Synthesis of hollow silica spheres with mesostructured shell using cationic-anionic-neutral block copolymer ternary surfactants

Hollow silica spheres with mesostructured shells (HSSMS) were prepared with a vesicle template of cetyltrimethylammonium bromide-sodium dodecyl sulfate-Pluronic P123 (C(16)TMAB-SDS-EO(20)PO(70)EO(20)) at a SDS/C(16)TMAB ratio of 0.6-0.8 following a fast silicification in dilute silicate solution at pH approximately 5.0. The mesostructure of the shell is disordered, and the mesopore size is about 5.5-7.5 nm. Moreover, the direction and length of the nanochannels of the shell change with the SDS/C(16)TMAB ratios. A bi-template model, in which the C(16)TMA(+)-DS(-) form the stable bilayer vesicle structure and the P123 copolymers anchored on C(16)TMA(+)-DS(-) vesicle act as the template for the mesoporous silica, was proposed to explain the formation of the HSSMS. This bi-template model can be applied extensively to prepare the HSSMS with different diameters and pore sizes by using other C(n)TMAX-SDS-EO(n)PO(m))EO(n) ternary-surfactant mixtures.     

Crystalline-like molecularly ordered mesoporous aluminosilicates derived from aluminosilica-surfactant mesophases via benign template removal

We report the preparation of mesoporous aluminosilicate materials that exhibit molecular-scale ordering in their pore wall framework. The materials were derived from mesoporous aluminosilica-surfactant mesophases via benign template removal methods, which allowed the retention of molecular ordering in surfactant-free materials. The molecularly ordered aluminosilica-surfactant mesophases were obtained from hydrothermal crystallization of cetyltrimethylammonium hydroxide/Al,Si/H2O systems at 135 degrees C for 12 days. Benign template removal via H2O2-mediated oxidation of the surfactant at room temperature was found to be the most effective method in generating surfactant-free materials with molecular ordering, high textural properties (depending on Al content), and high acidity. The Al in the resulting aluminosilicates was entirely incorporated in framework (tetrahedrally coordinated) sites. Template extraction in acidified ethanol also generated molecularly ordered materials but compromised the Al content and acidity. Template removal via conventional calcination generated porous materials with high textural properties but which exhibited only limited molecular ordering and had relatively low acidity and significant amounts of nonframework Al. This work demonstrates that molecular ordering in mesoporous silicate-surfactant mesophases is due to crystallographic ordering within inorganic frameworks rather than the arrangement/packing of surfactant molecules.     

Surfactant mediated control of pore size and morphology for molecularly ordered ethylene-bridged periodic mesoporous organosilica

A series of ethylene-containing mesoporous organosilica materials were fabricated via surfactant-mediated assembly of 1,2-bis(triethoxysilyl)ethylene (BTEE) organosilica precursor using alkyltrimethylammonium bromide (CnTAB) surfactants with different alkyl chain length (n=12, 14, 16, 18) as supramolecular templates. The presence of molecularly ordered ethylene groups in the resulting periodic mesoporous organosilica (PMO) materials was confirmed by XRD data along with 29Si and 13C MAS NMR analysis. Additional characterization techniques, namely nitrogen sorption, TEM, and TGA, confirmed the structural ordering and thermal stability of the molecularly ordered ethylene-bridged PMOs. The PMOs exhibit molecular-scale ordering (with a periodicity of 5.6 A) within the organosilica framework and tunable pore size, which depending on the alkyl chain length of the surfactant templates, varied in the range 23-41 A. Furthermore, depending on the alkyl chain length of the templates, the particle morphology of the PMOs gradually changed from monodisperse spheres (for C12TAB) to rod or cakelike particles (for C14TAB) and elongated ropelike particles for longer chain surfactants. Variations in the surfactant chain length therefore allowed control of both the pore size and particle morphology without compromising molecular-scale or structural ordering. The reactivity of ethylene groups was probed by bromination, which demonstrated the potential for further functionalization of the PMOs.     

