Coexistence of two kinds of fluorinated hydrogenated micelles as building blocks for the design of bimodal mesoporous silica with two ordered mesopore networks

A simple and effective route has been developed for the synthesis of bimodal (3.6 and 9.4 nm) mesoporous silica materials that have two ordered interconnected pore networks. Mesostructures have been prepared through the self-assembly mechanism by using a mixture of polyoxyethylene fluoroalkyl ether and triblock copolymer as building blocks. The investigation of the R(F)(8)(EO)(9)/P123/water phase diagram shows that in the considered surfactant range of concentrations the system is micellar (L(1)). DLS measurements indicate that this micellar phase is composed of two types of micelles; the size of the first one at around 7.6 nm corresponds unambiguously to the pure fluorinated micelles. The second type of micelles at higher diameter consists of fluorinated micelles that have accommodated a weak fraction of P123 molecules. Thus, in this study the bimodal mesoporous silica is really templated by two kinds of micelles.     

单分散核-壳结构介孔二氧化硅微球的合成

在酸性条件下, 采用非离子表面活性剂嵌段共聚物为模板剂, 季铵盐阳离子表面活性剂为共导向剂, 在预先合成的尺寸均一的单分散实心氧化硅微球表面包裹了有序介孔氧化硅层, 进一步通过高温水热处理, 获得了具有良好分散性和均匀尺寸的介孔壳层(孔径7 nm)氧化硅微球(~500 nm). 氧化硅微球外部包裹的介孔壳层具有较大的比表面积(188 m2/g)和孔容(0.23 cm3/g).     

Synergic effects of imidazolium ionic liquids on P123 mixed micelles for inducing micro/mesoporous materials

A series of micro/mesoporous silica composites were synthesized with P123 and imidazolium ILs ([C(n)mim]X) as the co-templates. [C(n)mim]X showed notable synergic interaction with P123. By changing the alkyl chain length n in methylimidazolium, ring-like micropores were observed in the wall of the mesoporous materials when n = 4. While increasing n to 10, micropores and mesopores were found in different separated regions. Various anions of Cl(-), Br(-), and BF(4)(-) of ILs have little effect on the aggregation behavior of P123/C4X mixed micelles. The strong hydrogen bonding effect of BF(4)(-) has resulted in the ordered mesoporous channels with numerous micropores in the wall at a low temperature of 313 K. Hydrophobic C4PF(6) can only be solubilized in the core of P123 micelles, which resulted in the swelling of P123/C4PF(6) mixed aggregates and the ordered hexagonal porous silica materials at 313 K. The fundamental understanding of the synergic interaction and formation mechanisms of various porous silica materials can provide a general convenient way toward a rational design and synthesis of the micro/mesoporous composites.     

Investigating the effect of randomly methylated β-cyclodextrin/block copolymer molar ratio on the template-directed preparation of mesoporous alumina with tailored porosity

Supramolecular assemblies formed between cyclodextrins and block copolymers can be efficiently used as templates for the preparation of mesoporous materials with controlled porosity. In this work, we use dynamic light scattering (DLS) and viscosity measurements to follow the variations occurring in the size and morphology of the triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (P123) micelles in the presence of various amounts of randomly methylated β-cyclodextrin (RAMEB). The results obtained with a series of solution compositions reveal that the cyclodextrin-to-copolymer (RAMEB/P123) molar ratio plays a crucial role in the growth rate of the micelles. At low RAMEB/P123 molar ratios (below ~7.5), a swelling effect of the cyclodextrin in the P123 micelles is noticed together with a modification of the micellar curvature from spherical to ellipsoidal. At high molar ratios (~7.5 and above), an abrupt transition toward large supramolecular assemblies, which no longer resemble micelles, occurs. When the RAMEB-swollen P123 micelles are used as templates to direct the self-assembly of colloidal boehmite nanoparticles, mesoporous γ-Al₂O₃ materials with high surface areas (360–400 m²/g), tunable pore sizes (10–20 nm), large pore volumes (1.3–2.0 cm³/g) and fiberlike morphologies are obtained under mild conditions. The composition of the mixed micellar solution, in particular the cyclodextrin-to-copolymer molar ratio, appears to be a key factor in controlling the porosity of alumina.     

