopy (AFM) and ellipsometric porosimetry analysis (EP) were employed to determine the orientation of the channels, pore size distribution, specific surface, thickness, and the accessible porosity. The present work constitutes an overall view of the different parameters which influence the formation of silica thin films, such as the thickness and the pore size distribution of a film which can be tailored to suit a potential application. The wettability properties of thin films have been studied by measuring the contact angle with different solvents such as water, isopropanol, and toluene.

Tailored Jeffamine Molecular Tools for Ordering Mesoporous Silica

Herein, we report the formation of organized mesoporous silica materials prepared from a novel nonionic gemini surfactant, myristoyl-end-capped Jeffamine, synthesized from a polyoxyalkyleneamine (ED900). The behavior of the modified Jeffamine in water was first investigated. A direct micellar phase (L(1)) and a hexagonal (H(1)) liquid crystal were found. The structure of the micelles was investigated from the SAXS and the analysis by generalized indirect Fourier transformation, which show that the particles are globular of core-shell type. The myristoyl chains, located at the ends of the amphiphile molecule, are assembled to form the core of the micelles and, as a consequence, the molecules are folded over on themselves. Mesoporous materials were then synthesized from the self-assembly mechanism. The recovered materials were characterized by SAXS measurements, nitrogen adsorption-desorption analysis, and transmission and scanning electron microscopy. The results clearly evidence that by modifying the synthesis parameters, such as the surfactant/silica precursor molar ratio and the hydrothermal conditions, one can control the size and the nanostructuring of the resulting material. It was observed that, the lower the temperature of the hydrothermal treatment, the better the mesopore ordering.

Mesoporous silica directly modified by incorporation or impregnation of some heteropolyacids: Synthesis and structural characterization

The synthesis of heteropolyacids–mesoporous silica composites was carried out in acidic media by impregnation and/or by direct incorporation of active phase. The effect of incorporation of heteropolyacids (HPAs) species into organized mesoporous silica was studied by using non-ionic and cationic surfactants. A comparison between direct incorporation of HPAs into mesoporous silica and impregnation of HPAs on mesoporous silica was done. The structure and texture of H 3PMo 12O 40 and H 4PVMo 11O 40 included on mesoporous silica were studied by XRD, SEM–EDS, FT-IR and Raman spectroscopies and BET and pore size distribution. Thermal stability was determined by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). FT-IR and Raman studies showed that HPAs anions preserved their Keggin structure after incorporation or impregnation on mesoporous silica support.

Solid-State NMR Characterization of Phenylbenzimidazolesulfonic Acid Coencapsulated with Cetyltrimethylammonium in Mesoporous Silica Materials

The hydrophilic molecule phenylbenzimidazolesulfonic acid (PBSA) has been coencapsulated with cetyltrimethylammonium chloride (CTAC), an amphiphilic surfactant, via an in situ method in a mesoporous silica matrix. The effect of coencapsulation on texture and structure of the mesoporous silica host has been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption experiments, and 29Si magic-angle spinning (MAS) NMR spectroscopy. It was clearly observed that the presence of PBSA led to different characteristics compared to the reference MCM-41 type organized mesoporous silica (OMS), which suggests that the active molecules perturb the silica network formation. The encapsulation of the hydrophilic PBSA molecule was found to be stable in aqueous media, indicating that strong interactions exist between PBSA and its environment (surfactant and silica framework). 1H−29Si and 1H−13C MAS NMR experiments evidenced their spatial proximity and confirmed the presence of interaction between PBSA and both CTA+ molecules and silanol of the silica framework. This NMR study gave an overall picture of the organic/inorganic interface.

Synthesis and characterization of new catalysts formed by direct incorporation of heteropolyacids into organized mesoporous silica

The direct incorporation of Keggin-type heteropolyacid H 3PW 12O 40 (PW) in a mesoporous organized silica molecular sieve during the synthesis was studied. The synthesis of silica-organized materials containing heteropolyacid was carried out in acidic media either by associating a non-ionic/cationic surfactants or just a non-ionic surfactant. The decomposition temperature of solids containing PW and prepared with TX100/CTMA, Tergitol 15-S-12 and Tween 60 starts at 130, 115 and 135 °C, respectively. The BET surface area of these solids is measured to be 892, 735 and 787 m 2/g, respectively. Their pore diameters are equal to 31, 24 and 34 Å, respectively.