Intercalation of poly(oxyethylene) alkyl ether into a layered silicate kanemite

Poly(oxyethylene) alkyl ether (CnEOm) is intercalated into the interlayer space of a layered silicate kanemite by using layered hexadecyltrimethylammonium (C16TMA) intercalated kanemite (C16TMA-kanemite) as the intermediate. C16TMA-kanemite was treated with an aqueous solution of C16EO10, and the intercalation of C16EO10 was confirmed by the slight increase in the basal spacing (from 2.92 to 3.34 nm) with the increase in the carbon content, yielding C16EO10-C16TMA-kanemite. The product was dispersed again in a C16EO10 aqueous solution, and then 1.0 M HCl was added to the suspension to remove C16TMA ions completely. The basal spacing was further increased (from 3.34 to 5.52 nm) and the content of nitrogen was virtually zero, indicating further intercalation of C16EO10 molecules and complete elimination of C16TMA ions simultaneously. Though C16EO10 molecules are not directly intercalated into kanemite, the mutual interactions among C16TMA ions, C16EO10 molecules, and the interlayer silicate surfaces effectively induce the intercalation of C16EO10. C16EO10-kanemite shows a reversible adsorption of n-decane and water owing to the hydrophobicity and hydrophilicity of C16EO10, respectively, in the interlayer space. Layered CnEO10-kanemites (n = 12 and 18) were also synthesized in a manner similar to layered C16EO10-kanemite.     

Investigation of the properties of organically modified ordered mesoporous silica films

Organically modified, ordered mesoporous silica films, which can provide hydrophobicity and low polarizability to the framework, were prepared using Brij-76 block copolymer as a template. Due to a fast condensation reaction of the silica precursor, mesostructured silica films were not properly synthesized. To circumvent this problem, a synthesis procedure was modified to provide an enhancement of pore periodicity through the incorporation of methyl ligands on the framework. The micropore volume was reduced, and the pore size was enlarged, as the concentration of the methyl ligands on the framework was increased. A mesophase transition from a two-dimensional hexagonal structure to a body-centered cubic (BCC) structure was observed according to the concentration of incorporated methyl ligands. The mechanical properties of the fabricated films were investigated according to the pore ordering and film density. The mechanical properties of the films with random pore geometry show a positive correlation between film density and elastic modulus. Meanwhile, the mechanical behavior of organically modified mesoporous silica films with periodic pore distribution represents a negative correlation within a certain density range, which is advantageous to the low-k materials. Especially, film with a low micropore volume fraction and BCC pore ordering is more applicable to a low-k material due to low dielectric constant and high mechanical strength.     

One-step nanocasting synthesis of highly ordered single crystalline indium oxide nanowire arrays from mesostructured frameworks

A one-step nanocasting route has been demonstrated to prepare highly ordered single-crystal indium oxide nanowire (IONW) arrays with mesostructured frameworks. Unlike the reported multistep nanocasting process (synthesis of mesoporous materials, and then incorporation of precursors and formation of inorganic frameworks), a highly ordered mesostructured surfactant-silica monolith with low external surface serves as both the template and the reducing agent and makes the formation of single-crystal IONWs in its channels easily in one step by using normal In(NO(3))(3) as an inorganic precursor. After silica is removed, highly ordered uniform single-crystal IONW arrays with hexagonal (p6mm) or cubic (Ia3d) mesostructures are derived. These new materials are studied by XRD, SEM, TEM, N(2) adsoption, and UV spectrum. Furthermore, this one-step nanocasting synthesis route is a generalized method and can be used to synthesized a highly ordered mesoporous silica monolith with metal oxide nanocrystals in its channels. To the best of our knowledge, this is the first report of a single crystalline mesostructured In(2)O(3) framework.     

Rapid micropatterning of mesoporous silica film by site-selective low-energy electron beam irradiation

Rapid microfabrication of mesoporous silica film at low temperature was achieved with low-energy electron beam (LEEB) irradiation. A mesostructured film (thickness approximately 200 nm), which was prepared through hydrolysis and condensation of tetramethoxysilane in the presence of hexadecyltrimethylammonium chloride, was irradiated with LEEB at 25 kV and 300 microA under pressures of 10 and 1000 Pa. The surfactant molecules can be eliminated completely at temperatures less than 40 degrees C after only 10 min (10 Pa) and 5 min (1000 Pa) of irradiation, resulting in conversion to a highly ordered mesoporous silica film without cracking. The LEEB-irradiated film also showed reasonable chemical resistance toward dilute hydrofluoric acid solution due to sufficient consolidation by cross-linking of silicate networks during the irradiation. The unirradiated regions were etched away preferentially to the irradiated areas; therefore, rapid micropatterning of the mesoporous silica film was possible by area-selective LEEB irradiation followed by chemical etching.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.     