Solvent evaporation induced aggregating assembly approach to three-dimensional ordered mesoporous silica with ultralarge accessible mesopores

A solvent evaporation induced aggregating assembly (EIAA) method has been demonstrated for synthesis of highly ordered mesoporous silicas (OMS) in the acidic tetrahydrofuran (THF)/H(2)O mixture by using poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) as the template and tetraethylorthosilicate (TEOS) as the silica precursor. During the continuous evaporation of THF (a good solvent for PEO-b-PMMA) from the reaction solution, the template molecules, together with silicate oligomers, were driven to form composite micelles in the homogeneous solution and further assemble into large particles with ordered mesostructure. The obtained ordered mesoporous silicas possess a unique crystal-like morphology with a face centered cubic (fcc) mesostructure, large pore size up to 37.0 nm, large window size (8.7 nm), high BET surface area (508 m(2)/g), and large pore volume (1.46 cm(3)/g). Because of the large accessible mesopores, uniform gold nanoparticles (ca. 4.0 nm) can be introduced into mesopores of the OMS materials using the in situ reduction method. The obtained Au/OMS materials were successfully applied to fast catalytic reduction of 4-nitrophenol in the presence of NaHB(4) as the reductant. The supported catalysts can be reused for catalytic reactions without significant decrease in catalysis performance even after 10 cycles.     

Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm^–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N₂ gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N₂ adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased     

Mixed micelles of a PEO-PPO-PEO triblock copolymer (P123) and a nonionic surfactant (C12EO6) in water. a dynamic and static light scattering study

The present article reports on static and dynamic light scattering (SLS and DLS) studies of aqueous solutions of the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) at temperatures between 25 and 45 degrees C. In water, P123 self-assembles into spherical micelles with a hydrodynamic radius of 10 nm, and at 40 degrees C, these micelles consist of 131 unimers. Addition of C12EO6 leads to an association of the surfactant molecules to the P123 micelles and mixed micelles are formed. The size and structure of the mixed micelles as well as interparticle interactions were studied by varying the surfactant-to-copolymer (C12EO6/P123) molar ratio. The novelty of this study consists of a composition-induced structural change of the mixed micelles at constant temperature. They gradually change from being spherical to polymer-like with increasing C12EO6 content. At low C12EO6/P123 molar ratios (below 12), the SLS measurements showed that the molar mass of the mixed micelles decreases with an increasing amount of C12EO6 in the micelles for all investigated temperatures. In this regime, the mixed micelles are spherical and the DLS measurements revealed a decrease in the hydrodynamic radius of the mixed micelles. An exception was found for C12EO6/P123 molar ratios between 2 and 3, where the mixed micelles become rodlike at 40 degrees C. This was the subject of a previous study and has hence not been investigated here. At high molar ratios (48 and above), the polymer-like micelles present a concentration-induced growth, similar to that observed in the pure C12EO6/water system.     

三嵌段共聚物EO20PO70EO20相分离行为的耗散粒子动力学模拟

采用耗散粒子动力学(DPD)方法研究了嵌段共聚物EO₂₀PO₇₀EO₂₀(P123)在水、乙醇/水溶液及二氧化硅溶胶体系中的相分离行为. 不同质量分数的P123在水溶液中共形成4种相分离状态: 球状胶束(10%); 椭球胶束(20%)、棒状胶束(30%)和三维立方胶束(50%). 在模板剂质量分数为10%的乙醇/水溶液中, 模板剂胶束稳定性随着乙醇含量的增加而变差. 在二氧化硅溶胶体系中, 模板剂质量分数低于5%时无胶束形成; 模板剂质量分数增至10%时, P123发生相分离形成三维球状胶束; 随着模板剂质量分数的进一步增加, 模板剂分子夹含着水分子形成三维椭球状结构(20%)、三维立方结构(40%)和层状结构(60%). 模拟结果与实验结果一致, 说明DPD模拟可以从计算角度推测模板剂对介孔材料结构的影响.     

