Design of ordered bimodal mesoporous silica materials by using a mixed fluorinated-hydrogenated surfactant-based system

Mesoporous silica materials have been prepared using aqueous solutions of hydrogenated-fluorinated surfactant mixtures. The phase behavior of the C18H35(OC2H4)10-C6F15C2H4(OC2H4)11OH [RH18(EO)10-RF6(EO)11] mixture in aqueous solution was first established at the temperature at which the silica source is added, i.e., 20 or 40 degrees C. We have delimited the different phase domains. Concerning the mesostructured silica, whatever the temperature at which the silica source is added, mesoporous material with a hexagonal array of their channel is formed via a cooperative templating mechanism (CTM), if the content of RF6(EO)11 in the surfactant mixture is lower than 50%. Moreover, when the silica source is added at 40 degrees C, the recovered materials exhibit a bimodal pore size distribution. The appearance of this bimodality has been related to the coexistence of hydrogenated micelles with fluorinated wormlike micelles. By contrast, the bimodality is not observed when the silica source is added at 20 degrees C.     

Rheological behavior of surfactant-based precursors of silica mesoporous materials

The linear and non-linear viscoelastic behaviors of polymer-like micellar solutions of cetyltrimethylammonium tosilate (CTAT) with added NaOH and tetraethyl orthosilicate (TEOS) to produce precursors of mesoporous materials are studied. The effect of TEOS/CTAT (T/C) ratio at fixed CTAT concentration, CTAT concentration at fixed T/C and aging time are reported. The systems show increasingly larger deviations from near-Maxwell behavior upon increasing T/C ratio, CTAT concentration and aging. Moreover, in steady and unsteady shear-flow, shear banding develops between two critical shear rates, which tend to fade as the T/C ratio and aging increase. The Granek-Cates model is employed to analyze linear viscoelastic behavior. The Bautista-Manero-Puig (BMP) model is used here to reproduce the steady and transient nonlinear rheology of these systems. We explain these results in terms of the changes in inter-macromolecular interactions that arise out of the presence of colloidal additives in the viscoelastic gel. The ordered mesoporous materials were identified by X-ray diffractometry (XRD) and high-resolution transmission electron microscopy.     

Nonionic fluorinated-hydrogenated surfactants for the design of mesoporous silica materials

We have investigated the influence of the ratio between the volume of the hydrophilic head ( V A) and the volume of the hydrophobic part ( V B) of the surfactant on the mesopore ordering. To understand the difference of behavior we have performed a complete study dealing with fluorinated [R m (F)(EO) n ] and hydrogenated [R m (H)(EO) n ] surfactants. Their mixtures have also been taken into account. Here only the phase diagrams and the structural parameters of the liquid crystal phases of the mixed systems are reported. We have shown that the mutual or partial miscibility of the fluorinated and the hydrogenated surfactants depends on the number of oxyethylene units of each surfactant. To follow, various systems were used for the preparation of silica mesoporous materials via a cooperative templating mechanism (CTM). Results clearly reveal that V A/ V B ratios in the range between 0.95 and 1.78 lead to the formation of well-ordered mesostructures. Wormhole-like structures are obtained for higher or lower values. Moreover, results show that from the V A/ V B point of view, polyoxyethylene fluoroalkyl ether surfactants behave like their hydrogenated analogues.     

Nonionic fluorinated surfactant: investigation of phase diagram and preparation of ordered mesoporous materials

The behavior of fluorinated surfactant F(CF2)8C2H4(OC2H4)9OH in water solution was investigated, and the preparation ofmesoporous molecular sieves was achieved. A direct micellar phase (L1) and a hexagonal (H1) liquid crystal were found. Small-angle X-ray scattering measurements proved that the hydrophobic chains are completely extended and that the cross sectional area remains constant in H1. At 80 degrees C, materials with a hexagonal array of their channel are prepared via a cooperative templating type mechanism in a wide range of surfactant concentrations (5-20 wt %). Decreasing the hydrothermal temperature leads to the formation ofwormhole-like structure. In this case the channel arrangement is no longer governed by the surfactant behavior but by the silica condensation and polymerization. An increase of the mean pore diameter with heating temperature is noted. This result is associated with changes of aggregation number with temperature. A comparison of the characteristics of the materials obtained with both hydrogenated and fluorinated surfactants is also made.     

Fast preparation of highly ordered nonsiliceous mesoporous materials via mixed inorganic precursors

Employing metal alkoxide as the main inorganic precursor and anhydrous metal chloride as the pH 'adjustor' and hydrolysis-condensation 'controller', very fast preparation of ordered nonsiliceous mesoporous materials has been demonstrated.     