Tetrafluoroborate salts as site-selective promoters for sol-gel synthesis of mesoporous silica

Tetrafluoroborate ion (BF(4)(-)) serves as a powerful and better-behaved promoter than fluoride ion (F(-)) for hydrolytic condensation of alkoxysilanes, such as tetraethoxy orthosilicate, in aqueous media containing amphiphiles with onium ion headgroups as templates, affording thermally and hydrothermally stable mesoporous silica. According to (19)F NMR spectral profiles, BF(4)(-) is localized on a positive-charged micellar surface, thereby allowing a site-selective growth of the silica framework. The resulting porous silica has an ordered hexagonal structure with a well-developed and thick silicate wall. Even without calcination, the condensation with BF(4)(-) as the promoter progresses to a large extent to furnish a [Si(OSi-)(4)]/([HOSi(OSi-)(3)] + [(HO)(2)Si(OSi-)(2)]) ratio of 6.2, which is greater than that of mesoporous silica formed without BF(4)(-) before (1.5) and even after calcination (3.5) to promote thermal condensation in the solid state.     

Molecular manipulation of two- and three-dimensional silica nanostructures by alkoxysilylation of a layered silicate octosilicate and subsequent hydrolysis of alkoxy groups

A novel methodology for constructing molecularly ordered silica nanostructures with two-dimensional (2-D) and three-dimensional (3-D) networks has been developed by using a stepwise process involving silylation of a layered silicate octosilicate with alkoxytrichlorosilanes [ROSiCl(3), R = alkyl] and subsequent reaction within the interlayer spaces. Alkoxytrichlorosilanes react almost completely with octosilicate, bridging two closest Si-OH (or -O(-)) sites on the silicate layers, to form new five-membered rings. The unreacted functional groups, Si-Cl and Si-OR, are readily hydrolyzed by the posttreatment with a water/dimethyl sulfoxide (DMSO) or water/acetone mixture, leading to the formation of two types of silicate structures. The treatment with a water/DMSO mixture produced a unique crystalline 2-D silicate framework with geminal silanol groups, whereas a water/acetone mixture induced hydrolysis and subsequent condensation between adjacent layers to form a new 3-D silicate framework. The 2-D structure is retained by the presence of DMSO molecules within the swelled interlayer spaces and is transformed to a 3-D silicate upon desorption of DMSO. The structural modeling suggests that both of the 3-D silicates contain new cagelike frameworks where solvent molecules are trapped even at high temperature (up to 380 degrees C, in the case of acetone). Both 2-D and 3-D silica structures are quite different from known layered silicates and zeolite-like materials, indicating the potential of the present approach for precise design of various silicate structures at the molecular level.     

Nanoporous silica films containing aluminum and titanium

By utilizing surfactant aggregates as supramolecular templates, mesoporous and mesostructured silicas with highly ordered structures became available. The resulting mesoporous silicas are promising candidates to host various photo- and electro-active species along with catalytically active species, due to their large and controllable pore sizes, highly ordered pore arrangements with low dimensional geometries, and reactive surfaces. We have developed the rapid solvent evaporation method, which is a modified sol-gel process, for synthesizing the mesostructured silica-surfactant films as well as the mesoporous silica films. Supported thin films, self-standing films and bubbles of mesoporous silicas have been synthesized by the rapid solvent evaporation method. The microstructures of the films have also been successfully controlled by changing the synthetic conditions. Taking advantage of the ease of synthetic operation and the transparency and homogeneity of the resulting materials, we have been interested in the introduction of functional units into the mesostructured materials. This paper reports the synthesis of transparent films of titanium- and aluminum-containing nanoporous silicas to modify the surface properties (such as adsorptive and catalytic) of nanoporous silicas. The incorporation of Al led to the formation of cation exchange or acidic sites on the mesopore surface, as revealed by the cationic dye adsorption experiments. The photocatalytic reactions of the Ti-containing nanoporous silica films were also examined.     

不同pH值下合成的双中孔和六方中孔SiO_2的表征(英文)