助表面活性剂对介孔二氧化硅孔径的影响

在十六烷基三甲基溴化铵(CTAB)与硝酸形成的胶束体系中,分别加入正戊醇与正辛胺作助表面活性剂,合成出介孔二氧化硅.经小角XRD和N₂气体吸附与脱附实验证实,随着CTAB与正戊醇摩尔比的增加,介孔二氧化硅的孔径增加;而随CTAB与正辛胺摩尔比的增加,介孔二氧化硅的孔径减小.主要原因是正戊醇增大了CTAB胶束体积,从而导致介孔二氧化硅的孔径增加.而在CTAB与正辛胺的混合胶束中,正辛胺同硅酸盐作用力比CTAB强,导致介孔二氧化硅的孔径减小.     

A calorimetry and light scattering study of the formation and shape transition of mixed micelles of EO20PO68EO20 triblock copolymer (P123) and nonionic surfactant (C12EO6)

The interaction between the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) has been investigated by means of isothermal titration and differential scanning calorimetry (DSC) as well as static and dynamic light scattering (SLS and DLS). P123 self-assembles in water into spherical micelles at ambient temperatures. At raised temperatures, the DSC data revealed a sphere-to-rod transition of the P123 micelles around 60 degrees C. C12EO6 interacts strongly with P123 micelles in aqueous solution to give mixed micelles with a critical micelle concentration (cmc) well below the cmc for pure C12EO6. The presence of C12EO6 also lowers the critical micelle temperature of P123 so aggregation starts at significantly lower temperatures. A new phenomenon was observed in the P123-C12EO6 system, namely, a well-defined sphere-to-rod transition of the mixed micelles. A visual phase study of mixtures containing 1.00 wt % P123 showed that in a narrow concentration range of C12EO6 both the sphere-to-rod transition and the liquid-liquid phase separation temperature are strongly depressed compared to the pure P123-water system. The hydrodynamic radius of spherical mixed micelles at a C12EO6/P123 molar ratio of 2.2 was estimated from DLS to be 9.1 nm, whereas it is 24.1 nm for the rodlike micelles. Furthermore, the hydrodynamic length of the rods at a molar ratio of 2.2 is in the range of 100 nm. The retarded kinetics of the shape transition was detected in titration calorimetric experiments at 40 degrees C and further studied by using time-resolved DLS and SLS. The rate of growth, which was slow (>2000 s), was found to increase with the total concentration.     

Synthesis and Characterization of Ordered Mesoporous Silica Spheres Using Anionic and Nonionic Mixed Surfactants for Their Potential Application in LC

Ordered mesoporous silicas (OMSs) with spherical morphology were synthesized by using mixed surfactants of anionic sodium dodecyl sulfate and nonionic block copolymer EO₂₀PO₇₀EO₂₀ (P123) as template through an acid-catalyzed silica sol?Cgel process. A variety of characterizations demonstrated that the silica products exhibited well-formed spherical morphology, ordered mesostructure, narrow pore size distribution and large surface area (~700 m² g^?1). It was found that the synthesized OMSs had high adsorption capacity by using oxymatrine as model solute. The column packed with the silica spheres exhibited low back pressure and baseline separation of aromatic compounds such as benzene and nitrobenzene could be achieved. These results demonstrated the synthesized OMSs as a potential stationary phase for liquid chromatography.     

A two-step route to synthesis of small-pored and thick-walled SBA-16-type mesoporous silica under mildly acidic conditions

Highly ordered SBA-16-type mesoporous silica materials were synthesized by using poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymer (EO(132)-PO(50)-EO(132), Pluronic F108) as template through a two-step pathway under mildly acidic conditions (pH 2.15-4.50). The highly ordered cage-like mesoporosity of the prepared SBA-16-type mesoporous silica materials having Im3m cubic mesostructure was proved by the well-defined X-ray diffraction patterns combined with transmission electron microscopy. Scanning electron microscopy shows a variation from the spherical agglomerations to the randomly shaped ones with an increase of pH value. The nitrogen adsorption-desorption analysis reveals that the prepared SBA-16-type mesoporous silica materials have a uniform small-sized pore diameter (3.37-4.24 nm) and very thick pore wall (8.84-10.2 nm). These features may make the SBA-16-type mesoporous silica materials synthesized in this study favor the incorporation of catalytically active heteroatoms in silica frameworks, and the functionalization of organic groups for applications in catalysis, sensor and separation. The two-step synthetic method under the mildly acidic conditions can also be extended to the production in the industrial scale as an environmentally friendly way.     