Efficient synthesis and sulfonation of ordered mesoporous carbon materials

Ordered mesoporous carbons (OMCs) with hexagonal structure were efficiently synthesized via cooperative self-assembly of phenol/formaldehyde resol and surfactant F127 under acidic aqueous conditions. Induced by HCl, a gel phase mainly containing phenol/formaldehyde resol and F127 was obtained within several hours. X-ray diffraction (XRD), transmission electron microscope (TEM) and nitrogen adsorption isotherms indicated that the synthesized samples possess 2-D hexagonal mesostructure. The influence of the synthesis conditions, including acid concentration and mass ratio of resol to F127, was investigated. When the acid concentration was fixed in the range of 0.6-2.0 M and the mass ratio of resol to F127 in the range of 3.5-4.0, highly ordered mesoporous carbon could be synthesized. The synthesized OMCs could be easily sulfonated in concentrated sulfuric acid at elevated temperature. The results indicate that the mesostructural stability and the content of the surface sulfonic acid (SO(3)H) groups depend mainly on the pyrolysis temperature of the OMCs and the sulfonation temperature, suggesting that the combination of pyrolysis and sulfonation temperature is essential for developing OMCs with high densities of SO(3)H groups.     

Comparative thermogravimetric and adsorption study of highly ordered mesoporous materials

A comparative study was carried out for highly ordered mesoporous materials using high resolution thermogravimetry (HR-TG) and adsorption techniques. These materials were synthesized with mixed surfactants of various alkyl chain lengths. For thermogravimetry measurements n-butanol was used to probe the adsorbent surface and high-resolution TG curves as well as their 1st and 2nd derivatives were obtained for this probe molecule. It is shown that the values of the mesopore volume and specific surface area evaluated from TG data are in a good agreement with those evaluated from low-temperature nitrogen adsorption isotherms. This comparative study was performed to confirm the usefulness of the HR-TG technique as an alternative method for evaluation of the mesopore volume and specific surface area of ordered mesoporous materials.     

Comparison of ordered mesoporous materials sorption properties towards amino acids

The adsorption of amino acids such as l-phenylalanine and l-histidine was carried out on a series of mesoporous carbons obtained with the use ordered silicas KIT-6, SBA-16, SBA-15 as templates and furfuryl alcohol as carbon precursor. Small angle XRD analysis confirmed the ordered mesoporous structures of all materials obtained. They were also characterised by well-developed surface areas and high pore volumes. Adsorption behaviour of amino acids on ordered mesoporous carbons was investigated in potassium phosphate buffer solutions with adjustable l-phenylalanine and l-histidine concentration, ion strength, and pH. The highest sorption capacity towards the amino acids were observed at pH close to the isoelectric point of l-phenylalanine (pI = 5.48) and l-histidine (pI = 7.59). Electrostatic, hydrophobic and steric interactions had very strong effect on the adsorption of amino acids on mesoporous carbons. The amount of l-phenylalanine and l-histidine adsorbed decreased in the following sequence: C_KIT-6 > C_SBA-16 > C_SBA-15 that was strongly related to their structure, surface areas and average pore diameters.     

Photochromic ordered mesoporous hybrid materials based on covalently grafted polyoxometalates

Novel polyoxometalate (POM)-grafting mesoporous hybrid silicas, XW(11)/MHS (X=P, Si) and TBAPW(11)Si(2)/MHS, have been prepared respectively by co-condensation and post-synthesis routes based on the employment of Keggin-type monovacant XW(11) or a Si-substituted compound TBAPW(11)Si(2) as POM precursors. Upon characterization of the samples by FT-IR, XRD, ICP-AES, TEM and N(2) adsorption-desorption measurement, it was found that Keggin units were retained perfectly in ordered hexagonal mesopore channels with SBA-15 architecture and immobilized by covalent linkages on the mesopore wall. These materials, especially the co-condensed samples, exhibited stable and reversible photochromic properties under UV irradiation although no special organic component was supplied additionally as an electron donor. An investigation of the photochromism revealed that the photochromic response depended on the centre atom of the POM species (i.e., the redox potential of the POM), the content of the POM and the synthetic route of the sample, while the bleaching process was correlated not only to the redox potential but also to the pore size of the sample. The photochromic mechanism was also studied in detail by cyclic voltammetry, ESR, FT-IR and XPS techniques. It was found that the remaining P123 template acted as a reducing agent and was oxidized during the photochromic process accompanied by the reduction of the POM to heteropolyblue. Thus, a close contact between the POM and the remaining P123 chain in the sample is necessary. Low close-contact degree results in poor photochromic behavior of the post-synthesized sample and impregnated samples.     

有序中孔炭的制备及电性能研究

采用微湿含浸法制备了一系列具有不同比表面积和孔径分布的超级电容器有序中孔炭材料,同时采用Al-SBA-15为模板剂制得具有六方排列的空心炭管CMK-5.所制得的有序中孔炭的BET比表面积随糠醇加入量的增加而减小.电化学性能测试结果表明,在1mA·cm-2的充放电电流密度下各中孔炭材料比电容的大小顺序与其BET比表面积的大小顺序相一致.在所有样品中AlSC-0.8由于具有最大的比表面积,因此其比电容最大,达87.8F·g-1.倍率性能测试结果表明,具有CMK-3结构的SC-2.0的倍率性能最好,在50mA·cm-2的放电电流密度下其放电比电容接近AlSC-0.8有序中孔炭的水平.     