A new series of optoelectronic nanocomposites: CMI-1 mesoporous core/ZnS shell

The conception of a totally new optoelectronic composite with a highly organized mesoporous silica core and a uniform ZnS shell (200 nm in thickness) with new optical properties is reported. The starting CMI-1 material was firstly functionalized with ethylenediamine groups and then the growth of the ZnS shell was targeted by the immersion of the functionalized CMI-1 material in a Zn(CH 3COO) 2 solution followed by a reaction with sodium sulfide. The new optoelectronic nanocomposite has been characterized by a series of techniques such as SEM, TEM and nitrogen adsorption–desorption. The optical properties of the new nanocomposite have been evaluated by photoluminescent spectroscopy. No quantum size effect has been observed due to the large size aggregates in ZnS later.

Organized mesoporous silica films as templates for the elaboration of organizednanoparticle networks

Tremendous work achieved in the last 20 years on nanoparticle synthesis has allowed us tostudy many new physical properties that are found in the nanometre size range. Newdevelopments are now expected when considering assemblies of nanoparticles such as 2Dor 3D organized arrays. These systems are indeed expected to exhibit originalphysical properties resulting from particle–particle interactions. Studies in this fieldare clearly dependent on the elaboration of materials with controlled particlesize, organization and interparticle distance. This paper presents a strategy ofelaboration that is based on the use of organized mesoporous silica films as templates.These films are made by sol–gel polymerization around surfactant assemblies andfurther elimination of the surfactant. This provides porous matrices with a poreorganization that is the almost perfect replica of the initial micellar structure. The use ofsuch films for the elaboration of organized arrays of nanoparticles is detailed inthe case of CdS and Ag particles. The formation of particles inside the pores isachieved through impregnation with precursors that are allowed to diffuse inside thepores. This leads to particles with a size and a spatial arrangement that is directlyrelated to the initial pore structure of the films. This process opens a wide range ofinvestigations due to the relative ease of fabrication over large surfaces and the numerouspossibilities offered by the elaboration of porous films with different pore sizes andorganizations.

A novel way to synthesize high regular and periodic organic mesoporous silicas

Organic mesoporous silicas (OMSs) were synthesized in the presence of urea via one-pot synthesis method, in which tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxysilica (APTES) were used as the silica resources, non-ionic surfactant was used as the template. XRD results showed that the average periodic mesopore sizes of OMSs in the presence of urea were larger than those in the absence of urea. It was also found that the pore sizes of the products in the presence of urea distributed more narrowly than those in the absence of urea, and the contents of organosiloxane incorporated into OMSs, the pore wall thicknesses, the pore volumes and the surface areas of the products all increased with the use of urea. This shows a novel way to synthesize high regular and periodic organic mesoporous silicas.

RMN du31P et mesure du temps de relaxation de l'acide 12-tungstophosphorique incorporé par synthèse directe dans une charpente silicique mésoporeuse

The catalytic function of heteropoly compounds has attracted much attention because of their variety and high potential as catalysts. Supported heteropoly acids are generally prepared by impregnation of the active phase by a solution. In this work, we present a new concept for the preparation of a new solid catalyst by direct incorporation of tungstophosphoric species (HPW) into organized mesoporous silica. Synthesis of organized mesoporous silica containing PW was carried out with a mixture of two surfactants, a non ionic one and a cationic one. Taking into account the instability of the tungstophosphate species, the pH domain was restricted to 4-6. The presence of PW species incorporated in the solids was evidenced by solid state 31 P NMR. The relaxation times of these solids indicate a weaker mobility of PW in comparison with the impregnated ones.

Self‐organization kinetics of mesoporous nanostructured particles

AbstractSpray drying a mixture of silica and polystyrene latex (PSL) colloids above the decomposition temperature of PSL results in the formation of porous silica particles. By appropriate selection of the experimental conditions, such as the use of a tubular temperature, the weight fraction of colloids, and the flow rate of carrier gas, the resulting silica particles contain organized pores with a hexagonal close‐packing arrangement. The process by which organized mesoporous silica particles are formed by the spray‐drying method was examined using elementary laws of topology. Although a direct test using experimental data was not performed, at least qualitatively, the existence of a “stationary state” at which organized mesoporous particles can be produced with hexagonal close packing could be defined. Deviation from this stationary state results in the formation of unorganized pores as well as a deformed particle shape, rather than spherical ones. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2583–2593, 2004

Supercapacitor electrodes from new ordered porous carbon materials obtained by a templating procedure