以混合表面活性剂为模板可控合成MCM-48和MCM-41分子筛

利用阳离子和三嵌段共聚物混合表面活性剂为模板,在水热条件、碱性介质中可控合成出MCM-48和MCM-41分子筛。在固定P123(聚氧乙烯-聚氧丙烯-聚氧乙烯三嵌段共聚物):TEOS(正硅酸乙酯)(物质的量的比)为0.01875的体系中,调节CTAB(十六烷基三甲基溴化铵)∶TEOS(正硅酸乙酯)物质的量比值m,当m在0.12~0.13范围合成出MCM-48分子筛;当m在0.04~0.08范围合成出MCM-41分子筛。通过XRD,TEM,N2物理吸附,IR等方法进行了表征。结果表明:聚氧乙烯-聚氧丙烯-聚氧乙烯三嵌段共聚物(P123)的加入可以更大程度地降低合成介孔材料所需阳离子表面活性剂的用量;可控合成的介孔材料具有高比表面积、高度有序的孔道结构、较集中的孔径分布。     

Surfactant solubilization and the direct encapsulation of interfacially active phenols in mesoporous silicas

The solubilization of phenols in micelles of cetyltrimethyl ammonium bromide leads to microstructural changes from spherical micelles to wormlike micelles and then to vesicles. These microstructures are then used to template silicas. There is a transition from highly ordered hexagonal mesoporous silicas of the M41S family to lamellar structures, as the phenolic dopant concentration is increased. The results have implication to the removal of phenols from aqueous waste streams through the micellar enhanced ultrafiltration process. The entrapment of phenols in mesoporous silicas provides a way to sequester such contaminants in concentrated form.     

Transition metal-chelating surfactant micelle templates for facile synthesis of mesoporous silica nanoparticles

Highly ordered mesoporous silica nanoparticles with tunable morphology and pore-size are prepared by the use of a transition metal-chelating surfactant micelle complex using Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions. These metal ions formed a metal-P123 micelle complex in an aqueous solution, while the metal ions are chelated to the hydrophilic domain such as the poly(ethylene oxide) group of a P123 surfactant. The different complexation abilities of the utilized transition metal ions play an important role in determining the formation of nano-sized ordered MSNs due to the different stabilization constant of the metal-P123 complex. Consequently, from a particle length of 1700 nm in the original mesoporous silica materials, the particle length of ordered MSNs through the metal-chelating P123 micelle templates can be reduced to a range of 180–800 nm. Furthermore, the variation of pore size shows a slight change from 8.8 to 6.6 nm. In particular, the Cu²⁺-chelated MSNs show only decreased particle size to 180 nm. The stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism of MSNs by the metal-chelating P123 complex templates. In addition, solid-state ²⁹Si, ¹³C-NMR and ICP-OES measurements are used for quantitative characterization reveal that the utilized metal ions affect only the formation of a metal-P123 complex in a micelle as a template.     

Controllable and repeatable synthesis of thermally stable anatase nanocrystal-silica composites with highly ordered hexagonal mesostructures

In this article, we report a controllable and reproducible approach to prepare highly ordered 2-D hexagonal mesoporous crystalline TiO2-SiO2 nanocomposites with variable Ti/Si ratios (0 to infinity). XRD, TEM, and N2 sorption techniques have been used to systematically investigate the pore wall structure, and thermal stability functioned with the synthetic conditions. The resultant materials are ultra highly stable (over 900 degrees C), have large uniform pore diameters (approximately 6.8 nm), and have high Brunauer-Emmett-Teller specific surface areas (approximately 290 m2/g). These mesostructured TiO2-SiO2 composites were obtained using titanium isopropoxide (TIPO) and tetraethyl orthosilicate (TEOS) as precursors and triblock copolymer P123 as a template based on the solvent evaporation-induced co-self-assembly process under a large amount of HCl. Our strategy was the synchronous assembly of titanate and silicate oligomers with triblock copolymer P123 by finely tuning the relative humidity of the surrounding atmosphere and evaporation temperature according to the Ti/Si ratio. We added a large amount of acidity to lower condensation and polymerization rates of TIPO and accelerate the rates for TEOS molecules. TEM and XRD measurements clearly show that the titania is made of highly crystalline anatase nanoparticles, which are uniformly embedded in the pore walls to form the "bricked-mortar" frameworks. The amorphous silica acts as a glue linking the TiO2 nanocrystals and improves the thermal stability. As the silica contents increase, the thermal stability of the resulting mesoporous TiO2-SiO2 nanocomposites increases and the size of anatase nanocrystals decreases. Our results show that the unique composite frameworks make the mesostructures overwhelmingly stable; even with high Ti/Si ratios (> or =80/20) the stability of the composites is higher than 900 degrees C. The mesoporous TiO2-SiO2 nanocomposites exhibit excellent photocatalytic activities (which are higher than that for commercial catalyst P25) for the degradation of rhodamine B in aqueous suspension. The excellent photocatalytic activities are ascribed to the bifunctional effect of highly crystallized anatase nanoparticles and high porosity.     