在相同的反应体系中当ｐｈ值从约９．５调变至１１时分别合成出双中孔ＳｉＯ２和六方中孔ＳｉＯ２材料,并用ＸＲＤ、Ｎ２吸附、ＴＥＭ、ＴＧ／ＤＴＡ和ＦＴＩＲ等测试手段对合成产物进行了表征。实验结果表明,双中孔ＳｉＯ和六 方中孔ＳｉＯ２是合成中必然出现的两种不同的中孔物相。与六方中孔ＳｉＯ２相比,双中孔ＳｉＯ２也具有典型中孔 材料的特征ＸＲＤ谱图,虽然仅呈现一个易让人产生不完全晶化误解的相对较宽的单ＸＲＤ衍射峰（ｄ＝５．２ｎｍ）,但它却给出一种独特的Ｎ２吸附等温线和窄的双峰中孔孔径分布曲线。由于孔壁的无定形及表面活性剂分子与ＳｉＯ２骨架间相似的相互作用,两类材料给出类似的ＦＴＩＲ谱图和ＴＧ／ＤＴＡ曲线。然而,在双中孔ＳｉＯ２的ＦＴＩＲ谱图中９６０ｃｍ处峰强度的微小变化可能意味着在锻烧脱除模板剂后双中孔ＳｉＯ２较六方中孔ＳｉＯ２具有更高的骨架聚合度。     

Study of the Pm3n space group of cubic mesoporous silica.

By using a Gemini surfactant, [C14H25N+(CH3)2-(CH2)2-N+(CH3)2C14H25]2 Br-(C(14-2-14)), with a short spacer group (s = 2) as structure-directing agent and sodium silicate as precursor, high-quality, ordered cubic mesoporous silica with space group Pm3n was prepared by the S+I-route (S = surfactants, I = precursor). The samples were characterized by small-angle X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption. The results showed that the pore structure of the resulting mesoporous silica belonged to the cubic system (space group Pm3n). The unit-cell parameter of the cubic system was in the range of 8.81-9.14 nm. The high-quality cubic mesoporous structure was formed at molar ratios of C(14-2-14) to sodium silicate of 0.33:1 to 0.16:1 and a molar ratio of ethyl acetate to sodium silicate of 2:1. N2 adsorption-desorption curves revealed type IV isotherms and H1 hysteresis loops. The primary pore volume, and the most probable pore size according to the Barrett-Joyner-Halenda (BJH) model, increased with increasing molar ratio of C(14-2-14) to sodium silicate.     

Novel route to periodic mesoporous aminosilicas, PMAs: ammonolysis of periodic mesoporous organosilicas

A new route to periodic mesoporous aminosilicas (PMAs) that contain amine functional groups in the framework of a mesoporous network is reported. The materials are prepared via thermal ammonolysis of periodic mesoporous organosilicas (PMOs) under a flow of ammonia gas. PMOs integrate similar or even higher quantities of nitrogen-containing groups upon ammonolysis than similarly treated ordered mesoporous silicas (MCM-41). The quantity of amine groups introduced into the materials was found to depend strongly on the ammonolysis temperature. The largest loading of amine groups was obtained when a well-ordered cubic methylene PMO material without prior vacuum-drying was thermolyzed in ammonia. The ordered mesoporosity of PMOs was preserved during the ammonolysis with only a slight decrease in the mesopore size and the degree of mesostructural ordering. The extent of substitution of framework oxygen by amine and nitride groups was established by solid-state (29)Si CP-MAS, (29)Si MAS, (15)N MAS, and (13)C CP-MAS NMR spectroscopies, elemental analysis, and X-ray photoelectron spectroscopy. In some cases, methylene and methyl functional groups were also present in the PMAs along with amine functional groups, as inferred from elemental analysis and gas adsorption, particularly in cases where PMOs were subjected to ammonolysis at 400 and 550 degrees C for several hours. This resulted in new multifunctional mesoporous organoaminosilica nanomaterials with properties that could be tuned by systematically varying the relative amounts of hydrophilic amine and hydrophobic hydrocarbon pendent and framework groups. The stability upon storage was found to be much higher for PMAs obtained from PMOs than for those obtained from MCM-41 silicas under the same conditions.     

Synthesis of Ordered Mesoporous Carbon Materials by Dry Etching

A novel synthesis method for ordered mesoporous carbons is presented. The inverse replication of a silica template was achieved using the carbonization of sucrose within mesoporous KIT‐6. Instead of liquid acid etching, as in classical nanocasting, a novel dry chlorine etching procedure for template removal is presented for the first time. The resultant ordered mesostructured carbon material outperforms carbons obtained by conventional hard templating with respect to high specific micro‐ and mesopore volumes (0.6 and 1.6 cm³ g^?1, respectively), due to the presence of a hierarchical pore system. A high specific surface area of 1671 m² g^?1 was achieved, rendering this synthesis route a highly convenient method to produce ordered mesoporous carbons.     