Confinement and controlled release of bisphosphonates on ordered mesoporous silica-based materials

Bisphosphonates have been confined in siliceous ordered mesoporous materials, and the drug release rate of these systems has been investigated. The bisphosphonate adsorption rate has been increased from 1% in oral administration to around 40% locally delivered. Drug dosage can be modulated through amine modification of the material surface, leading to a bisphosphonate adsorption in the ordered mesoporous matrices 3 times larger than that for unmodified materials. The use of these drug delivery systems opens new fields with new possibilities for tissue engineering.     

Enhanced release of itraconazole from ordered mesoporous SBA-15 silica materials

This in vitro study reports on the enhanced release of the hydrophobic drug itraconazole from the ordered mesoporous SBA-15 silica material and on the existence of a critical mesopore diameter for enhancing release.     

Direct synthesis of ordered mesoporous materials constructed with polymer-silica hybrid frameworks

Highly ordered mesoporous materials constructed with integrated polymer-silica hybrid frameworks can be obtained via a one-step synthetic strategy using a mixture of polymer and silicate as the framework sources in the presence of a structure-directing agent.     

Multifunctional hybrids by combining ordered mesoporous materials and macromolecular building blocks

This critical review presents and discusses the recent advances in complex hybrid materials that result from the combination of polymers and mesoporous matrices. Ordered mesoporous materials derived from supramolecular templating present high surface area and tailored pore sizes; pore surfaces can be further modified by organic, organometallic or even biologically active functional groups. This permits the creation of hybrid systems with distinct physical properties or chemical functions located in the framework walls, the pore surface, and the pore interior. Bringing polymeric building blocks into the game opens a new dimension: the possibility to create phase separated regions (functional domains) within the pores that can behave as "reactive pockets" of nanoscale size, with highly controlled chemistry and interactions within restricted volumes. The possibilities of combining "hard" and "soft" building blocks to yield these novel nanocomposite materials with tuneable functional domains ordered in space are potentially infinite. New properties are bound to arise from the synergy of both kinds of components, and their spatial location. The main object of this review is to report on new approaches towards functional polymer-inorganic mesostructured hybrids, as well as to discuss the present challenges in this flourishing research field. Indeed, the powerful concepts resulting from the synergy of sol-gel processing, supramolecular templating and polymer chemistry open new opportunities in the design of advanced functional materials: the tailored production of complex matter displaying spatially-addressed chemistry based on the control of chemical topology. Breakthrough applications are expected in the fields of sustainable energy, environment sensing and remediation, biomaterials, pharmaceutical industry and catalysis, among others (221 references).     

Guest-host encapsulation of microporous zeolites in ordered mesoporous materials by molecular simulations

The present work provides the first study of ordered mesoporous materials SBA-15 coated with microporous zeolites ZSM-5 using molecular simulations. Several model structures with characteristics such as periodic arrangement of mesopores, randomly arranged micropores, surface hydroxyls and bulk deformations of SBA-15 were used. Cartesian coordinates of ZSM-5 unit lattice were obtained from the literature and the 100 face of H-ZSM-5 unit cell was then placed on the surface of SBA-15 and the entire structure was equilibrated to obtain final configuration. The resulting structure was characterized using simulated small angle and wide angle X-ray diffraction, Connolly surface area (to compare BET area), accessible pore volume for nitrogen molecules (to compare with t-plot volume of micro and mesopores) and methane adsorption at 303 K. The orientation of ZSM-5 on the SBA-15 had no effect on the surface area, pore volume or adsorption capacity. In order to find out if the addition of microporous ZSM-5 should increase the total methane adsorption capacity due to addition of micropores, we studied adsorption on bare and coated SBA-15. However, total adsorption capacity was found to decrease, while the number of methane molecules adsorbed per unit cell of the SBA-15 structure increased. An existing experimental method (J. Am. Chem. Soc., 2004, 126, 14324) of the synthesizing hybrid ZSM-5/SBA-15 structure was studied using accessible micropore volume (by t-plot). It was found that the procedure made all the micropores inaccessible. A modification of the method or use of other host materials is suggested to use the benefits of narrow micropore distribution in ZSM-5.     

孔壁富含微孔有序介孔材料的设计合成及表征

通过调节水热处理溶液的酸度和温度,进而调控材料孔壁上硅羟基与模板剂的相互作用以及模板剂亲水嵌段嵌入到孔壁内的量,制备出了墙壁富含微孔的有序介孔材料SBA-15.氮气吸附测试表明,当水热处理溶液的pH值和温度分别为2.2和100℃时,经300℃焙烧脱除模板剂后的样品具有较高的微孔含量,其微孔体积为0.176cm3/g,占总孔体积的21.6%.     

Synthesis of ordered mesoporous materials using surfactant liquid crystals or micellar solutions

Formation of ordered mesoporous materials using surfactant templating proceeds via mechanisms relying on optimising interactions between the inorganic and organic components of the synthesis. For oxides, the rates of hydrolysis and condensation of the inorganic species relative the rate of assembly of the mesostructure is crucial. Synthetic strategies to control these factors have been reviewed and it appears that mesostructured silica can be prepared in most phases found in binary surfactant–water systems by optimising the volume fraction of the surfactant and the hydrolysed inorganic precursor.