立方规则孔道结构含锆介孔氧化硅的合成与表征

以三嵌段共聚物为模板剂, 利用溶剂挥发法合成了具有立方相的含锆介孔氧化硅材料, 并对其结构进行了表征, 初步研究了其生成机理.     

Advances in the Interfacial Assembly of Mesoporous Silica on Magnetite Particles

Interfacing magnetic particles with ordered mesoporous materials is an effective direction for the development of functional porous composite materials with rationally designed core–shell structures. Owing to the combined properties of magnetic nanoparticles and mesoporous silica (high surface area, large pore volume, porosity, and biocompatibility), core–shell magnetic mesoporous silica materials have generated tremendous interest in various disciplines, including chemistry, materials, bioengineering, and biomedicine. Interfacial assembly strategies enable the rational construction of magnetic mesoporous silica materials with well‐defined core–shell structure, morphology, pore parameters, and surface wettability, which can decisively influence their physical and chemical properties and thus improve their application performance. This Minireview summarizes recent progress in the synthesis of core–shell magnetic mesoporous silica and the adjustment of key parameters, including pore size, morphology, and pore orientation.     

Preparation of mesostructured barium sulfate with high surface area by dispersion method and its characterization

The spherical and cubic mesoporous BaSO(4) particles with high surface area were successfully produced via one-step process through precipitation reaction in aqueous solution of Ba(OH)(2) and H(2)SO(4) with ethylene glycol (n-HOCH(2)CH(2)OH) as a modifying agent. The BaSO(4) nanomaterial revealed that the high surface area and the mesoporous was stable up to 400 degrees C. Agglomerate mesoporous barium sulfate nanomaterials were obtained by the reaction of Ba(2+) and SO(2-)(4) with ethylene glycol aqueous solution. The ethylene glycol was used to control the BaSO(4) particle size and to modify the surface property of the particles produced from the precipitation. The dried and calcined mesoporous BaSO(4) nanomaterials were characterized by X-ray diffraction (XRD), BET surface area and N(2) adsorption-desorption isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared resonance (FTIR) and thermogravimetric analysis (TGA). The as-prepared mesoporous dried BaSO(4) possesses a high BET surface area of 91.56 m(2) g(-1), pore volume of 0.188 cm(3) g(-1) (P/P(0)=0.9849) and pore size of 8.22 nm. The SEM indicates that the morphology of BaSO(4) nanomaterial shows shell like particles up to 400 degrees C, after that there is drastically change in the material due to agglomeration. Synthesis of mesoporous BaSO(4) nanomaterial is of significant importance for both sulphuric acid decomposition and oxidation of methane to methanol.     

Gas diffusion and microstructural properties of ordered mesoporous silica fibers

Pore and surface diffusion of carbon dioxide (CO(2)) and ethylene (C(2)H(4)) in the nanopores of ordered mesoporous silica fibers about 200 microm in length was measured by the transient gravimetric method. The experimentally determined pore diffusivity data, coupled with the porosity, pore size, and fiber length, are used to obtain the actual length of the nanopores in silica fibers. These measurements reveal a structure of the ordered nanopores whirling helically around the fiber axis with a spiral diameter of about 15 microm and a pitch value of 1.6 microm. At room temperature the surface diffusion contributes about 10% to the total diffusional flux for these two gases in the nanopores of the ordered mesoporous silica fibers. The surface diffusion coefficients for the ordered mesoporous silica fibers are about 1 order of magnitude larger than the non-ordered mesoporous alumina or silica with similar pore size.