Novel coassembly route to Cu-SiO2 MCM-41-like mesoporous materials

A series of mesostructured Cu-SiO2 composites have been synthesized with sodium metasilicate (Na2SiO3) and cuprammonia nitrate (Cu(NH3)4(NO3)2) respectively used as Si and Cu sources. The synthetic procedures were conducted at room temperature, and cetyltrimethylammonia bromide was used as a template. Under our experimental conditions, ordered mesoporous Cu-SiO2 composites could be obtained with a copper content up to 16.8 wt %. Average pore diameters (2.80-3.15 nm), wall thickness (1.30-2.20 nm), and specific surface area (1020-690 m2/g) are found to vary linearly with copper content (0-16.8 wt %). Results of thermal gravimetry-differential thermal analysis reveal the collapse temperature of the order structure starts at approximately 1250 K for mesoporous Cu-SiO2 with 16.8 wt % copper content. As indicated by the outcomes of inductively coupled plasma and X-ray photoelectron spectroscopy studies, copper is mainly incorporated inside the pore wall rather than embedded on the wall surface. Copper species strongly interact with silica, and calcination at high temperatures cannot cause phase separation between silica and copper oxide. Cu status in mesoporous Cu-SiO2 composites is similar to that in copper silicate in neighboring structures. Based on the results, a S+ I- I+ I- mechanism is proposed in which copper entities are surrounded by silicon species during synthesis of the mesostructured composite.     

Incorporation of organic groups within the channel wall of spin-on mesostructured silica films by a vapor infiltration technique

Organically functionalized mesoporous silica films have been prepared by a novel synthetic procedure that involves spin-coating of mesostructured silica films and a vapor infiltration (VI) technique, using organosiloxanes, before the removal of surfactant. The VI-treated mesostructured films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and a field emission scanning electron microscope (FE-SEM). Nitrogen adsorption/desorption measurements were performed using films attached with a silicon substrate. The XRD and FE-SEM measurements show that the mesochannel wall, densified and modified with organosilyl groups by the VI treatment, hardly contracts under calcination. FE-SEM observations for the films' cross section support the view that organosiloxane vapor is not deposited on the surface of the film. These results show that organosiloxane molecules penetrate the film and are selectively incorporated into the silica wall. Thus, hydrophobic mesoporous silica films can be synthesized without a reduction in pore size, a result that cannot be attained by conventional grafting and co-condensation methods. The excellent high porosity and hydrophobicity of the mesostructured composite films may be of advantage for next-generation low-k dielectric films.     

Investigation of the effect of calcination temperature on HMDS-treated ordered mesoporous silica film

To reduce signal delay in ultra-large-scale integrated circuits, an intermetal dielectric with low dielectric constant is required. Ordered mesoporous silica film is appropriate for use as an intermetal dielectric due to its low dielectric constant and superior mechanical properties. To reduce the dielectric constant, an ordered mesoporous silica film prepared by a tetraethoxysilane/methyltriethoxysilane silica precursor and Brij-76 block copolymer was surface-modified by hexamethyldisilazane (HMDS) treatment. HMDS treatment substituted OH with Si(CH₃)₃ groups on the silica surface. After treatment, ordered mesoporous silica films were calcined at various calcination temperatures, and the calcination temperature to obtain optimal structural, electrical, and mechanical properties was determined to be approximately 300 °C.     

Synthesis of Highly ordered Large Size Mesoporous Silica and Effect of Stabilization as Enzyme Supports in Organic Solvent

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A "teardown" method to create large mesotunnels on the pore walls of ordered mesoporous silica

A "teardown" method to create large mesotunnels (approximately 9 nm) on the pore walls of ordered mesoporous silicas is demonstrated by digesting the organic constituents from polymer-silicate nanocomposites. The ordered mesostructured polymer-silicate composites were first obtained via the evaporation-induced triconstituent co-assembly method by using a low-molecular-weight phenolic resin (resols) as an organic precursor; prehydrolyzed TEOS as an inorganic precursor, and triblock copolymer F127 as a template. All of organic components including F127 and phenolic resins are removed by the microwave digestion (MWD) method from mesostructured polymer-silica composites. While the removal of triblock copolymer F127 generates main pore channels, the phenolic resins can also be torn down from the pore walls, yielding mesotunnels between the channels. The resulting silica products exhibit ordered 2-D hexagonal mesostructure, large pore volume (up to 1.92 cm(3)/g), and very large pore size (up to 22.9 nm), which is even larger than their mesostructural cell parameter (14.2 nm). TEM images confirm the existence of mesotunnels on the silica pore walls. FT-IR and (29)Si solid-state NMR results reveal that these silica products have a large number of silanol groups.