Interesting carbon materials with a highly ordered porous structure, including micro- and mesopores, were successfully prepared by a templating procedure using an organized mesoporous silica (type MCM-48) as template and various carbon precursors (propylene, sucrose or pitch). The carbon material is obtained by introducing the carbon precursor by means of two different routes (liquid or gas) into the porous structure of the silica matrix. After the removal of silica by acid treatment, a carbon material with an organized porosity and porous characteristics defined mainly by the nature of the carbon precursor is recovered. The as-synthesized carbon exhibits an interesting electrochemical double-layer capacitance behavior due to its original and particular nanostructure and especially its regular interconnected nanoporosity. The performance of the supercapacitors was investigated in acidic, alkaline and organic electrolytic solutions. High values of capacitance in aqueous and organic media were obtained. The cyclic voltammograms display a rectangular shape over a wide range of scan rates indicating a quick charge propagation. The possibility to synthesize well-tailored nanostructured carbon materials is of prime importance to further forecast the optimal porous characteristics of an electrode material used for capacitor applications.

Determination of pore size distribution in thin organized mesoporous silica films by spectroscopic ellipsometry in the visible and infrared range

Determination of pore size distribution in thin organized mesoporous silica films by spectroscopic ellipsometry in the visible and infrared range

Determination of pore size distribution in thin organized mesoporous silica films by spectroscopic ellipsometry in the visible and infrared range

Spectroscopic ellipsometry is a non-destructive technique, well adapted to the determination of pore volume fraction, pore size distribution and accessible surface area of porous thin films; it is particularly attractive for low- k films. These quantities are deduced from the variation of the refractive index during adsorption and desorption of gas. Several difficulties are encountered for the interpretation of the ellipsometric spectra, in particular the density and refractive index of the skeleton, the determination of the micropores fraction and the variation of the film thickness during adsorption/desorption process should be taken into account. We present results obtained on organized mesoporous oxide films prepared by surfactant templating methods. A combination of spectroscopic ellipsometry measurements in the visible and the infrared ranges is shown to solve part of the uncertainties mentioned above, in particular for silica films, where a realistic estimation of the skeleton refractive index can be obtained.

Preparation of Organized Mesoporous Silica from Sodium Metasilicate Solutions in Alkaline Medium Using Nonionic Surfactants

A new procedure has been developed, which is based on homogeneous precipitation of organized mesoporous silica from an aqueous solution of sodium metasilicate and a nonionic poly(ethylene oxide) surfactant serving as a structure-directing agent. The decrease in pH, which induces the polycondensation of silica, is achieved by hydrolysis of ethyl acetate. Owing to the complexation of Na+ cations by poly(ethylene oxide) segments, assembling of the mesostructure appears to occur under electrostatic control by the S0Na+I- pathway, where S0 and I- are surfactant and inorganic species, respectively. As the complexation of Na+ cations causes extended conformation of poly(ethylene oxide) segments, the pore size and pore volume of organized mesoporous silica increase in comparison with materials prepared under neutral or acidic conditions. The assembling of particles can be fully separated from their solidification, which results in the formation of highly regular spherical particles of mesoporous silica.

Magnetic Nanocomposites Built by Controlled Incorporation of Magnetic Clusters into Mesoporous Silicates

Nanomagnets have been created by the incorporation of magnetic clusters into mesoporous silica. It is shown that, for a given cluster, the pore size has a strong influence on the degree of incorporation. Furthermore, the incorporation of these nanoclusters into three-dimensional organized mesoporous silica ensures that the integrity of the host phase as well as that of the incorporated clusters is maintained. This high degree of stability opens new perspectives for the organization of nanomagnets into mesoporous silica layers or as monolayers on silica surfaces.

In Situ Investigations on Cetyltrimethylammonium Surfactant/Silicate Systems, Precursors of Organized Mesoporous MCM-41-Type Siliceous Materials

Organized mesoporous silica (OMS) constitutes new materials with many potential applications. These materials with very well organized pores can be obtained by lowering the pH of precursor systems, i.e., highly alkaline silicate solutions containing cationic surfactants such as cetyltrimethylammonium bromide (CTAB) or chloride (CTAC). The precursor systems of OMS have been investigated prior to precipitation by in situ techniques. 29Si liquid-state NMR spectroscopy has been used to determine the type of silicate species in the investigated systems and how it is affected by the presence of the surfactant. Fluorescence probing techniques with the fluorescent probes pyrene and dipyrenylpropane have been used to study the variation of properties of the CTAB and CTAC micelles upon successive additions of a large excess of base (sodium hydroxide or tetramethylammonium hydroxide) and silicate (water glass or octameric species Si8O208-) as to generate the precursor systems that have the compositions that are used...